Temperature tolerance of larval muskellunge (Esox masquinongy) F1 hybrids reared under hatchery conditions

Critical thermal maxima (CTM) of larval muskellunge (Esox masquinongy) and norlunge (Esox masquinongy females × E. lucuis males) were determined under hatchery conditions. Norlunge had higher temperature tolerance and developed faster. CTM of larval norlunge (30.9–36.0°C,X= 34.0°C) were significantly higher (P ≤ 0.01) than those of muskellunge (29.9–35.6°C,X= 32.8°C). Both fish exhibited a sharp decrease in CTM during swim-up, followed by a slow recovery period characterized by a general increase in CTM values. Both age and past thermal history had important effects on temperature tolerance of fry. Norlunge fry were better able to physiologically adjust to changing environmental conditions than were muskelunge.