Bacterial microbiota of hatchery-reared freshwater prawn Macrobrachium rosenbergii (De Man, 1879) and their pathogenicity

Abstract

Quantitative and qualitative analyses of bacterial microbiota associated with hatchery of Macrobrachium rosenbergii (de Man, 1879) were conducted over three larval cycles, along with important water quality parameters. Physicochemical parameters (temperature, DO, salinity, pH, and total ammonia) of culture water were within the optimum level required for the hatchery phase of M. rosenbergii. Significant differences in aerobic plate count (APC) among larval stages were observed. Ten genera and 17 species were identified with the predominance of Gram-negative bacteria constituting 63 % of all isolates (n = 706). A total of 17 dominant bacterial isolates randomly selected from freshwater prawn larvae were screened for in vitro hemolysin activity using blood agar plate (BAP) medium with 5% sheep blood. Pathogenicity of the isolated bacterial strains was assessed through in vivo infection bioassay. Out of the 17 isolates tested, six isolates showed α – β zone of hemolysis on the BAP, i.e., Aeromonas caviae, Bacillus cereus, Plesiomonas shigelloides, Staphylococcus warneri, Vibrio cholerae non-01, and Vibrio furnissii, were used in the infection bioassay. The current data indicate that the six bacterial isolates tested, particularly B. cereus and V. cholerae non-01, are opportunistic pathogens capable of inducing disease epizootics, particularly in freshwater prawn hatcheries with suboptimal rearing water conditions. Thus, control measures to reduce the influx of pathogenic microbes in the system by maintaining good water quality and good farm management practices through disinfection of culture facilities, rearing water, and Artemia cysts, the practice of good hygiene of personnel, regular water exchange, and feed regulation, among others, and cautionary use of antibiotics, can be adopted.