Acute toxicity of residual chlorine on the white shrimp Litopenaeus vannamei juveniles at different salinity levels

Abstract

White shrimp Litopenaeus vannamei juveniles (body weight 1.15 ± 0.21 g) were exposed to different concentrations of residual chlorine at different salinity levels (15 per mille, 25 per mille and 35 per mille) using the static renewal method. The 24-, 48-, 72-, 96-, 120-, and 144-h LC_(50) (median lethal concentration) of residual chlorine on L. vannamei juveniles were 4.07, 3.22, 2.83, 2.58, 2.44, and 2.44 mg/l at 15 per mille; 6.86, 6.16, 5.14, 4.86, 4.77, and 4.73 mg/l at 25 per mille; and 7.59, 6.95, 6.30, 5.81, 5.71, and 5.61 mg/l at 35%, respectively. As the salinity decreased from 35 per mille to 15 per mille, susceptibility of residual chlorine after 24-, 48-, 72-, 96- and 120-h increased by 186%, 216%, 223%, 225%, and 234%, respectively. The ＂safe level＂ for rearing L. vannamei juveniles was estimated to be 0.24, 0.48 and 0.57 mg/l at salinity 15 per mille, 25 per mille, and 35 per mille, respectively. The toxicity of residual chlorine on L. vannamei juveniles decreased with the increase of salinity level. The relationship among LC_(50) of residual chlorine (mg/l), salinity (S) and exposure time (T) is as follows: LC_(50) = 2.6608 + 0.1642S - 0.0214T (R^2 = 0.8355).本研究利用利用半靜置換水法，將白蝦Litopenaeus vannamei幼蝦（體重1.15 ± 0.21 g）放置於不同鹽度下（15 per mille，25 per mille及35 per mille）並暴露在不同殘留氯環境中，實驗結果測得在24、48、72、96、120及144小時的半致死濃度（LC_(50)）於鹽度15 per mille。時分別為4.07、3.22、2.83、2.58、2.44及2.44 mg/l；於鹽度25 per mille。時分別為6.86、6.16、5.14、4.86、4.77及4.73 mg/l，於鹽度35 per mille。時分別為7.59、6.95、6.30、5.81、5.71及5.61 mg/l。當鹽度從35 per mille降至15 per mille時，白蝦幼蝦暴露24、48、72、96及120小時後對殘留氯的敏感性分別增加至186 %、216 %、223 %、225 %及234 %。經計算過後發現白蝦幼蝦馴養在鹽度15 per mille、25 per mille及35 per mille下，其殘留氯對白蝦幼蝦之「安全濃度」分別為0.24、0.48及0.57 mg/l，此實驗結果證實外界鹽度的增加將降低殘留氯對白蝦幼蝦的毒性。殘留氯對白蝦幼蝦之LC_(50)與鹽度（S）、暴露時間（T）之關係式為LC_(50) = 2.6608 + 0.16428 - 0.0214T（R^2= 0.8355）。