Effects on growth performance and body composition in Nile tilapia,Oreochromis niloticus, fry fed organic diets containing yeast extract and soyabean meal as a total replacement of fish meal without amino acid supplementation

Fish meal (FM) is the main protein source in aquaculture diets owing to its palatability and quality. Available quantities of FM have remained constant for the past several decades; however, demand has dramatically increased due to its inclusion in diets used for the global aquaculture industry. There are various alternative protein sources that can be used in aquaculture diets, with soyabean meal (SBM) being the most widely used plant protein ingredient; however, use of SBM as the sole protein source has often resulted in reduced fish growth. There is a growing segment of consumers who desire organically grown foods, and since Nile tilapia is one of the most-cultured fish in the world and has herbivorous/omnivorous feeding habits, Nile tilapia fed an organic diet may allow producers to enter this rapidly developing market. A feeding experiment was conducted to evaluate the combination of organic SBM and an organic yeast extract (YE) as complete replacements for FM. Five isonitrogenous, isocaloric diets were fed to small (0.1 g) Nile tilapia, Oreochromis niloticus, for 6 weeks. Diets contained various percentages (0%, 10%, 20%, 30% and 40%) of YE, with Diet 1 formulated to be similar to a high-quality commercial diet containing 0% YE and 20% FM. At the conclusion of the feeding trial, fish fed Diet 1 had statistically significantly (p < 0.05) higher mean final weight (3.99 g) and specific growth rate (8.48% day− 1), and a lower feed conversion ratio (1.40) than fish fed all other diets. Based upon the data, an organic diet which replaces FM with a combination of SBM and YE appears promising but further research is needed to refine formulation so as to have similar growth performance with a FM-based diet.