FINNY LIGHT-BEARERS.
If it were possible for human beings to penetrate to the abyssal
depths of the ocean, finny torch-bearers would be found from the very
surface to nearly four miles beneath it; existing in many cases under
conditions almost incomprehensible when the enormous attendant pressure
is considered. While it is extremely difficult to tell the exact depth
from which a fish is taken by the dredge, sufficient data has been
secured for naturalists to assume, though there is great difference
of opinion, that, to a greater or less degree, the forms of certain
depths have certain peculiarities. These are often seen in the organs
of vision, which have been modified in many ways by the lack of light.
Thus the eyes of forms that are found living five or six hundred feet
below the surface are often extremely large, as in _Beryx_ (Plate
XVIII., Fig. 1), as if to absorb the faintest beams of sunlight that
may penetrate this distance. As we descend to twelve hundred feet, the
eyes seem to grow larger; and beyond this, large and small eyed fishes
are found indiscriminately. The former evidently use these organs;
while those with small eyes are provided with remarkable organs of
touch,--long feelers which can be thrown forward, or moved to a more or
less extent, and used as the blind man uses his cane. An interesting,
indeed remarkable, example of this is seen in the fish _Bathypterus
longipes_, Günther found at a depth varying from one-half to
three-quarters of a mile from the surface in the Atlantic. The eyes are
extremely small, apparently useless; but the blind man’s cane is here,
as the pectoral fins are modified to serve as feelers, two rays almost
as long as the entire fish extending from the back of the head. As the
fish swims freely, the fins are trailed behind; but, does it approach a
prospective victim, the articulation of these wonderful feelers enables
them to be thrown forward as a cane in advance of the fish. They are
divided at the tip, and form a delicate sense-organ with which to
explore the depths of this abyssal world. Upon the ventral fins, there
are two similar rays, that serve a like purpose.
Many fishes having remarkable feelers have quite recently been
discovered, and among them _Eustomias obscurus_ (Plate XIX.), a fish
found at a depth of twenty-seven hundred meters, which has a long
tentacle dependent from the lower jaw.
When we penetrate beyond a certain depth, we find blind fishes as well
as those possessing eyes; and all the forms of the greater depths are
adapted to their life under the consequent enormous pressure in a
remarkable manner. The bones are friable and cavernous, and loosely
connected. Many are covered with a thick mucus, while many more have
curious plates, that are so many torches or lanterns to emit light for
their possessors. As some of the fishes have eyes and no phosphorescent
organs, while others are luminous and perhaps blind, and knowing that
all are carnivorous, we may well imagine that a fierce struggle for
existence is carried on in this distant world of the sea. The lamps of
some forms must attract their enemies; while, on the other hand, they
may constitute a lure, dazzling weaker forms, which fall victims to
their curiosity.
Among all the light-givers, these deep-sea lantern-bearers are the
most interesting, and typical of the mysterious realm from which they
are taken by the ingenious inventions of mankind. Some are luminous
over their entire surface, as the _Harpodon_, or Bombay duck (Plate
XVIII., Fig. 2). Others have a series of plates extending along the
side, that resemble the open ports of a steamer. Some possess gleaming
head-lights, the locomotives of the sea; while others have their lights
confined in groups.
While the expeditions of the “Challenger,” “Talisman,” “Albatross,”
and “Travailleur” have resulted in the discovery of what seems a
remarkable presentation of these light-givers, we can well imagine,
understanding the difficulties of deep-sea dredging, that the largest
and perhaps most interesting of these forms are yet undiscovered, and
that the greatest mysteries may never be revealed. The difficulties
that attend, and the chances against, the capture of deep-sea fishes,
can be perhaps realized by my young readers, if they imagine a large
balloon sailing along over the country at an elevation of from four to
five miles, dragging a dredge ten or twelve feet wide. Few active boys
or girls would be caught by such a device; only the sluggards that were
fast asleep would be trapped. The comparatively small dredge at the end
of a six-mile rope, dragging along and creating an unusual commotion
in the silent submarine world, secures only a few forms, the sluggards
and mud-lovers, as a rule: so that fishes taken at extreme depths
are prizes indeed. The “Talisman” took the fish _Bythites crassus_
from a depth of about two miles. The naturalists of the “Challenger”
expedition captured the _Bathyophis ferox_ about three miles from
the surface, or, to be exact, five thousand and nineteen meters. The
American exploring-vessel, the “Albatross,” under the direction of
Professor Spencer F. Baird, has exceeded any of these hauls; in 1883
making a capture of five species in twenty-nine hundred and forty-nine
fathoms.
