DETERMINATION OF METHIONINE REQUIREMENT AND EFFICACY OF METHIONINE SUPPLEMENTS FOR PACIFIC WHITE SHRIMP Litopenaeus vannamei FED WITH SOY-BASED DIETS

Soybean meal and other plant based protein sources have been studied as alternatives to fishmeal.  However, the amino acid profile of many of these meals is less than ideal. Methionine is usually the first limiting amino acid in many diets, especially those containing high level of soy protein. To improve the acceptance of high soy feed formulations for Pacific white shrimp Litopenaeus vannamei, two growth trials were conducted and one growth trial is ongoing exploring the methionine requirement and efficacy of different methionine supplements. In the first growth trial, the basal diet was formulated to contain 38% protein, 9% lipid and 0.54% methionine. Two sources of methionine were supplemented to basal diet to produce diets containing graded dietary methionine levels of 0.6%, 0.63%, 0.73% and 0.83% with DL-methionine supplementation, and 0.61%, 0.63%, 0.75% and 0.81% with micro-capsulated methionine supplementation. Additionally, the tenth diet was formulated by using corn gluten meal as a replacement for gelatin, dietary methionine level of this diet was 0.62%. Four replicate tanks of 15 juvenile shrimp (initial weight 0.22±0.02g) were randomly fed one of the diets for six weeks. At the end of the growth trial, shrimp were counted and weighed, whole shrimp body samples were collected for proximate and amino acids analysis. In the second growth trial, the basal diet was formulated to contain 35% protein, 9% lipid and 0.49% methionine. Coated methionine and DL-methionine were supplemented to basal diet to produce diets containing dietary methionine level of 0.67%. Additionally, the fourth diet was formulated by replacing gelatin and some level of soybean meal with corn gluten meal, dietary methionine level of this diet was 0.64%. Triplicate aquaria of 10 juvenile shrimp (initial weight 0.55±0.04g) were randomly fed one of the diets for six weeks. At the end of the growth trial, shrimp were counted and weighed, tail muscle and hepatopancreas samples were collected for amino acids and protein analysis. There were no significant differences with regard to final biomass, final meal weight, percent weight gain and feed conversion ratio among treatments for the two trials. Analysis for whole shrimp body samples and tissue samples is ongoing. The third growth trial exploring the potential of intact protein for meeting the methionine requirement of Pacific white shrimp is ongoing.