_MARINE VERTEBRATES_
The vertebrates form the highest sub-kingdom of animal life--the
sub-kingdom to which we ourselves belong, the chief distinguishing
characteristic of the group being the presence of an internal skeleton,
the principal part of which consists of a rod or column of cartilaginous
or bony material running along the dorsal side of the body, known as the
_vertebral column_.
[Illustration: FIG. 225.--TRANSVERSE SECTION THROUGH THE BONY
FRAMEWORK OF A TYPICAL VERTEBRATE ANIMAL
1. Spinous process of the vertebra. 2. Neural arch. 3. Transverse
process. 5. Body of the vertebra. 6. Breast-bone. 7. Rib. The space
between 2 and 5 is the neural cavity; and that between 5 and 6 is
the visceral cavity]
This column is usually composed of a number of elements called vertebræ,
each of which gives off two processes that unite and form an arch on its
dorsal side, while all the arches form a tube through which passes the
central portion of the nervous system.
Below, or on the ventral side of the column, is the body-cavity
containing the organs of digestion and circulation; so that if we make a
transverse section of a vertebrate animal we find that there are two
distinct tubes or cavities--a _neural_ or _cerebro-spinal cavity_ on
the dorsal side of the vertebral column, formed by extensions from the
substance of the latter, and enclosing the chief portion of the nervous
system; and a _body-cavity_ on the ventral side containing the viscera
or internal organs.
The above features are highly important, and will always prove quite
sufficient to enable us to decide whether any particular animal is a
vertebrate or an invertebrate, for it will be remembered that the body
of the latter has only one cavity, containing the nervous system as well
as the viscera, and that the nervous system is commonly placed along the
ventral side, but never along the dorsal. In addition to this the
vertebrates never have more than two pairs of limbs, and these are
always directed _from_ the nervous system; and the jaws, which are
appendages that move in the horizontal plane in invertebrates, are, in
the higher animals, portions of the framework of the head and move
vertically. In vertebrates, too, there is always a complete blood
system, consisting of a heart with two, three, or four cavities, a
system of arteries to convey the blood to the different parts of the
body, veins to return the blood to the heart, and networks of fine
capillaries connecting the former with the latter.
All vertebrates, at an early stage of their existence, have a
cartilaginous rod running through the dorsal portion of the body, called
the _notocord_. In some of the lowest animals of the division this rod
persists without any important alterations in structure, while in the
higher forms it gives place to the series of cartilaginous or bony
elements above referred to as the vertebræ; and the arrangement of the
vertebrates into their relative positions in the scale of life is based
largely on the degree of development of the vertebral column from the
notocord. Another interesting feature in the development of a vertebrate
is the formation of five or more transverse, archlike thickenings on
each side of the digestive tube, just behind the head; and, in the
spaces between them, of a series of slits forming a communication
between the pharynx and the exterior. These arches and clefts have but a
brief existence in many vertebrates, while in others they persist
throughout life; and, like other points referred to, they assist us in
recognising the relations of the vertebrates to one another.
The vertebrates are divided into the following classes:--
1. _Cyclostomata_--Lampreys.
2. _Pisces_--Fishes.
3. _Amphibia_--Frogs, Toads, Newts, &c.
4. _Reptilia_--Snakes, Lizards, Tortoises, &c.
5. _Aves_--Birds.
6. _Mammalia_--Mammals.
The first of these includes only a few species, one of which is found in
our seas, and will receive a short notice here. The fishes will, of
course, demand a fair share of our attention. Amphibians and reptiles
have no British marine representatives, and are therefore quite excluded
from this work. As to the birds, although there are so many that live
entirely on the sea and in its immediate neighbourhood, these have been
so ably dealt with by Mr. Hudson in one of the books of this series that
it would be superfluous to mention them. The mammals include a
considerable number of marine species, but as only one of these--the
Porpoise--is really commonly observed round our coasts, it alone will be
selected for description.
Lampreys and their few allies were formerly classified with fishes, but
are now made to form a small class by themselves; and there is abundant
reason for the separation. It will be remembered that vertebrates, in
the early stages of their development, are characterised by a
cartilaginous rod running through the dorsal region of the body, below
the central cord of the nervous system, and that they possess a series
of slits opening into the sides of the pharynx. Now, while these
characteristics are usually only transitory in the vertebrates, the
Lampreys and their relatives are the only animals in which they persist
throughout life, and it is for this reason that they are exalted to the
dignity of a class under the title _Cyclostomata_.
This name signifies ‘round-mouthed,’ while the Lampreys themselves form
the still smaller division _Marsipobranchii_, which means
‘pouch-gilled,’ these two being among the most evident characters of the
creatures concerned. They have no true jaws, the circular mouth being
supported by a ring of cartilage, and provided with a rasp-like tongue
that enables them to divide their food. They have no true bone in their
bodies, the simple skeleton, without limbs and ribs, being entirely
cartilaginous, and the rudimentary skull is not movable on the dorsal
cartilage. Their bodies are elongated and eel-like, with a single medial
fin, supported by fine cartilaginous rays, and with seven little slits
on each side of the neck, communicating with as many gills in the form
of little pouches. The mouth is suctorial, presenting, when open, a
circular adhesive disc, by which the animals can attach themselves to
any solid object, but assumes the form of a mere slit when closed. The
young differ from the adult in a few points of structure. Thus they have
no eyes, and the long fin, divided in the adult, is continuous. With the
above characteristics in mind, there will be no danger of confusing the
lampreys with the eels and other similar fishes.
There are three or four British lampreys, two or three of which inhabit
fresh water. Their habits do not seem to be well understood, but it
appears certain that the Sea Lamprey (_Petromyzum marinus_), which
reaches a length of from one to two feet, ascends rivers to spawn, while
the smaller River Lamprey (_P. fluviatilis_) has been caught in the sea;
and it is probable that the migrations of both, together with the
sojourn of the young of the former for a longer or shorter period in
fresh waters, have been the cause of the widespread confusion between
species.
Lampreys are carnivorous creatures, and attach themselves to fishes by
their suctorial mouths, and rasp away the flesh. They have also been
known to attack bathers.
[Illustration: FIG. 226.--THE SEA LAMPREY]
Passing now to the true fishes, we must first study the general features
of the group by which they are to be distinguished from other animals.
Since there are so many creatures outside this class that are more or
less fishlike in some respects, it becomes no easy matter to give a
concise definition of a fish, and the shortest satisfactory description
must necessarily include several points of structure. Thus, we may
define a fish as a cold-blooded vertebrate that does not undergo
metamorphoses, with limbs modified into fins, possessing also median
fins on the dorsal and ventral surfaces, having distinct jaws, a heart
with two chambers, and breathing by gills. To this we may add that the
young are generally produced from eggs, and that the skin is covered
with scales or bony plates, or is naked.
But let us now look more closely into the structure of fishes, so that
we may be enabled to see how marvellously they are adapted to their
aquatic life, and in order that we may become acquainted with the few
technical terms which will, as a matter of convenience, be used in the
descriptions of species.
Taking first the external features, we note that the body is generally
covered with scales, sometimes very large and distinct, but often so
small and closely set that they are not visible without careful
examination; indeed they are often so small, and so thoroughly embedded
in the slimy skin as not to be discovered without the aid of a
microscope. When the scales have unbroken edges and overlap one another
they are said to be _cycloid_, but when the projecting edges are toothed
or serrated, giving a roughness to the touch, they are described as
_ctenoid_. Sometimes the scales are modified into bony plates or little
isolated bony granules, and in either case they are practically
identical in structure with teeth, consisting as they do of dentine,
capped with a little harder substance resembling enamel.
[Illustration: FIG. 227.--THE PILCHARD
1. Dorsal fin. 2. Pectoral fin. 3. Pelvic fin. 4. Ventral or anal
fin. 5. Caudal fin.]
We often observe a row of scales, of a different nature from those
covering the body generally, running along each side of a fish from near
the eye to the end of the tail; and these constitute what is called the
_lateral line_. If we examine these scales closely, we observe that each
one is pierced by a hole that communicates with a little sac beneath
containing a gelatinous material, and in which a nerve tendril
terminates. The presence of the nerve filament evidently denotes that
the scales in question, with the little sacs beneath them, are organs
connected with sensation, and it is also believed that they have
something to do with the secretion of the slimy mucus that covers the
scales of the body.
