A study was made regarding the relationship between the toxicity and acetylcholinesterase (AChE) inhibition of three organophosphorothionates (fenitrothion, FS; diazinon, DIN; phenthoate, PAP) and three oxo-forms (fenitrooxon, FO; diazoxon, DOX; dichlorvos, DDVP) in tiger shrimp Penaeus japonicus at different larval stages. The shrimp larvae at nauplius and zoea stages showed relatively high resistance to FS, DIN and PAP, i.e.> the respective 24-h LC60values were 1.84, 10.5 and 5 ppm. However, the toxicity of these thiono-form phosphates increased abruptly with the progress of the larval stages, especially after metamorphosis into the postlarva, resulting in the increase by ca. 2,600, 1,200 and 850 times respectively to that of nauplius stage. On the other hand, the toxicity of FO and DDVP to the larvae was almost unchanged throughout these stages, at the levels of ca. 7 ppb and 5.6 ppm as the 24-h LCe0value, respectively. The susceptibility of the larval AChE to the tested phosphates was almost unchanged from zoea to postIarva. The concentrations of FO, DDVP, DOX, FS, PAP and DIN producing 50% inhibition (I50) of the AChE activity were approx. 0.015, 0.35, 1.27, 200, 650 and 1,200 μm, respectively. Although FS showed the highest AChE inhibition among the thiono-forms; its oxon (FO) displayed 12,000 times high AChE inhibition compared to FS. The high AChE inhibition of FO was in good correlation with its high toxicity to the larvae even at the early stage.
All Science Journal Classification (ASJC) codes
- Aquatic Science