Response of largemouth bass Micropterus salmoides to dietary supplementation of lysine, methionine, and highly unsaturated fatty acids

A 12-wk feeding trial was conducted in aquaria with juvenile (36.0 +/- 1.2 g) largemouth bass Micropterus salmoides to examine the effects of dietary supplementation of methionine, lysine, and long-chain polyunsaturated fatty acids (PUFA) on growth, feed conversion and body composition. Diets were f ormulated to increase dietary concentrations of methionine, lysine, and PUF As to match levels found in whole body samples of largemouth bass. The cont rol diet was formulated similar to diets previously tested for largemouth b ass. Diets 2 and 3 were similar to the control diet but were supplemented w ith 2% lysine and 1% methionine, respectively. Diet 4 was formulated to inc rease PUFAs, especially docosahexaenoic acid (DHA) (22:6n-3), by replacing menhaden fish oil with squid oil. Fish were fed all they would consume in 1 0 min, twice daily. At harvest, there were no statistically significant dif ferences (P > 0.05) in average individual weight or specific growth rate (S GR) among fish fed the four diets. The feed conversion ratio (FCR) of large mouth bass fed the diet supplemented with methionine (1.7) was significantl y lower (P less than or equal to 0.05) than fish fed the control diet (2.5) . Fish fed the diet high in PUFA had significantly lower (P less than or eq ual to 0.05) whole body lipid levels and significantly higher (P less than or equal to 0.05) protein levels than fish fed the other three diets. These data indicate that the control diet in this study likely contained suffici ent lysine, methionine and PUFA to meet the requirements of largemouth bass ; however, additional methionine may improve feed conversion efficiency, an d increased levels of PUFAs or other factors in squid oil may have a signif icant impact on body composition.