The mouth of a fish is generally situated on the extreme front of the
head, but occasionally, as in the sharks and rays, quite on the under
side. If it contains a tongue at all, this organ is of small size and
simple structure; thus it is highly probable that the sense of taste is
very feeble in these animals, and this is just what one might expect
when one remembers that fishes never retain their food in the mouth for
any length of time, but simply bolt it without any attempt at
mastication.
The arrangement and nature of the teeth are very variable. Often they
are developed on the membrane of the mouth only, in which case they are
generally renewed as fast as they are worn down, but sometimes they are
persistent structures more or less embedded in the bone of the jaws. In
some cases teeth are altogether wanting, but in others they are situated
not only on the jaws, but also on the tongue, the roof of the mouth, and
even on the bony arches that support the gills.
A glance at the fins of a typical fish will suffice to show that they
may be divided into two groups--the paired fins, representing the two
pairs of limbs in most of the higher animals, and the median fins
occupying the middle line of the body. The former comprise the two
_pectoral fins_ that correspond with our arms, and are attached to the
bones of the pectoral or shoulder girdle; and the _pelvic fins_,
corresponding with the lower extremities. The pectorals, too, are
present in nearly all fishes, while the pelvic pair are rather more
frequently absent than the pectorals.
The medial fins comprise the _dorsal_, the _ventral_, and the _caudal_
or tail-fin, and are not to be regarded as limbs, but rather mere
outgrowths of the skin. They are not directly connected with any part of
the main bony framework of the body, though they are generally jointed
with a series of bones (interspinal bones) that run between processes of
the vertebral column. The dorsal and ventral fins are often divided into
two or more parts, and the tail fin is commonly distinctly forked.
Although the seven fins above mentioned differ considerably in general
form, some being fanlike, while others form fringe-like expansions, yet
they generally agree in that they consist of bony or cartilaginous rays,
between which is a soft membrane. The rays, however, vary much in
character, being sometimes developed into very hard and sharp spines,
and sometimes quite soft and flexible. The fins also differ in function,
as will be seen when we observe the movements of a fish as it swims. It
will then be noticed that the caudal fin, which is spread in the
vertical plane and moved sharply from side to side by the powerful
muscles of the tail, is the chief propelling organ, while the others are
concerned principally in maintaining the balance of the body. This
latter point becomes much more evident when we observe the movements of
a fish in which one or more of the fins have been injured or lost, as we
shall see presently.
It is true that the pectoral fins are sometimes used to propel, but
forward movement is brought about almost entirely by the caudal fin,
which acts much in the same way as the blade of the propelling ‘screw’
of a steam-vessel, the pectorals being used at the same time for
steering. Occasionally, too, the latter are both spread out at right
angles to the body when the fish desires to stop suddenly, and are even
employed at times in swimming backwards.
When a fish wants to turn to one side, it will be seen to give the tail
a sharp motion to the opposite side. The pectoral of the latter side is
also brought into play, while the other is kept close against the body.
If the pectoral or pelvic fin of one side is injured, the body of the
fish will incline to the opposite side; and if all the paired fins are
functionless the fish swims with its head inclined downwards.
Observations of fishes in which the dorsal or ventral fins are injured
will also show that these organs are necessary to maintain a steady
motion in the water.
In addition to the above facts, it may be mentioned here that the paired
fins are often modified into long finger-like processes that serve as
organs of touch, and even as means by which the fish can creep along the
bottom. This is notably the case with gurnards and a few of the other
fishes that spend their time almost exclusively on the bed of the sea.
Fishes are essentially gill-breathers, the gills being generally
fringe-like organs, supported on bony arches (the gill arches),
numbering four on each side, the cavity containing them being covered by
a gill-cover (_operculum_) that opens behind. Water is taken in at the
mouth, whence it passes into the gill-chamber; and after passing between
and around the gills, it escapes under the opercula. The gills
themselves are richly supplied with bloodvessels that are distributed
close to the surface, and an exchange of gases takes place through their
exceedingly thin walls, carbonic acid gas passing from the blood to the
surrounding water, and oxygen, held in solution in the water, passing
from the water to the blood.
When fishes are in foul water, containing but little oxygen in solution,
they rise to the surface in order to make up the deficiency by taking
oxygen direct from the air. This, however, is an unnatural proceeding
with the majority of fishes; but there are some that are provided with
accessory breathing organs specially adapted to the extraction of oxygen
direct from the air, and these are so dependent on the supply from this
source that they are suffocated if prevented from reaching the surface.
In other fishes, such as the sharks and rays, the gills are of an
entirely different character from those described above, for they are
pouch-like and five in number on each side, each pouch communicating
with the pharynx as well as with the exterior by a slit-like opening.
Before leaving the external characters of fishes we must say a word or
two about their forms and colours. As regards the former, it is well
known that fishes are well adapted for rapid progression through water,
but there are many exceptions to this rule. These exceptions, however,
apply principally to those species that have no need to swim rapidly,
and a study of their habits will show that their form is just as
perfectly adapted to their mode of life. They are often species that
live on the bottom, or hide in the crevices and holes of rocks, and
examples will be given in our future descriptions.
Variations in colour are even more interesting, especially as they are
so commonly connected with the nature of the surroundings and the
protection of the animals. In nearly all cases the colour is darker on
the upper surface than on the lower, thus making it appear that the
influence of light has something to do with the formation of the
pigments of the skin, and experiment proves that this is, at least to a
certain extent, the case; for when fishes have been kept for some time
in an aquarium into which light is admitted through the bottom only,
pigment spots have formed in the skin on the lower surface.
Fishes that swim at the surface are generally tinted on the dorsal side
with some shade that closely resembles the colour of the water as viewed
from above, and are white and silvery below. Such colouring is of course
highly protective, for they are not readily distinguished by the sea
birds and other enemies that would pounce on them from above, and are
almost invisible against the sky to eyes below. This form of protective
resemblance is beautifully illustrated in the mackerel, which is barred
on the back with black and green, closely imitating the ripples on the
surface of the deep green sea, while the under side is of a silvery
whiteness that is hardly visible from below with the bright sky as a
background.
The flat fish afford other interesting examples, for these live on the
bottom, and are coloured above so as to resemble the bed on which they
live; the tints being those of mud, sand, or gravel.
But what are we to say of the gaudy colours of the gurnards, rock
fishes, &c.? These are certainly not protective in all cases, for we
sometimes find brightly coloured species conspicuous among duller
surroundings. Such instances, however, are comparatively rare, the gaudy
species living principally among the variously coloured rocks, weeds,
and corals; and when they do occur it is probable that they serve
principally as a means by which the brightly coloured sex--usually the
male--attracts its mate. We say ‘usually the male,’ but why so? Because
the female requires the protection of a more sombre colour in order that
she may with safety deposit her spawn for the perpetuation of her
species. Again, the male referred to needs the assistance of his gaudy
coat only during the breeding season, hence we find that he assumes the
bright colours as a wedding garment, to be cast off when the breeding
season is over.
This leads us to the subject of changeability of colours in the same
individual. That such changes do occur is well known, and it is still
more remarkable that they are produced in rapid succession, apparently
at the will of the fish concerned; for its tints will vary as it moves
from place to place so as to always harmonise with the surroundings, and
also in response to other conditions. The mechanism by which such
variations are produced has also been studied and explained:--The
colouring matter is held in little vesicles beneath the skin, and these
vesicles are capable of being compressed by muscles quite under the
control of the fish. When they are globular in form the contained
pigment appears dark, but when they are flattened by muscular
compression, the pigment is spread over a much larger area, and thus
greatly reduced in depth of tint.
As with all vertebrates, the central axis of the internal skeleton of a
fish consists of the backbone and the skull. The structure of the latter
is so complicated, and its description so full of technicalities, that
we deem it advisable to pass it over in a work like this where the scope
is so large in proportion to the space available; and this we do with
reluctance, because the detailed study of the skull is of real
importance to those who would thoroughly understand the principles of
classification.
The backbone consists of a variable number of cylindrical vertebræ,
united end to end to form a continuous column, both the anterior and
posterior faces of each being concave. On the dorsal surface of each
vertebra there is a V-shaped arch, surmounted by a spine, the former
serving to protect the spinal cord, and the latter giving attachment to
the muscles of the back. Some of the vertebræ are also provided with
processes for the attachment of the ribs, and those of the tail possess
an arch and a spine on the ventral as well as on the dorsal side.
