Body elongate, compressed. Cleft of the mouth oblique; villiform teeth in the jaws. Opercular bones not armed; infraorbitals covering the cheek; parts of the skeleton forming incomplete external mails. Scales none, but generally large scutes along the side. Isolated spines in front of the soft dorsal fin. Ventral fins abdominal, joined to the pubic bone, composed of a spine and a small ray. Branchiostegals three.
Fig. 230.—Gastrosteus noveboracensis.
Of “Sticklebacks” (Gastrosteus) about ten species are satisfactorily known, one of which (G. spinachia) lives in salt and brackish water, whilst the others inhabit principally fresh waters, although they all are able to exist in the sea. They are confined to the Temperate and Arctic zones of the northern hemisphere. The British freshwater species are the Three-spined Stickleback (G. aculeatus), which sometimes, especially in Central Europe, lacks scutes, sometimes has a series of scutes along the side of the body; the Four-spined Stickleback (G. spinulosus) and the Nine-spined Stickleback (G. pungitius). The commonest North American species is G. noveboracensis. The habits of all the freshwater species are very similar. The common European species (G. aculeatus) is an active and greedy little fish, extremely destructive to the fry of other species, and consequently injurious in ponds where these are sought to be preserved. It is scarcely to be conceived what damage these little fishes do, and how greatly detrimental they are to the increase of all the fishes in general among which they live; for it is with the utmost industry, sagacity, and greediness that they seek out and destroy all the young fry that come their way. A small Stickleback, kept in an aquarium, devoured, in five hours’ time, seventy-four young dace, which were about a quarter of an inch long, and of the thickness of a horse hair. Two days after it swallowed sixty-two; and would, probably, have eaten as many every day could they have been procured. The Stickleback sometimes swarms in prodigious numbers. Pennant states that at Spalding, in Lincolnshire, there was once in seven years amazing shoals, which appear in the Welland, coming up the river in the form of a vast column. The quantity may, perhaps, be conceived from the fact that a man employed in collecting them, gained, for a considerable time, four shillings a-day by selling them at the rate of a halfpenny a bushel. Costa, who studied the manners of these small fishes, relates that, on the approach of spawning time, the male builds a nest of stalks of grass and other matters in a hollow of the bottom, a little above three inches wide and about six inches and a half deep, creeping over the materials on his belly, and cementing them with the mucus that exudes from his skin. The bottom of the nest is first laid, then the sides are raised, and lastly the top is covered over. A small hole is left on one side for an entrance. When the erection is complete, he seeks out a female, and conducting her, Costa says, with many caresses, to the nest, introduces her by the door into the chamber. In a few minutes she has laid two or three eggs, after which she bores a hole on the opposite side of the nest to that by which she entered, and makes her escape. The nest has now two doors, and the eggs are exposed to the cool stream of water, which, entering by one door flows out at the other. Next day the male goes again in quest of a female, and sometimes brings back the same, sometimes finds a new mate. This is repeated until the nest contains a considerable number of eggs, and each time the male rubs his side against the female and passes over the eggs. Next the male watches a whole month over his treasure, defending it stoutly against all invaders, and especially against his wives, who have a great desire to get at the eggs. When the young are hatched and able to do for themselves his cares cease.
The Sea-Stickleback (G. spinachia) is likewise a nest builder, choosing for its operations especially the shallows of brackish water, which are covered with Zostera.
Second Family—Fistulariidæ.
Fishes of greatly elongated form; the anterior bones of the skull are much produced, and form a long tube, terminating in a narrow mouth. Teeth small; scales none, or small. The spinous dorsal fin is either formed by feeble isolated spines or entirely absent; the soft dorsal and anal of moderate length, ventral fins thoracic or abdominal, composed of five or six rays, without spine; if abdominal, they are separate from the pubic bones, which remain attached to the humeral arch. Branchiostegals five.
The “Flute-mouths” are also frequently called “Pipe-fishes,” a name which they have in common with the Syngnathidæ. They are gigantic marine Sticklebacks, living near the shore, from which they are frequently driven into the open sea; some of the species, therefore, have a wide geographical range. Probably all enter brackish water. They are distributed over the whole of the tropical and sub-tropical parts of the Atlantic and Indo-Pacific. The species are few in number, but some of them are very common.
This family is well represented in Eocene formations; some of the remains belonging to the existing genera, Fistularia, Aulostoma, and Auliscops, the two former of which occur not rarely at Monte Bolca and in the schists of Glaris. Well-preserved remains of Auliscops have been found in the Marl-slates of the highlands of Padang in Sumatra. Extinct genera from Monte Bolca are Urosphen, the cylindrical body of which is terminated by a large cuneiform fin; and Rhamphosus, which has an immense spinous ray, denticulated behind, inserted on the nape.
Fistularia.—Body scaleless; caudal fin forked, with the two middle rays produced into a filament; no free dorsal spines.