Isolation of probiotic bacteria from the hybrid South American catfish Pseudoplatystoma reticulatum × Pseudoplatystoma corruscans (Siluriformes: Pimelodidae): A haematological approach

•Fish fed Weissella cibaria showed higher value of total lactic acid bacteria in Man, Rogosa and Sharpe (MRS) media.•Supplemented fish showed an increase in the red blood cell count.•This study showed the efficacy of this method for screening probiotic bacterium.

This study investigated bacterial strains with probiotic potential isolated from the middle portion of healthy hybrid surubim catfish foregut (Pseudoplatystoma reticulatum female × P. corruscans male). Twenty surubims weighing 1.5 ± 0.3 kg were used for bacterial isolation. In total, 41 strains of bacteria were selected in vitro. Ten strains had inhibition zones >10 mm against Aeromonas hydrophila. Five of those strains presented inhibition zones > 9 mm against other pathogenic bacteria and reached concentrations greater than 105 CFU mL−1 in tubes containing de Man, Rogosa and Sharpe (MRS) medium. In particular, Weissella cibaria (P36) reached 106 CFU mL−1 in MRS and was able to reduce the pH of the medium to 3.85. In the in vivo intestinal colonization studies, 72 healthy hybrid surubims were fed with a commercial diet supplemented with probiotic W. cibaria for 15 days. Changes in gut community composition were then analyzed, and probiotic profile of W. cibaria was determined molecularly by amplification of rRNA 16S gene was performed using PCR. Compared to control fish, W. cibaria-supplemented fish showed an increase in RBC. These results show the efficacy of our haematological approach to probiotic screening in hybrid sorubim.