Acute toxicity of nitrite on white shrimp Litopenaeus vannamei (Boone) juveniles in low-salinity water

The nitrite toxicity was estimated in juveniles of L.vannamei. The 24, 48, 72 and 96h LC50 of nitrite-N on juveniles were 8.1, 7.9, 6.8 and 5.7mgL(-1) at0.6gL(-1); 14.4, 9.6 8.3 and 7.0mgL(-1) at 1.0gL(-1); 19.4, 15.4, 13.4 and 12.4mgL(-1) at2.0gL(-1) of salinity respectively. The tolerance of juveniles to nitrite decreased at 96h of exposure by 18.6% and 54.0%, when salinity declined from 1.0 to 0.6gL(-1) and from 2.0 to 0.6gL(-1) respectively. The safe concentrations at salinities of 0.6, 1.0 and 2.0gL(-1) were 0.28, 0.35 and 0.62mgL(-1) nitrite-N respectively. The relationship between LC50 (mgL(-1)), salinity (S) (gL(-1)) and exposure time (T) (h) was LC50= 8.4688+5.6764S - 0.0762T for salinities from 0.6 to 2.0gL(-1) and for exposure times from 24 to 96h; the relationship between survival (%) and nitrite-N concentration (C) for salinity of 0.6-2.0gL(-1), nitrite-N concentrations of 0-40mgL(-1) and exposure times from 0 to 96h was as follows: survival (%)=0.8442+0.1909S - 0.0038T - 0.0277C+0.0008ST+0.0001CT-0.0029SC, and the tentative equationfor predicting the 96-h LC50 to salinities from 0.6 to 35gL(-1) in L. vannamei juveniles (3.9-4.4g) was 96-h LC50=0.2127 S-2+1.558S+5.9868. For nitrite toxicity, it is shown that a small change in salinity of waters from 2.0 to 0.6gL(-1) is more critical forL. vannamei than when wider differences insalinity occur in brackish and marine waters (15-35gL(-1)).