Gobius.—Body scaly. Two dorsal fins, the anterior generally with six flexible spines. Ventral fins united, forming a disk which is not attached to the abdomen. Gill-opening vertical, moderately wide.
Fig. 220.—Gobius lentiginosus, from New Zealand.
The “Gobies” are distributed over all temperate and tropical coasts, and abundant, especially on the latter. Nearly three hundred species have been described. They live especially on rocky coasts, attaching themselves firmly with their ventrals to a rock in almost any position, and thus withstanding the force of the waves. Many of the species seem to delight in darting from place to place in the rush of water which breaks upon the shore. Others live in quiet brackish water, and not a few have become entirely acclimatised in fresh water, especially lakes. The males of some species construct nests for the eggs, which they jealously watch, and defend even for some time after the young are hatched. Several species are found on the British coast: G. niger, paganellus, auratus, minutus, ruthensparri. Fossil species of this genus have been found at Monte Bolca.
A very small Goby, Latrunculus pellucidus, common in some localities of the British Islands and other parts of Europe, is distinguished by its transparent body, wide mouth, and uniserial dentition. According to R. Collett it offers some very remarkable peculiarities. It lives one year only, being the first instance of an annual vertebrate. It spawns in June and July, the eggs are hatched in August, and the fishes attain their full growth in the months from October to December. In this stage the sexes are quite alike, both having very small teeth and feeble jaws. In April the males lose the small teeth, which are replaced by very long and strong teeth, the jaws themselves becoming stronger. The teeth of the females remain unchanged. In July and August all the adults die off, and in September only the fry are to be found.
There are several other genera, closely allied to Gobius, as Euctenogobius, Lophiogobius, Doliichthys, Apocryptes, Evorthodus, Gobiosoma and Gobiodon (with scaleless body) Triænophorichthys.
Sicydium.—Body covered with ctenoid scales of rather small size. Cleft of the mouth nearly horizontal, with the upper jaw prominent; lips very thick; the lower lip generally with a series of minute horny teeth. A series of numerous small teeth in upper jaw, implanted in the gum, and generally movable; the lower jaw with a series of conical widely-set teeth. Two dorsal fins, the anterior with six flexible spines. Ventral fins united, and forming a short disk, more or less adherent to the abdomen.
Small freshwater fishes inhabiting the rivers and rivulets of the islands of the tropical Indo-Pacific. About twelve species are known; one occurs in the West Indies. Lentipes from the Sandwich Islands is allied to Sicydium.
Periophthalmus.—Body covered with ctenoid scales of small or moderate size. Cleft of the mouth nearly horizontal, with the upper jaw somewhat longer. Eyes very close together, immediately below the upper profile, prominent, but retractile, with a well-developed outer eyelid. Teeth conical, vertical in both jaws. Two dorsal fins, the anterior with flexible spines; caudal fin with the lower margin oblique; base of the pectoral fin free, with strong muscles. Ventral fins more or less coalesced. Gill-openings narrow.
The fishes of this genus, and the closely-allied Boleophthalmus, are exceedingly common on the coasts of the tropical Indo-Pacific, especially on parts covered with mud or fucus. During ebb they leave the water and hunt for small crustaceans, and other small animals disporting themselves on the ground which is left uncovered by the receding water. With the aid of their strong pectoral and ventral fins and their tail, they hop freely over the ground, and escape danger by rapid leaps. The peculiar construction of their eyes, which are very movable, and can be thrust far out of their sockets, enables them to see in the air as well as in the water; when the eyes are retracted they are protected by a membranous eyelid. These fishes are absent in the eastern parts of the Pacific and on the American side of the Atlantic; but singularly enough one species reappears on the West African coast. About seven species are known (including Boleophthalmus), P. koelreuteri being one of the most common fishes of the Indian Ocean.