Periodic Nocturnal Activities in the Catfish Silurus asotus in Captivity

Abstract

Nocturnal activities in the catfish Silurus asotus were investigated experimentally with an actograph.Most of their nocturnal action commenced nearly at or soon after sunset when ambient light intensities were close to 0.001 lux at various water temperatures (10°-25°C) under natural light conditions.Their nocturnal action, however, terminated a little or more before sunrise depending on the difference of water temperature, when the ambient light intensities were 0.0001 lux or less.The nocturnal activities of this catfish were controlled not only by the daily changes in the ambient light but also by an endogenous circadian rhythm which was detected in light: dark pulses repeated with a short period, and in constant darkness.Their daily activities in nature were regarded as a result of synchronous cooperation of the endogeneous rhythmical system and daily light: dark stimuli.