The most obvious feature of the three-spined stickleback is its spines ('stickles' on its back). As its name suggests, there are usually three spines but this small fish can have two or four spines instead. Sticklebacks are 4–6 cms in length although they can grow up to 10cm. They generally have a greyish or bluish-green back and silvery sides. During the breeding season the male develops a metallic sheen over his back and sides and a bright red or orange patch on his throat which extends down towards his belly.