Abstract:
Development of probiotics to improve the growth of cultured species is a key to sustainable aquaculture. The present study investigates the potential of salt pan bacteria as probiotics for Litopenaeus vannamei. Halotolerant bacteria (100) were screened for enzyme production and mucus adhesion in vitro. The bacteria (SK07, SK27, ABSK55, FSK444, TSK17, TSK71) exhibiting promising enzyme activity and adhesive property in vitro were selected to study their effect on the growth and metabolism of L. vannamei in vivo. When administered to shrimps individually as a water additive in experiment I, SK07, SK27 and TSK71 significantly (p<0.05) increased shrimp weight as compared to the control. In experiment II, a lyophilized bacterial consortium (test) prepared with the four best isolates (SK07, SK27, ABSK55, TSK71), exhibited significantly higher weight gain of shrimps, better feed efficiency and final yield as compared to control. Total enzyme activity (amylase, protease, lipase) in the shrimp gut was significantly higher in the test than the control. The four isolates showed 99% nBLAST similarity with Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus licheniformis and Pseudomonas sp. Presence of these bacteria in the shrimp gut was confirmed by using specific PCR-based molecular probes and 16S rDNA sequencing. Safety evaluation by antibiotic susceptibility test and hemolytic activity test indicated that the bacteria are safe as bioinoculants. The increased enzyme activity by colonisation of the isolates in the shrimp gut, along with improved growth and feed utilisation efficiency, strongly confirms that these salt pan bacteria are prospective probiotics in shrimp aquaculture.