While luminous fishes have been known for many years, the “Challenger”
expedition brought many new forms to light, and the work accomplished
by her officers may be said to have given a new impetus to the
study of deep-sea forms. Off the north-west coast of Australia, the
“Challenger’s” trawl captured the curious black fish _Echiostoma
microdon_. The luminous spots were few in number, but so arranged as
to be of the greatest service: thus two are found just below the eyes;
above the maxillary there is a narrow, elongated one, with a smaller
spot nearer the eye. _E. micripnus_, found in twenty-one hundred and
fifty fathoms, has long, fringed barbels, and small, round luminous
spots above the maxillary, resembling a rudimentary eye.
Referring to this interesting torch-bearer,[43] Dr. Günther says, “The
fishes of the family _Stomiatidæ_, to which this genus belongs, are
armed with formidable teeth,--a certain indication of their predaceous
habits and voracity. Their long body is covered with a smooth,
scaleless skin, of an intensely black color. The vertical fins are
close together, near the end of the tail, as in the pike, forming a
powerful propeller, by a single stroke of which the fishes are enabled
to dart with great rapidity to a considerable distance. A long filament
is suspended below the chin; and, as it is frequently fringed at
its extremity, it evidently serves as a lure for other fishes or
_animalculæ_. Series of luminous, globular bodies run along the lower
half of the body and tail; and some others of larger size occupy the
side of the head, generally below the eye or behind the maxillary bone.
This fish is sixteen inches in length. The end of the barbel, which
was thickened, was flesh-color with a rose tint; there was also a rose
tint on the dorsal and anal fins. The rest of the animal was of a dark
color. The phosphorescent spots along the belly and radial and lateral
line were red, as was also that below the eye.”
It is not often that the light of these fishes is seen; but the late
Professor Willemoes Suhm, while watching the great trawl come over the
side upon a calm night, noticed a gleaming spot, and taking it out
found it to be the little fish _Sternoptyx_. In referring to it
he says, “It hung in the net like a golden star, as it came out of the
darkness.”
As the _Sternoptyx_ is a delicate little creature, and quite
defenceless, its illumination must be a fatal gift. This is equally
true of the _Argyropelecus hemigymnus_ (Plate X., Fig. 3), a
curiously formed fish,--deep in the body, tapering off suddenly to the
tail, as if a piece had been bitten out by some large fish. Referring
to the figure, it will be seen that the luminous organs are grouped;
four being at the side of the tail, six midway between it and the line
of the dorsal fin, and many others around the edge of the ventral
surface,--one hundred and six in all: so that if all these plates are
luminous, the _Argyropelecus_ must present a dazzling sight as it
darts along in the blue waters of the Mediterranean, where it has been
most commonly observed.
Concerning the functions of these organs, there is still much
controversy. The opinions of Ussow, Leydig, and others will be found in
their papers referred to in the bibliography; and, as the question is
thoroughly a technical one, its further discussion is omitted. As early
as 1865 Professor Leuckart suggested that the curious plates (Plate X.,
Fig. 4) were organs of sight, or accessory eyes. In 1879 Dr. M. Ussow,
of the University of St. Petersburg, gave the world an account of his
researches upon the plates of the genera _Astronesthes_, _Stomias_
(Plate XX.), _Chauliodus_ (Plate XXI., Fig. 4), _Scopelus_ (Plate X.,
Fig. 1), _Maurolicus_, _Gonostoma_, and _Argyopelecus_, small fishes,
most of which were found in the Mediterranean. This was followed by
similar investigations by Dr. Leydig of Bonn, and Dr. Günther.
A well-known phosphorescent fish is seen in _Scopelus_, which bears
upon its sides and various parts of the body numbers of spots (Plate
X., Fig. 1), which, if all luminous, mark it as one of the most
brilliant of the light-givers. The appearance of these organs in
reflected light is shown in Plate X., Fig. 2.
The snake-like _Stomiasboa_ (Plate XX.), from a depth of twenty-seven
hundred feet, is perhaps the most hideous of the light-givers; its
large mouth and ferocious teeth giving it a bull-dog aspect, which
in a large fish would make a veritable dragon. But _Stomias_ is not
over twelve or fifteen inches in length, though quite large enough to
terrify the smaller fry. The specimen figured was taken in the Gulf of
Gascony by the naturalists of the “Talisman,” from its home, a mile and
a quarter beneath the surface. The sides of the body are provided with
a double row of luminous disks, which, according to M. Filhol, “cause
the fish to be surrounded by a brilliant luminous aureola.”
[Illustration:
PLATE XVIII.
CHIASMODUS. SUN-FISH. PLAGIODUS. HARPODON. BERYX.]
