STICKLEBACK, a group of small fishes (Gasterosteus) which inhabit the fresh and brackish waters as well as the coasts of the temperate zone of the northern hemisphere. The majority have a compressed well-proportioned body, which in the marine species is of a more elongate form. Their mouth is of moderate width, oblique, and armed with small teeth. The head is protected by hard bone. There are a series of scutes protecting the sides. The first dorsal fin and the ventrals are transformed into pointed formidable spines, and joined to firm bony plates of the endo skeleton. A remarkable degree of variability is shown by many species. Sticklebacks construct a nest for the reception of the spawn, which is jealously guarded by the male until the young are hatched, from ten to eighteen days after oviposition. He also protects them for the first few days of their existence.
Sticklebacks are short-lived animals said to reach an age of three or four years. In spring each male selects a territory, which he fiercely defends and to which he invites all females, until the nest is filled with ova. At this period he assumes a dress of blue
and red. The eggs are comparatively large, one female depositing from 50 to 100.
The three-spined stickleback (G. aculeatus) is found every where in northern and central Europe, northern Asia, and North America.
The ten-spined stickleback (G. pungitius) is smaller than the three-spined species, rarely exceeding tin. in length. Its geo graphical range nearly coincides with that of the other species.
The sea-stickleback (G. spinachia) attains a length of 7in., and is armed with 15 short spines. It is common round the British coasts. At suitable localities which are sheltered from the waves and overgrown with seaweed, especially in rock-pools and shallows covered with Zostera, one or two males establish them selves with their harems. The nest is firmly attached to seaweed.