CHAPTER VII.

_PIPE-FISHES, SEA-HORSES, GLOBE-FISHES, SUN-FISHES, AND THEIR ALLIES._

BY W. P. PYCRAFT, F.L.S., F.Z.S.

The fishes described in the present chapter form two well-marked groups, known as the TUFT-GILLED and the COMB-GILLED FISHES, on account of the peculiar arrangement of the gills, or breathing-organs; they are also remarkable for their peculiar shapes. The breast-fins are present in all; but in three of the families the second pair of fins, corresponding to the hind limbs of the higher animals, are wanting.

The TUFT-GILLED FISHES are represented by two families--the MAILED TUBE-MOUTHS and the PIPE-FISHES and SEA-HORSES, all of which have undergone very considerable modification of form, the body being encased in mail-like armour, whilst the jaws are toothless and produced into a long tube.

The first family is composed of a few small fishes from the Indian Ocean. Grotesque in appearance, they are remarkable also for the fact that the female takes sole charge not only of the eggs, which are exceedingly minute, but the young fry also. Only one other fish is known in which the care of the eggs and young is undertaken by the female: this is one of the Cat-fishes, described in a later chapter. The eggs in the TUBE-MOUTHS are carried in a pouch formed by the union of the inner borders of the ventral fins, which are long and broad. For the retention of the eggs within the pouch its wall develops long filaments, which serve the purpose of slender fingers.

The second of these families contains the PIPE-FISHES and SEA-HORSES. They are small marine fishes, inhabiting the seas of tropical and temperate regions wherever there is sufficient vegetation to offer shelter, for they are peculiarly defenceless creatures. They possess but feeble powers of swimming, and consequently are not seldom borne away by strong currents far out to sea or on to distant shores. Their method of locomotion is, indeed, quite different from that of other fishes, as they progress neither by undulatory motions of the body nor by powerful strokes of the tail, but by wriggling in the case of the pipe-fishes, or vibrating motions of the back-fin in the sea-horses.

The long, semi-cylindrical PIPE-FISHES, partly on account of their peculiar form and colour, and partly on account of their swaying motions, so closely resemble the fronds of seaweed amongst which they dwell as to pass unnoticed by their enemies. Unlike the Tube-mouths, just described, the care of the eggs and young devolves upon the males. The young are borne in a pouch, but, ventral fins being wanting, this is formed by a fold of skin developed from each side of the trunk and tail, the free margins being united in the middle line. Here the eggs remain till they are hatched. But the pouch is by no means done with after this event, for the young continue to occupy it for some time, returning when danger threatens--a habit which recalls the custom of the young of the kangaroo. Mr. Yarrell relates a curious fact which he gleaned from some fishermen--to wit, that if they take a pipe-fish, open the pouch, and drop the young into the sea, they will not disperse, but hover around the spot, as if waiting for their parent. Then, if the newly opened fish be held in the water, the young immediately return and enter the pouch. In another species of pipe-fish the eggs, instead of being carried in a pouch, are held by a sticky secretion to a groove in the under surface of the parent. This groove would seem to indicate the beginning from which the complete pouch has been developed. The pipe-fishes swim in a very peculiar manner, holding the body now in a vertical, and now in a horizontal position, accompanied by contortions of every conceivable kind, poking their long snouts into bunches of seaweed in search of food as they go.

The SEA-HORSES have a still more eccentrically modified form, inasmuch as the body is thrown into a series of curves, the head being bent upon the trunk in a manner suggestive of the head and neck of the horse; hence the name of the group. The tail, which lacks the membranous portion, or fin, can be spirally coiled, and is used as an organ of prehension, and on this account is unique amongst fishes. Gripping the stems of seaweeds with this tail, and swaying the body to and fro among the vegetation, the fish is rendered comparatively inconspicuous, the lines of the body being broken up by numerous more or less filamentous processes, which in one species, the FUCUS-LIKE SEA-HORSE, become excessively developed, forming long, frond-like blades. These, streaming in the water, both by their shape and coloration render the resemblance to the vegetable growths in which the animal hides so perfect that detection is almost impossible. Thus they furnish one of the most remarkable examples of adaptation to the environment amongst living animals. The males of most sea-horses, like the pipe-fishes, carry the eggs and young in a pouch on the abdomen, but in the species just mentioned the eggs are embedded in the soft skin on the under surface of the tail.

