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 morpho genesis in fish. The present work investigated hatching time and the t ransition from endogenous to exogenous feeding at five constant temper atures over the range 15-35 degrees C. Clarins gauiepinus eggs can be successfully hatched in ambient water temperatures between 20 and 35 d egrees C, although at 30 degrees C the hatching rate is significantly improved. At 15 degrees C embryos do not survive. The period of hatchi ng is inversely related to temperature such that synchronous hatching is encouraged by high temperature within the specific temperature rang e. The extent to which development rate and metabolic rate in C. garie piilus are accelerated by temperature is not the same. The duration be tween first feeding, yolksac absorption and the point-of-no-return is inversely related to temperature. The same threshold temperature, belo w 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 est imated directly from embryo survival. The effect of temperature can be usefully modelled in C. gariepinus using the linear relationship V=abt to estimate t(0) (threshold temperature) and D-eff(0) (effective da y-degrees) and the hyperbolic relationship tau=D-eff(0)/(t-t(0)) to de termine 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 y oll<sac absorption respectively for C. gariepinus. Unlike day-degrees, effective day-degrees remain independent of temperature over the rang e 20-35 degrees C. An approximate guide to development time at differe nt constant temperatures within this range is given.