The effects of dietary saponin and tannin on growth performance and digestion in Oreochromis Niloticus and Clarias Gariepinus.

Abstract

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< 0.05) were observed in dry matter digestibility among the diets in all studies. Fish fed diet IV showed the poorest values (SGR, 0.31/0.21; FCR, 9.51/4.75; PER, 0.39/0.69; PPV, 4.37/-0.35 and APD, 84.04/80.63 with saponin), (SGR, 1.89/2.01; FCR, 1.36/1.05; PER, 2.31/2.97; PPV, 36.93/54.76 and APD, 86.49/95.33 with tannic acid) and (SGR, 2.16/1.85; FCR, 1.19/1.03; PER, 2.55/2.92; PPV, 37.88/50.93 and APD, 89.59/91.31 with catechin) in O. niloticus and C. gariepinus respectively in comparison with others. In terms of carcass composition, there were an increases in moisture and ash contents in fish fed diets III and IV of the study on saponin whereas lipid content was markedly decreased in proportion to the level of saponin in the diets. However, fish in all treatments did not show any significant difference (P< 0.05) in their body protein content. In the studies with tannic acid and catechin, carcass composition of fish showed no significant difference (P< 0.05) in all treatments.

Histological examination showed cytoplasmic vacoulation of intestinal cells, disruption of straited borders and infiltration of lamina propria especially in O. niloticus and fatty degeneration in liver of fish fed diets III and IV of the study of saponin. However, fish in other studies (tannic acid and catechin) showed no abnormalities.

Digestive enzyme activities were inhibited by the inclusion of dietary tannic acid or catechin, and the inhibition was in proportion to the level of the antinutrients. However, both forms of tannins had no effect on lipase activity of O. niloticus while the opposite was observed in C. gariepinus. It was shown that the activities of proteolytic enzymes were more inhibited by the inclusion of tannic acid or catechin than the activities of a-amylase and lipase.

The results of the present thesis show that saponin and tannin (hydrolysable and condensed) acted as neutral or negative factors with respect to growth and feed performance, digestive enzyme activities and histology of intestine and liver.