Stickleback, small fish with spines on its back that lives in fresh and salt waters of the Northern Hemisphere. There are sticklebacks with 3,4, and 10 spines and the marine stickleback has 15. Sticklebacks are very abundant. They feed on small animals. The male builds a nest of waterweed and entices several females to lay their eggs in it. He stays with the young and drives away enemies.