Heavy Metals Bioaccumulation Characteristics And Influence Factors Of Swordtip Squid In The East China Sea

The East China Sea,which covers an area of about 700,000 square kilometers,is one of China’s most important fishing grounds thanks to its complex current circulation system,which provides good breeding conditions for a variety of fish.There are many industrial cities near the East China Sea,and the area is largely affected by human activities,resulting in high levels of heavy metals in sediments.There are about 45 kinds of heavy metals in nature,and the concentration of such elements in the body will affect the growth of the body,and excessive intake will have negative effects.Studies have shown that Hg,Cd,Pb and metal-like As will have serious effects on marine organisms and human bodies,and these elements are also important indicators for the detection of toxic and harmful substances in China.Heavy metals are highly toxic,difficult to decompose,can only be converted in different chemical forms,and are easily absorbed by aquatic organisms after entering the water body,which will pose a serious threat to marine ecosystems and human beings.Uroteuthis edulis is a shallow marine species with warm temperature in the offshore area,which is widely distributed in the northwest Pacific Ocean and the eastern coast of Africa,among which the East China Sea is the richest resource density.This species has the characteristics of vertical movement day and night,and has a wide range of migration,and is one of the important economic cephalopod resources currently developed and utilized in China and Japan.The squid feeds on crustaceans,small fish,and other organisms that are easily enriched with heavy metals,and is also an important prey for high-trophic predators such as large fish and marine mammals,and is an important link in the food chain.Cephalopod species such as the sword-tipped squid have a fast growth rate and a short life cycle,and are sensitive to heavy metal contaminants at all stages of their life history.In recent years,there have been extensive studies on the concentration of heavy metals in fish and shellfish around the world,but there are few studies on the concentration of heavy metals in cephalopods.For this purpose,this study takes the squid in the East China Sea as the research object,analyzes the distribution characteristics of heavy metal elements in different body tissues,and explores the correlation and difference between heavy metal elements in different tissues.Combined with the analysis ofδ¹³C andδ¹⁵N stable isotope data to cause the difference in heavy metal bioaccumulation,the results of this study will enhance people’s understanding of the heavy metal bioaccumulation characteristics in squid,and provide basic information and scientific basis for a comprehensive grasp of the life history characteristics of squid.The results of the study are as follows:（1）Distribution characteristics of heavy metals in the tissues of Uroteuthis edulis.The results showed that heavy metal elements were mainly enriched in the carcass,and the load of Cr,Co,As and Zn in the carcass reached more than 50%of the systemic load.The rest is mainly enriched in the gonads.The load of heavy metal elements in the digestive glands is generally small.Spearman analysis showed that there was no correlation between Cr and Cu,Zn,As and Cd in the carcass,and there was a positive correlation between all other elements,and there was a strong positive correlation between Co and Zn,Co and As,Co and Cd,Cr and Zn in the digestive gland,and there was no obvious correlation between other elements.The correlation between gonads and elements in the gills was not strong,and there was a positive correlation between Cr and Co,Cu and As,Cu and Cd in the gills.（2）Characteristics and influencing factors of heavy metal element transfer of Uroteuthis edulis.Mann-Whitney U was used to investigate whether there was a difference in the concentration of heavy metals in the tissues of the sample before and after sexual maturity of the squid,and to explore the transfer characteristics of heavy metals between tissues in the squid.The Mann-Whitney U test showed that there was no significant difference in the concentration of all elements of carcass muscle tissue before and after sexual maturity（p>0.05）,there was no significant difference in all other elements except Zn（p<0.05）,and there were significant differences in the three elements of Cr,Cu and As in the gonads,while there were no significant differences in Co,Zn and Cd.There were significant differences in Co and As in ctenophores,while Cr,Cu,Zn and Cd were absent.The box plot shows that the concentration of heavy metal elements in each tissue decreases after sexual maturity.（3）Ecological factors of feeding on changes in heavy metal concentrations of Uroteuthis edulis.The two-stage GAM（generalized additive model）was used to reveal the effect of stable isotope ratio changes on heavy metal bioaccumulation concentration before and after gonad maturation,and the T-test and Spearman correlation analysis compared the correlation between heavy metal elements and fatty acid content before and after gonad maturation in Squid squid.The results showed that the heavy metals Cu,As and Cd showed a significant relationship with sexual maturity（P<0.05）,in which Cu showed nonlinear and negative correlation,As showed linear and positive correlation,and Cd showed linear and positive correlation.,δ15N had a significant positive correlation with each heavy metal,whileδ13C correlation was not significant.There was a certain correlation between fatty acids C16:0,C22:2n6,C22:6n3 and DHA/EPA and heavy metal elements before and after sexual maturity.Before sexual maturity,C16:0 and C22:2n6increased with the increase of Cr content,and C16:0 and C22:2n6 showed a gradual decline when the Cr content was higher than 2μg/g after sexual maturity.The characteristic fatty acids C22:6n3 and DHA/EPA changed slightly with the content of each heavy metal.