UREA AND AMMONIA EXCRETION BY EMBRYOS AND LARVAE OF THE AFRICAN CATFISH CLARIAS-GARIEPINUS (BURCHELL-1822)

Yolk-sac larvae and starved larvae of Clarias gariepinus (Burchell 182 2), reared at 28 degrees C, were predominantly ammonotelic, but urea e xcretion contributed about 19 +/- 7% to the total nitrogen excretion. Exogenously feeding larvae of C. gariepinus were mainly ammonotelic un til 180-205 h post fertilization, but from then on the relative urea e xcretion stabilized at 44 +/- 13%. The contents of total free amino ac ids (FAA) and ammonia in C. gariepinus peaked around complete yolk abs orption. During the first period after hatching 64% of the FAA and 60% of the total ammonia were located in the yolk compartment. The body c ompartment contained the highest amount of FAA. and total ammonia at t he end of the yolk-sac period (65 and 77%, respectively). The amount o f nitrogen originating from catabolism of amino acids was balanced wit hin 6% by the excreted sum of ammonia and urea. The high degree of ure otelism in C. gariepinus larvae may constitute an adaptive mechanism t o a habitat of temporal water shortage.