REDUCING DIETARY PROTEIN LEVELS TO A MORE ENVIRONMENTAL-FRIENDLY TILAPIA Oreochromis niloticus PRODUCTION

Dramatic growth of aquaculture production in the past two decades has significantly contributed to meet the growing demand for seafood consumption. Sustainable growth of aquaculture industry is challenged by raising production cost and increasing environmental impact. Tilapia are the second most cultivated finfish group. Cost of aqua feeds, including tilapia feed, is largely dictated by dietary protein levels and sources. Supplemental amino acids provide an opportunity to reduce excess dietary protein level by formulating diets that match close to ideal amino acid profile. Reducing excess dietary protein allows minimizing diet cost as well as reducing nitrogen output. In this context, the aim of this study was to evaluate performance of juvenile Nile tilapia (Oreochromis niloticus, ~ 6 g, initial body weight) to reduced dietary protein levels, using supplemental crystalline amino acids. Furthermore, metabolic trials were performed aiming to obtain an in vivo snapshot of protein utilisation in Nile tilapia juveniles as a function of dietary protein content. A growth trial was performed using five isoenergetic plant protein-based diets (without fish meal or fish oil inclusion) with decreasing levels of crude protein: 36, 34, 32, 30 and 28%. All the diets were formulated to meet the minimum requirements of amino acids for juvenile Nile tilapia based on NRC and AMINOTilapia^® software (Evonik Nutrition & Care GmbH) recommendations. Dietary protein utilisation was also assessed by metabolic trials using a radiolabelled amino acid mixture. Triplicate tanks were randomly assigned to one of the five dietary treatments. Fish were fed to visual satiety by hand, three times a day (09h30, 12h30 and 16h30) for approximately eight weeks (59 days). Performance of fish fed experimental diets is shown in Table 1. Fish in all treatments showed similar growth performance and feed intake. Tilapia fed 28%-protein diet showed significantly higher feed conversion ratio relative to those fed the 36%-protein diet, while no differences were found in fish fed other diets. However, fish fed 30%-protein diet showed significantly better protein retention than those fed the 36%-protein diet.  Metabolic trials showed that amino acid catabolism increased in fish fed the 36%-protein diet, while no significant differences were found in amino acid retention in muscle. This study demonstrates that dietary protein levels can be reduced to 30% without hindering tilapia growth and feed conversion ratio, while reducing nitrogen and phosphorus losses to the environment.