In Plate XVIII., Fig. 4, is shown a large light-giver,--the
_Plagiodus_, a fish six feet in length. According to Dr. Günther, it
emits light from various parts of its surface; the tips of the fins
gleaming with a soft phosphorescence similar to that of the large-eyed
_Beryx_ (Fig. 1) of same plate. The latter attains a length of about
twenty inches.
Quite as ferocious in appearance as the _Stomias_ is _Chauliodus_
(Plate XXI., Fig. 4), with long, lance-like teeth, gleaming fins, and
a row of small phosphorescent plates that perhaps sparkle like so many
gems as their bearer sails along in the greater depths.
Exaggerations are often termed “fish-stories,” for the reason perhaps
that improbable tales are related concerning the denizens of the sea
by fun-loving mariners; but the most remarkable stories that the vivid
imagination of those who go down to the sea in ships has ever devised
are not as remarkable as the simple truths regarding the every-day
history of fish-life. What can be more astonishing than the fact that
these delicate forms are enabled to live in water where the pressure
is so great that hard wood is crushed and glass reduced to powder?
If a decade or so ago a statement had appeared in the daily press,
to the effect that a fish had been discovered which could swallow
another five times its own bulk, it would in all probability have been
classed as a “fish-story,”--too big an one, indeed, to have even the
merit of comical exaggeration: yet such a fish does exist in the black
swallower, or _Chiasmodus_ (Plate XVIII., Fig. 5); the fish, besides
being luminous, possessing this extraordinary faculty. The jaws, by
a special arrangement, are capable of great extension; so that the
fish actually draws itself over its prey, that may be many times its
own bulk. The skin of the swallower seems to possess a rubber-like
character, stretching to enormous dimensions, and often, when filled
with gas, carrying the glutinous light-bearer into the upper regions of
the ocean.
_Malacosteus niger_, Ayres (Plate XXII.), is a rare fish, from a
depth of two-thirds of a mile; though several specimens have recently
been taken by the United-States Fish-Commission, and others by the
“Talisman” off Morocco, in forty-eight hundred feet of water. It is
of small size, from thirteen to fourteen centimeters in length, of
a velvet-black hue, and possesses two large luminous organs upon
the head; one of which, according to M. Filhol, who observed the
light in the living fish, emits a golden, and the other a greenish
phosphorescence. We have here, then, a fish that vies with the
_Appendicularia_, and other forms which we have seen emitting
light of more than one color. It is possible that the rays of light
from these spots project ahead of the fish, in the manner shown in
the accompanying figure, in which the appearance of the light is of
course conjectural; but as to the meaning of the different colors,
are they a system of signals cunningly devised by Nature to enable
_Malacosteus_ to distinguish its kind in the profound depths of
the ocean, or are they merely lures of more than ordinary brilliancy?
In some fishes the luminous organs are extremely small, almost
invisible to the naked eye, and often spread over a large extent of
surface. Such an instance is seen in _Eustomias obscurus_ (Plate XIX.)
and _Neostoma_. In the former, an attenuated carnivorous fish of a
jet-black color, we see another example of remarkable feelers, or
sense-organs.
While these forms are probably free swimmers, there are many others
that are mud-dwellers, of most extraordinary make-up, literally living
bags, or rather mouths. The _Melanocetus Johnstoni_ (Günther, Plate
XXIII.) is one of these; having an enormous pouch, with a fishing-rod
upon its head similar to that of our common _Lophius_. _Melanocetus_
probably buries itself in the ooze, as shown in the engraving, allowing
the tip of its tentacle, or rod, to protrude; and, when the living bait
is touched, it opens its cavernous mouth and seizes the victim.
Still more remarkable is the _Eurypharynx pelecanoides_, which
has a mouth of enormous dimensions (Plate XXIV.), from which depends a
pelican-like pouch. This form is interesting, from many peculiarities;
among which may be mentioned the fact, that the branchial arches
are here simple bars, five in number, having no connection with the
cranium. The mouth can open to a surprising extent, the lower jaw being
composed of two pieces attached to the cranium by a movable joint,
so that it swings literally in various directions. The fish probably
feeds by swimming along the bottom blindly, ingulfing various animals,
holding them by its interlocked teeth. This phenomenal fish was taken
in 1882 by Vaillant, the French scientist, twenty-five hundred metres
from the surface; while another genus of these deep-sea, eel-like
creatures was described in 1883 by Gill and Ryder, who called it
_Gastrostomus bairdii_. In the latter, the jaw is six or seven
times as long as the cranium.
