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. More than one female may be chosen. When the nest is full, the male becomes its guard and caretaker, aerating the eggs until they hatch and aggressively defending eggs and young from intruders. Several stickleback species are familiar and abundant fishes.