Characteristics Of Corbicula Clams Germplasm Resources From The Dingcheng Section Of Yuan River,Hunan Province

It is an important fishery resource in our country because of its rich nutrition and medicinal value,which has been deeply loved by people in the southeast coast of our country,Japan and South Korea.In recent years,factors such as overfishing and habitat destruction have led to the decline of clam resources.It is urgent to strengthen scientific evaluation and effective management of clam resources.This study evaluated the germplasm resources of Corbicula clams in Dingcheng district of Yuan river in Hunan province from five aspects of morphology,sex,ploidy,sperm morphology and genetic diversity,to provide scientific management basis.The main research conclusions are as follows:(1)The outer shell of Corbicula clams in Yuan River is yellow brown(n =144),while the pearl layer of the inner shell is white(n = 60)and purple(n = 84).Variance analysis with wet weight as covariate showed that shell length and shell height of inner shell white clam were significantly larger than those of inner shell purple individuals.(2)Histological analysis of gonads showed that 94 individuals were hermaphrodite,30 females and 20 males out of 144 Corbicula clams,indicating that the sex type of Corbicula clams in this section of the river is dioecious and hermaphrodite coexisting type,and hermaphrodite predominates(65.3%).(3)DNA content analysis of the adductor muscle tissue of the sample clam was carried out by flow cytometry,taking diploid Pacific Oyster and Loach as the reference respectively,and both showed that there were diploid and triploid Corbicula clams in the river section.Karyotype analysis further confirmed that the karyotype formulas of diploid and triploid Corbicula clams are2n=36=2M+2SM+32ST and 3n=54=3M+15SM+36ST respectively.In addition,the two ploidies Corbicula clams are mainly hermaphrodite,with 61.2% of diploid and70.3% of triploid clams being hermaphrodite.(4)Among the 30 samples of Corbicula clams analyzed,12 were hermaphrodite and 9 were male,of which 7 were uniflagellate and 5 were biflagellate,6 were uniflagellate and 3 were biflagellate.Therefore,according to the typical feature of double flagellate sperm,it is speculated that androgenesis may exist in Corbicula clams in Yuan area.(5)The haplotype diversity(hd),nucleotide diversity(?)and average nucleotide difference number(K)of Corbicula clams were 0.5990,0.01236 and6.5030 respectively,which indicated that Corbicula clams in this river segment had high genetic diversity.(6)Corbicula clams in Dingcheng district of Yuan River was similar in morphology,sex,sperm morphology and genetic diversity in Dongting Lake and Datong Lake.Therefore,it is suggested that Corbicula clams in Dingcheng district of Yuan River and Dongting Lake should be managed as the same unit.