It has already been shown that the pectoral fins are jointed to a
girdle. This girdle corresponds with the shoulder-blade of higher
animals, and gives direct attachment to the rays of the fin, which may
be regarded as the equivalent of the fingers, and thus there is no part
of the limb corresponding with the arm. The pelvic fins also are
frequently jointed to a pelvic girdle or hip, but this is a very
rudimental structure, or is even entirely absent in some species.
The rays of the caudal fin articulate with the extremity of the
backbone, but this portion of the fish’s anatomy undergoes such
remarkable changes that we must devote a few words to it. It is probably
well known to our readers that the tails of fishes exhibit three
distinct forms. The first of these is a simple fringe formed by the
union of unaltered dorsal and ventral fins; the second is the
unsymmetrical or unequally lobed tail so characteristic of sharks,
dogfishes, and rays; and the third is the broad symmetrical tail fin,
often distinctly forked or bi-lobed, such as we meet with in the
majority of our bony fishes. These three kinds are known respectively as
the _diphycercal_, _heterocercal_, and the _homocercal_ tails.
[Illustration: FIG. 228.--THE SKELETON OF A FISH (PERCH)
_d_, dorsal fin; _p_, pectoral fin; _v_, pelvic fin; _t_, tail fin;
_a_, anal fin]
Now, it is an interesting fact that the most ancient fishes of our globe
possessed tails of the first type; and that these gradually gave place
to the heterocercal form; while the higher fishes of the present day
nearly all possess the homocercal tail. Thus as time advanced the
heterocercal tail was gradually evolved from the diphycercal, and the
homocercal from the heterocercal.
Further, if we watch the development of one of the highest fishes of the
present day from its embryo, we find that similar changes take place in
the individual. At first its tail is a simple fringe round the extremity
of the backbone, the latter being straight, or nearly so, to the end, so
that the embryo fish, as yet still in the egg, reflects a characteristic
of its very early ancestors. Then the end of the vertebral column turns
upward, and strong fin-rays are developed on its ventral side, so that
the tail becomes a heterocercal one like that of the less remote
ancestors of a later geological period. Next, the upward-bending portion
of the vertebral column is slowly absorbed, till nothing of it remains
except a small upturned bony spine, while, at the same time, the ventral
lobe expands on the upper side until the tail fin is once more of a
symmetrical form.
[Illustration: FIG. 229.--THE INTERNAL ORGANS OF THE HERRING
_a_, œsophagus; _bc_, stomach; _e_, intestine; _l_, duct of
swimming bladder; _k_, air-bladder; _h_, ovary]
Following these interesting changes, it becomes evident that the
symmetry of the tail fin of the bony fishes is really a false one, the
whole of it having been formed from the ventral lobe of a heterocercal
tail; and although the backbone seems to terminate abruptly exactly
opposite the middle of the fin, it still contains the remnant of the
raised extremity of the backbone that ran to the tip of the dorsal lobe
when the tail was of the heterocercal type.
The flesh or muscle of fishes is usually white, but it often assumes a
pink colour in the case of those fishes that feed largely on
crustaceans. This is due to the presence of a substance in the horny or
calcareous skins of the crustaceans that is turned red by the action of
the digestive fluids--the same substance that is turned red when the
crustaceans are boiled. This is notably the case with the salmon; but
the red pigment thus derived originally from the crustaceans frequently
shows itself more in the skin of the fish than in the flesh, as
observed in the common red gurnard.
Most fishes possess a membranous bag containing air, situated just below
the backbone, and known as the air-bladder; but this organ does not
exist in sharks and rays and in some of the heavier bony fishes that
live on the bottom. The air-bladder is capable of being compressed by
the action of certain muscles, and its principal use seems to be the
adjustment of the specific gravity of the fish to that of the
surrounding water; but it is interesting to note that the development of
this air-bladder is precisely the same as that of the lungs of
air-breathing animals, and that in some fishes which live in foul muddy
waters it is really a functional lung by means of which the fishes can
breathe direct from the atmosphere.
We can find space to refer only to one other internal structure of the
fish, namely, the roe of the female. This usually consists of a very
large number of eggs of small size, sometimes numbering many thousands,
and even millions, in a single individual. So numerous, indeed, are the
eggs, that were it not for the multitudes of carnivorous animals that
devour both eggs and fry, the sea and fresh-water lakes and rivers would
soon become so thickly populated that the fish would die in millions for
lack of food and air.
In some cases, however, the eggs are much larger and fewer in number,
but these are generally protected from the ravages of predaceous species
by a hard covering, as we shall observe in the sharks and rays.
Finally, a word or two must be said about the distribution of fishes. We
have already referred briefly to species that live principally at the
surface, and others that make the bottom their home: but some of the
former go to the bottom for food or to deposit their spawn, while some
of the latter occasionally rise to the surface and swim in shoals. We
have noticed, too, that the paired fins of bottom fishes are sometimes
modified into feelers, or into fingerlike processes adapted for
creeping. Similar organs, employed undoubtedly as organs of touch, and
called barbels or barbules, are often developed on the chins or jaws of
these fishes.
Although we have to deal principally with the species that belong more
or less to the shore--the _littoral_ fishes--we should like to refer
briefly to one or two interesting features of those that live at great
depths. It will be readily understood that much light is lost as the
rays penetrate into deep water, so that the bottoms of deep seas must
be more or less darkened. To allow for this loss, we find that the
species living at moderate depths are provided with larger eyes to
enable them to see their prey and their mates; but at still greater
depths, where the sun’s light cannot penetrate, the fishes are either
blind, or are possessed of luminous organs which enable them to see
their way. Again, as the sea is so thinly populated at such great
depths, the carnivorous species do not find abundant food always at
hand, hence they are often provided with such mouths and stomachs as
will allow them to make the best of favourable opportunities, some being
capable of swallowing a fish quite as large as themselves.
We often find fishes roughly classified into fresh-water and salt-water
species, and although such a division is at times convenient, it must be
remembered that some of the former migrate into brackish and even into
salt water, while some of the latter ascend estuaries and rivers either
for the purpose of obtaining suitable food, or for the deposition of
their eggs.
The fishes that frequent our coasts may be classified into two main
groups, those with cartilaginous skeletons (_Elasmobranchii_), and the
bony fishes (_Teleostomi_). Both these are divided into family groups,
and we shall deal more or less briefly with all the important families
that include common British marine fishes, but giving more attention to
those species that are truly littoral in habit--species that may be
found in the rock pools or under stones at low tide, and which may be
obtained by the amateur angler working from rocks, piers, &c.
The cartilaginous fishes include the Sharks, Dogfishes, and Rays. They
have pouchlike gills, five or more on each side, each one opening to the
exterior by a separate slit. The skin generally contains bony elements
that are toothlike in structure and often in form; the mouth is usually
on the under side of the head, and the tail is nearly always of the
heterocercal kind. They are all carnivorous creatures, and often
exceedingly voracious; and are represented in our seas by the Rays and
Dogfishes.
Rays or Skates (family _Raiidæ_), of which there are six or seven
British species, are readily known by their broad flattened rhomboidal
bodies, with the mouth on the under side of the head, a longitudinal
fold on each side of the tail, and pectoral fins extending quite or
nearly to the front point of the head.
Two of these fishes are very common in our markets, one being the
Thornback Skate (_Raia clavata_), distinguished by the clawlike spines
down the middle of the back as well as on other parts of the body; and
the Common Skate (_R. vulgaris_), a very voracious species, from two to
four feet long, with a very sharp muzzle.
All the members of this family are bottom fish, without air-bladders;
and their eggs, which are large and detached, are enclosed in horn
capsules which are so commonly washed up on the beach that they are well
known to frequenters of the sea-side, who call them Skates’ Barrows or
Shepherds’ Purses. These cases are oblong in form, with a process at
each corner, and the material of which they are composed looks very much
like that of some of the coarser sea weeds after they have been dried in
the sun. As a rule only the empty cases are cast ashore by the waves,
open at the end where the little skate made its escape; but occasionally
we meet with the complete egg, and the case, while still wet, is
sometimes sufficiently transparent to show the form of the embryo
within.
