Stickleback

Stickleback, any fish of the spiny-finned gemls Gasterosteus, with some ten species, from the North Temperate and Arctic zones. They are of small size, and have the first dorsal fin replaced by spines, and bony plates along the sides. All are nest-builders, and in the breeding season the males are brilliantly coloured. The Three-spined Stickleback (G. aculeatus) is exceedingly common in Britain.