The different sticklebacks can be distinguished by the number of spines on their back: three-spined stickleback has three spines, the brook stickleback usually has five spines, but the number varies between four and seven spines, and the nine-spined stickleback usually has nine spines, but the number varies between seven and twelve. The nine-spined stickleback is usually only four to five centimetres long (that is about 1.5 inches to 2 inches).
The nine-spined stickleback live among aquatic plants, hidden from predators. It eats water fleas and copepods. During spawning season in the summer, it builds a nest among water plants where the female deposits her eggs after a complex breeding ceremony. The male guards the nest while the eggs develop, which usually takes less than a week. Nine-spined stickleback is an inhabitant of large lakes and the costal areas in Finland.