Sea-horses swim with the body more or less vertical, the motive power being supplied by rapid vibration of the back-fin. Both pipe-fishes and sea-horses occur in British seas, the first being the more common.

The COMB-GILLED FISHES, to which we come next, are divided into two families, whose members are as remarkable for their extraordinary shape as are the tuft-gilled forms just discussed. The abnormal shapes which mark out certain fishes so conspicuously from the more normal and typical forms are generally regarded as adaptations, serving to ensure concealment, to ward off attack, or to effect the capture of prey otherwise unattainable. Instances illustrating all three of these ends are furnished by these two groups of the tuft- and comb-gilled fishes.

The FILE-FISHES and COFFER-FISHES, which form the first of the two families, present considerable variation in shape as well as in the covering of the body, which may be naked, covered with rough scales or bony spines, or invested in a complete bony cuirass.

The file-fishes are represented by numerous species, the typical one being known also as the TRIGGER-FISH, on account of an armature of spines on the top of the back. These spines are three in number; the first is very strong, roughened like a file--hence the name File-fish--and hollowed out behind to receive the second much smaller spine, which has a projection in front at its base, fitting into a notch in the first. Thus these two spines can only be raised or depressed simultaneously, and the first cannot be forced down unless the second has been previously depressed. These fishes have very powerful teeth, to break off pieces of coral, which form a large part of their diet. They also destroy a large number of shell-fish, and work great destruction amongst pearl-oysters. Frequently these fishes, when eaten, prove highly poisonous, from having fed on poisonous corals, jelly-fish, or decomposing substances.

As a rule file-fishes are of small size, but some attain a length of 2 feet, and many are beautifully and symmetrically marked.

The COFFER-FISHES derive their name from the box-like cuirass in which they are invested. This is formed by numerous closely fitting, hexagonal bony plates, forming a mosaic, and leaving only the fins and hind part of the tail free. This bony case varies greatly in form, in some species being three-ridged, in others four- or even five-ridged; while in some long horns are developed, making the defensive armature still more complex. More than twenty species are known, all confined to tropical and sub-tropical seas.

The GLOBE-FISHES and SUN-FISHES constitute the last family of this really extraordinary assemblage. The covering of the body consists either of minute scales or large spines, which can frequently be raised or depressed at will. All the members inhabit tropical or sub-tropical seas, and a few occur in the fresh-waters of the same regions.

The GLOBE-FISHES have short, thick bodies, covered either with small spines, as in the TOAD-FISH, or very large ones, as in the PORCUPINE-FISH, or SEA-HEDGEHOG. They are remarkable for their habit of filling the gullet with air, and then distending the body to an enormous size. This device enables the fish to escape its enemies; for when so inflated it rises to the surface and floats belly-upwards, and, the inflated portion projecting above the water, the fish is blown along by the wind to more secure regions. The more heavily armed species become still more formidable when inflated, as the spines are then fully erected. Escaping from enemies below by flight, they are thus secure from enemies above by reason of their armature. Globe-fishes have been found floating alive and unhurt within the stomachs of sharks which had swallowed them, and one has even been known to eat its way out through its captor's side, and so killing its would-be devourer! When a globe-fish desires to return to its normal elongated shape, it expels the air from the gullet through the mouth and gills, the expulsion causing a curious hissing sound.

Extremely unlike the foregoing members of the group of comb-gilled fishes, the SUN-FISH is nevertheless quite as remarkable in form, looking as if it had undergone the amputation of its hind parts. The singular shape of the other members of the comb- and tuft-gilled fishes are undoubtedly adaptations to avoid enemies, either by rendering the animal inconspicuous, or hurtful by reason of its powerful armature. The form of the sun-fish appears to be an adaptation for the capture of food, as this fish preys largely upon the fry of other fishes which inhabit enormous depths, and consequently can only be obtained by diving. Sun-fishes inhabit the surface-waters, but as divers have few equals.

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