EFFECTS ON GROWTH PERFORMANCE OF PACIFIC WHITE SHRIMP Litopenaeus vannamei TO INCREASING LEVELS OF MET + CYS, UNDER POND CULTURE CONDITIONS  

Traditionally fishmeal (FM) has been the protein source of choice in commercial aquaculture feeds due to its high nutritional value. Due to its limited supply and increasing price, there is a need for replacement with alternative protein sources such as soybean meal. In this case, there is a deficiency of critical amino acids (AA), so supplemental AA, like Methionine (Met), are needed in order to meet the species requirements for optimum growth. Additional challenges the industry faces, are leaching losses because of the species feeding behaviour (external masticators). The dipeptide DL-methionyl-DL-methionine, is the mixture of four different stereoisomers designed especially to address these issues. Previous studies in clear water system have shown improvement on the growth performance of the shrimps. However in commercial ponds (green water) where the shrimps have access to natural food sources (microscopic algae, zooplankton, benthic fauna and microflocs) studies are lacking. But first and foremost, before the practical application of the previously mentioned advances, it is fundamentally important to understand the species nutritional requirements of Met and Met+Cys (cysteine) under these conditions. Hence, the present study was conducted in order to evaluate the growth performance of Pacific white shrimp (Litopenaeus vannamei) fed increasing levels of dietary Met and Met+Cys (by supplementing increased levels of DL-methionyl-DL-methionine), under green water system

In the current study, 7 experimental diets were fed to quintuplicated groups of 35 Pacific white shrimps/cage with an average body weight of 5.05 ± 0.22 (mean ± 1 SD) g, for 60 days. The cages (1×1×1 m) were installed in a commercial pond (1500 m² area) and all the diets were fed 3 times per day. Diet 1 used as basal control (0% DL-methionyl-DL-methionine) and diets 2-6 had the same composition but supplemented with increasing levels of DL-methionyl-DL-methionine (0.05%, 0.10%, 0.15%, 0.20% and 0.40%, total, as-is basis) containing 0.98%, 1.02%, 1.08%, 1.13%, 1.18% and 1.38% respectively of total Met + Cys. While Diet 7 (commercial feed known to have high FM, around 15%) had no AA supplementation, a total Met + Cys at 1.12% and was used as a positive control diet. The daily recorded water temperature ranged from 25.3 to 29.1°C and the salinity from 0.2 to 0.5 ppt.

The shrimps fed with increasing levels of Met and Met+Cys (Diets 2-6) had significantly higher feed intake, final body weight, weight gain and lower FCR compared to the basal diet (Diet 1). The FCR was significantly lower in shrimp fed the Diets 2-6, compared with both basal (Diet 1) and commercial diet (Diet 7). The shrimps fed with the commercial diet showed better weight gain than those fed with diets 1, 2 and similar to groups fed diet 3 and 4. However, shrimps fed the experimental diets 5 and 6 significantly increased their body weight compared to the rest of the groups, including the ones fed the commercial diet (Table 1). Finally, fitting the quadratic broken line model to the weight gain data showed an optimal weight gain of Pacific white shrimp at dietary level of 0.80% Met (R² = 99.1%) and 1.23% Met + Cys (R² = 99.4%) (Figure 1).