ANTAGONISTIC EFFECT OF BACILLUS THURINGIENSIS SUB-SPECIES (H12) ON PATHOGENS OF TILAPIA SPECIESU.S. BAGDE, B. V. BILOLIKAR AND R.S. PANDITAbstract The aquaculture in Asia has evolved dramatically during the last decade, leading to major structural changes and capital intensive production system. Asian countries have increased their aquaculture production significantly, but it has not been without environmental and socioeconomic impacts; among the most important are increasingly fish health issues. However, fish disease is the major risk factor in commercial aquaculture with millions of dollars lost annually, and the fish disease has emerged as a major constraint to sustainable development of aquaculture. Hence in the present investigation the antagonistic effect of Bacillus thuringiensis subs. sp. H12 on pathogens from Tilapia viz. Aeromonas salmonicida, Vibrio anguillarum biotype II, Vibrio anguillarum biotype I, Aeromonas hydrophila sub. sp. Hydrophila, Aeromonas hydrophila sub. sp. anerogenes and Pseudomonas putida have been studied. When effect of B. thuringiensis (1-112) was studied on isolated pathogens, by agar well diffusion method all the pathogens showed zones of inhibition ranging from 21mm to 39mm diameter thereby confirming biocontrol activity of B. thuringiensis sub. Sp. H12 on pathogens of the fish Tilapia. In an aquarium experiment, fishes when challenged with pathogens in absence of probiotic cells of B. thuringiensis sub. sp. H12, showed mortality with various disease symptoms like descaling patches, body fin rot; tail fin rot, red ulcerative patches on trunk, on operculum, deterioration of fins. However, fishes after treatment with probiotics B. thuringiensis (H12), when challenged with pathogens did not develop any disease and remained healthy thereby again confirming biocontrol activity of B. thuringiensis sub. Sp. (H12) on fish pathogens.
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