Compensatory growth and nitrite management in the Pacific white shrimp (Penaeus vannamei) cultured in biofloc system

Determining safe nitrite exposure limits for Penaeus vannamei in biofloc technology system (BFT) is crucial, as nitrite peaks frequently occur during BFT culture. This study evaluated the effects of chronic nitrite exposure on performance, compensatory growth, and immune response of shrimp cultured at a salinity of 25 g·L⁻¹. A 2 × 3 factorial experiment was performed with two nitrite concentrations (two- and three-fold the recommended safe level, 30.4 and 45.6 mg·L⁻¹ NO₂─N) and three “stress” exposures (7, 14, and 21 days), followed by recovery of 42, 35, and 28 days, respectively. A control was maintained with nitrite below 25% of the safe level (3.8 mg·L⁻¹ NO₂─N). After the stress phase, survival decreased in shrimp exposed to three-fold the safe level and in those exposed to two-fold levels for 21 days. Growth was reduced in the treatments exposed to high nitrite concentrations during 14 and 21 days, and the immune response was negatively affected. By the end of the recovery phase (day 49), final weight was reduced by exposures longer than 7 days, and the yield was inversely proportional to the exposure time and nitrite concentrations. Differential hemocyte count (DHC) recovered to the optimal range for healthy shrimp reared in BFT. Nevertheless, shrimp subjected to high nitrite concentration during the first phase grew at high rates again when control nitrite levels were reestablished. If exposure of animals to high levels of nitrite cannot be avoided, a maximum of two-fold the safe level of nitrite should not be exceeded for a period of up to 14 days. This will avoid productivity reduction because of mortality, and animals will return to normal growth after the stress period.