STICKLEBACK, Gasterostens, a genus of acanthopterous fishes, referred by many naturalists to the family of mailed cheeks (q.v.) (sderogenidee or triglidce); by others, to a distinct family (gasterosteider), in which the first dorsal fin is represented by a number of detached spines, a single strong spine occupies the place of the ventral fins, there are only three branchiostegal rays, the gill-covers are not armed, and the body is mailed by plates ou the lateral line, and destitute of scales. The species are found in fresh and brackish waters, and in the sea, in cold and temperate regions; and are small fishes, very interesting from their habits and the beauty of their colors, which they change in a remarkable manner, partly according to the colors of surrounding objects, and partly through the influence of their own passions. The THREE-SEINED STICKLEBACK (G. aculeatus or trachurus), having three spines instead of the first dorsal, is extremely abundant in rivers, ponds, and brackish waters in most parts of Britain and of Europe, and is sometimes also found in the sea. Sticklebacks caught in a river readily accom modate themselves to living in a salt-water aquarium. It seldom exceeds two inches and a half, or three inches in length. Cuvier and Valenciennes, Yarrell, and others, dis tinguish from this several other species, some of which are also British, differing in size, the armature of the sides, and other particulars (4 to 15 spines); but some naturalists are still inclined to regard them as mere varieties. The common fresh-water species are sometimes so abundant in ponds, ditches, and the still parts of rivers, as in Lincolnshire and other flat parts of the e. of England, that they are used for manure. They are sel
dom used as food, yet they are said to be excellent for this purpose. Oil has sometimes been expressed from them. In the aquarium, or in their native waters, their combats are very amusing. They are excessively pugnacious, particularly at the breeding season. The larger often devour the smaller, and they destroy the fry of fishes to a prodigious extent; they feed also on aquatic larva?, and are probably of great use in preventing the excessive multiplication of many kinds of insects. Their nest-building is particularly interesting, and in them nest-building was first observed among fishes. They collect small pieces of straw or stick, with which the bottom of the nest is laid among water plants, and these they cement together by an exudation from their own bodies which forms % thread through and round them in every conceivable direction. The thread is whitish, fine, and silken. The sides of the nest are made after the bottom. The nest of the fresh-water stickleback is about the size of a small hazel nut. The eggs, about the size of poppy-seeds, are deposited within. The male inches the nest, into which he introduces the female for the laying of the eggs, and he afterward watches it with great care—a care not unnecessary, as the eggs are most acceptable food to any other stickle back which can get at them.