DOMESTICATED AND ACCLIMATISED FISHES; ARTIFICIAL IMPREGNATION
OF OVA--TENACITY OF LIFE AND REPRODUCTION OF LOST
PARTS--HYBERNATION--USEFUL AND POISONOUS FISHES.
A few fishes only are thoroughly domesticated--that is, bred in
captivity, and capable of transportation within certain climatic
limits--viz. the Carp, Crucian Carp (European and Chinese varieties),
Tench, Orfe or Ide, and the Goramy. The two former have accompanied
civilised man almost to every place of the globe where he has effected
a permanent settlement.
Attempts to acclimatise particularly useful species in countries in
which they were not indigenous have been made from time to time, but
were permanently successful in a few instances only; the failures
being due partly to the choice of a species which did not yield the
profitable return expected, partly to the utter disregard of the
difference of the climatic and other physical conditions between the
original and new homes of the fish. The first successful attempts of
acclimatisation were made with domestic species, viz. the Carp and
Gold-fish, which were transferred from Eastern Asia to Europe. Then,
in the first third of the present century, the Javanese Goramy was
acclimatised in Mauritius and Guiana, but no care seems to have been
taken to insure permanent advantages from the successful execution
of the experiment. In these cases fully developed individuals were
transported to the country in which they were to be acclimatised. The
most successful attempt of recent years is the acclimatisation of the
Trout and Sea-Trout, and probably also of the Salmon, in Tasmania and
New Zealand, and of the Californian Salmon (_Salmo quinnat_?),
in Victoria, by means of artificially-impregnated ova. The ova were
transported on ice, in order to retard their development generally,
and thus to preserve them from destruction during the passage of the
tropical zone.
_Artificial impregnation_ of fish-ova was first practised by
J. L. JACOBI, a native of Westphalia, in the years 1757–63,
who employed exactly the same method which is followed now; and there
is no doubt that this able observer of nature conceived and carried
out his idea with the distinct object of advantageously restocking
water-courses which had become unproductive, and increasing production
by fecundating and preserving all ova, of which a great proportion,
in the ordinary course of propagation, would be left unfecundated
or accidentally perish. Physiology soon turned to account Jacobi’s
discovery, and artificial impregnation has proved to be one of the
greatest helps to the student of embryology.
Fishes differ in an extraordinary degree with regard to tenacity of
life. Some will bear suspension of respiration--caused by removal from
water, or by exposure to cold or heat--for a long time, whilst others
succumb at once. Nearly all marine fishes are very sensitive to changes
in the temperature of the water, and will not bear transportation from
one climate to another. This seems to be much less the case with some
freshwater fishes of the temperate zones: the Carp may survive after
being frozen in a solid block of ice, and will thrive in the southern
parts of the temperate zone. On the other hand, some freshwater
fishes are so sensitive to a change in the water that they perish
when transplanted from their native river into another apparently
offering the same physical conditions (Grayling, _Salmo hucho_).
Some marine fishes may be abruptly transferred from salt into fresh
water, like Sticklebacks, some Blennies, and _Cottus_, etc.;
others survive the change when gradually effected, as many migratory
fishes; whilst again, others cannot bear the least alteration in the
composition of the salt water (all pelagic fishes). On the whole,
instances of marine fishes voluntarily entering brackish or fresh water
are very numerous, whilst freshwater fishes proper but rarely descend
into salt water.
Abstinence from food affects different fishes in a similarly different
degree. Marine fishes can endure hunger less than freshwater fishes,
at least in the temperate zones, no observations having been made in
this respect on tropical fishes. Goldfishes, Carps, Eels, are known to
be able to subsist without food for months, without showing a visible
decrease of bulk; whilst the Trigloids, Sparoids, and other marine
fishes, survive abstinence from food for a few days only. In freshwater
fishes the temperature of the water is of great influence on their
vital functions generally, and consequently on their appetite,--many
cease to feed altogether in the course of the winter; a few, like the
Pike, are less inclined to feed during the heat of the summer than when
the temperature is lowered.
