Marine Fish In China Research Articles

Epinephelus coioides Sec3 promotes Singapore grouper iridovirus infection by negatively regulates immune response

Exocyst, a protein complex, plays a crucial role in various cellular functions, including cell polarization, migration, invasion, cytokinesis, and autophagy. Sec3, known as Exoc1, is a key subunit of the Exocyst complex and can be involved in cell survival and apoptosis. In this study, two subtypes of Sec3 were isolated from Epinephelus coioides, an important marine fish in China. The role of E. coioides Sec3 was explored during Singapore grouper iridovirus (SGIV) infection, an important pathogen of marine fish which could induce 90 % mortality. E. coioides Sec3 sequences showed a high similarity with that from other species, indicating the presence of a conserved Sec3 superfamily domain. E. coioides Sec3 mRNA could be detected in all examined tissues, albeit at varying expression levels. SGIV infection could upregulate E. coioides Sec3 mRNA. Upregulated Sec3 significantly promoted SGIV-induced CPE, and the expressions of viral key genes. E. coioides Sec3 could inhibit the activation of NF-κB and AP-1, as well as SGIV-induced cell apoptosis. The results illustrated that E. coioides Sec3 promotes SGIV infection by regulating the innate immune response.

Swimming Performance in Large Yellow Croaker: Effects of Group Size, Test Protocol, and Recovery Time On Critical Swimming Speed.

Swimming is critical for fish survival, and little attention has been paid to the swimming performance of large yellow croaker, the largest farmed marine fish in China. To address this gap, we conducted a study to measure the critical swimming speed (Ucrit) of 1050 croaker in a designed swim test flume. Our findings shed light on the effects of group size, Ucrit test protocol, and recovery time on swimming performance. The water flow in the swim flume increased steadily and linearly. The linear fit equation was y = 2.89x + 1.79 with an R2 of 0.99. With the help of the swim flume, we found that group size, and the Ucrit test protocol had a significant effect on the Ucrit values, except for the recovery time: The Ucrit values obtained in the ramp-Ucrit test averaged 28.32 ± 6.11cm.s-1, which was significantly lower than that obtained in the traditional Ucrit test of 32.75 ± 7.60cm.s-1; The Ucrit value of a group size of 50 fish was 33.51 ± 5.96cm.s-1, which was significantly higher than that of a group of 200 fish (28.49 ± 6.37cm.s-1). These results provide insights into the swimming performance of large yellow croaker and can be used to standardize the swimming test protocols.

Transcriptomic analysis of large yellow croaker (Larimichthys crocea) reveals the suppression of the inflammatory response from Cryptocaryon irritans infection

Large yellow croaker (Larimichthys crocea) is the most productive marine fish in China. Cryptocaryon irritans is an extremely destructive parasite that causes great economic losses in large yellow croaker aquaculture industry. Therefore, it is very necessary to study the immune response of large yellow croaker in response to C. irritans infection. In this study, the transcriptomic profiles of large yellow croaker were sequenced and analyzed in the brain and head kidney at 72 h after C. irritans infection. Cytokines and chemokines related terms were significantly enriched based on the GO enrichment of down-regulated differentially expressed genes (DEGs) from the head kidney. Meanwhile, cytokine-cytokine receptor interaction was significantly enriched based on the KEGG enrichment of up-regulated DEGs from the brain and down-regulated DEGs from the head kidney, respectively. Moreover, the majority of inflammation-related DEGs were significantly up-regulated in the brain, but distinctly down-regulated in the head kidney. These results showed that the brain and head kidney might play different roles against C. irritans infection, and the inflammatory response of large yellow croaker may be restrained during C. irritans infection. Taken together, the transcriptomic analyses will be helpful to more comprehensively understand the immune mechanism of teleost against C. irritans infection, and provide a theoretical basis for the prevention and treatment of Cryptosporidiosis.

