Effects of saponin on survival, growth, molting and feeding of Penaeus japonicus juveniles

The median lethal concentration (LC(50)) of saponin on juvenile Penaeus japonicus was 20.82 mg 1(-1) and 18.14 mg 1(-1) at 48 h and 96 h, respectively, in sea water of 34 practical salinity units. The mortality rate of juvenile P. japonicus exposed to 0 (control), 0.1, 0.5, 1 and 2 mg 1(-1) saponin after 60 days was 3.3%, 6.6%, 10%, 33.3% and 43.3%, respectively. After 36 days of exposure, the weight of shrimps exposed to 1 and 2 mg 1(-1) saponin was significantly lower than for those exposed to 0.1 and 0.5 mg 1(-1) saponin. The growth factor of shrimps exposed to 0.5 mg 1(-1) saponin was significantly lower than those exposed to 0.1 mg 1(-1) saponin and the control solution. Following exposure to saponin as low as 0.5 mg 1(-1), P. japonicus shortened the time to the first molt, and decreased its feeding, growth and molting frequency. The maximum acceptable toxicant concentration was 0.1 mg 1(-1) saponin.