Captivity is easily borne by most fishes, and the appliances introduced
in our modern aquaria have rendered it possible to keep in confinement,
and even to induce to propagate, fishes which formerly were considered
to be intolerant of captivity.
Wounds affect fishes generally much less than higher Vertebrates. A
Greenland Shark continues to feed whilst his head is pierced by a
harpoon or by the knife, as long as the nervous centre is not touched;
a Sea-perch or a Pike (Fig. 97) will survive the loss of a portion of
its tail; a Carp that of half of its snout. However, some fishes are
much more sensitive, and perish even from the superficial abrasion
caused by the meshes of the net during capture (_Mullsn_.)
The power of _reproduction_ of _lost parts_ in Teleosteous fishes is
limited to the delicate terminations of their fin-rays and the various
tegumentary filaments with which some are provided. These filaments are
sometimes developed in an extraordinary degree, mimicking the waving
fronds of the seaweed in which the fish hides. Both the ends of the
fin-rays and the filaments are frequently lost, not only by accident,
but merely by wear and tear; and as these organs are essential for the
preservation of the fish, their reproduction is necessary.
[Illustration: Fig. 97.--Pike caught in the Thames, which, when
young, had lost part of the tail with the caudal fin.]
In Dipnoi, _Ceratodus_, and _Protopterus_, the terminal portion of the
tail has been found to have been reproduced, but without the notochord.
* * * * *
_Hybernation_ has been observed in many Cyprinoids and Murænoids
of the temperate zones. They do not fall into a condition of complete
torpidity, as Reptiles and Mammals, but their vital functions are
simply lowered, and they hide in sheltered holes, and cease to go
abroad in search of their food. Between the tropics a great number
of fishes (especially Siluroids, Labyrinthici, Ophiocephaloids, the
Dipnoi), are known to survive long-continued droughts by passing the
dry season in a perfectly torpid state, imbedded in the hardened mud.
Protopterus, and probably many of the other fishes mentioned, prepare
for themselves a cavity large enough to hold them, and coated on the
inside with a layer of hardened mucus, which preserves them from
complete desiccation. It has been stated that in India fishes may
survive in this condition for more than one season, and that ponds
known to have been dry for several years, and to the depth of many
feet, have swarmed with fishes as soon as the accumulation of water
released them from their hardened bed.
* * * * *
The principal _use_ derived by man from the class of Fishes consists in
the abundance of wholesome and nourishing food which they yield. In the
Polar regions especially, whole tribes are entirely dependent on this
class for subsistence; and in almost all nations fishes form a more or
less essential part of food, many being, in a preserved condition, most
important articles of trade. The use derived by man from them in other
respects is of but secondary importance. Cod-liver oil is prepared from
the liver of some of the Gadoids of the Northern Hemisphere, and of
Sharks; isinglass from the swim-bladder of Sturgeons, Sciænoids, and
Polynemoids; shagreen from the skin of Sharks and Rays.
* * * * *
The flesh of some fishes is at times, or constantly, _poisonous_.
When eaten, it causes symptoms of more or less intense irritation of
the stomach and intestines, inflammation of the mucous membranes, and
not rarely death. The fishes, the flesh of which appears always to
have poisonous properties, are _Clupea thrissa_, _Clupea venenosa_,
and some species of _Scarus_, _Tetrodon_, and _Diodon_. There are
many others which have occasionally or frequently caused symptoms of
poisoning. Poey enumerates not less than seventy-two different kinds
from Cuba; and various species of _Sphyræna_, _Balistes_, _Ostracion_,
_Caranx_, _Lachnolæmus_, _Tetragonurus_, _Thynnus_, have been found
to be poisonous in all seas between the tropics. All or nearly all
these fishes acquire their poisonous properties from their food which
consists of poisonous Medusæ, Corals, or decomposing substances.
Frequently the fishes are found to be eatable if the head and
intestines be removed immediately after capture. In the West Indies it
has been ascertained that all the fishes living and feeding on certain
coral banks are poisonous. In other fishes the poisonous properties are
developed at certain seasons of the year only, especially the season of
propagation: as the Barbel, Pike, and Burbot, whose roe causes violent
diarrhœas when eaten during the season of spawning.