Genome-wide DNA methylation mediates the resistance to vibriosis in Cynoglossus semilaevis

Chinese tongue sole (Cynoglossus semilaevis) is an economically important marine fish in China. However, vibriosis has caused huge mortality and economic losses in its culturing industry. To reveal the effect of DNA methylation on the resistance to vibriosis in tongue sole, we conducted RNA sequencing and whole genome bisulfite sequencing (WGBS), and compared the gene expressions and DNA methylation patterns between the resistant and susceptible families. We identified a total of 741 significantly differentially expressed genes (DEGs) in kidney and 17460 differentially methylated genes (DMGs), which were both enriched in immune-related pathways, such as “cAMP signaling pathway” and “NOD-like receptor signaling pathway”. Through the correlation analysis of DEGs and DMGs, we identified two important immune pathways, including “complement and coagulation cascades”, and “cytokine-cytokine receptor interaction”, which played important roles in regulating the inflammation level and immune homeostasis. For example, the expression of proinflammatory cytokine il17c was down-regulated under the regulation of DNA methylation; in addition, the expression of protease-activated receptor 3 (par3) was up-regulated, which could induce the up-expressionof il8. These results demonstrated that the regulation of DNA methylation on the genes involved in immune responses might contribute to the resistance to vibriosis in tongue sole, and provided a basis for the control of diseases in fish aquaculture.

Development and characterization of a spleen cell line from yellowfin seabream Acanthopagrus latus and its susceptibility to Mandarinfish ranavirus.

Yellowfin seabream (Acanthopagrus latus) is one of the most commercially important marine fish in China. In this study, a new continuous cell line, named ALS cells, was developed from the spleen tissue of A. latus. The cell line was maintained in Dulbecco's modified Eagle medium/Nutrient Mixture F-12 Ham (DMEM/F-12) supplemented with 10% fetal bovine serum (FBS) and successfully cultured up to 50 passages. The cell line was authenticated by amplifying and sequencing mitochondrial cytochrome C oxidase subunit-I (coi-I) gene. The ALS cell line had the maximum growth rate in DMEM/F-12 medium containing 20% FBS at 27°C. Chromosome number analysis showed that the ALS cells have a modal diploid chromosome number of 34. The ALS cell line was transfected with the pEGFP-N1 plasmid, and green fluorescence was observed. The ALS cell line was used for testing Mandarinfish ranavirus (MRV) susceptibility, and the cytopathic effects in the cell line were observed at 4 days post-infection (dpi). Furthermore, the susceptibility of the ALS cell line to MRV and the levels of MRV mRNA and viral loads were found to be significantly increased at 1-7 dpi. This study revealed that the ALS cell line could be useful for molecular, virological, and biotechnological studies on yellowfin seabream.

Comparative study of transcriptome profiles in the eyes and brain of the tiger puffer Takifugu rubripes brooder under red light filtered LED

Light spectrum is an important environmental factor affecting fish activities. However, the existing studies on spectrum are usually conducted under monochromatic light, which are multiple variables compared to the natural light conditions and increase uncertainty. The results may be caused by the absence of all other chromatic lights. The tiger puffer Takifugu rubripes is an important commercial marine fish in China, Japan, and Korea. In this study, the effects of red light on the eyes and brain of T. rubripes brooder, including histological changes in retina and optic tectum, the levels of oxidative stress indicators in serum, and changes in gene expression at transcriptome level were examined, after the treatment of full spectrum LED (Fs) and red light filtered LED (Rf) for 52 days. The results showed that the growth and histological structure of retina and optic tectum were not significantly altered. While, Rf significantly decreased the activity of superoxide dismutase and catalase, and increased the content of cortisol (P < 0.05), but had no effect on the levels of glutathione peroxidase and malondialdehyde. Transcriptome data revealed that there were 147 differentially expressed genes (DEGs) in the eyes of Rf vs Fs. Many DEGs related to vision changed significantly. KEGG enrichment and GSEA analyses showed that the significantly enriched arachidonic acid pathway down-regulated in the Rf group, in which genes related to sexual maturation and ovulation presented significant changes, suggesting that Rf may affect the ovulation process through this pathway. In the brain, the number of DEGs was only 20, which are most correlated with circadian rhythm. The present study displayed for the first time the role of red light in promoting ovulation in mature fish by filtering it, which may provide more supports to highlight the function of red light in fish culture.

Quality attributes of large yellow croaker (Larimichthys crocea) during refrigerated storage as affected by theaflavins.

