Effects Of Chronic Prometryn Exposure On Growth Performance,Antioxidative Status,and Morphology In Sea Cucumber (Apostichopus Japonicus)

Sea cucumber,as a representative seawater species in the north of China,is very popular among consumers.On one hand,it can be washed from farmlands by rainwater,thus,easily polluting the nearby ponds.On the other hand,the wastewater from aquaculture eventually flows into the river mouth and poses a threat to the sea cucumber.Therefore,This study investigated the toxic effects of prometryn oral exposure on growth performance,antioxidant status,and the histomorphology of sea cucumbers.The study contents and results are as follows:Ⅰ.Acute toxicity test of prometryn on juvenile sea cucumbersThis study was conducted to investigate the effects of acute toxicity of prometryn on sea cucumbers from aspects of toxic symptoms,toxicity,and antioxidant and non-specific immune enzyme indexes.The experiment was divided into 6 experimental groups,respectively the conventional control group（seawater）,the solvent control group（seawater containing 45ml ethanol）,and the prometryn treatment groups of 10 mg/L（group A）,25 mg/L（group B）,62.5mg/L（group C）and 100 mg/L（group D）which were prepared by diluting the mother solution of prometryn by dissolving it in co-solvent ethanol.The exposure period was 96 hours.The results showed that:the medial lethal concentration in 96 hours（96h-LC50）of prometryn for juvenile sea cucumbers was 43.938 mg/L.The total antioxidant capacity of coelomic fluid in groups C and D was significantly higher than that in the control group（P<0.05）.The superoxide dismutase（SOD）activity in groups B,C and D were significantly higher than that in the control group（P<0.05）.Compared with the control group,alkaline phosphatase（AKP）activity in groups B,C and D was significantly decreased（P<0.05）.In conclusion,this study indicates that prometryn is a low toxicity pesticide for sea cucumbers.In addition,exposure to prometryn had an effect on antioxidant enzymes of sea cucumbers..Ⅱ.Chronic toxic effects of prometryn in water on antioxidant system and tissue cells of sea cucumberThis study was conducted to investigate the effects of chronic exposure to prometryn in water on antioxidant status,respiratory tree morphology,m RNA expression levels of heat stress proteins and apoptosis-related genes of sea cucumbers.0,25,50 and 100 mg prometryn were respectively weighed and dissolved in 25L fresh seawater to obtain the control group,LP group,MP group and HP group with prometryn concentrations of 0,1,2 and 4 mg/L;Random sampling was performed on day 1,7 and 14 and the test period was 14 days.The results showed that:The ACP enzyme activity in groups MP and HP was always significantly higher than that in the control group（P<0.05）,while the total nitric oxide synthase activity in groups MP and HP was always significantly lower than that in the control group（P<0.05）.After treatment with prometryn for 24h,there were cavities in the submucosal connective tissue of the HP group and there was a rupture in the muscle layer.The other treatment groups had no obvious injury.After14 days of continuous exposure to prometryn,the respiratory tree morphology of the HP group showed muscle layer rupture and loss,endothelial cell vacuolization,increased cell secretion and increased quantity of endothelial cells.Compared with the control group,m RNA relative expression levels of Hsp90,Hsp70 and CASP2 in the HP group were significantly higher than those in the control group（P<0.05）.Therefore,the study confirmed that the effect of 1mg/L prometryn on the health of sea cucumbers was not obvious,while the 4mg/L prometryn damaged the balance of the antioxidant system of sea cucumbers,reduced the immune capacity,and caused severe tissue damage to the respiratory tree.The inhibition of T-NOS activity by prometryn may be one of the reasons for disturbing the nervous system of sea cucumbers,and meanwhile,prometryn can also induce cell apoptosis.Ⅲ.Effects of chronic prometryn in feed exposure on antioxidative status,intestinal morphology,and microbiota in sea cucumber（Apostichopus japonicus）This study investigated the toxic effects of prometryn oral exposure on antioxidants,and the intestinal histomorphology and microbiome of sea cucumbers.Results showed that the accumulation of prometryn in the intestine,respiratory tree,and body wall decreased sequentially under the same level.Severe pathological damages were observed in the intestines of sea cucumbers fed with 0.080 and 1.595 g/kg prometryn（measured concentration）.Moreover,hydrogen peroxide（H₂O₂）and malondialdehyde（MDA）concentrations were significantly increased in prometryn treatment groups compared to the control group（P<0.05）,while the catalase（CAT）activity was significantly decreased（P<0.05）in the coelomic fluid of treatment groups.At the phylum level,the abundance of Proteobacteria was significantly higher in the0.080 g/kg treatment group than in the control group.In addition,prometryn exposure reduced the diversity of intestinal microflora in sea cucumbers.In conclusion,these results suggest that prometryn has potential toxicity to sea cucumber.Therefore,the harm of prometryn deposited in the sediment to aquatic animals must be a concern in aquaculture.