In order to investigate the antinutritive effects produced by the intake of saponin and tannin (hydrolysable and condensed), ten experiments were conducted on Oreochromis niloticus and Clarias gariepinus utilising casein/gelatin purified diets. Fish were fed (3% body weight/day) four isoenergetic isoproteic diets containing 0.02/0.01, 0.08/0.09, 0.42/0.47 and 0.87/0.91% saponin, (for O. niloticus and C. gariepinus respectively), 0.05, 0.08, 0.27 and 0.71% tannic acid or 0.06, 0.16, 0.73 and 1.66% catechin which represent diets I, II, III and IV respectively in each study.

In all studies fish fed diet I showed the maximum weight gain, highest specific growth rate (SGR), the best feed conversion (FCR) , the best protein efficiency ratio (PER) and the best apparent protein digestibility (APD) in comparison with all other diets; whereas no significant differences (P