Large yellow croaker (Larimichthys crocea) is an economical marine fish in China. Theaflavins have antibacterial and antioxidant properties. However, there is a lack of its application in the large yellow croakers during refrigerated storage. This study investigated the effect of theaflavins on the quality large yellow croaker (Larimichthys crocea) during 12 days of storage at 4°C. The results showed that theaflavins treatment was able to inhibit microbial growth and reduce the production of total volatile basic nitrogen (TVB-N). Meanwhile, theaflavins were beneficial in reducing the unfolding of myofibrillar proteins, decreasing the degree of protein aggregation, and improving the stability of protein structure. Therefore, the degree of protein oxidation was lower in the theaflavin-treated group compared with untreated group. In addition, theaflavins treatment effectively inhibited the increase in acid value (AV), peroxide value (PV), and malonaldehyde (MDA) content due to the ability of scavenging free radical. The effect of theaflavin was positively correlated with the increase in concentration under refrigeration conditions. Therefore, this study suggests that theaflavins handling is an auspicious and valid method to extend the preservation of refrigerated large yellow croaker. Overall, adding theaflavins to large yellow croaker can be an effective method of quality preservation during refrigerated storage. This article is protected by copyright. All rights reserved.

Population structure and genome-wide evolutionary signatures reveal putative climate-driven habitat change and local adaptation in the large yellow croaker

The large yellow croaker (Larimichthyscrocea) is one of the most economically valuable marine fish in China and is a notable species in ecological studies owing to a serious collapse of wild germplasm in the past few decades. The stock division and species distribution, which have important implications for ecological protection, germplasm recovery, and fishery resource management, have been debated since the 1960s. However, it is still uncertain even how many stocks exist in this species. To address this, we evaluated the fine-scale genetic structure of large yellow croaker populations distributed along the eastern and southern Chinese coastline based on 7.64 million SNP markers. Compared with the widely accepted stock boundaries proposed in the 1960s, our results revealed that a climate-driven habitat change probably occurred between the Naozhou (Nanhai) Stock and the Ming-Yuedong (Mindong) Stock. The boundary between these two stocks might have shifted northwards from the Pearl River Estuary to the northern area of the Taiwan Strait, accompanied by highly asymmetric introgression. In addition, we found divergent landscapes of natural selection between the stocks inhabiting northern and southern areas. The northern population exhibited highly agminated signatures of strong natural selection in genes related to developmental processes, whereas moderate and interspersed selective signatures were detected in many immune-related genes in the southern populations. These findings establish the stock status and genome-wide evolutionary landscapes of large yellow croaker, providing a basis for conservation, fisheries management and further evolutionary biology studies.

The involvement of oxidative stress mediated endoplasmic reticulum pathway in apoptosis of Golden Pompano (Trachinotus blochii) liver under PS-MPs stress

Globally, microplastics (MPs) are highly prevalent, especially in coastal areas. Unfortunately, golden pompano as a major marine fish in China is typically raised in floating marine cages near coasts, facing these MPs sources. However, toxicological studies on Golden Pompano which farm in coastal areas and face actual microplastic exposure are rare. Therefore, golden pompano were exposed to 10.0 μg/L, 100.0 μg/L, and 1000.0 μg/L polystyrene MPs (PS-MPs) for 14 days to study the potential impact of the microplastics on the Golden Pompano. Fish show slowed growth after 14 days of exposure. Histopathology shows irregular shaped nuclei and nuclear and cytoplasmic vacuolation traits in liver. Oxidative stress-related enzyme activity and gene expression data show that oxidative damage occurs in the high-concentrations (100.0 μg/L and 1000.0 μg/L) of PS-MPs exposures. Up-regulation of Grp78, Xbp-1, Eif-2α and chop gene expression indicates the occurrence of endoplasmic reticulum stress, and the western blot results also confirmed this. Severe oxidative stress also caused ERS, which ultimately increased BAX/Bcl-2 ratios and induces apoptosis. Furthermore, up-regulated anaerobic respiration, altered lipid metabolism, and immune disturbance were exhibited during PS-MPs stress. Therefore, oxidative stress appeared to be the main toxicity issue caused by MPs, while ERS-mediated apoptosis, metabolic alterations, and immune responses were induced by this stress. Notably, endoplasmic reticulum stress and apoptosis are a self-protective mechanism, which may be an intermediate link in the toxicity of microplastics. This study highlights the role of endoplasmic reticulum stress in MPs toxicology and assesses the adverse effects of microplastics on Golden Pompano.

