CHAPTER XII.
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.]