Effect of biofloc on the production of Litopenaeus vannamei (Boone, 1931) and characterization of microbial community in biofloc

The effect of biofloc on the water quality and growth performance of Litopenaeus vannamei (Boone, 1931) was conducted by culturing the animals for 90 days in indoor tanks of 500 L capacity. Three biofloc treatments i.e. sugarcane molasses (BFTS), tapioca flour (BFTT), wheat flour (BFTW) and a control in triplicate were maintained for 30 days before starting the culture experimet. The PL with an average body weight of 0.15 ± 0.02 g were stocked at the rate of 130 PL m -2 and feed was applied @ 1.5% of the total biomass. The total suspended solid (TSS) level was maintained at around 500 mg L -1 in all the treatments. The addition of carbohydrate significantly (P<0.05) reduced the total ammonia-N (TAN), nitrite-N and nitrate-N and also increased the total heterotrophic bacterial (THB) population in the treatments. There was a significant differences (P<0.05) between the treatments and control groups in terms of final average body weight (ABW), food conversion ratio (FCR) and growth rate. The BFTW showed significantly higher growth rate (0.09±0.001 g day-1 ) and ABW (8.49±0.09 g) than the other treatments and control. Survival of the shrimps was not affected (P>0.05) by the treatments and it ranged between 82.2% and 90.3%. The nutritional quality of the biofloc and the proximate composition of the shrimp were significantly different between the treatments and control. Tintinids, ciliates, copepods, cyanobacteria and nematodes were observed in all the treatment tanks. The bacterial community profile of bioflocs was analysed by denaturing gradient gel electrophoresis (DGGE) by amplifying bacterial 16S rRNA gene. From sequence analyses, Ruegeria sp. Chitinophaga pinensis, Roseobacter litoralis, Hyphomonas neptunium and Phaeobacter gallaeciensis were found to be the most dominant bacteria in all the treatments. It can be concluded that the use of wheat flour (BFTW) effectively enhances the biofloc production which contributed effectively in maintenance of good water quality resulting higher production of shrimp