Sexual dimorphism
Differences in size, shape or colour between males and females of the same species.
Also: breeding colours, nuptial colours
In many fish the sexes look different. Male guppies, bettas and swordtails are brightly coloured with long fins, while females are plainer. Male salmon grow a hooked jaw, called a kype, and turn red as they head upriver to spawn. In many anglerfish the male is tiny and fuses to the female's body for life. Some differences appear only in the breeding season, such as the bright colours of male sticklebacks and many cichlids, and the white bumps called tubercles on the heads of male carps.