* * * * *
[Illustration: Fig. 98.--Portion of tail, with spines, of
_Aëtobatis narinari_, a Sting-ray from the Indian Ocean.
_a_, nat. size.]
_Poison-organs_ are more common in the class of Fishes than was
formerly believed, but they seem to have exclusively the function
of defence, and are not auxiliary in procuring food, as in venomous
Snakes. Such organs are found in the Sting-rays, the tail of which is
armed with one or more powerful barbed spines. Although they lack a
special organ secreting poison, or a canal in or on the spine by which
the venomous fluid is conducted, the symptoms caused by a wound from
the spine of a Sting-ray are such as cannot be accounted for merely by
the mechanical laceration, the pain being intense, and the subsequent
inflammation and swelling of the wounded part terminating not rarely
in gangrene. The mucus secreted from the surface of the fish and
inoculated by the jagged spine evidently possesses venomous properties.
This is also the case in many Scorpænoids, and in the Weaver
(_Trachinis_), in which the dorsal and opercular spines have the
same function as the caudal spines of the Sting-rays; however, in the
Weavers the spines are deeply grooved, the groove being charged with a
fluid mucus. In _Synanceia_ the poison-organ (Fig. 99,) is still
more developed: each dorsal spine is in its terminal half provided
with a deep groove on each side, at the lower end of which lies a
pear-shaped bag containing the milky poison; it is prolonged into a
membranous duct, lying in the groove of the spine, and open at its
point. The native fishermen, well acquainted with the dangerous nature
of these fishes, carefully avoid handling them; but it often happens
that persons wading with naked feet in the sea, step upon the fish,
which generally lies hidden in the sand. One or more of the erected
spines penetrate the skin, and the poison is injected into the wound by
the pressure of the foot on the poison-bags. Death has not rarely been
the result.
[Illustration: Fig. 99.--A dorsal spine, with poison-bags, of
_Synanceia verrucosa_. Indian Ocean.]
[Illustration: Fig. 100.--Opercular part of the Poison-apparatus
of _Thalassophryne_ (Panama).
1. Hinder half of the head, with the venom-sac* _in situ._
_a_, Lateral line and its branches; _b_, Gill-opening;
_c_, Ventral fin; _d_, Base of Pectoral fin; _e_,
Base of dorsal.
2. Operculum with the perforated spine.]
The most perfect poison-organs hitherto discovered in fishes are those
of _Thalassophryne_, a Batrachoid genus of fishes from the coasts of
Central America. In these fishes the operculum again and the two dorsal
spines are the weapons. The former (Fig. 100, ^2) is very narrow,
vertically styliform and very mobile; it is armed behind with a spine,
eight lines long, and of the same form as the hollow venom-fang of
a snake, being perforated at its base and at its extremity. A sac
covering the base of the spine discharges its contents through the
apertures and the canal in the interior of the spine. The structure of
the dorsal spines is similar. There are no secretory glands imbedded
in the membranes of the sacs; and the fluid must be secreted by their
mucous membrane. The sacs are without an external muscular layer, and
situated immediately below the thick loose skin which envelops the
spines to their extremity; the ejection of the poison into a living
animal, therefore, can only be effected, as in _Synanceia_, by the
pressure to which the sac is subjected the moment the spine enters
another body.
Finally, a singular apparatus found in many Siluroids may be mentioned
in connection with the poison-organs, although its function is still
problematical. Some of these fishes are armed with powerful pectoral
spines and justly feared on account of the dangerous wounds they
inflict; not a few of them possess, in addition to the pectoral spines,
a sac with a more or less wide opening in the axil of the pectoral fin;
and it does not seem improbable that it contains a fluid which may be
introduced into a wound by means of the pectoral spine, which would
be covered with it, like the barbed arrow-head of an Indian. However,
whether this secretion is equally poisonous in all the species provided
with that axillary sac, or whether it has poisonous qualities at all,
is a question which can be decided by experiments only made with the
living fishes.