| Wild stock of marine fish is heavily depleted and resources have dramatically decreased due to a few factors like overfishing. Fishery resource enhancement and release is an effective method for restocking and enhancing fishery biomass, and repairing the marine fish ecological environment. The black rockfish Sebastes schlegelii, as an important commercial fish, has been one of important fish species for marine fishery stock enhancement. This study analyzed the changes of genetic impacts on wild stock and fish composition after S. schlegelii enhancement in Lidao Bay,Rocheng, China, in 2013. This study would provide basic data for resource protection,stock enhancement and sustainable restoration for S. schlegelii in this area.1. The analysis of fish resources in Lidao Bay. Investigation of fish resources in Lidao Bay was carried out from May 2013 to November 2014. Fish samples were collected seasonally using stake nets. The results showed that there were 20 species of fishes were captured in Lidao Bay, belonging to 18 genus, 13 families and 5 orders.Among them, Perciform fish species, accounting for 50.00%, enjoys the highest amount in the total fish species. Index of Relative Importance(IRI) was used to determine dominant fish species, and the result showed that the S. schlegelii and Hexagrammos otakii are the dominant fish species in this area. And both were suitable for stock enhancement in this area. A total of 119 specimens collected from 20 different species were DNA barcoded using mitochondrial cytochrome coxidase subunit I(COI) gene. All fish species could be discriminated by their COI sequences,and DNA barcoding could provide sufficient information to identify and delineate fish in Lidao Bay. Average GC% content of the 20 fish species was 46.8%. Average Kimura 2-parameter genetic distances within species, genus, family, and order were0.14%, 5.17%, 21.30%, and 23.25%, respectively. The effects of water quality parameters on Liadao Bay fish abundance were analyzed by redundancy analysis(RDA) method. The result showed that the most important factor affecting fish communities in this area was water temperature. The abundance of dominant fishes, S.schlegelii and H. otakii, was affected by positive influences of temperature and ORP,and by negative influences of salinity and DO.2. The species and amount of fish in Lidao Bay before and after S. schlegelii stock enhancement were analyzed to learn the influences on fish community structure. The results showed that the fish species in this area don’t nearly change before and after stock enhancement, and the dominant species still were S. schlegelii and H. otakii. There were also no obvious changes in the evenness and abundance indexes before and after the stock enhancement. Meanwhile, the length–weight relationships(LWRs), total length(TL) – standard length(SL) relationships(LLRs) and Fulton’s condition factor(K) of male and female S. schlegelii in Lidao Bay were comparised to study the biological effects stock enhancement exerts on natural stock. The results showed that there were more males than female(1 M : 0.79 F) in Lidao Bay. The LWRs were significant(P <0.05) with all coefficients of determination(r2) values being higher than 0.95. The b value varied from 2.947 to 3.277. The LLRs for TL to SL, and vice versa, were all linear.The K values ranged from 0.791 to 2.981 in males and from 0.752 to 2.681 in females.There were no significant changes in these biological parameters of S. schlegelii stocks after stock enhancement.3. The genetic impacts of S. schlegelii enhancement in Lidao Bay were investigated by using partial sequence data of the mitochondrial DNA control region and 38 microsatellite DNA loci. The 678-bp segments of the mitochondrial DNA control region were sequenced from 288 samples, which identified a total of 78 haplotypes. The haplotype diversity parameter(h) and nucleotide diversity parameter(π) in hatchery-released stock were 0.902 and 0.00483, respectively. Meanwhile, the h values in wild stocks before and after stock enhancement were 0.970 and 0.939, and the πvalues were 0.00581 and 0.00526, respectively. Analysis of Molecular Variance(AMOVA) indicated that 99.00% of genetic variation occurred within stocks and only1% of genetic variation occurred between stocks. The Fixation index(FST) between hatchery-released stock and natural stock was 0.01488. The results showed that the hatchery-released stock was less diverse and diverged weakly but significantly from the natural stock before enhancement. And the FST between wild stocks before and after stock enhancement was-0.00404, showing that there was almost no significant difference between these two stocks. Above results were also confirmed by using microsatellite markers. According to analysis of microsatellite markers, the mean effective numbers of alleles(Ne) in hatchery-released stock was 4.76, mean polymorphism information content(PIC) was 0.674, observed heterozygosity(Ho) was0.668, and the expected heterozygosity(He) was 0.697. In wild stocks before and after stock enhancement, the Ne, PIC, Ho and He values were 6.01 and 5.82, 0.698 and 0.716,0.709 and 0.741, 0.735 and 0.754, respectively. AMOVA results indicated 91.54% of genetic variation occurred between individuals, 3.77% occurred between individuals within stocks, and only 4.69% occurred between stocks. The FST between hatchery-released stock and natural stock was 0.03980, and between the natural stocks before and after restocking was 0.03359. The results of the two markers showed that genetic diversity levels in natural stocks were higher level compared with hatchery-released stock, and the level of genetic diversity in the natural stocks was not significantly different from that before stock enchantment. Therefore, the restoration program for S. schlegelii in Lidao Bay is feasible. However, the consideration of the genetic risks of releasing hatchery-reared juveniles into the wild in stock enhancement is necessary. |
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