| Resumo: |
The accumulation of inorganic toxic substances such as ammonia and nitrite, is a major water quality problem in intensive aquaculture systems. Often the levels of nitrogen compounds in aquaculture systems or in the nature, exceed the values of LC50, although, experiments on exposure subchronic/chronic nitrogenous compounds on the growth and/or feeding rates are relatively limited. Thus, the aim of this study was to evaluate the toxicity of nitrite on survival, food consumption and immune response of Litopenaeus vannamei shrimp grown in the biofloc technology and clear water. To evaluate the toxicity of the nitrite on growth, survival and total amount of hemocytes in the hemolymph of L. vannamei juveniles. Four concentrations of nitrite (0, 10, 20 e 40 mg N-NO2 L-1) were tested in two culture systems - clear water and biofloc for 30 days. Survival of shrimp was negatively influenced (P<0.05) by clear water system. The interaction between the N-nitrite concentrations and culture systems did not affect significantly (P≥0.05) the total amount of hemocytes. Based on the results obtained, it is possible to culture the L. vannamei shrimp at concentrations of 10 and 20 mg N-NO2 L-1 for a period of 30 days without compromising growth and survival. To evaluate toxicity of the nitrite on growth, survival and juvenile shrimp L. vannamei feed consumption grown in clear water system six nominal concentrations of nitrite-N 0, 10, 20 40, 60 e 80 mg N-NO2 L-1 were adopted. After 30 days of culture, the final weight (from 2.50 to 5.01 g), weight gain (from 0.01 to 2.51 g), specific growth rate (from 0.03 to 2.32% day-1 ), survival (0.00 to 100%), length of antennae and feed consumption of shrimps were significantly affected (P <0.05) for higher N-nitrite concentrations of. Thus, it is possible to culture the L. vannamei shrimp at concentrations of 10 and 20 mg N-NO2 L-1 for a period of 30 days without affecting survival and feed consumption. |
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