Chronic effects of nitrogenous compounds on survival and growth of juvenile pink shrimp.

In response to growing worldwide market demand, intensive shrimp farming, based on high feed, has developed over the past decade. The nitrogenous compounds mainly generated by animal excretion can cause deterioration of water quality and produce chronic or even acute toxicity to aquatic animals. As prevention, theoretical safety levels have been estimated from acute toxicity tests and they are traditionally used to prevent toxic effects on biota. However, are those concentrations of nitrogenous compounds really safe to Farfantepenaeus paulensis? The current study aimed to investigate the lethal and sublethal effects of ammonia, nitrite and nitrate to juvenile F. paulensis based on safety levels. Each experiment was performed independently in 100 L tanks for 30 days. The survival rates and wet weight of all shrimps were recorded every 10 days. The concentrations tested for ammonia, nitrite and nitrate were respectively: treatment "T1/4", a quarter of the safety level (0.91 mg/L TA-N, 2.55 mg/L NO2--N and 80.7 mg/L NO3--N); treatment "TSL", the safety level (3.65 mg/L TA-N, 10.2 mg/L NO2--N and 323 mg/L NO3--N); and treatment "T2X", twice the safety level (7.30 mg/L TA-N, 20.4 mg/L NO2--N and 646 mg/L NO3--N). For F. paulensis cultivation, the real safety level for nitrite was estimated to be 2.55 mg/L NO2--N. For ammonia and nitrate, the recommended concentrations were <0.91 mg/L TA-N corresponding to 0.045 mg/L NH3-N and <80.7 mg/L NO3--N, respectively.