Addition of sodium nitrite and biofilm in a Litopenaeus vannamei biofloc culture system/Adición de nitrito de sodio y biofilm a un sistema de cultivo biofloc de Litopenaeus vannamei

This study evaluates the effects of the previous addition of sodium nitrite (NaNO^sub 2^) and biofilm in a Litopenaeus vannamei biofloc culture. Five treatments were tested in 180 L - tanks: NaNO^sub 2^ (-20) addition of NaNO^sub 2^ for 20 days before stocking and without artificial substrates; NaNO^sub 2^+B (-20) addition of NaNO^sub 2^ for 20 days before stocking, with 150% additional artificial substrates; NaNO^sub 2^ (Stocking) addition of NaNO^sub 2^ at stocking and no artificial substrates; NaNO^sub 2^ +B (Stocking) addition of NaNO^sub 2^ at stocking, with 150% additional artificial substrates and; Control, without NaNO^sub 2^ 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^sup -2^/1,100 ind m^sup -3^, for 30 days (nursery). After this period, the animals were restocked at a lower density (120 ind m^sup -2^/400 ind m^sup -3^) for 18 more days (grow-out). The turbidity and seattleable solids were higher in treatments without artificial substrates, independently of the addition of NaNO^sub 2^. The ammonia and nitrite were lower in control, and the nitrate concentrations were higher in treatments with addition of NaNO^sub 2^ without biofilm. At the end of the nursery, the survival was lower in treatment NaNO^sub 2^ (-20), and at the end of grow-out the final biomasses were higher in treatments with addition of NaNO^sub 2^ at the stocking day. In conclusion, the use of a dose of NaNO^sub 2^ 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.