One of the most striking phosphorescent fishes is a small shark,
_Squalus fulgens_, also described and figured by Kner as _Leius
ferox_, which, in general appearance, somewhat resembles the black or
brown nurse (or _Scymnus_) of our Southern coast. This interesting
light-giver was discovered by Dr. Bennett, and the following is his
version of the find: “Being dark when I first saw it shining in
the net, it resembled a _Pyrosoma_, emitting, as it did, a bright
phosphorescent light. This was in latitude 2° 15′ south, longitude 163°
west. The length of my specimen was five inches and a half. It is not
a little singular that my brother, the late D. F. Bennett, obtained a
specimen of this fish in the same latitude, and another in latitude 55°
north, longitude 110° west. The first was taken in the daytime, and
was ten inches in length,--much larger in size than my specimen. The
second was taken at night, and its entire length was a foot and a half:
both were alive when captured, and fought fiercely with their jaws,
tearing the net in several places. On placing my fish in sea-water, and
observing it in the dark cabin, it swam about for some time, emitting
a bright phosphoric light; and when this had become so faint as to be
almost imperceptible, it was readily rekindled on the animal being
disturbed or excited. My specimen was of a perfectly black color, and
died about four hours after it had been taken. The luminosity was
retained for some hours after life was extinct.
“The form of the shark, as indeed its whole structure, is peculiar. It
no doubt belongs to the subgenus _Scymnus_. My specimen having been
accidentally lost, I am unable to give a minute description of it. My
brother was more fortunate. I will, therefore, give his account of so
novel and interesting a fish. The body is cylindrical, rather slender,
and tapers finely towards the tail. Its prevailing color is dusky
brown; a broad black band, or collar, passes around the throat; and the
fins are partially margined with white (my specimen, being small and
young, varied in this respect, being black, with the fins of a less
intensity of color); the skin rough, as is usual in the shark tribe.
The number of gill-apertures is five on each side. The fins are short,
and for the most part disposed in a round form; the dorsals are two in
number, small, and placed far back; the tail-fin is unequally divided,
the upper being the longest and largest lobe. The head is flat; the
snout prominent, rather pointed, and has two nostrils at its extremity.
There is, also, on each side of the upper and back part of the head, a
large oval orifice, like a spiracle or nostril, provided with a valve,
and communicating with a corresponding aperture in the roof of the
mouth. The mouth is capacious; and the dark skin around it is incised
on each side to some extent beyond the commissure of the lips, exposing
a white elastic membrane beneath. The upper jaw is armed with many
rows of small, sharp teeth; while the lower has only a single row of
perpendicular teeth, or, rather, an elevated plate of bone, sharply
toothed on its summit, and bearing a close resemblance to a segment of
the surgical circular-saw called a trephine. The eyes are much more
prominent and dilated than is usual in sharks; the iris is black, the
pupil transparent and of a greenish color.
“When the larger specimen, taken at night, was removed into a dark
apartment, it afforded a very extraordinary spectacle. The entire
inferior surface of the body and head emitted a vivid and greenish
phosphorescent gleam, imparting to the creature, by its own light,
a truly ghastly and terrific appearance. The luminous effect was
constant, and not perceptibly increased by agitation or friction. I
thought at one time it shone brighter when the fish struggled, but I
was not satisfied that such was the fact. When the shark expired (which
was not until it had been out of the water more than three hours),
the luminous appearance faded entirely from the abdomen, and more
gradually from other parts; lingering the longest around the jaws and
on the fins.
“The only part of the under surface of the animal which was free
from luminosity was the black collar around the throat; and while
the inferior surface of the pectoral, anal, and caudal fins shone
with splendor, their superior surface (including the upper lobe of
the tail-fin) was in darkness; as also were the dorsal fins, back,
and summit of the head. I am inclined to believe that the luminous
power of this shark resides in a peculiar secretion from the skin.
It was my first impression that the fish had accidentally contracted
some phosphorescent matter from the sea, or from the net in which it
was captured; but the most rigid investigation did not confirm this
suspicion, while the uniformity with which the luminous gleam occupied
certain portions of the body and fins, its permanence during life, and
decline and cessation upon the approach and occurrence of death, did
not leave a doubt in my mind that it was a vital principle, essential
to the economy of the animal. The small size of the fins would appear
to denote that this fish is not active in swimming; and, since it is
highly predaceous, and evidently of nocturnal habits, we may, perhaps,
indulge in the hypothesis that the phosphorescent power it possesses is
of use to attract its prey, upon the same principle as the Polynesian
Islanders and others employ torches in night-fishing.”
[Illustration:
PLATE XIX.
LUMINOUS FISH.
(_Eustomias obscurus._)
From depth of 8,100 feet.]