Gs. Haylor et Mfa. Mollah, CONTROLLED HATCHERY PRODUCTION OF AFRICAN CATFISH, CLARIAS-GARIEPINUS- THE INFLUENCE OF TEMPERATURE ON EARLY DEVELOPMENT, Aquatic living resources, 8(4), 1995, pp. 431-438
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.