VARIATION IN NUMBER OF DORSAL SPINES IN THE BROOK STICKLEBACK, EUCALIA INCONSTANS

The brook stickleback, Eacalia inconstans (Kirtland), is usually described as possessing five or six dorsal spines and the species is commonly called the five-spine stickleback. In Homing Lake, Manitoba, fish with six dorsal spines predominate. The occurrence of sticklebacks with a high number of dorsal spines is noted from other Manitoba lakes and to a lesser extent in samples from some Ontario lakes. Indications are that the dorsal spines are more numerous in fish from the Hudson Bay drainage than from the Great Lakes region. An increase in the number of dorsal spines with increasing latitude is apparent.