[Illustration: FIG. 230.--THE EGG-CASE OF DOGFISH]
Dogfishes are also fairly well known to sea-side ramblers, for not only
are some species used as food in many places, but they are also
frequently to be seen cast aside with the refuse from the fishermen’s
nets. The common Spiny Dogfish (_Acanthias vulgaris_), belonging to the
family _Spinacidæ_, frequents all parts of our coasts. It reaches a
length of three or four feet, and is of a slate-blue colour above and
very pale yellow below. The pectoral fins are very large, the ventral
fin absent, and there is a very sharp spine in front of each dorsal. The
creature is ovo-viviparous; that is, the eggs are hatched while still
within the body of the parent.
Another family (_Scylliidæ_) contains two British species without
spines, and is also characterised by having the first dorsal fin far
behind. They are the Larger Spotted Dogfish (_Scyllium canicula_) also
known as the Nurse Dog and the Bull Huss; and the Lesser Spotted
Dogfish (_S. catulus_), called also the Huss and the Rough Hound. The
egg capsules of both these are occasionally washed on the beach, and
those of the latter species may be known by the yellowish colour and the
long tendrils by which they are anchored to sea weeds.
In addition to these we may briefly refer to two of the Blue Sharks
(family _Carchariidæ_) that frequent our shores, distinguished by their
long and prominent muzzle, and the crescent-shaped mouth. They may be
regarded as higher in the scale of fish life, as compared with the
sharks and rays previously named, because the vertebræ are more or less
hardened by the deposit of calcareous matter, and, therefore, make a
nearer approach to the character of true bone. The species referred to
are the Common Blue Shark (_Carcharius glaucus_), and the Smooth Hound
(_Mustelus lævis_). The former often exceeds twelve feet in length, and
is commonly seen off our south and west coasts during the summer months.
It is a nocturnal marauder, and is said to sleep at the surface by day
with its tail exposed above the water. The Smooth Hound is a bottom
feeder, subsisting on molluscs and crustaceans, the shells of which are
easily crushed by its flat and blunt teeth. It is a small shark,
measuring only three or four feet in length, and brings forth its young
alive.
[Illustration: FIG. 231.--THE SMOOTH HOUND]
The next division (_Teleostomi_) contains all the bony fishes, which may
be distinguished generally from the cartilaginous group by the following
features:--The skeleton is more or less hardened by the deposit of
calcareous matter, and the tail is generally not of the heterocercal
type. The paired fins are fan-like, and the pectoral girdle is attached
to the hinder part of the skull. These fishes generally have an
air-bladder, and the gills lie close together in a cavity covered by an
operculum. The eggs, too, are generally very small and numerous, and
massed together.
Of these we will take first the family _Salmonidæ_, of which the Salmon
(_Salmo salar_), and the Smelt (_Osmerus eperlanus_) are well-known
examples. Several species of the family are remarkable for their
periodical migrations from fresh to salt water or _vice versa_, and we
cannot do better than briefly relate the interesting life-history of the
salmon as a striking instance of these peculiar wanderings. This fish
quits the sea at the close of the summer, and ascends the rivers for the
purpose of depositing its spawn, the colder water of the rivers being
necessary for the development of the young. Its upward journey is beset
with many difficulties, for it has to shoot the various rapids and leap
the cascades, the latter often demanding the most prodigious efforts on
the part of the fish, which frequently leaps several feet out of the
water, and even then has sometimes to renew its attempts over and over
again before it finally succeeds. Indeed, the difficulties to be
overcome are so numerous that the fish often reaches the goal in such an
exhausted condition that it would hardly be recognised as the salmon by
those who have only seen it in the prime condition in which it is
captured during its return to the sea in the following spring or summer.
The male, at this period called the _kipper_, is of a dull red colour,
irregularly blotched with yellow and light brown, and its skin is
covered with a slimy secretion. Its body is lean, and the head, now
large and out of all proportion, is rendered still more unsightly by the
protrusion of the lower jaw, which at this season, when the males are
particularly pugnacious, becomes a formidable weapon of offence. The
condition of the female, now called the _baggit_, is equally poor, and
the skin has changed its bright silvery colour for dark and dingy
shades.
The female digs a nest in the form of a deep trench by wriggling her
body in the gravel of the bed of the stream, and there deposits her
eggs, many thousands in number, small quantities at a time. As each
batch is deposited the eggs are fecundated by the kipper, and then
covered over lightly with gravel by the baggit; and this work having
been accomplished, both male and female rest and feed, with the result
that their condition is rapidly improved.
After about eighteen weeks the eggs begin to hatch, and the fry wriggle
out of the nest and seek shelter under stones in the immediate
neighbourhood. They are now peculiar little creatures, as much like
tadpoles as fishes, with big heads and narrow bodies, and a bag of
albuminous yolk-matter attached to the ventral side. The young subsist
on this store of food for from twelve to twenty days, during the whole
of which time they remain under shelter, having, of course, no need to
expose themselves to the numerous enemies with which they are
surrounded, and they then leave their hiding-place in search of food,
being now about an inch in length. They feed on aquatic and other
insects, which are now becoming plentiful on the approach of the warm
weather; and, growing rapidly, reach a length of four inches in a month
or two. They are now called _parr_, and are distinguished by the dark
bars that cross their bodies transversely--a feature that persists for a
year or more from this time.
Towards the end of May the parr migrate seawards, accompanied by the
adult salmon, but as their enemies include the voracious fishes, wading
birds, and even the adults of their own species, it is probable that
only a small proportion of the original number ever enter salt water.
In the sea they feed on crustaceans, molluscs, and small fishes, the
young still growing rapidly, and attaining a weight of about five pounds
in the following autumn, when both young (now called _grilse_) and old
again ascend the rivers to spend the colder half of the year; the former
will have reached a weight of ten pounds or more on their return to the
sea in the following year.
The Smelt may be seen in thousands in our estuaries during the spring,
for at that time they come up to spawn in the brackish water. In the
summer they swim about in shoals along the coast, and are caught largely
in nets for the market. In some parts they are taken in large shallow
circular nets suspended on a line. This is lowered into the water, and
hauled up when the fish are seen swimming above it. Many amateurs secure
numbers of smelt by means of rod and line, fishing from piers, jetties,
&c. They bite freely at almost any kind of bait, and will snap at an
almost bare hook, with the tiniest fragment of the bait at its point.
The Herring family (_Clupeidæ_) contains some well-known food-fishes to
which we need only casually refer. They are mostly littoral species,
none inhabiting deep water, and none straying into the open ocean. Their
bodies are covered with silvery scales, and are laterally compressed, so
much so on the ventral side that there is a moderately sharp ridge along
the middle line. The principal fishes of the family are the Herring
(_Clupea harengus_), the Sprat (_C. sprattus_), and the Pilchard (_C.
pilchardus_).
These fishes are particularly interesting on account of their gregarious
habits and the enormous size of the shoals they form, a single shoal
often containing millions of individuals; and they are often captured in
such quantities that large numbers are sold to farmers as manure to
enrich the soil. The shoals are followed closely by many larger
carnivorous species that devour them in great numbers, as well as by
flocks of sea birds that prey on them, and yet their numbers are not
appreciably reduced by such ravages. They spawn in shallow waters near
the coast, and feed principally on the crustaceans and worms of the
littoral zone.
Sprats were once considered to be the young of the Herring, but it is
now universally acknowledged that they are a distinct species, and quite
a number of characteristics have been given as a means of distinguishing
between the two. The young of the herring are, however, used largely as
food, for that miscellaneous mixture of fry and small species known as
Whitebait consists largely of these and the young of the sprat.
[Illustration: FIG. 232.--THE COMMON EEL]
Herrings are captured principally off the north and east coasts, but the
pilchards, which are often confused with them, and even at times sold
under the same name, are caught chiefly off the coast of Cornwall.
Although the Eels (_Anguillidæ_) are so readily distinguished by their
general form and appearance, yet it may be advisable to call attention
to one or two of the leading characters that would possibly be
overlooked by an ordinary observer, and in doing this we ask the reader
to note that our remarks apply to the true eels only, and not to the
sand eels and other fish that may be confused with them.
The elongated bodies of the _Anguillidæ_ are covered with a slimy skin
that is apparently scaleless, but an examination with the microscope
will show that there are small scales embedded in it. The dorsal and
ventral fins extend to the tail, and the pelvics are absent; the
gill-slits, which are very narrow, are at the base of the pectorals.
