PERFORMANCE OF WHITE LEG SHRIMP (Litopenaeus vannamei) FED HIGH OR LOW FISH MEAL DIET SUPPLEMENTED WITH INCREASING LEVELS OF DL-METHIONYL-DL-METHIONINE

Shrimp feed industry is constantly looking for opportunities to reduce inclusion of dietary fish meal. Replacement of fish meal with alternative protein sources requires balancing diets for dietary nutrients, while maintaining palatability. Methionine (Met) is typically the first limiting amino acid in soybean-based shrimp feed and thus, supplementation of methionine is essential in those diets. DL-Methionyl-DL-Methionine, 'Met-Met' in short (AQUAVI^® Met-Met,), is a dipeptide of DL-Methionine and is shown to be an effective supplemental methionine source for shrimp in the recent studies. The objective of the current study was to evaluate and compare the performance of shrimp fed low fish meal diet (8%) with increasing levels of supplemental Met-Met, relative to those fed a high fish meal diet (16%) under green water system.

Shrimp (3.47±0.02 g, mean ± SD, initial weight) were randomly stocked into 20 cages (1×1×1.5 m). The experiment consisted of five dietary treatments (~38% crude protein) including: a positive control (PC) diet containing 16% fish meal with 0.10% DL-Met supplementation (D1), a negative control (NC) diet containing 8% fish meal without supplemental methionine (D2) and three other NCs with increasing levels of Met-Met supplementation at 0.03%, 0.06%,and 0.10%, respectively (D3-D5). Analyzed Lys, Met and Met+Cys levels (as-is basis) were 1.83%, 0.76% and 1.23%, respectively in the PC diet and 1.75-1.81%, 0.57-0.72% and 1.05-1.20%, in the NC diets with or without supplemental Met. Each dietary treatment was allotted randomly to four replicate cages and shrimp were fed four times daily to apparent satiation for 42 days. Data were analyzed with ANOVA and means were separated using Tukey test (P <0.05).

Results of the study are shown in Table 1. Shrimp fed the NC diet showed significantly lower weight gain, feed intake and protein retention efficiency (PRE, %), marginally lower specific growth rate (SGR) (P=0.06) and similar feed conversion ratio (FCR) relative to those fed the PC diet. Growth rate, FCR and PRE significantly improved for the groups fed with increasing levels of supplemental Met-Met (D3-D5). Shrimp fed NC+0.10% Met-Met diet (0.72% Met and 1.20% Met+Cys) showed the best performance with significantly better body weight gain, and FCR relative to the group fed NC diet without supplemental Met.  Overall, results showed that AQUAVI^® Met-Met can be used as an effective supplemental methionine source in reducing fish meal level from 16% to 8% in shrimp feed without compromising growth performances.