Super-intensive culture of white leg shrimp (Litopenaeus vannamei) in outdoor biofloc systems with different sunlight exposure levels: Emphasis on commercial applications

Light is an important environmental factor for aquatic organisms. In biofloc systems, light intensity and photoperiod length might also affect the performance and biomass of culture animals as well as the microbial communities. This study aimed to evaluate the impacts of light intensity on the nitrogen removal process, microbial communities and Litopenaeus vannamei performance at the commercial scale. The experiment was conducted in an outdoor biofloc system with four treatments (control, T1, T2, T3) in triplicate, consisting of natural light (control) and restricted light treatments produced by covering the tank surface with one light attenuation shade net of one (T1), two (T2), or three (T3) layers. Shrimp post-larvae (0.015 +/- 0.01 g) were stocked in 10m3 tanks at 500 individuals/m(3) of density and 15 ppt of salinity for 90 days. Molasses was applied to maintain the C:N ratio at 12. A significant difference in water quality parameters (lower concentrations of TAN, nitrite, and nitrate) was recorded in the control and T1 treatments; these treatments also displayed a greater biofloc performance and chlorophyll-a value. Proximate nutrient compositions of the biofloc showed the highest values of protein and lipid in the control and T1 treatments compared to T2 and T3. The low-light treatments (T2 and T3) showed higher densities of heterotrophic bacteria and Vibrio spp. counts, which was significantly different than the results for control and T1. Shrimp performance registered higher survival rates and biomass in control and T1, but no statistical difference in shrimp growth was noticed. The results indicated that high stocking density and low light exposure might result in low survival and biomass of shrimp. It also suggested that a mixture of microalgae and bacteria in an appropriate proportion is more beneficial for the shrimp farming.