Genetic analysis of hypermelanosis in Chinese tongue sole (Cynoglossus semilaevis)

Chinese tongue sole (Cynoglossus semilaevis) is an economically important marine fish in China. Generally, the eyeless side of the Chinese tongue sole is white and the side with eyes is brown after metamorphosis, hypermelanosis may still occur in the eyeless side in certain individuals after metamorphosis, which greatly decreases consumer acceptance and market price. In order to study the possibility of genetic improvement, we determined genomic markers in Chinese tongue sole using the genotyping-by-sequencing method and analyzed their association with hypermelanosis area. Genetic analysis showed that hypermelanosis was a complicated quantitative trait, and the estimated heritability for hypermelanosis incidence and area ratio were 0.16 and 0.21, respectively. Genomic selection analysis showed that selection based on hypermelanosis incidence and area ratio had similar reliabilities and prediction accuracies, indicating the feasibility of genetic improvement. Nine loci were significantly associated with hypermelanosis, few of which included genes or flanked genes potentially associated with skin disease, indicating the potential complicated genetic mechanisms underlying hypermelanosis in the Chinese tongue sole.

Establishment of the first cell line from the small yellow croaker (Larimichthys polyactis) and its application in unraveling the mechanism of ROS-induced apoptosis under hypoxia

Cell lines play an important role in studying biological processes in vitro. In this study, we aimed to establish and characterize the first cell line isolated from the small yellow croaker (Larimichthys polyactis), an economically important marine fish in China. The small yellow croaker fry (SYCF) cells proliferated well in Leibovitz's 15 medium containing 2% antibiotics, 0.1 M NaCl, and 10% fetal bovine serum at 27 °C. Sequence analyses of mitochondrial genes confirmed the origin of SYCF cells. Furthermore, we unraveled the mechanism of hypoxia-induced apoptosis, a major threat to aquatic animals using the SYCF cell line. The HIF-PHD pathway of the SYCF cells can be activated under hypoxic stress, suggesting that this cell line is impressible for hypoxia and can serve as a superb model in vitro to study the cell physiology in L. polyactis in a hypoxic setting. We found that hypoxia results in morphological abnormalities, excess reactive oxygen species (ROS) production, and dysfunctional redox homeostasis, indicating the occurrence of oxidative stress in the SYCF cells. In addition, decreased cell viability and severe apoptosis were detected under hypoxic conditions. Through monitoring the indicators of the intrinsic and extrinsic apoptosis pathways, including the mitochondrial membrane potential, the expression of bax, bcl2, bnip3, and fas, Bcl2, and Caspase-3 protein, and activity of Caspases-3/8/9, we found that both pathways are involved. Considering that ROS-induced oxidative stress may be the main reason of apoptosis, we investigated whether the addition of an antioxidant, N-Acetyl-L-cysteine (NAC), will ameliorate the apoptosis. Interestingly, we found that both intrinsic and extrinsic apoptosis indicators were markedly recovered by adding NAC in culture media, significant remissions were also observed in the cell viability and apoptosis rate. These results suggested that hypoxia-induced apoptosis of SYCF cells may be mediated by the overproduction of ROS, and the antioxidant may be a useful material to relieve cell damage under hypoxia in fish. In general, this study established a marine fish cell line of SYCF cells, which can be used as an in vitro research model of L. polyactis and for revealing the mechanisms of ROS-induced apoptosis under hypoxic conditions in this species. This provides important insights into the cellular physiology of marine fish under hypoxia.

