Some species live in freshwater, some in the sea, and some in both.
The members of the family are characterized by a row of spines on the back, in front of a soft-rayed dorsal fin. The scaleless skin is generally protected by a variable number of hard armour plates on the sides. Images are approximately actual size for typical adults. 3-spine stickleback, Gasterosteus aculeatus Sticklebacks are noted for their reproductive behaviour. After building a nest of plant materials glued together with a threadlike, mucous secretion from his kidneys, he coaxes and drives a female into the nest to lay her eggs and follows her to fertilize them.