The autochthonous microbiota of the freshwater omnivores jundia (Rhamdia quelen) and tilapia (Oreochromis niloticus) and the effect of dietary carbohydrates

Previous studies have shown that the gut microbiota of fish differs depending on host feeding habits and these populations may also be influenced by dietary ingredients. In this study, the bacterial populations of the intestinal tract of the opportunistic omnivore jundia Rhamdia quelen and the typical omnivore tilapia Oreochromis niloticus were investigated in two experiments. In experiment I, the levels of amylolytic, cellulolytic, lipolytic, proteolytic and total culturable bacteria were compared in the proximal, mid and distal intestine using selective agar. Higher levels of amylolytic, cellulolytic, lipolytic, proteolytic and total culturable bacteria were observed in the tilapia than jundia, in all intestinal regions. Jundia contained higher levels of proteolytic bacteria and lipid digesting bacteria in the distal intestinal portion as compared with the mid intestine; both fish species also presented more amylolytic bacteria in the distal intestine. In experiment II, the amylolytic intestinal microbiota between the two species was compared after administration of diets containing different carbohydrate sources. Jundia fed broken rice presented higher total culturable bacterial levels; however, dietary cassava bagasse and ground corn significantly elevated the population of amylolytic bacteria in tilapia (P>0.05). PCR-DGGE was also used to assess the bacterial communities in experiment II. A Cetobacterium spp. was detected in jundia fed diets containing broken rice, and tilapia fed cassava bagasse, dextrin, broken rice and ground corn. Microbial differentiation was further demonstrated between jundia and tilapia, because an uncultured bacterium was unique in tilapia and an uncultured spirochete was observed only in jundia; the presence of these bacterial species was also influenced by dietary carbohydrate sources.