Influence of Oral Administration of Bacillus subtilis on Growth Performance and Physiological Responses in Litopenaeus vannamei Cultured in Low Saline Waters.

The present study examined the effect of Bacillus subtilis on growth performance, digestive enzyme activity, and immune response of juvenile white-leg shrimp (Litopenaeus vannamei) in 100 m2 lined ponds. Control (without B. subtilis) and experimental (with B. subtilis) diets were fed at 10% of animal body weight, four times daily for 6 weeks in duplicate ponds. Significantly increased final weight, weight gain, specific growth rate, average daily growth, and survival rate were observed in the B. subtilis treated group (P < 0.05). Significantly higher (P < 0.05) digestive enzyme activities of protease, lipase, amylase, and cellulase were found in the B. subtilis supplemented diet fed group. At the end of trial, a challenge study, using Vibrio alginolyticus, found lower (15.00 ± 2.88%) cumulative mortality in the B. subtilis treated group compared to control (73.33 ± 3.33%). Activities of immune and antioxidant enzymes (phenoloxidase, SOD, and catalase) were significantly higher (P < 0.05) in the B. subtilis-incorporated diet fed group. Interestingly, histopathology of the hepatopancreas and intestine revealed that the B. subtilis-supplemented group showed no deformity. Overall, the study found inclusion of B. subtilis in P. vannamei diet improves growth, physiometabolic activities, and immunity, indicating B. subtilis as a potential probiotic for shrimp feed.