Saponin fractions from fenugreek, Trigonella foenum graecum L. and the soap bark tree,Quillaja saponariaL., as dietary additives for Nile tilapia,Oreochromis niloticus(L.)

Abstract

Since 2006, hormones and sub-therapeutic antibiotics have been prohibited in the European Union. However, they were the most efficient feed additives promoting growth and nutrient utilization. Saponins, naturally occurring plant metabolites, could possibly fill the role of alternative feed additives. These compounds were previously known only as anti-nutritional factors that had to be inactivated before plant meals like soybean meal could be fed to fish, but in several experiments it was shown that low levels of Quillaja saponaria (South American soap bark tree) saponins had various positive effects on common carp, Cyprinus carpio L. and Nile tilapia, Oreochromis niloticus (L). Improved growth and reduced oxygen consumption per unit protein gain have been observed in both species. In Nile tilapia, a sex ratio skewed towards a higher percentage of males, and a tendency for females to produce fewer eggs, have been found. Experiments have been conducted to evaluate the effects of fractionated saponins from fenugreek (Trigonella foenum-graecum), and from the South American soap bark tree (Quillaja saponaria), on growth, feed, and nutrient utilization, GH and IGF-1 gene expression, oxygen consumption, sex ratio, gonad development, and reproduction. Saponin fractions from fenugreek did not improve growth, feed, or nutrient utilization, or oxygen consumption significantly. In all experiments examining a single fraction, eluted with 40% methanol, produced poorer results compared to the control. In a preliminary study, the results of the effects of saponin fractions on sex ratio were encouraging but in a larger scale repetition, the observed effects could not be confirmed. No effect on sex ratio was observed during the long term experiment in Jericho, where, due to limited amounts of available fractionated saponins, commercially available Q. saponaria saponins were used. Data from these experiments do not support the application of the tested saponins and saponin fractions to promote growth, improve metabolism, or as a substitute for methyltestosterone to produce male monosex tilapia. The observed effects on growth and nutrient utilization support use of saponins or their fractions in animal nutrition. However, more research on the specific nature, and effects of saponins in fish, both at a molecular and at a macro level, is imperative.