It might well be expected that eels would be possessed of some form of
accessory breathing apparatus, seeing that they can live so long out of
water, but this is not the case. They have, however, a pouch-like
gill-cavity which can be inflated and filled with water by the fish,
thus keeping the gills moist and functional. In most other fishes the
gill-chamber is not capable of holding water, and thus the gills soon
become dry and sticky, so that they adhere together and fail to absorb
the necessary oxygen when the fish is out of water.
Thus the Eel (_Anguilla vulgaris_), in the remarkable migrations for
which it is noted, is capable of travelling over dry land for
considerable distances in search of suitable homes.
If an eel be taken out of the water, these gill-pouches will be seen to
swell out almost immediately, and remain filled with water as long as
the fish is kept on land; but when it is returned to its natural
element, it will at once discharge the water that kept its gills moist,
and which has become foul with the products of respiration, and, with a
few vigorous gulps, renew the supply.
Eels spend their breeding season, which extends from July to September,
in salt or brackish waters; and early in the following summer, the
young, which are now called _elvers_, and measure from three to five
inches in length, ascend the rivers, travelling enormous distances and
overcoming obstacles that we might well expect to be insurmountable.
Thus they perform two migrations annually, though it is thought by some
observers that the adult never returns to the sea, but dies soon after
it has deposited its spawn.
The family of Flat-fishes (_Pleuronectidæ_) present many interesting
points of structure and habit in which they stand alone, the variations
in structure as compared with other fishes being due, of course, to the
habits which they have acquired.
One of the first features that strike the observer on looking at a
flat-fish is the unsymmetrical form of the body. It is very much
compressed, and the fish having acquired the habit of lying on the bed
of the sea, sometimes on the left and sometimes on the right side, the
lower surface has become flattened more, and is of an almost pure white
colour, while the upper convex side is more or less coloured with
pigment produced by exposure to light. The dorsal and ventral fins are
both very long; and, as is usual with bottom fishes, the swimming or air
bladder is absent.
Young flat-fish are at first perfectly symmetrical in form, with one eye
on each side of the head, and they swim freely in the water with their
bodies in a vertical plane; but they very soon acquire the habit of
swimming on one side, and the eye of that side slowly passes round to
the other side of the skull, rotating in its orbit as it moves, till at
last both are on the uppermost surface. This, of course, is accompanied
by a considerable distortion of the bones of the skull, which is very
evident in the skeleton of the adult. The young fish then takes to the
bottom, with the result that its under-surface is flattened, while the
upper becomes strongly pigmented.
These fish spend almost the whole of their time on the bottom, only
occasionally rising for short intervals, when they swim by undulatory
movements of their bodies and fins; their food consists of crustaceans,
worms, and other small marine animals.
They furnish very interesting illustrations of protective colouring, the
upper surface always closely resembling the ground on which they rest
and feed; and thus they are not only protected from their own enemies,
but are enabled to lie unseen by the animals that form their prey. Those
which live on sandy shores are finely spotted with colours that closely
imitate the sand, while those that lie on mud are of dark and dingy
hues. Others, again, are irregularly marked with spots of various sizes
and colours that resemble a gravelly bottom; and most species are still
further protected by their habit of throwing sand or mud on the top of
their bodies by means of their dorsal and ventral fins.
Small flat-fishes, especially young Plaice and Flounders, live so close
to the shore that they are often left behind in rock pools and sandy
hollows by the receding tide, and it is very interesting to observe the
habits of these in their natural conditions. It will generally be
noticed that it is most difficult to detect them while they are at rest;
and when disturbed, they usually swim but a short distance, settling
down very abruptly, and immediately throwing a little sand over their
bodies by a few vibrations of their fins.
Another peculiarity of some of the flat-fishes is their indifference to
the nature of the water in which they live. Flounders may not only be
caught in the estuaries of our rivers, but they even ascend to, and
apparently live perpetually in, perfectly fresh water. In many
instances they may be seen miles from the sea, and even flourishing in
little fresh-water streams only a few feet in width. Thus they may be
found in numbers in the upper waters of the small rivers of the Isle of
Wight and of many streams of the mainland.
The principal British flat-fishes are the Plaice (_Pleuronectes
platessa_) and Flounder (_P. flexus_) above mentioned, and also the Sole
(_Solea vulgaris_), the Lemon Sole (_S. aurantiaca_), the Turbot
(_Rhombus maximus_), and the Halibut (_Hippoglossus vulgaris_); and as
all these are well-known food-fishes it is hardly necessary to describe
them.
[Illustration: FIG. 233.--THE LESSER SAND EEL]
Sand Eels (family _Ophidiidæ_) resemble the true eels in the general
form of their elongated bodies, but may be readily distinguished by
their bright silvery colour, the large gill-openings, and the more
strongly developed dorsal and ventral fins, the former of which extends
almost along the whole length of the back. The lower jaw is also longer
than the upper.
Two species are to be found on our shores--the Lesser Sand Eel
(_Ammodytes tobianus_), and the Greater Sand Eel (_A. lanceolatus_), the
former attaining a length of six or seven inches, and the latter nearly
three times this size. They may be seen off the south coast, swimming in
shoals over sandy bottoms, and when disturbed they descend and burrow
into the sand with remarkable agility. They approach the shore so
closely that they are often washed up by the waves, but immediately
disappear into the sand; and large numbers commonly remain behind as
the tide recedes, burying themselves to the depth of a few inches, and
are dug out by fishermen for bait.
The smaller species is by far the more common, and is taken in large
numbers by means of the draw net to be sold as food. It is particularly
abundant at Teignmouth, where it is known as the Sand Sprat, and forms
an important article of diet.
Quite a number of our important food-fishes belong to the Cod family
(_Gadiadæ_), and although some of these are caught almost entirely in
deep water some distance from shore, others give employment to the
angler fishing from rocks, piers, and jetties.
In all, the gill-openings are very wide, and the body is covered with
small overlapping scales. The caudal fin is quite free, the dorsal is
generally divided into three distinct parts which extend over the
greater part of the back, and the ventral fin is also frequently
divided.
[Illustration: FIG. 234.--THE THREE-BEARDED ROCKLING]
The typical species--the Cod (_Gadus morrhua_)--is too well known to
need a description, and although it is a large fish, often measuring
four feet and more, it approaches so close to the shore that it may be
caught with a hand line thrown out from rocks or piers. The barbel
projecting from the chin denotes that it is a bottom feeder.
On the rocky coast of the south the Pollack or Pollock (_G. pollachius_)
is very abundant, and may be taken with rod and line from the shore. It
also enters estuaries in large numbers, and may be caught close to quays
and jetties. This species is a very free biter, and will take almost any
of the baits used for sea fishing. It has no barbel.
The same genus includes the Whiting (_G. merlangus_), distinguished by a
black spot at the base of the pectoral fin and the absence of barbels;
the Whiting Pout (_G. luscus_), with a similar black spot at the base of
the pectorals, also dark, transverse bands, and a barbel; and the
Haddock (_G. æglefinus_), with a black patch on either side above the
pectorals, and a dark lateral line. The family also includes the Ling
(_Molva vulgaris_) and the Hake (_Merluccius vulgaris_), both of which
are caught in deep water; and the Rocklings (genus _Motella_), three
species of which frequent our rocky shores.
[Illustration: FIG. 235.--THE SNAKE PIPE-FISH]
The last mentioned are interesting little fishes that may be found on
stony beaches at low tide, for they often remain under cover between the
tide-marks, and may be seen on turning over stones and weeds. Perhaps
the commonest of them is the Five-bearded Rockling (_M. mustela_), which
has four barbels on the upper lip and one on the lower. It is of a
dark-brown colour above, and light below, and makes nests of corallines
in rock cavities. The Three-bearded Rockling (_M. tricirrhata_), known
also as the Sea Loach and the Whistle-fish, is a larger species,
sometimes reaching a length of a foot or more. Its colour is light
brown, marked with darker spots, and, like the other species, it lives
in the shallow water of rocky and weedy places. Another species--the
Four-bearded Rockling (_M. cimbria_), known by the three barbels on the
upper lip and one on the lower, is about eight inches long when full
grown, and is found principally on the northern shores.
Our next family (_Syngnathidæ_) contains some peculiar creatures called
Pipe-fishes because their jaws are united into a tube. They have long
and slender bodies that are covered with bony plates which form a kind
of coat of mail and give them an angular form. They have very small
gill-openings, a single dorsal fin, and no pelvics.
