Adição do nitrito de sódio em sistema de biofloco e toxicidade do nitrito para o camarão Litopenaeus vannamei

Abstract

The accumulation of nitrite is one of the major constraint on water quality in system biofloc. This nitrogen compound is very toxic to aquatic organisms and systems without water exchange, concentrations can reach lethal levels. This study was divided into two experiments. The first objective was to evaluate the contribution of prior addition of sodium nitrite (NaNO2) in the formation of nitrogenous compounds in system biofloc with Litopenaeus vannamei. It was used a completely randomized design with two treatments and eight replications: 1) with the addition of sodium nitrite to 10 days before storage (NaNO2) and 2) without the addition of sodium nitrite (CTL). The post-larvae (0.143 ± 0.001 g) were stocked in 50 L tanks at a density of 1 PL L-1 for 28 days. Daily we measured physical and chemical parameters of the water weekly and ammonia, nitrite, nitrate, alkalinity and volume of flocs. The second experiment aimed to determine the acute toxicity of nitrite in post-larvae (0.012 ± 0.03 g) and juveniles (2.49 ± 0.20 g) for L. vannamei in salinity 30. Experimental units were used with a volume of 10 L and 1.6 L for post-larvae and juveniles respectively. The experiment was conducted in the following concentrations: 0, 20, 40, 80, 160, 240, 320, 400 and 480 mg NO2-N L-1. We determined the median lethal concentration (LC50) for post-larvae and juveniles in 24, 48, 72 and 96 h. In the first experiment, the addition of NaNO2 may have accelerated the formation of nitrate, however the other variables did not influence water quality. There was no difference between treatments for the results of zootechnical performance of shrimp. The survival data for both treatments were above 95%. In the second experiment, the values of lethal concentration (LC50) of nitrite in post-larvae and juveniles for 24, 48, 72 and 96 h were respectively 224.6, 109.43, 41.16, 25.52 mg NO2-N L-1, and 273.51, 147.97, 113.97, 83.78 mg NO2-N L-1. According to the results of LC50 was possible to estimate the levels of security for post-larval and juvenile L. vannamei at 2.55 and 8.38 mg NO2-N L-1.