Isolation and evaluation of autochthonous Bacillus subtilis strains as probiotics for fat snook (Centropomus parallelus Poey, 1860)

The objective of this study was to isolate and select autochthonous strains of Bacillus subtilis from the fat snook, Centropomus parallelus, and examine the viability of the Bacillus bacteria to determine their beneficial effect on gut colonization in reared fish. Twenty strains of Bacillus were isolated and further confirmed as B.subtilis using PCR. Among the 20 strains, two strains (B02 and B03) exhibited an inhibitory performance against five tested pathogens. The Bacillus strains B02 and B03 were added to the fish ration, and after 30days the number of viable colonies were maintained or increased under the conditions of refrigeration (5 degrees C), freezing (-18 degrees C), or room temperature (30 degrees C). These strains showed a growth rate of 0.18-0.21h and a doubling time of 3.34-3.9h. Both strains were tolerant to variations in NaCl, and B03 was also tolerant to bile exposure. The ability to colonize the gastrointestinal tract was also examined in healthy fat snook juveniles fed diets enriched for 30days with strains B02 and B03. The amount of B.subtilis in the gastrointestinal juvenile tract was significantly higher in fish fed the enriched ration compared to controls. Based on these results, strains B02 and B03 were considered as candidate probiotics for fat snook.