Breeding

Sticklebacks normally breed between late March and early August. During these months there is plenty of food around for the young fish. In the early spring, the male stickleback undergoes quite a dramatic transformation. His throat and belly become a bright orange-red, his eyes turn bright blue and silvery scales appear on his back. These colours act as a warning to other males to keep away from his territory, and they also attract females.

Attired in his bright colours, the male then sets about building a mound-shaped nest in a hollow on the bottom, using bits of water plants, bound by sticky threads ejected from his kidneys. He uses his mouth to glue the bits of plants together. When the nest is finished, the male tries to entice as many females as he can into his nest. Each female lays her eggs in the nest and the male fertilises them. He then guards the eggs, fighting off possible predators, until they hatch, which may take anything from one week to a month. The eggs need plenty of oxygen to develop, so the male directs waves of oxygen-filled water over them with his fins. About 100 young leave the nest and their father continues to look after them for another week or more until they leave to lead an independent life. They feed on water fleas and tiny worms and take about a year to develop into adults.