The effect of saponin (Quillaja saponaria) on the growth performance and body composition of rainbow trout larvae (Oncorhynchus mykiss)

Saponin has been recognized as an anti-nutritional factor in plant ingredients. However, this substance has been also introduced as a natural growth promoter by reducing viscosity, increasing nutrient digestibility and promoting anabolic synthesis. The main goal of this study was to assess the effect of different levels of saponin (Quillaja saponaria) as a feed supplement on the growth parameters and body compositions of rainbow trout larvae. This experiment has been performed for 18 weeks using rainbow trout larvae with initial weight of 171±6 mg. Five experimental diets were prepared by addition of 50, 150, 250, 350 and 450 mg/kg saponin to a control diet. In this study, 40-L tanks were used to grow the larvae up to 1g, afterward the fingerlings were transformed into concert ponds (4×2) by the end of the experiment. Feeding level was regulated according to the feeding table for rainbow trout and given to the each tank. At the end of the experiment, growth parameters, feed intake and body composition were measured. The results showed that the addition of different levels of saponin did not influence growth parameters and feed efficiency, but saponin increased fat content of the carcass (P<0.05). It appears that the saponin efficiency in carnivorous species like rainbow trout is dependent on other feed ingredients especially carbohydrate