Histological alterations in gills of shrimp Litopenaeus vannamei in low-salinity waters under different stocking densities: Potential relationship with nitrogen compounds

摘要

Two experimental modules with different stocking densities (M1=70 and M2=120 shrimp /m(2)) were examined weekly over a culture cycle in tanks with low-salinity water (1.9g/L) and zero water exchange. Results showed survival rates of 87.7 and 11.9% in M1 and M2, respectively. Water temperature, pH, dissolved oxygen, electrical conductivity and chlorophyll a were not significantly (p>.05) different between modules. In contrast, the concentrations of nitrogen compounds were significantly (p.05) different between modules, except nitrite-N (M2 were 2.31 +/- 1.38mg/LN-TAN, 0.18 +/- 0.49mg/LN-NO2- and 6.83 +/- 6.52mg/LN-NO3-; in M1: 0.97 +/- 0.73mg/LN-TAN, 0.05 +/- 0.21mg/LN-NO2- and 0.63 +/- 0.70mg/LN-NO3-). When waters of both modules reached higher levels of ammonia and nitrite, histological alterations were observed in gills. The histological alterations index (HAI) was higher in M2 (5-112) than in M1 (2-22).