Gar Fish, Or Gar Pike (Lepidosteus), a ganoid fish, belonging to the same order as the polyp-terns of Africa, the mud fish (amia) of America, and the sturgeon family; it is the only genus of its family, and there are more than 20 species, all American. As in other ganoids, the body is covered with smooth enamelled scales, of a rhombic form, arranged in oblique rows, and so hard that it is impossible to pierce them with a spear; this enamel is like that of teeth, and the scales contain the fluorine and lacunae of ordinary bone structure. The internal skeleton is bony; the snout is elongated, varying in width according to the species; both jaws and nasal bone are covered with small teeth, with long and pointed ones along the edge; the teeth are in double rows of unequal size, the larger resembling those of reptiles, and the smaller fish-like, the front ones of the lower jaw being received into sheath-like cavities in the upper, as in the alligators; their structure resembles that of the labyrinthodont reptiles, having processes of the pulp cavity radiating toward the circumference; the vertebrae also present a reptilian arrangement in having ball-and-socket articulations, the anterior surface of each bone being convex and the posterior concave; this gives greater flexibility to the spine, and enables this genus (alone among fishes) to move the head independently of the trunk, and also to retain the posterior part of the body in a curved position.
The gills on the four arches have a perfect bifoliate structure, and behind the last and the hyoid bone there is the usual fissure; there is a respiratory opercular gill as well as a pseudobranchia, but no blow-hole; branchiostegal rays three, the .membrane passing from side to side, undivided. The anterior edge of all the fins is protected by hard spiny scales, and all the fin rays are articulated; the dorsal and anal fins are far back, and nearly opposite one another; the caudal fin is abruptly truncated, and its rays are inserted partly at the end of and partly beneath the extremity of the spine. There are the usual numerous valves in the arterial bulb, no decussation of the optic nerves, and abdominal ventral fins; the stomach is continued without caeca to a slender twice-folded intestine, which has a slightly developed spiral valve, but numerous pancreatic caeca; the long air or swim bladder is muscular, freely supplied with blood from the aorta, divided into cells like the lung of a reptile by muscular bundles, and opening into the throat by a wide duct and long slit guarded by a sphincter muscle; the ovaries are sacciform, with oviducts issuing from their middle.
Gar fish are not uncommon in the western rivers and northern lakes communicating with the gulf of Mexico and the St. Lawrence, and probably every separate basin and watershed has its peculiar species. They frequent shallow, reedy, or grassy places, basking in the sun like the pike, and devouring living prey with great voracity. The manner of seizing prey differs from that usually observed in fishes, and resembles that of reptiles; instead of taking their food at once with open mouth and swallowing it immediately, they approach it slily and sideways, and then, suddenly seizing the fish or other animal, hold it until by a series of movements it is placed in a proper position for being swallowed, in the manner of alligators and lizards; the ball of food is also seen to distend the body as it passes downward, as in snakes. This reptilian fish, like the ichthyoid reptiles, is in the habit of approaching the surface of the water, and of apparently swallowing air; at any rate, a large amount of air escapes from the mouth, most of which had probably been previously swallowed, and a part of which may have been secreted by the lung-like air bladder.
As in the menobranchus and other fish-like salamanders, this air bladder doubtless performs certain respiratory functions, and perhaps more than in the naked-skinned reptiles; at any rate gar pikes live longer out of water than fishes generally, and to a degree not explicable by any arrangement of the gills. The gar pike and the African polypterus (described below) are the only two existing genera of a type of sauroid fishes which were very numerous in the secondary geological epoch, extending also in diminished numbers through the palaeozoic age at a time when reptiles proper did not exist; they are found from the low-er Silurian strata to the present time, gradually diminishing through the tertiary to the two existing genera; they present one of the first steps in the geological succession of bony fishes, at a time when the etenoids and cycloids had not appeared; after the rhizodont reptiles and the common osseous fishes were created, the ganoids began to diminish.-The common gar fish (L. osseus, Linn.), called also bony pike and Buffalo fish, attains a length of 5 ft. The color is umber brown on the back and head, the sides yellow, and the belly white; there are circular black spots on the caudal, dorsal, and anal fins.
It is found in Lakes Erie, Huron, and Champlain, the Ohio and its tributaries, and other western rivers. The great length of its jaws will distinguish it from other species; it is often seen apparently sleeping on the surface, and gently carried round in an eddy for an hour at a time; it leaps often out of water in pursuit of its prey, and is so swift and strong a swimmer as to stem the most furious rapids. The alligator gar fish (Z. ferox, Raf.) has a shorter head, the jaws forming not quite half the length, broad and flat above; the skin is rough, the scales imbricated and sculptured; teeth numerous, strong, and prominent; the upper jaw, as in the preceding species, expanding into a knob at the end; the color is yellowish brown. It inhabits the Mississippi and Ohio rivers and their tributaries, and is usually from 4 to 6 ft. long; according to Rafinesque, it attains a length of 12 ft., and is a match for an alligator; its impervious coat of mail, strong teeth, size, strength, and agility must make it a very formidable fish, though probably not superior to the equally well armed and powerful alligator. It may well be called the shark of fresh water, though not belonging to the placoid group of fishes.
There are several other species described, more or less resembling the above; but these will serve to give an idea of the general characters of this singular fish, the living type of the dominant family of its class during the carboniferous period.-The allied genus polypterus (Geoffr.), from the Nile, Senegal, and other African rivers, is characterized by similar enamelled scales, and by a number of finlets extending from the middle of the body to the tail; the throat is covered with hard, nearly immovable plates, which would greatly embarrass respiration were it not for two openings on the top of the head, which answer the purpose of blowholes and allow the water to pass through them; the lobes of the tail are of unequal size; the abdominal organs occupy a very small space, being packed close to the spine; the upper jaw is not in several pieces, but the mandibles and skull are as in osseous fishes generally; there is no opercular gill, nor pseudo-branchia; the nostrils are very complicated, with labyrinthine gill-like folds; the stomach is ca3cal, the intestine provided with a well marked spiral valve, and there is a single pancreatic caecum; the air bladder is double, communicating with the throat by a duct opening on the ventral side, and its arteries are formed by the union of the blood vessels coming from the last gill, carrying therefore oxygenated blood.-The lepidosteus is by far the best known and most interesting of the sauroid fishes, and has been of such value to palaeontologists that it has been well said by Hugh Miller, in his "Lectures on'Geology," that "it would almost seem as if the lepidosteus had been spared, amid the wreck of genera and species, to serve us as a key by which to unlock the marvels of the ichthyology of those remote periods of geologic history appropriated to the dynasty of the fish." (See Ganoids.)
Gar Fish, br Gar Pike (Lepidosteus osseus).