Tiger muskellunge (Esox masquinony × E. lucius) juveniles were reared at constant temperatures in the temperature range 14–28°C. For fish 3–4 cm long, growth, production and feed conversion efficiency were greatest at 20–22°C. Survival was reduced and unaccountable mortality (cannibalism index) was greatest at 24°C. Growth per unit of temperature was about equal over the range 16–22°C. For fish 12–13 cm long, feed conversion efficiency and mean individual growth were greatest at 23°C; growth per unit of temperature was nearly equal over the range 20–24°C.