Effects of Quillaja saponins on growth,metabolism, egg production and muscle cholesterol in individually reared Nile tilapia (Oreochromis niloticus)

The effects of supplementation of a Quillaja saponin (QS) mixture in the diets of tilapia have been studied using a respirometer system that allowed feeding and continuous measurement of oxygen consumption of individual fish. Five fish each were given control diet (C group) and control diet supplemented with 150 mg kg^?1 (S150 group) or 300 mg kg^?1 (S300 group) QS. At the end of 14 weeks the weight gain of the S300 group was significantly higher than control (P<0.05) whereas that of the S150 group had an intermediate value. The S150 group had a higher growth rate (P=0.05) after the first 3 weeks of feeding with the experimental diets, compared to the other two groups. At the end of the experiment the S300 group had significantly higher (P<0.05) average values for energy retention, apparent lipid conversion, carcass fat, energy and significantly lower (P<0.05) average values for apparently unutilised energy and carcass ash content compared to the C group. The corresponding values of the S150 group were intermediate between the C and S300 groups. One out of two female fish in the S150 group and both female fish in the S300 group never produced eggs during the entire 14-week experimental period. Contrarily, all three female fish in the control group and one out of the two female fish in the S150 group regularly produced eggs, at a rate of approximately once in every 14 days. The muscle cholesterol level in the S300 group was significantly higher than that of the C group. Possible mechanisms of action of the dietary saponins are discussed.