Effects Of Combined Stress Of Microplastics,Cadmium And Phenanthrene On Antioxidant Immunity And Energy Metabolism Of Symphysodon Haraldi

As a research hotspot of environmental problems,microplastic pollution has attracted much attention all over the world.In the natural environment,microplastics often coexist with other pollutants.Microplastics have the characteristics of large specific surface area and strong hydrophobicity,and can absorb heavy metals and organic pollutants,especially polychlorinated biphenyls?PCBs?,polycyclic aromatic hydrocarbons?PAHs?and other persistent organic pollutants?POPs?from the surrounding water environment.Studies have found that microplastics have been detected in major freshwater sources,surface water and even drinking water in the world.According to statistics,about 389,000 tons of river water in the Amazon River is polluted by microplastics each year.At the same time,due to increased industrial activities and crude oil leakage,heavy metal and organic matter pollution also exist in the waters of this area,which affects the growth and survival of fish.Discus fish?Symphysodon spp.?belonging to the family Cichlidae?Teleostei?,it is one of the endemic species in the region and was later artificially cultivated to make it one of the most popular tropical ornamental fishes,and it has great ornamental value and economic value.At present,the living environment is also threatened by various pollutants such as microplastics.The Symphysodon haraldi has a special nurturing behavior and is often used as a model organism for ecotoxicological research.In this study,the Symphysodon haraidi was selected as the research object.The same batch of newly hatched juveniles were reared for 8 weeks to explored the effects of microplastics,cadmium and phenanthrene on the Symphysodon haraidi.The results provide a scientific basis for improving the ecological risk assessment of microplastics,heavy metals,polycyclic aromatic hydrocarbons and other pollutants in the growth environment of Symphysodon haraidi and the environment of fishery waters.1.Effects of combined stress of microplastics and cadmium on antioxidant immune system of juvenile Symphysodon haraidi:To investigate the effect of microplastics and cadmium combined stress on the antioxidant immune system of juvenile discus fish,in this experiment,three microplastic concentrations(0,50,500?g L^-1)and two cadmium concentrations(0,50?g L^-1)were set up.A total of six exposure experimental groups were set up.The growth and survival,antioxidant enzyme activity,oxidative damage level and immune indexes of Symphysodon haraidi were measured respectively.The results showed that exposure to microplastics and cadmium had no effect on the growth and survival of the juvenile.Exposure to microplastics alone has reduced the accumulation of metallothionein?MT?and cadmium?Cd?in fish.However,exposure to microplastics alone increased the levels of four antioxidant substances,such as superoxide dismutase?SOD?,catalase?CAT?,glyphosate catalase?GPx?and glutathione?GSH?,as well as the two oxidative damage products of malondialdehyde?MDA?and protein carboxyl?PC?,and the immune parameters such as phosphatase in the body.When co-exposure exposed to microplastics and cadmium,it has produced an antagonistic effect,which has reduced the CAT activity and GSH content in the fish,but it has also caused oxidative damage to the juvenile fish,which has led to an increase in the body's PC content.The innate immune system of fish has been activated,and the activity of LZM,ACP and ALP has been enhanced.2.Effects of combined stress of microplastics and phenanthrene on energy metabolism of juvenile Symphysodon haraidi:In order to investigate the effect of combined stress of microplastics and phenanthrene on the energy metabolism of juvenile discus fish,in this experiment,three microplastic concentrations(0,100,1000?g L^-1)and two phenanthrene concentrations(0,50?g L^-1)were set,and a total of six exposure experimental groups were set.The growth and survival,energy metabolism,stable isotopes and chemometrics of Symphysodon haraidi were measured respectively.The results showed that exposure to microplastics and phenanthrene had no effect on the growth and survival of Symphysodon haraidi.Exposure to microplastics could reduced the hepatosomatic index ratio and condition factor of juvenile fish,and consumed energy such as carbohydrates and phospholipids,but also increased the body's fat content to maintain the energy balance and growth of juveniles at the same time.Exposure to microplastic or phenanthrene could caused harm to detoxification organs such as the fish's liver.Co-exposure to microplastics and phenanthrene has affected the turnover of C,N,and P elements in the fish body,has changed the stable isotope and stoichiometry,and has finally led to changes in the energy storage of the fish body,which has affected its size and ornamental value.In summary,under the conditions of this study,exposure to microplastics at a concentration of 1000?g L^-1and cadmium or phenanthrene at a concentration of 50?g L^-1had no effect on the growth and survival of juvenile Symphysodon haraidi.However,when faced with the stress of microplastics and cadmium,it would caused oxidative damage to the fish body and activate the antioxidant immune system of the fish.When faced with the stress of microplastics and phenanthrene,it would changed the element turnover in the fish and change the energy metabolism pathway in the fish.The results reveal the possible toxicological effects of the combined toxicity of microplastics and other pollutants on freshwater fish,and provide a scientific basis for the healthy breeding and evaluation of freshwater fish.