Effects of DL-methionyl-DL-methionine supplementation on growth performance, immune and antioxidative responses of white leg shrimp (Litopenaeus vannamei) fed low fishmeal diet

The study was conducted to investigate the effects of DL-Methionyl-DL-Methionine (Met-Met) (a dipeptide of two DL-methionine molecules) on growth performance, immune and antioxidative responses for Litopenaeus vannamei fed low fishmeal diet. Tested treatments consisted of positive control diet (PC) with 20 % fishmeal or 7 % fishmeal (basal diet) diets supplemented with different levels of Met-Met (0.00 %, 0.1 %, 0.15 %, 0.20 %, 0.25 % and 0.3 %). A total of 1680 shrimp (0.071 +/- 0.001 g) were randomly distributed into 42 tanks (6 repetitions / each diet, 40 shrimp / tank) and fed for 91 days. Results showed that reduction of fishmeal from 20 % down to 7 % did not affect the survival rate of shrimp. Weight gain rate and feed efficiency were significantly decreased in the basal group compared to the PC group, while these were significantly increased with the increasing of MetMet into the diets up to 0.15 % compared to the basal group. Malondialdehyde in 0.15 % Met-Met and PC groups were significantly lower than the basal group. Shrimp fed the diet with 0.15 % Met-Met had the highest phenol oxidase content and peroxidase and total antioxidant capacity. The highest values of intestinal wall thickness were observed in 0.15 % Met-Met and PC groups. The similar morphology of the hepatopancreas was observed between 0.15 % and PC groups. Overall, the present study indicated that Met-Met could improve adverse effects of Met deficiency on growth caused by low fishmeal. Low fishmeal diet with 0.15 % Met-Met (0.65 %-0.66 % Met and 1.14 % Met + Cys) is beneficial to the health of intestine and hepatopancreas, improves immunity and antioxidative capacity and promotes the growth of L. Vannamei.