AMINOACID NUTRITION OF NILE TILAPIA: A REVIEW OF AVAILABLE DATA AND PROGRESS IN MODELLING APPROACH

Tilapia is currently the second largest produced farmed fish, just after carp. The industry is however facing major challenges with rising feed cost. Among nutrients, protein has a major share of diet cost and there has been continuous efforts in finding alternative cost-effective protein sources. Quality of the dietary protein is determined by its amino acid composition and digestibility in relation to the requirements of fish. Improving our understandings on the amino acid requirements of tilapia is therefore very important in order to be flexible with the diet formulations and maximize profitability. Knowledge on the amino acid requirements of tilapia is increasing over the years. Quantitative requirements for essential amino acids (EAA) of Nile tilapia was first reported back in 1980s. Since then several studies (n >15) have been published on the amino acid requirements of Nile tilapia. In due course, efforts were also made to provide amino acid recommendations for feed industry which included table recommendations given by NRC, and also by Evonik for different growth stages of tilapia. The main objective of this project was to do a critical review of the available datasets and provide recommendations determined via factorial approach.

Studies in the past have used dose-response approach, diet dilution technique and deletion method for determining amino acid requirements of tilapia, with dose-response approach being the most commonly used method. Among the EAA, requirements for sulfur amino acids (methionine and cysteine), lysine and threonine were most commonly studied, understandably because these are often the first three limiting amino acids in practical fish feeds. Table 1 illustrates the summary of various published data on the amino acid requirements of Nile tilapia. Data show a wide range of variations in the requirement data published for several EAA. Variations among studies are partly because of differences in methods used and mathematical models adopted for the estimation of EAA requirements. Furthermore, Nile tilapia has been genetically improved over the years for better growth which suggests that dietary EAA requirements for modern tilapia can be quite different and likely higher than the previously reported values. Finally, effort was also made to provide EAA recommendations for different life stages and production scenarios of Nile tilapia based on factorial approach. Factorial approach treats the total requirement for an amino acid as the sum of its amounts needed to meet the physiological demands of fish for maintenance and growth. Available data on maintenance requirements, amino acid retention and utilization were considered in developing amino acid recommendations for Nile tilapia.