Pipe-fishes are very sluggish in habit, swimming but little, and living
in the shelter of weeds and stones on rocky coasts. In fact, they are
not adapted for swimming, and their attempts at this mode of locomotion
are awkward in the extreme, for their bodies are rigid and the tail very
small. When removed from their hiding-places they move but little, and
look as much like pieces of brown or greenish wood as fishes; and their
rigid bodies are so completely encased in the bony plates that they
alter but little in appearance when dried, and consequently the dried
specimens are often seen in museum collections.
All the British species, four in number, are small fishes, inhabiting
the shallow water of rocky shores, and are often found hiding under
stones near low-water mark. The largest is the great Pipe-fish or
Needle-fish (_Syngnathus acus_), which grows to a length of about
fifteen inches; and the smallest is the Worm Pipe-fish (_S.
lumbriciformis_), which is of an olive-green colour, and has a short,
upturned snout. The Lesser Pipe-fish (_S. typhle_), also known as the
Deep-nosed Pipe-fish, is very abundant on nearly all rocky coasts, and
may be distinguished from the others by having the ridge on the tail
continuous with the lateral line and not with the dorsal angle. The
other species is the Slender-nosed Pipe-fish or Snake Pipe-fish
(_Nerophis ophidium_), the body of which is extremely slender, and the
tail long and narrow. The male is provided with a series of small,
cup-like cells, in each of which he carries an egg.
In all the bony fishes previously mentioned the fin rays are soft and
flexible, and in this respect they differ from those that are to follow,
for the remaining families are all characterised by the presence of one
or more sharp rigid spines on the dorsal fin, and often by similar
spines on other fins. They constitute the group of Spiny-finned fishes.
Of these we shall first take the prettily coloured Wrasses (family
_Labridæ_), which live in the holes of rocks and under the cover of
weeds on rugged coasts. These fishes are very voracious in habit, and
the sea angler will find that they are ready to seize almost any bait
that may be offered them, and even to attack almost everything that
moves within sight; but they are likely to give much trouble since they
will rush into the crevices of rocks or among large weeds when hooked,
and thus frequently lead to the breaking of the line.
Wrasses feed principally on molluscs and crustaceans, and are provided
with extensile telescopic lips that enable them to pull the former from
the rocks on which they creep, and the latter from their hiding-places
among the rocks. They have also strong teeth in the gullet, by which
they can crush the shells of their prey.
There are several British species of Wrasses, one of which is shown in
the accompanying illustration. The commoner ones are known to fishermen
and juvenile anglers by quite a variety of local names.
[Illustration: FIG. 236.--THE RAINBOW WRASS (_Labrus julis_)]
The family _Gobioesocidæ_ contains some small and very prettily coloured
fishes of very peculiar habits, known popularly as Sucker-fishes. They
have one or two adhesive suckers between the pelvic fins by which they
attach themselves to rocks, stones, and shells. Some are littoral
species, and may be searched for at low tide; but others inhabit deeper
water, and are seldom obtained without a dredge.
[Illustration: FIG. 237.--THE CORNISH SUCKER]
One of the former is the Cornish Sucker (_Lepadogaster cornubiensis_),
which may sometimes be taken in a hand net by scraping the rocks and
weeds at low tide on the south-west coast. It has two suckers, each
circular in form, surrounded by a firm margin, within which is a soft
retractile centre. This central portion is attached to muscles by which
it can be withdrawn; and a vacuum is thus produced, so that the sucker
adheres by atmospheric pressure. The structure of the sucking organs can
be seen to perfection when the fish attaches itself to the side of a
glass aquarium, and if it be taken in the hand it will cling quite
firmly to the skin.
This peculiar little fish is only about three inches long, and its broad
head is marked with two conspicuous purple spots, with a blue dot in the
centre, and surrounded by a yellowish ring.
The allied species include the very small Two-spotted Sucker (_L.
bimaculatus_), which is of a bright red colour, and adheres to stones
and shells in deep water; the Sea Snail (_Cyclopterus liparis_), about
four or five inches long, with a soft and slimy semi-transparent body;
and Montagu’s sucker (_C. Montagui_), which is usually under three
inches in length, and may be distinguished by its peculiar habit of
curling the body laterally when at rest.
Equally interesting are the little Sticklebacks (family _Gastrosteidæ_),
the fresh-water representatives of which are known to almost everyone.
Their pugnacious habits, the bright colours assumed during the breeding
season, and the wonderful nests which they build for the protection of
their eggs and young, have all served to make them popular with those
who take interest in the forms and ways of animals. They are, moreover,
such hardy creatures that they may be kept alive for a considerable time
in any well-managed aquarium.
[Illustration: FIG. 238.--THE FIFTEEN-SPINED STICKLEBACK AND NEST]
In this family the hindmost portion of the dorsal fin is soft-rayed, but
the front portion is represented by a row of strong, sharp, erectile
spines, which constitute a formidable weapon of offence and defence.
Most of the species live in fresh water, but all the members of the
family seem to be able to live almost equally well in both salt and
fresh water.
We have one marine species--the Sea Stickleback or Fifteen-spined
Stickleback (_Gastrosteus spinachia_), which may be caught on rocky and
weedy coasts. It derives one of its popular names from the presence of
fifteen spines along the middle of the back. Its tail is long and
narrow, and its snout elongated, with the under jaw projecting beyond
the upper.
The nest of this species is a pear-shaped mass of soft sea weeds and
corallines, all bound together by a silky secretion, and suspended to
the rock in a sheltered spot. Within this the female deposits her eggs
in little clusters, all of which are bound together and to the nest
itself by the silk. If the nest is damaged while occupied, it is
immediately repaired, the male, it is said, taking upon himself the
responsibility of this task.
Sand Smelts (family _Atherinidæ_) resemble the true smelts previously
described, but may be readily distinguished by the anterior dorsal fin,
which is small and spinous. We have two species of this family, of which
_Atherina presbyter_ is by far the more common. It is a very pretty
fish, about five inches long, with a broad silvery stripe along each
side. It is very common on the sandy coasts of the south, where it also
enters the brackish waters of estuaries. Young anglers catch them in
considerable numbers by means of rod and line; but the professional
fisherman, taking advantage of the fact that sand smelts swim in shoals,
captures them in large, round, shallow nets. The net is baited with
bread, crushed mussels, or offal of almost any kind, and is then lowered
several feet below the surface by means of a long pole, to the end of
which it is suspended. It is raised to the surface at short intervals,
and will often enclose dozens of fish in a single haul.
The shallow waters of our southern coasts, including the estuaries and
harbours, are also frequented by the Grey Mullet (_Mugil capito_), of
the family _Mugilidæ_. This fish may be distinguished from other similar
species by the four stiff spines of the front dorsal fin, and by the
absence of a lateral line. The mouth is small, and without teeth, and
the mode of feeding is somewhat peculiar. The food consists of worms,
molluscs, and various organic matter contained in the sand or mud of the
bottom. It is sucked into the mouth, together with more or less of the
mud and sand, and the former is strained through a special straining
apparatus situated in the pharynx.
The Grey Mullet may be taken with rod and line, and bites freely when
the rag-worm is employed as bait. It is often taken in the fisherman’s
drag net; but, being a splendid jumper, it frequently makes its escape
as the net is drawn on the beach.
Few of our littoral fishes are so well known as the Little Blennies
(family _Blenniidæ_), which are to be found hiding amongst the weeds in
almost every rock pool, and under stones as they await the return of
the tide. Their bodies are generally cylindrical, and are either naked
or covered with very minute scales. The dorsal fin runs along the whole
length of the back, and each pelvic has one spine and two soft rays.
When taken out of the water the gill-cavities widen considerably, and
the eyeballs will be seen to move independently of each other, like
those of the chamæleon.
Most of the blennies are very active and voracious fishes, often giving
considerable trouble to the angler when fishing with a rod among the
rocks. They will bite at almost anything that moves, and, completely
swallowing the angler’s hook, will immediately rush into a crevice from
which it is often difficult to remove them.
Most of them have tentacles on the head by which they assist their
movements among the rocks and stones; and some actually creep up the
rugged surfaces of rocks by means of their ventral fins. They can all
live for a long time out of the water, being able to retain a supply of
water in their expanded gill-chambers to keep the gills moist.
