The Toxicity Of Cyhalofop-Butyl,Pyribenzoxim And Metamifop To Procambarus Clarkii

Rice-crayfish co-culture is an efficient and green production model which combines rice cultivation with crayfish farming in recent years.This model controls the occurrence of weeds to a certain extent,reduces applications of herbicides,and protects the ecological system efficiently.However,with the extension of rice-crayfish co-culture period,the occurrence and diversity of weeds in the field showed a decrease first and then an increase.At present,there is no herbicide registered for the rice-crayfish co-culture field weed control,and the safety of herbicides to Procambarus clarkii is unknown,which may pose a safety risk to green production of rice-crayfish co-culture.Therefore,the occurrence of weeds and herbicides applied in the fields of rice-crayfish co-culture and direct sowing fields were investigated and compared.The toxic effects of herbicides cyhalofop-butyl,pyribenzoxim and metamifop on P.clarkii were studied in this paper.This research has significant implications for scientific and rational use of herbicides under rice-crayfish co-culture and will contribute to the green-healthy development of the model.The main results are as follows:?1?Echinochloa crus-galli and Leptochloa chinensis are the two major species of weeds in the fields of the two rice-cultivation models,and many groups of herbicides were used in the rice-crayfish co-culture fields,including butachlor,bensulfuron-methyl,quinclorac,metamifop,cyhalofop-butyl,halosulfuron-methyl,and pyribenzoxim.The dosage of cyhalofop-butyl has exceeded the recommended dosage in some areas.?2?The LC₅₀?96 h?values of cyhalofop-butyl,pyribenzoxim,and metamifop to P.clarkii were 10.24,103.94 and>200 mg/L,respectively.The three herbicides showed low toxicity to P.clarkii according to the guidelines on macro-crustacean toxicity test.The body weight,length,rock length,carapace,and tail of P.clarkii were inhibited significantly?P<0.05?when exposed to cyhalofop-butyl?1.024 mg/L?for 28 days.The body weight,length,rock length,and carapace of P.clarkii were inhibited significantly?P<0.05?when exposed to pyribenzoxim?5.2 and 10.4 mg/L?for 28 days.Metamifop had no significant effect on the growth of P.clarkia in this study.?3?The activities of superoxide dismutase?SOD?,catalase?CAT?,and glutathione s-transferase?GST?and the contents of malondialdehyde?MDA?and glutathione?GSH?in P.clarkii exposed to cyhalofop-butyl?1.02,3.07 and 5.12 mg/L?and pyribenzoxim?5.2,10.4 and 52 mg/L?for 24,48,72 and 96 h were determined.Significant decreases of SOD and CAT activities and increases of GST activity and GSH content in P.clarkii were showed when exposed to cyhalofop-butyl.Cyhalofop-butyl had no effect on the contents of MDA.Significant decreases of SOD and CAT activities and increases of GST activity and content of GSH and MDA were showed when exposed to pyribenzoxim.The activities of SOD,CAT,GST and the contents of MDA and GSH in P.clarkii exposed to cyhalofop-butyl?0.064,0.128,0.256,0.512 and 1.024 mg/L?,pyribenzoxim?0.65,1.3,2.6,5.2 and 10.4 mg/L?and metamifop?1.25,2.5,5,10 and 20 mg/L?for 28 d were determined.Long-term exposure with low doses of cyhalofop-butyl,pyribenzoxim and metamifop increased activities of SOD,CAT,and GST and contents of MDA in P.clarkii.Low doses of cyhalofop-butyl and pyribenzoxim increased contents of GSH in P.clarkii.Therefore,high concentrations of cyhalofop-butyl and pyribenzoxim could inhibit the activities of antioxidant enzymes and destroy the antioxidant enzyme system in P.clarkii.Long-term exposures to low concentrations of cyhalofop-butyl,pyribenzoxim,and metamifop could induce the oxidative stress responses in P.clarkia..