Genetic Diversity And Multiple Paternity Of Black Rockfish (Sebastes Schlegelii)

Black rockfish (Sebastes schlegelii Hilgendorf,1880), alias kurosoi in Japan, is a kind of familiar fish along the coast of Northwest Pacific Ocean, and it is also one of the most important inshore commercial fishes in China, but its resources appeared distinct recession on account of overfishing and environmental changes of fishing ground over the past decade years. In China, the Sebastes schlegelii enhancement and releasing activities were started in 1990s, but these activities would probably impact the wild resources of Sebastes schlegelii as most of the releasing larvae were come from the aquatic farm directly. In addition, the mature males and females of black rockfish are mating between November and December every year, and the females spawn during the period of May and June in next year. The mating systems of fishes have a potential impact on genetic diversity and effective population size. The special reproductive pattern and long-term sperm storage characteristic of black rockfish may result in intense sperm competition and multiple paternity, and different mate encounter rate of populations may excert critical influence on multiple paternity rate and male reproductive success. This study aims to estimate the genetic diversity of cultured populations and confirm multiple paternity frequency and reproductive skew of different males. The main results of the study are presented as follows:1. Comparative analysis of genetic variation in cultured and wild populations of black rockfish (Sebastes schlegelii)To investigate the genetic variation and diversity of black rockfish Sebastes schlegelii among four cultured populations and six wild populations, the 451bp hypervariable fragments of mitochondrial DNA control region were sequenced and analyzed. The results revealed that the gene diversity indices of cultured populations ranged from 0.540±0.067 to 0.815±0.021, which were significantly lower than those of wild populations (0.883±0.053-0.944±0.028), while the values of nucleotide diversity for both cultured and wild populations were at low level. Among the 52 haplotypes defined, only 12 of them were in the possession of cultured populations which shared 6 haplotypes with the wild populations. The result of pairwise Fst and AMOWA indicated that significant genetic differentiation existed among cultured populations, as well as between wild and cultured populations, which was contrast to that detected among wild populations, no significant genetic differentiations were detected between cultured and wild groups. Significant genealogical structure was also not detected corresponding to the cultured and wild populations based on the MST and NJ analyses.2. Comparative analysis of multiple paternity in natural and cultured viviparous black rockfish, Sebastes schlegelii, a fish with long-term female sperm storageIn this stuy, six polymorphic microsatellite markers were adopted to genotype 23 pregnant females (11 natural and 12 cultured) and their 609 embryos (20-35 embryos per female), which were collected from Jiaonan, Rushan and Penglai in Shandong Peninsula of China. The minimum number of sires and the quantity of paternal contributions for each litter were estimated. Multiple paternity phenomenon was detected in 10 of 11 litters in natural group (FMp= 90.9%) and 11 of 12 litters in cultured group (FMp= 91.7%). respectively. The substantially high incidences of multiple paternity in both groups were partly due to high rate of mate encounter. However, the average sires’number of natural group (2.45±0.82) was slightly less than that of cultured group (3.08±1.44), which was consistent with the hypothesis that mate encounter frequency is an important factor affecting multiple paternity. Additionally, the significantly skewed reproductive success of these two groups (70%; 81.8%) indicates that sperm competitions and cryptic female choice may play an important role in post-copulatory paternity biasing in this species. Whereas, the standard deviation of sire numbers in cultured group (1.44) was almost the double of natural group’s (0.82), suggesting that the sire number in natural group fluctuated fiercely than cultured group.These studies may provide theoretical foundation for the protection and rational utilization of resources, artificial breeding and stock enhancement strategy of Sebastes schlegelii. It may also enrich the related theoretical research for multiple paternity and sperm competition as well as afford references for mating systems and reproductive strategies of fishes with internal fertilization.