STICKLEBACK (so called from the sharp spines on its back). A general name for the small active fresh-water hemibranch spiny-rayed fishes of the family Gastrosteida., interesting because of their nest-building. They are natives of Northern America, Europe, and Asia. There are a dozen or so species, none exceeding six inches long. The body is slender and more or less compressed, without scales, but usually mailed with plates. The anterior dorsal fin is replaced by several strong, widely separated spines. The ventral fin consists of a strong spine and one or two rudimentary rays. The typical form is the common European stickle back or 'burnstiekle' (Gasterostcus aeulcatus), represented in Eastern North America by the very similar or identical Gasterosteus bispino sus. It is four inches long, is olivaceous and dotted on the back, and has three dorsal spines. In the spring the male of this species builds upon the bottom of the stream a nest composed of bits of straw, sticks, leaves of plants, and sand, glued together by a secretion produced by a special gland. This secretion is drawn out
into a silk-like thread by which the materials are entangled or woven together as the fish in moving about trails it after him. The completed shape is like that of a hand-muff, smooth inside, and with its openings in the direction of the current. When the house is completed the male induces a female to enter and deposit her eggs, a process lasting only a few minutes. The female then leaves by one of the openings and the male enters by the other to deposit milt over the eggs. In turn other females are invited in, until the nest contains layer after layer of eggs and milt. These the male guards with care against many enemies, until the young are hatched and able to shift for themselves. Stick lebacks are remarkably voracious and extremely destructive to the young fry of fishes. Con sult authorities cited under AQUARIUM and FISH. See the accompanying Plate of STICKLE BACKS.