The use of a commercial flocculant additive and its effect on the formation of bioflocs in the cultivation of the shrimp Litopenaeus vannamei (Boone, 1931) in the BFT system (Biofloc Technology System)
The biofloc technology system is based on a community of microorganisms that act as food, probiotic and improve the quality of cultivated water. Water quality is improved by the removal of nitrogen compounds. It can be made by phytoplankton or bacteria. Bacteria act in two ways: the first through chemoheterotrophic bacteria that synthesize bacterial biomass from ammonia and a second group that metabolize ammonia into less toxic compounds, nitrifying bacteria. Most bacteria live in aggregate forms around a surface that can be organic or inorganic. Clay minerals with their adsorption property, high surface area and flocculant properties may be an alternative to accelerate the formation of these bioflocs, thereby also accelerating the formation of substrate that acts as a bacterial fixation surface, increasing their production. The growth of bacterial production can guarantee the maintenance of water quality in this system. Thus, the objective of this work was to evaluate the addition of clay mineral in the formation of bioflocs and its influence on the microbial community and nitrification in the cultivation of the Pacific -White -Shrimp L. vannamei in a biofloc technology system. The study had three experiments that evaluated the concentration and frequency for application of the clay mineral. The density used was 400 shrimp / m3. In experiment 1 the frequency and dosage of application were analyzed and outlined with the following treatments: Control (without addition of clay minerals), 2 mg /L, 5 mg/L and 10 mg/L daily application, 10 mg/L, 30 mg/L and 50 mg /L weekly application. In the second experiment, higher dosages were evaluated with daily application outlined with the following treatments: Control (without addition of clay minerals), 10 mg/L, 50 mg/L and 100 mg/L. In experiment 3 the effect of a single concentration with and without the presence of a biofloc inoculum delineated with the following treatments was evaluated: Control without product and without inoculum, Control without product and with inoculum, 50mg / L clay mineral without inoculum and 50mg / L of clay mineral with inoculum. All treatments in the three experiments had three repetitions each. Shrimps were fed 38% protein diets twice daily. In experiment 1 the parameters of water quality and zootechnical performance showed no significant differences (p >0.05). Experiment 2 showed significant differences in nitrite concentration, total suspended solids, turbidity and zootechnical performance parameters (p ≤0.05). In this experiment the abundance of microorganisms did not present significant differences between treatments. In the third experiment there were significant differences (p ≤0.05) in the parameters of ammonia and nitrite. The addition of clay mineral did not influence the abundance in the microbial community, however the proximal flake composition showed significant differences (p ≤0.05), presenting better results in the control treatments with and without biofloc inoculum. The addition of clay mineral influenced the formation of bioflocs and their proximal composition, but did not affect the abundance of microorganisms and nitrification. On the other hand, L. vannamei zootechnical performance was not affected by the addition of the compound.