Efficacy and variations in bacterial density in the gut of Litopenaeus vannamei reared in a BFT system and in clear water supplemented with a commercial probiotic mixture

The purpose of this study was to evaluate the colonization ability of a commercial probiotic mixture in the gut of Litopenaeus vannamei reared in BFT and a clear water culture and to verify the effects of the probiotic on the gut bacterial abundance of Vibrio sp. and Bacillus sp. when added to the biofloc or clear water culture system. The 45-day experiment contained four treatments: Biofloc with no Probiotic application (BFT); Biofloc with Probiotic application (BFT + P); Clear Water with no Probiotic application (CW); and Clear Water with Probiotic application (CW + P). The commercial probiotic mixture (Sanolife PRO-W (R) - INVE Aquaculture) was composed of Bacillus subtilis-complex and Bacillus licheniformes strains and was added to the water every 48 h. The bacterial abundance in the gut of shrimp was assessed using fluorescence in situ hybridization (FISH) in which rRNA-targeted oligonucleotide probes were used to identify Bacillus sp. and Vibrio sp. Total bacterial abundance was higher in the probiotic application treatments (BFT + P and CW + P). However, the percentage of Bacillus sp. of the total bacterial abundance was higher in clear water than in BFT when the probiotic mixture was added. The percentage of Vibrio sp. was higher in the treatments without probiotic addition. The use of Sanolife PRO-W (R) decreased the bacterial abundance of Vibrio sp. in both the BFT and clear water culture systems, while the abundance of Bacillus increased. The results obtained in this study can contribute to our understanding of the microbial ecology of biofloc, which is currently considered a key issue of this culture system.