Effect of Dietary Supplementation of Bacillus spp. on Growth Performance, and Resistance of Pacific White Shrimp (Litopenaeus vannamei) to Acute Hepatopancreatic Necrosis Disease

This study was conducted to investigate effect of dietary supplementation of three Bacillus spp. on disease resistance of L. vannamei against Vibrio parahaemolyticus, a main causative pathogen for acute hepatopancreatic necrosis disease (AHPND), and growth performance and feed efficiency. Four diets were prepared by supplementing powder forms of Bacillus spp. (1 x 10(10) CFU/g) with a combination at 0.2% (BS, B. subtilis only), 0.4% (BS/BP, a mixture of B. subtilis and B. pumilus), and 0.6% (BS/BP/BL, a mixture of B. subtilis, B. pumilus and B. licheniformis) into a control diet (no supplement). Quadruplicate groups of shrimp (average body weight, 0.51 g) per each diet were hand-fed the diets for 33 days. Shrimp fed the BS diet had significantly higher growth performance than those fed the control diet or other diets (BS/BP and BS/BP/BL) (P<0.05). After the feeding trial, the shrimp were challenged with V. parahaemolyticus through an immersion method at a concentration of 2 x 10(5) CFU/ml water for 193 h. The shrimp groups fed the Bacillus supplemented diets showed significantly increased (P<0.05) cumulative survival rates compared to the control diet group. At the last sampling (193h), AHPND toxin was not detected in shrimp fed BS diet while no hepatopancreas was sampled due to 100% mortality in the control group. The findings indicate that growth performance and disease resistance of L. vannamei against AHPND could be improved when shrimp are fed the tested Bacillus spp.