Effect of light limitation on the water quality, bacterial counts and performance of Litopenaeus vannamei postlarvae reared with biofloc at low salinity

The aim of this study was to evaluate the effect of light limitation on the water quality, bacterial counts and performance of Litopenaeus vannamei postlarvae reared with biofloc at low salinity (≈9 g L⁻¹). Two treatments were designed: T₁ = culture with natural sunlight and T₂ = culture in darkness. After 28 days, in both treatments, the final weight of shrimp was over 0.6 g with a specific growth rate over 7.4% d⁻¹, and a survival rate over 70%. In both treatments, Vibrio sp. concentration presented low values (culture with natural sunlight = 0.1 to 9.9 × 10² CFU mL⁻¹, culture in darkness = 0.4 to 11.7 × 10² CFU mL⁻¹) and Bacillus sp. had high values (culture with natural sunlight = 0.7 to 66.0 × 10⁴ CFU mL⁻¹, culture in darkness = 0.7 to 65.8 × 10⁴ CFU mL⁻¹). All water quality parameters remained within the ranges suitable for shrimp culture, except for alkalinity during the first stage of the study. Although in some sampling periods some significant differences were found in bacterial counts and water quality parameters, shrimp productive performance under culture with biofloc at low salinity was not affected significantly by light limitation.