Controlled hatchery production of African catfish, Clarias gariepinus: The influence of temperature on early development

Temperature is the major abiotic factor controlling the rate of morphogenesis in fish. The present work investigated hatching time and the transition from endogenous to exogenous feeding at five constant temperatures over the range 15-35 degrees C. Clarins gauiepinus eggs can be successfully hatched in ambient water temperatures between 20 and 35 degrees C, although at 30 degrees C the hatching rate is significantly improved. At 15 degrees C embryos do not survive. The period of hatching is inversely related to temperature such that synchronous hatching is encouraged by high temperature within the specific temperature range. The extent to which development rate and metabolic rate in C. gariepiilus are accelerated by temperature is not the same. The duration between first feeding, yolksac absorption and the point-of-no-return is inversely related to temperature. The same threshold temperature, below which development is theoretically arrested, can be estimated for C. gariepinus from the linear relationship between development rate and temperature up to hatching, first feeding and yolksac absorption. This closely approximates the lower lethal temperature of 15 degrees C estimated directly from embryo survival. The effect of temperature can be usefully modelled in C. gariepinus using the linear relationship V=a+bt to estimate t(0) (threshold temperature) and D-eff(0) (effective day-degrees) and the hyperbolic relationship tau=D-eff(0)/(t-t(0)) to determine development time. From the present work, t(0) is 14.5 degrees C and D-eff(0), is 13, 26.3 and 35.7 for hatching, first feeding and yoll<sac absorption respectively for C. gariepinus. Unlike day-degrees, effective day-degrees remain independent of temperature over the range 20-35 degrees C. An approximate guide to development time at different constant temperatures within this range is given.