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 di ets of tilapia have been studied using a respirometer system that allowed f eeding and continuous measurement of oxygen consumption of individual fish. Five fish each were given control diet (C group) and control diet suppleme nted with 150 mg kg(-1) (S150 group) or 300 mg kg(-1) (S300 group) QS. At t he end of 14 weeks the weight gain of the S300 group was significantly high er than control (P < 0.05) whereas that of the S150 group had an intermedia te value. The S150 group had a higher growth rate (P = 0.05) after the firs t 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 high er (P < 0.05) average values for energy retention, apparent lipid conversio n, carcass fat, energy and significantly lower (P < 0.05) average values fo r apparently unutilised energy and carcass ash content compared to the C gr oup. The corresponding values of the S150 group were intermediate between t he 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-wee k experimental period. Contrarily, all three female fish in the control gro up 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 choleste rol level in the S300 group was significantly higher than that of the C gro up. Possible mechanisms of action of the dietary saponins are discussed. (C ) 2001 Elsevier Science Inc. All rights reserved.