Responses of Young American Shad, Alosa sapidissima, to Low Temperatures

Abstract Responses of young American shad, Alosa sapidissima, to low temperatures in fresh water were studied in large aquaria with rapid temperature decreases (about 24 to 12 C) and with slow (1.9 to 0.5 C/day) decreases to 0.7 C in a tank with a temperature gradient. Rapid temperature decreases had no apparent effect. With slow decreases, the fish weakly avoided the cold end below 8 C and strongly below 5 C. Other sublethal effects included extremely sluggish movements below 6 C; cessation of feeding, frequent temporary equilibrium loss, wobbly swimming, and no response to hand movements below 4.4 C; and frequent collision with objects shortly before death. The lower thermal tolerance limit is about 2.2 C; prolonged exposure may increase this, because lethal temperatures depended on exposure time. Sublethal effects suggest that this species may not survive prolonged exposure to 4 to 6 C, particularly during autumn and early winter when the fish may not be acclimated. Temperature plays a multiple role in...