Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ±s.e. fork length, LF, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method (Cm). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature (IU) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C2. In a separate experiment, the IU of large age 2+ year fish (34·4 ± 0·5 cm LF) was 1·2 and 0·6° C lower (P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm LF) at acclimation temperatures of 16 and 23° C. Using the Cm, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.