REEVALUATING THE ESSENTIAL FATTY ACID REQUIREMENTS OF NILE TILAPIA Oreochromis niloticus

A major constraint for the aquafeed manufacturing industry is the availability of cost-effective feed ingredients. Fish oil has long been utilized as an energy dense ingredient with a complete suite of long-chain polyunsaturated fatty acids (LC-PUFA). Although alternative lipid sources are plentiful, they often lack appreciable amounts of essential fatty acids (EFA). Accordingly, we evaluated the growth performance of Nile Tilapia fed diets containing different combinations of n-3 and n-6 C₁₈ polyunsaturated fatty acids (C18 PUFA) or LC-PUFA. Diets varied only in lipid source and composition, containing menhaden fish oil (positive control, "FO Control"), hydrogenated soybean oil (negative control, "EFA-Free Control"), or soybean oil amended with ethyl esters of 18-3n:3 ("ALA"), 18:2n-6 and 18:3n-3 ("C18 PUFA"), 22:6n-3 ("DHA"), 22:6n-3 and 20:4n-6 ("ARA+DHA"), or 22:6n-3, 20:4n-6, and 20:5n-3 ("LC-PUFA"). Diets were randomly assigned to quadruplicate tanks (N=4) of Nile Tilapia (10 fish/tank; 25.7 g/fish), fish were fed to satiation twice daily for 7 weeks. At harvest, individual fish weights were collected to analyze growth performance. Data were analyzed by one way analysis of variance, followed by Tukey's HSD test when omnibus tests indicated significant treatment effects (P < 0.05).

As anticipated, fish fed the FO Control experienced significantly greater weight gain (223.4%) compared to those fed the EFA-Free Control diet (147.1%; Figure 1). However, diets containing both C₁₈ PUFA performed numerically superior (390%) compared to diets formulated with all three intact LC-PUFA (365%) (Figure 1). Results from this trial agree with historical data that Nile Tilapia can effectively utilize dietary C₁₈ PUFA.