[Illustration: FIG. 239.--THE SMOOTH BLENNY]
The Smooth Blenny or Shanny (_Blennius pholis_) is one of the commonest
species. It reaches a length of four or five inches, and has no
tentacles on the head. The Eyed Blenny or Butterfly Blenny (_B.
ocellatus_) may be distinguished by the conspicuous spot on the spinous
portion of the dorsal fin. The Large Blenny (_B. gattorugine_) inhabits
deeper water, chiefly off the south-west coast, and reaches a length of
a foot or more. The Crested Blenny (_B. cristatus_) is named from the
small crest on the head which can be raised and depressed; and the
Viviparous Blenny (_Zoarces viviparus_), as its name implies, brings
forth its young alive. The last species often exceeds a foot in length,
and is found principally on the north and east coasts. The newly-born
young are so transparent that the circulation of the blood within the
body may be seen under the microscope quite as easily as in the web of
the frog’s foot and in the tail of the tadpole.
One very common species of the _Blenniidæ_ differs considerably in
general form from the others, its body being elongated and eel-like, but
much compressed laterally. We refer to the Butterfish or Butter Gunnel
(_Blennius gunellus_), which is often mistaken for a small eel by young
sea-side naturalists. It is exceedingly common under stones at low tide,
and may be recognised at once by the light rectangular spots along the
flattened sides of the body. It is quite as slippery and as difficult to
hold as the eel itself.
It will be interesting to note that the ugly Sea Cat or Wolf-fish
(_Anarrhichas lupus_), which is sometimes sold for food in our large
towns, is also a member of the blenny family. It is a powerful,
rapacious fish--a veritable wolf of the sea, always ready to attack
anything. It feeds on molluscs and crustaceans, the shells of which are
easily reduced between the powerful crushing teeth that line the jaws
behind the formidable canines.
[Illustration: FIG. 240.--THE BUTTERFISH]
The Gobies (_Gobiidæ_) form another interesting family of small littoral
fishes, easily distinguished by the fact that the ventral fins are
united in such a manner that they enclose a conical cavity. The first
portion of the dorsal fin has also six flexible spines. The Spotted Goby
(_Gobius minutus_) is commonly to be found on sand-banks, where it is
well protected by the colouring of its upper surface, which closely
resembles that of the sand on which it rests. It is said to make a nest
by cementing fragments together round some little natural hollow, or to
utilise an empty shell for a similar purpose, fixing the shell to the
surrounding bed, and constructing a tunnel by which it can enter or
leave. The eggs are deposited in this nest, and the male keeps guard
over the home. The Black or Rock Goby (_G. niger_) inhabits rocky
coasts, clinging to the rocks by means of a sucker formed of the
modified pelvic fins.
A brightly coloured fish known as the Dragonet (_Callionymus lyra_) is
sometimes classed with the Gobies, though its pelvic fins are not
united. It is not a well-known species, and is seldom obtained except
with the dredge, as it inhabits deep water.
[Illustration: FIG. 241.--THE BLACK GOBY]
A peculiar little fish called the Pogge or Hook-nose (_Agonus
cataphractus_), also known as the Armed Bull-head, is commonly taken in
shrimpers’ nets on the south and east coasts. Its head and body are very
angular, and are covered with an armour of keeled scales. It seldom
exceeds six inches in length, and is classed with the Flying Gurnards in
the family _Dactylopteridæ_.
[Illustration: FIG. 242.--THE FATHER LASHER]
The true Gurnards and the Sea Bullheads form the family _Cottidæ_.
Several species of the former are included among our food-fishes, and
are therefore more or less familiar to our readers. They are
characterised by their large, square, bony heads, and by the finger-like
rays of the pectoral fins which are used as organs of touch and for
creeping along the bottom of the sea. The Bullheads are represented by
the peculiar Father Lasher or Sting Fish (_Cottus bubalis_), which is
very common on our rocky coasts and is frequently captured in shrimp
nets. Its head and cheeks are armed with sharp spines which constitute
formidable weapons of offence. When taken out of the water it distends
its gills enormously; and, unless very cautiously handled, its sharp
spines may be thrust deeply into the flesh. Young specimens, with
imperfectly developed spines, may be seen in almost every rock pool, and
the full-grown fish is easily taken with rod and line by fishing in the
deep gulleys between the rocks.
The remarkable Angler Fish (_Lophius piscatorius_), known also as the
Fishing Frog and the Sea Devil (family _Lophiidæ_) is sometimes taken
off the coasts of Devon and Cornwall; and although it cannot be truly
described as a littoral species, its structure and habits are so
peculiar that it deserves a passing notice. It is an ugly fish, with an
enormous head, a short naked body, and a comparatively slender tail. The
mouth is very capacious, sometimes measuring over a foot from angle to
angle, and is directed upwards. The scaleless body is furnished with
numerous slender filaments that resemble certain filamentous sea weeds,
and these together with the dull colouring of the body generally enable
the fish to rest unobserved on the bottom. The front portion of the
dorsal fin is on the head and fore part of the body, and consists of a
series of six tentacles, three long ones on the top of the head and
three shorter just behind them; and the foremost of these, which is the
longest, terminates in a little expansion which is kept in constant
movement by the fish. The mouth is armed with rasplike teeth which can
be raised or depressed at will, and when raised they are always directed
backward; the eyes are directed upward, and the gill-openings are very
small.
This strange creature habitually rests on the bottom of the sea,
disguised by its filamentous appendages and adaptive colouring, dangling
the expanded extremity of its first dorsal filament just over its
upturned cavernous mouth. It does not swim much, indeed it is at the
best but a bad swimmer; and when it moves it simply shuffles its heavy
body along the bottom, gliding between the stones and rocks, where it
may remain unobserved, its movements being produced by the action of the
tail, and of the paired fins, which are better adapted for walking than
for swimming. Unwary fishes, attracted by the dangling of the angler’s
bait, approach the watchful monster, and while speculating on the nature
of the bait, are suddenly engulfed in the capacious mouth, from which
there is no escape on account of the backward direction of the teeth.
The family _Trachinidæ_ contains the fishes known popularly as the
Stargazers and the Weavers. These are small, carnivorous species, with
rather elongated bodies, terminating in tail fins that are not forked.
The first dorsal fin is distinct and spinous, and the spines, as well as
others that are developed on the gill-covers, are grooved for the
passage of a poisonous fluid that is secreted at their bases.
Our littoral species include two well-known fishes (the Greater and
Lesser Weavers) that are dreaded by fishermen on account of the very
painful wounds they are capable of inflicting, and the smaller of the
two is also a considerable annoyance to bathers on certain sandy coasts.
[Illustration: FIG. 243.--THE LESSER WEAVER]
The Greater Weaver (_Trachinus draco_) lives at the bottom of deep
water, and is often dredged up in the trawl. Some fishermen call it the
Sting Bull, and always take the precaution of cutting off the poisonous
spines before disposing of the fish. It lives on the bottom with its
mouth and eyes directed upward, always in readiness to seize its unwary
prey, and the sharp spines of the dorsal fins are kept erect for the
purpose of promptly attacking approaching foes. Its mouth and palate are
armed with sharp teeth which render the escape of its prey almost
impossible. The smaller species (_T. vipera_) seldom exceeds six inches
in length. It lives in shallow water on sandy coasts, with dorsal spines
erect; and the wounds it produces on the unprotected feet of bathers are
often exceedingly painful on account of the injected poison, which also
causes the part to swell and turn to a dark purple colour.
The remaining important families, although they contain well-known
British food-fishes, do not include littoral species, and for this
reason we shall pass them over with but brief notice.
The Mackerel (_Scomber vernalis_) belongs to the family _Scomberidæ_,
and is so well known that no description need be given for the purposes
of identification. We have already referred to it as a beautiful
illustration of protective colouring, its upper surface resembling the
ripples of a deep green sea and the lower the brightness of the sky.
Mackerel swim in shoals in the open sea, pursuing and devouring the fry
of herrings and other fish; and in order that they may be enabled to
cover enormous distances their muscles are richly supplied with blood.
This not only gives a pinkish colour to the flesh, but results in a
greater amount of oxidation and the maintenance thereby of a body
temperature several degrees higher than that of the surrounding water.
We would also call attention to the five or six small fins behind the
dorsal and anal fins as characteristic of the _Scomberidæ_.
