Variation of the bacterial composition of biofloc and the intestine of Nile tilapia Oreochromis niloticus, cultivated using biofloc technology, supplied different feed rations

The effect of different feed rations on the productive performance and bacterial composition of the intestine of Nile tilapia (Oreochromis niloticus) reared using biofloc technology (BFT), in addition to water quality and the bacterial composition of the biofloc, was evaluated. During a 4-month period, five feed rations were evaluated: B-100, complete feed ration; B-90, 10% reduction; B-80, 20% reduction; B-70, 30% reduction; and B-60, 40% reduction, and a control group (C) supplied with clean water and a full feed ration. Each treatment was evaluated in triplicate. Fish were stocked into 18 circular tanks (3.14 m(3)) at a density of 50 tilapia/m(3) per tank. At the end of the study, water samples and sections of fish intestine were taken. Colony-forming units (CFU) were counted on a plaque, and bacterial identification was carried out using the polymerase chain reaction, amplifying the 16S rRNA gene. All treatments exhibited good water quality throughout the study. Seventeen different species of bacteria were encountered in water and 15 species of bacteria were identified in the intestine of the tilapias. Treatments B-70 and B-60 were exhibited the highest number of bacteria recorded in water and intestine. The productive performance of Nile tilapia of treatment groups B-100, B-90, and B-80 was similar to C. The results indicate that during tilapia cultivation using BFT, it is possible to reduce the feed ration by 20% without apparent damage to the health and productive performance of Nile tilapia. The bacteria contribute to the maintenance of growth and survival of Nile tilapia by acting as a probiotic.