Characteristics Of Microplastic Distribution In Gills And Gastrointestinal Tissues Of Seawater And Ctenochaetus Striatus In Xisha Sea,South China Sea

As a new type of marine environmental pollutant,microplastics(MPs)are chemically stable and difficult to degrade,and can accumulate in the marine environment for a long time,and are easily ingested by marine organisms and transmitted through the food chain,which may eventually pose a threat to human health.At present,most studies are based on the content of microplastics in various tissues of near-shore inlets,lakes and rivers water environments and wild fish,and studies on MPs in water environments and wild fish in the South China Sea are very limited.In this study,we analyzed the accumulation,shape,color,particle size and composition of microplastics in the gill and gastrointestinal tissues of 119 wild Ctenochaetus striatus(C.striatus)from 11 sampling sites in the Xisha Islands of the South China Sea collected by a Chinese production survey vessel in January 2022,and simultaneously analyzed the characteristics of MPs in 21 water sampling sites in the Xisha Sea,and then correlated the microplastics in the gill and gastrointestinal tissues of C.striatus with the MPs content in their habitat.In this study,we further investigated the correlation analysis of MPs content in gill and gastrointestinal tissues of C.striatus with their body length and body weight.The main findings were as follows:(1)The abundance of MPs in the water column of Xisha Sea in the South China Sea ranged from 0.20 to 1.36 items/L,with an average abundance of 0.64±0.39 items/L.The shape of MPs was mainly fibers,followed by fragments and films;the color of MPs was mainly blue,followed by transparent and black;the size of MPs ranged from 24.62 to4674.54 μm,of which the particle size <1 mm accounted for more than 80%.The polymers types of MPs in the water mainly include polyethylene terephthalate,cellophane and polypropylene.(2)A total of 119 C.striatus samples from 11 stations were tested for MPs,and MPs were found in 108 fish,accounting for 90.76% of all samples.The average abundance of MPs at each sampling stations ranged from 2.21-4.13 items/individual,and the average abundance of MPs in the gills and gastrointestinal of the fish were 1.14±0.41items/individual and 1.80±0.49 items/individual,respectively.The mean abundance of MPs in individual individuals of C.striatus ranged from 1.0 to 9.0 items/individual,with a mean abundance of 2.90 ± 1.86 items/individual.The shapes of MPs in both gills and gastrointestinal of C.striatus were predominantly fibrous,followed by fragmented films;the colors of MPs were all predominantly blue,followed by black and transparent;the particle sizes of MPs ranged from 10.36-4150.09 μm,with more than 90% of the particles<1 mm.The polymers types in the gill and gastrointestinal tissues of C.striatus of MPs mainly include polyethylene terephthalate,cellophane and polypropylene.(3)Pearson correlation analysis showed that the abundance of MPs in the water was strongly and positively correlated with the abundance of MPs in the gills(r=0.661,p=0.027<0.05)and gastrointestinal tissues(r=0.628,p=0.039<0.05)of the ctenophores.This study shows that microplastics in the gills and gastrointestinal of C.striatus are closely related to the abundance of MPs in their habitat,further supporting that the bioavailability of MPs in fish increases with the abundance of MPs in the marine environment.(4)In this study,the body length of C.striatus ranged from 93-171 mm,with the mean length was 138.82±16.18 mm,and body weight ranged from 28.71-223.28 g,with the mean weight was 121.82±42.32 g.Pearson correlation analysis showed that the body length of C.striatus was strongly correlated with the abundance of MPs in their gills(r=0.514,p=0.000<0.01)and gastrointestinal(r=0.331,p=0.002<0.01).The results of Pearson correlation showed that the body length of C.striatus was strongly correlated with the abundance of MPs in gills(r=0.331,p=0.002<0.01)and gastrointestinal(r=0.331,p=0.002<0.01),and the body weight of C.striatus was strongly correlated with the abundance of MPs in gills(r=0.443,p=0.000<0.01)and gastrointestinal(r=0.259,p=0.017<0.05).Based on the results of the above study,the distribution characteristics of MPs in the water and gill and gastrointestinal tract of the C.striatus.in the Xisha South China Sea,were determined to be widely distributed in the Xisha Sea.The shape,color,particle size and composition of MPs in the C.striatus were positively correlated with the MPs distribution in the water of Xisha South China Sea.The size of the ctenophore was also positively correlated with the content of MPs in its gill and gastrointestinal tissues,so controlling the input of MPs in the water environment had a direct impact on reducing the accumulation of MPs in wild fish.