Our next family (the _Cyttidæ_) contains the John Dory (_Zeus-faber_),
concerning which some superstitions are still prevalent in parts. It is
brightly coloured, but not graceful in form, and is often caught in
large numbers off the coasts of Devon and Cornwall. Some fishermen call
it the Cock, on account of the crest on the back; while others know it
as St. Peter’s Fish, and will point out the impression of the Apostle’s
finger on each side--a black spot surrounded by a light ring.
The Horse Mackerel (_Caranx trachurus_) is found principally in the same
parts, where it devours the fry of other fishes. It is not a very close
relative of the common mackerel, but belongs to a distinct family
(_Carangidæ_), of which it is the only British representative. It is a
carnivorous fish, easily distinguished from _Scomber_ by its conical
teeth, as well as by the bony plates of the lateral line, the posterior
of which are keeled or spined.
While the last-mentioned families contain only fishes of truly pelagic
habits, the next (_Sparidæ_), formed by the Sea Breams, generally keep
near the coast, and often enter fresh waters. In these the body is much
compressed laterally, and is covered with large scales; the first half
of the dorsal fin is also spinous. The Common Sea Bream (_Sparus
auratus_), characterised by its red colour with brilliant golden
reflections, and by a dark spot on the shoulder, may often be angled
from rocks and piers. The young, in which the dark spots have not yet
appeared, are known as Chads, and are often regarded as a distinct
species. The Black Bream (_Cantharus lineatus_) is an omnivorous feeder,
and will take both animal and vegetable baits.
The Red Mullets (family _Mullidæ_) may be distinguished from the grey
mullets previously described by the two long erectile barbules on the
lower jaw. The scales are large and thin, with serrated edges, and the
front portion of the dorsal fin has weak spines. The common British
species (_Mullus barbatus_) frequents our south and east coasts, being
specially abundant round Devon and Cornwall, where they often occur in
vast shoals, and the young are often to be caught in estuaries and
harbours.
Our last example is the Common Bass or Sea Perch (_Morone abrax_), of
the family _Serranidæ_. It is also known locally as the White Salmon
and the Salmon Dace. This fish may be taken with rod and line on rocky
coasts and at the mouths of rivers. The sand-eel, or an artificial
imitation of it, is commonly used as bait, but the Cornish fishermen
more frequently employ a piece of herring or pilchard for the purpose.
The first dorsal fin of this fish has very strong spines which may
inflict severe wounds when the live creature is carelessly handled.
* * * * *
Omitting all mention of sea birds, for the reason previously given, we
now pass to the highest division of vertebrates--the Mammals--of which
we shall describe but one species--the Common Porpoise, this being the
only marine mammal that can be regarded as a frequent visitor to the
British coasts in general.
It may be well at the outset to understand exactly why the porpoise is
classed with the mammals and not with the fishes--to see how its
structure and functions correspond with those of our own bodies rather
than with those of the animals dealt with in the preceding portion of
the present chapter.
First, then, while the young of fishes are almost invariably produced
from eggs and are not nourished by the parents, the young of the
porpoise are produced alive, and are nourished with milk secreted by the
mammary glands of the mother. This is an all-important feature, and is
the one implied in the term _mammal_. The porpoise also differs from
nearly all fishes in that it breathes by lungs instead of gills,
obtaining its air direct from the atmosphere, and not from the water.
Hence we find it coming to the surface at frequent intervals to
discharge its vitiated air and to inhale a fresh supply. The body-cavity
of a mammal is divided into two parts by a muscular diaphragm, the
foremost division, called the thorax, containing the heart and lungs,
and the other (the abdomen) the remainder of the internal organs, while
the diaphragm itself plays an important part in the respiratory movement
by which air is drawn into the lungs. The body of the porpoise is so
divided, but no such division ever occurs in any of the fishes. Lastly,
the heart of the porpoise, in common with the rest of the mammals, is
divided into four cavities, and the blood is warm, while the heart of a
fish has generally only two divisions, and the blood propelled by it is
of about the same temperature as that of the surrounding medium. Several
other important differences between the porpoise and the fish might be
given, but the above will be quite sufficient to show why they are
placed in different classes.
Mammals are divided into several classes, and one of these (_Cetacea_)
includes the fish-like Whales, Porpoises, and Dolphins, all of which are
peculiarly adapted to a purely aquatic life. Like most of the fishes,
their upper surfaces are of a dark colour, and the lower very light.
Their fore limbs are constructed on the same plan as those of the higher
mammals, the bones of the arm being attached to a large shoulder-blade,
and the hand formed of four or five well-developed fingers which are
enclosed in skin, so that they constitute a paddle or flipper well
adapted for propulsion through water. There is no collar-bone, however,
and the fingers have no nails or claws. There are no hind limbs visible
externally, but a rudimentary pelvic girdle forms a part of the internal
skeleton. A dorsal fin exists, but this is merely an extension of the
skin of the back, and is not supported by either bones or rays. The skin
itself has no scales, like that of most fishes, but is smooth and naked;
and below it lies a large amount of fat, which, being a very bad
conductor of heat, serves to prevent the escape of heat from the body.
The tails of cetaceans are also mere folds of the skin, supported in the
centre by the extremity of the vertebral column; but unlike the tail
fins of fishes, they are expanded horizontally instead of in the
vertical plane. This latter is an important adaptive feature of the
cetaceans, since the vertical movement of a tail so disposed is exactly
what is required to assist the animals as they alternately rise to the
surface for air and again descend into the sea in search of their food.
Among the other external characters of the cetacean we may note the
nostrils, which are always situated on the highest point of the head,
and are thus the first part exposed when the creature rises to renew its
supply of air; also the ears, which are two small apertures behind the
eye, without any form of external appendages.
The skeleton of the cetacean is formed of light spongy bones, saturated
with oily matter; and although the animal has no true neck, visible as
such externally, it is interesting to note that, in common with all
other mammals, even with the long-necked giraffe, it possesses its seven
cervical or neck vertebræ.
Porpoises and Dolphins together form the family _Delphinidæ_,
characterised by having the blow-hole in the form of a crescent with its
convexity turned towards the front, and of these the Porpoises
constitute the genus _Phocæna_.
The Common Porpoise (_P. communis_) is the species that is so often
seen close to our shores and in the harbours and estuaries, swimming in
shoals with a graceful undulatory movement. Porpoises move forward
entirely by the vertical action of their powerful horizontal tails, and
extend their flippers only to change their course or to arrest their
progress. At short intervals they rise to the surface, exposing their
slate-coloured backs and dorsal fins for a moment, and then immediately
dive downwards in such a manner as to appear to turn a series of
somersaults. Occasionally they will leap quite out of the water,
exhibiting their white under surfaces, which shine with a sudden flash
when illuminated by the rays of a bright sun. The blow-hole is the first
part exposed, and if one is sufficiently near the shoal a fountain of
spray may be seen to shoot into the air, and the outrush of the expired
air may be heard as each one makes its appearance.
[Illustration: FIG. 244.--THE COMMON PORPOISE]
The true nature of the spouting of a cetacean seems to be very generally
misunderstood, the fountain of spray produced at each exhalation giving
the idea that the animal is expelling a quantity of water from its
nostrils. This, of course, is not the case; for the cetacean, being an
air-breather, has no need to take in a supply of water, as the
gill-breathing fishes have. Air only is expelled through the nostrils;
but as the expiration sometimes commences before these apertures are
brought quite to the surface, a certain amount of water is shot upwards
with the expired air; and even if the expiration commences after the
nostrils are exposed, the small quantity of water they contain is blown
into a jet of spray; and in a cool atmosphere, the density of this is
increased by the condensation of vapour contained in the warm and
saturated air from the lungs of the animal. It will be noticed, too,
that the creature does not check its course in the least for the purpose
of respiration, the foul air being expelled and a fresh supply taken in
exchange during the short time that the blow-hole remains above the
surface of the water.
The Common Porpoise measures five or six feet in length, and subsists on
pilchards, herrings, mackerel, and other fish, the shoals or ‘schools’
of which it pursues so closely that it is often taken in the fishermen’s
nets. Its flesh was formerly eaten in our own country, but it is now
seldom hunted except for its oil and its hide. About three or four
gallons of the former may be obtained from each animal; and the latter
is highly valued on account of its durability, though it should be known
that much of the so-called porpoise-hide manufactured is really the
product of the White Whale.