ANNUAL CYCLE OF THERMAL TOLERANCE IN SHAM-PINEALECTOMIZED AND PINEALECTOMIZED AIR-BREATHING CATFISH CLARIAS-BATRACHUS

Annual variations in thermal tolerance and the influence of the pineal there on were investigated in the ectotherm, Clarias batrachus, expos ed to natural photothermal conditions in the laboratory. Thermal toler ance was assayed by measuring the critical thermal maximum (CTM) in sh am-pinealectomized and pinealectomized animals every month for 1 year. A pronounced annual rhythm of thermal tolerance was validated, with t he maximum recorded during the spawning phase and the minimum during t he resting phase of the annual reproductive cycle of the catfish. This may have an adaptive significance since, during the spawning period, the fish ventures to nearby inundated areas, even going over a land ro ute. An elevation in CTM will thus allow the ''walking'' catfish to be tter exploit the environment. Pinealectomy did not have any significan t effect on the annual rhythm in thermal tolerance.