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

Abstract

Two experimental modules with different stocking densities (M1 = 70 and M2 = 120 shrimp /m2) were examined weekly over a culture cycle in tanks with low-salinity water (1.9 g/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 ± 1.38 mg/L N-TAN, 0.18 ± 0.49 mg/L N-NO2− and 6.83 ± 6.52 mg/L N-NO3−; in M1: 0.97 ± 0.73 mg/L N-TAN, 0.05 ± 0.21 mg/L N-NO2− and 0.63 ± 0.70 mg/L N-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).