Beneficial antagonistic bacteria from freshwater fishes and culture environment as probiotics in ornamental fish culture

Abstract

A search for beneficial antagonistic bacteria from freshwater fishes and culture environment, and their use as probiotics in ornamental fish culture was attempted. In freshwater fishes, the antagonistic bacterial populations were found to be in the range of <0.002 - 13.12% of the total population; while in ornamental fish culture environment, their populations were in the range of <0.14 - 24.39%. Asporogenous Gram-positive rods (31.7%) and aerobic spore forming Bacillus spp. (30%) were the dominant antagonist groups followed by Micrococcus (18.3%), Lactobacillus, Lactococcus and Streptococcus in the fish gut. Eighteen opportunistic fish pathogenic bacteria
belonging to the genera Aeromonas, Bacillus, Citrobacter and Pseudomonas were inhibited by the antagonistic bacterial strains in vitro at varying levels. The potential probiotic strains,
Bacillus sp. P43 and Lactobacillus sp. P21 from fish gut were capable of adhering to different substrates and conferred protection to Carassius auratus and Xiphophorus helleri. Bacillus sp. P43 survived well both in pelleted feed and water while the Lactobacillus sp. P21 failed to do so. The dominance of Gram-positive antagonistic bacteria in freshwater fishes imply that these bacteria could be useful as probiotics and / or biocontrol agents in freshwater ornamental fish culture.