Addition of sodium nitrite and biofilm in a Litopenaeus vannamei biofloc culture system
This study evaluates the effects of the previous addition of sodium nitrite (NaNO2) and biofilm in a Litopenaeus vannamei biofloc culture. Five treatments were tested in 180 L - tanks: NaNO2 (-20) addition of NaNO2 for 20 days before stocking and without artificial substrates; NaNO2+B (-20) addition of NaNO2 for 20 days before stocking, with 150% additional artificial substrates; NaNO2 (Stocking) addition of NaNO2 at stocking and no artificial substrates; NaNO2 +B (Stocking) addition of NaNO2 at stocking, with 150% additional artificial substrates and; Control, without NaNO2 addition and without artificial substrates. The study was carried out in two phases: shrimps (0.21 ± 0.08 g) were stocked at a density of 400 ind m-2/1,100 ind m-3, for 30 days (nursery). After this period, the animals were restocked at a lower density (120 ind m-2/400 ind m-3) for 18 more days (grow-out). The turbidity and seattleable solids were higher in treatments without artificial substrates, independently of the addition of NaNO2. The ammonia and nitrite were lower in control, and the nitrate concentrations were higher in treatments with addition of NaNO2 without biofilm. At the end of the nursery, the survival was lower in treatment NaNO2 (-20), and at the end of grow-out the final biomasses were higher in treatments with addition of NaNO2 at the stocking day. In conclusion, the use of a dose of NaNO2 at the stocking day could increase the nitrite-oxidizing bacteria, and the biofilm may contribute to the reduction in suspended particles in water, enhancing shrimp production in biofloc technology system.