Identification and characterization of lncRNAs and the interaction of lncRNA-mRNA in Epinephelus coioides induced with Singapore grouper iridovirus infection

Singapore grouper iridovirus (SGIV) is a highly pathogenic double-stranded DNA virus, and the fatality rate of SGIV-infected grouper is more than 90%. Up to now, there is no effective methods to control the disease. Long non-coding RNAs (lncRNAs) might play an important role in individual growth and development, immune regulation and other life processes. In this study, lncRNAs were identified in Epinephelus coioides, an important economic aquaculture marine fish in China and Southeast Asia, and the regulatory relationships of lncRNAs and mRNA response to SGIV infection were analyzed. A total of 11,678 lncRNAs were identified and classified from the spleen and GS (grouper spleen) cells. 105 differentially expressed lncRNAs (DElncRNAs) were detected during SGIV infection. The lncRNAs and the regulated mRNAs were analyzed using co-expression network, lncRNA target gene annotation and GO enrichment. At 24 and 48 h after SGIV infection, 118 and 339 lncRNA-mRNA pairs in GS cells were detected, and 728 and 688 differentially expressed lncRNA-mRNA pairs in spleen were obtained, respectively. GO and KEGG were used to predict the DE lncRNAs' target genes, and deduce the DE lncRNAs-affected signaling pathways. In GS cells, lncRNAs might participate in cell part, binding and catalytic activity; and lncRNAs might be involved in immune system process and transcription factor activity in spleen. These data demonstrated that lncRNAs could regulate the expression of immune-related genes response to viral infection, and providing a new insight into understanding the complexity of immune regulatory networks mediated by lncRNAs during viral infection in teleost fish.

Study of cooking coefficient of five toxic metals in marine fish in China

Study of cooking coefficient of five toxic metals in marine fish in China

Nutrients, temperature, and oxygen mediate microbial antibiotic resistance in sea bass (Lateolabrax maculatus) ponds

Antibiotic resistance genes (ARGs) have drawn increasing attention as novel environmental pollutants because of the threat they impose on human and animal health. The sea bass (Lateolabrax maculatus) is the third most cultured marine fish in China. Therefore, a study of ARG pollution in the sea bass culture environment is of great significance for the healthy and sustainable development of the sea bass industry. Here, we systematic investigated the contents of 23 antibiotic resistance-related genes (ARRGs), including 19 ARGs and four mobile genetic elements, and analyzed bacterial community composition and environmental parameters in sea bass ponds. The relative abundance (ARRG copies/16S ribosomal RNA gene copies) of ARRGs was up to 3.83 × 10−2. Sul1 was the most abundant ARRG, followed by ereA, intI-1, sul2, dfrA1, and aadA. Both the ARRG changes and aquatic microbiota succession were mainly driven by water temperature (WT), dissolved oxygen (DO), and NO3−. WT is positively correlated with the most ARGs and some of the top 38 Operational Taxonomic Units (OTUs) belonging to the orders of Frankiales, Micrococcales, Chitinophagales, and Sphingomonadales. Furthermore, WT is negatively related with some other OTUs of the orders Frankiales, Xanthomonadales, Micrococcales, and Rhizobiales. However, DO and NO3− have the opposite function with WT on specific taxa and ARGs. These results indicate that sea bass ponds are reservoirs of ARGs, and are driven mainly by the nutrient, temperature, and oxygen with inducing specific microbial taxa. The regulation of environmental factors (increasing DO and NO3−) can be conducted to reduce drug resistance risk in aquaculture ponds. Therefore, environmental factors and specific taxa could be the indicators of ARG contamination and can be used to establish an antibiotic elimination system and consequently realize a sustainable aquaculture industry.

Development of Recombinant Dihydrolipoamide Dehydrogenase Subunit Vaccine against Vibrio Infection in Large Yellow Croaker

