Isolation and characterization of indigenous microorganisms for antagonizing Fusarium incarnatum and preventing swollen swim bladder disease in Pangasius hypophthalmus

Abstract

Fusarium incarnatum is known to cause swollen swim bladder disease in Pangasius hypophthalmus, leading to significant losses for aquaculture households. The objective of this study was to isolate local strains of microorganisms capable of antagonizing F. incarnatum, in order to reduce the use of antibiotics that may have adverse effects on both the environment and human health. Samples were collected from five Pangasius hypophthalmus fish, five water sources, and five sludge samples from fish ponds located in Lap Vo district, Dong Thap province. A total of 24 bacterial strains were isolated and subjected to the dual culture method to identify the 20 strains with the ability to antagonize F. incarnatum. The inhibitory ability of F. incarnatum was then evaluated using the two-culture method with the 20 selected strains. Results revealed that two strains, B19 (with a colony radius of 1.42 cm and corresponding inhibitory effect of 77.51% after 12 days) and B23 (with a colony radius of 1.55 cm and corresponding inhibitory effect of 75.40% after 12 days), demonstrated the strongest antagonistic effects against F. incarnatum. The identified strains were found to be Bacillus sp. (with a similarity of 90.22%) and Bacillus amyloliquefaciens (with a similarity of 92.41%). These results suggest that the use of Bacillus spp. can be an effective strategy to inhibit swollen swim bladder disease caused by F. incarnatum, and maybe a viable alternative to the use of antibiotics in the future.