Resource Status and Effect of Long-Term Stock Enhancement of Large Yellow Croaker in China

Jigui Yuan,Junkai Ma,Hungdu Lin,Shaoxiong Ding,Xuan Zhuang,Bin Kang,Lisheng Wu

doi:10.3389/fmars.2021.743836

Abstract

The large yellow croaker, Larimichthys crocea, was once the most abundant and economically important marine fish in China. Thus far, it has also been the most successful mariculture fish species in China. However, its wild stock severely declined in the 1970s because of overexploitation, and therefore hatchery release has been carried out for stock enhancement since 2000. As a migratory fish, large yellow croaker was divided into three geographical stocks according to ambiguous morphological and biological characteristics in early documents. To investigate the identity of wild large yellow croaker populations and assess the influence of hatchery supplementation on wild populations, a total of 2,785 cultured individuals and 591 wild individuals were collected from 91 hatcheries and six wild populations along the coast of mainland China and analyzed using two mitochondrial genes [cytochrome oxidase I (COI) and cytochrome b (Cyt b)] and one nuclear gene (RyR3). The higher haplotype diversity and moderate nucleotide diversity of wild large yellow croaker indicated that overexploitation, which caused a sharp decrease in biomass, did not lead to a loss of genetic diversity. According to phylogenetic construction and network analysis, the absence of a significant population structure pattern revealed a single panmictic population of wild large yellow croaker with exception of a population collected from the Sansha Bay, which showed high genetic relatedness to the cultured population, suggesting significant genetic effects resulting from stock enhancement. Overall, our study suggests no genetic differentiation in the entire wild population of large yellow croaker, which means that we have great flexibility in mixing and matching farmed and wild populations. However, since the result showed that domestication, the relaxation of purifying selection, increased genetic loads, and maladapted farmed fish will be at a selective disadvantage when cultured juveniles are released in the wild, the effectiveness of stock enhancement and the negative impact of hatchery-wild fish hybridization on the wild population must be carefully evaluated in future.

Highlights

China has a very long history of fishing, and marine catches have been the main source of protein for coastal residents for a long while, maintaining their livelihoods
The goals of this study are (1) to investigate the population classification of wild large yellow croaker, (2) to determine the role of the long-term stock enhancement of large yellow croaker, (3) to quantify the level of genetic effects associated with restocking intensity in wild populations, and (4) to provide useful information on fisheries management to improve the effectiveness of stock enhancement
We defined a total of 199 mtDNA haplotypes (602 bp of cytochrome oxidase I (COI) and 1,055 bp of cytochrome b (Cyt b)) from 571 individuals and 196 nuDNA haplotypes (704 bp) from 529 individuals in the wild populations, whereas we identified 30 mtDNA haplotypes from 2,739 individuals and 44 nuDNA haplotypes from 2,637 individuals in the cultured populations

Summary

Introduction

China has a very long history of fishing, and marine catches have been the main source of protein for coastal residents for a long while, maintaining their livelihoods. Large yellow croaker is the most successful mariculture fish species, its cultured population originates from only two populations from different sources One of these populations consists of offspring of individuals captured from the 1987 broodstock that migrated to Sansha Bay (in northern Fujian Province) for breeding (Liu and Mitcheson, 2008; Liu, 2013); the annual output of this population has reached 3 billion fry (Chinese Fishery Statistical Yearbook, 1956–2019) (most hatcheries of this population are located in northern Fujian Province, especially in Ningde City, and it is referred to as the Fujian cultured population, FJC, in this study) (Supplementary Figure 2). The other population originated from a spawning ground near Zhoushan Island in Zhejiang Province in 2000 (Liu and Mitcheson, 2008; Liu, 2013) and shows annual production of 50 million fry (Chinese Fishery Statistical Yearbook, 1956–2019) (referred to as the Zhejiang cultured population, ZJC, in this study) (Supplementary Figure 2)

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Conclusion