ANALYSIS OF GENETIC DIVERSITY IN BREEDING AND CULTIVATED POPULATIONS OF PSEUDOSCIAENA CROCEA

Large yellow croaker Pseudosciaena crocea, a commercially important marine fish, distributes mainly in nearshore and offshore areas of Zhejiang and Fujian Provinces, in southeastern China.In past two decades, the fish resources were under serious threat due to over-fishing and marine pollution.The production of wild fish of the species has decreased dramatically since the 1980s whereas the fish farming developed quickly by successful artificial mass production.The seeds for aquaculture were from the strains in two localities of Fujian and Zhejiang.This study is to clarify the population genetic structures of the strains and to assess the genetic differences between the strains for genetic potential and better management of breeding resource in future.The random amplified polymorphic DNA (RAPD) technique was applied to study the genetic diversity in the breeding population and cultivated population of P.crocea respectively.All of the RAPD markers were generated from 20 index samples each in the two populations.Fifteen of forty random decamer primers, which produced clear and polymorphic band patterns, were selected to detect the RAPD bands.Total 96 RAPD bands, each representing a RAPD locus, were obtained in experiment.Among them, 32 RAPD loci (accounting for 1/3) were polymorphic in the breeding population, while 42% or 43.75% were found in the cultivated population.The average heterozygosity and Shannon's Information Index were 0.3008 and 0.0879 in the breeding population and 0.3298 and 0.1221 in the cultivated population, respectively, indicating very low-level genetic variations in the two populations.It was found that 93.52% of the genetic variation existed within the populations in contrast to only 6.48% between the populations.The average genetic similarity (S) and genetic distance (D) calculated by Nei and Li's (1979) statistic method were 0.9079 and 0.0921, and 0.8784 and 0.1216, respectively in the two populations, suggesting a small genetic variation in both populations.The low inter-population genetic differentiation was further revealed by Nei's (1972) standard genetic distance (Ds) at 0.0123 between the two populations.The population genetics parameters indicated that although the breeding population displayed a greater genetic diversity than the cultivated one, the genetic diversity within or between the two populations was very low.Appropriate measurements must be taken to protect the germplasm of P.crocea from the reduction in genetic diversity.