Large yellow croaker (Larimichthys crocea), an economically important marine fish in China, has suffered from serious vibriosis, which has resulted in great economic losses for the large yellow croaker industry. Vaccination has been considered to be a safe and effective method to prevent and control vibriosis. However, due to the complex diversity and serotypes of the Vibrio genus, the progress of Vibrio vaccine development is still slow. In this study, we prepared recombinant Vibrio dihydrolipoamide dehydrogenase (rDLD) protein and investigated its potential as a candidate to be a subunit vaccine against Vibrio. The lysozyme activity and the rDLD-specific antibody level in sera of large yellow croakers immunized with rDLD were significantly higher than those in the control group, and the transcript levels of proinflammatory cytokines (IL-6, IL-8, IL-1β), MHC IIα/β, CD40, CD8α, IL-4/13A, and IL-4/13B were significantly up-regulated in the spleen and head kidney of large yellow croakers immunized with rDLD, suggesting that rDLD could induce both specific and nonspecific immune responses in this species. In addition, rDLD protein increased the survival rate of large yellow croakers against Vibrio alginolyticus and Vibrio parahaemolyticus, with the relative percent of survival (RPS) being 74.5% and 66.9%, respectively. These results will facilitate the development of a potential subunit vaccine against Vibrio in large yellow croaker aquaculture.

Inhibitory effect and mechanism of various fruit extracts on the formation of heterocyclic aromatic amines and flavor changes in roast large yellow croaker (Pseudosciaena crocea)

The large yellow croaker ( Pseudosciaena crocea ) is one of the most commercially important marine fish in China and is a fixture at Chinese tables. Herein, we determined the formation of heterocyclic aromatic amines (HAAs) in roasted yellow croaker and evaluated the inhibitory effect of natural fruits extracts (blueberry extract, acerola cherry extract and grape seed extract) on the formation of HAAs in roast yellow croaker. All the three fruit extracts treatments minimize the amount of HAAs and the addition of blueberries extracts is the most effective approach on reducing the total HAAs content, which caused a signification reduction of 94.85% and 71.15% of the Norhaman and PhIP content, respectively, led IQ, 8-MeIQX, 4,8-DiMeIQX below the detected limitation, compared to the control group. Furthermore, antioxidant index of fruits extracts, precursors (free amino acids, creatine, creatinine and glucose) of HAAs, lipid and protein oxidation, flavor changes are evaluated to determine the mechanism and physical/chemical changes of fruit extracts on the formation of HAAs. This research develops a new method to minimize the amount of HAAs, which is helpful to food manufacturers for the production of healthier yellow croaker products and may be applicable to various meat systems. • The formation of HAAs in roasted large yellow croaker was determined. • Various fruits extracts could inhibit HAAs in roast large yellow croaker. • Fruits extracts positively affected lipid/protein oxidation and content of precursors. • Flavor changes are introduced to determine the possible mechanism involved.

Epinephelus coioides Hsp27 negatively regulates innate immune response and apoptosis induced by Singapore grouper iridovirus (SGIV) infection

Heat shock proteins (Hsps) are important for maintaining protein homeostasis and cell survival. In this study, Hsp27 of Epinephelus coioides, an economically important marine fish in China and Southeast Asian countries, was characterized. E. coioides Hsp27 contains the consered ACD_HspB1_like domain and three p38 MAPK phosphorylation sites, located at Thr-13, Thr-60 and Ser-167. E. coioides Hsp27 was distributed in both the cytoplasm and nucleus, its mRNA was detected in all 14 tissues examined, and its expression was up-regulated after challenge with Singapore grouper iridovirus (SGIV), an important E. coioides pathogen. Over-expression of E. coioides Hsp27 significantly upregulated the expressions of the key SGIV genes (VP19, LITAF, MCP, and ICP18), downgraded the expressions of the E. coioides immune factors (IRF3, IRF7, ISG15, and TRAF6) and proinflammatory factors (TNF-α, IL-8), downgraded the activation of nuclear factor kappa-B (NF-κB) and activator protein-1 (AP-1), and substantially inhibited the cell apoptosis induced by SGIV infection. These data illustrated that E. coioides Hsp27 might be involved in SGIV infection by negatively regulating the innate immune response.

Genome-wide association analysis on host resistance against the rotten body disease in a naturally infected population of large yellow croaker Larimichthys crocea

Large yellow croaker (Larimichthys crocea) is one of the most important marine fish in China, representing the highest yield of fish species in marine net cage aquaculture. In recent years, the rotten body disease caused by scuticociliate was the main perniciousness for the fish fry, and led considerable economic losses. To date, no treatments had proven to be effective to the disease, so it was urgent to carry out the researches on disease-resistance breeding of this fish. Based on genome resequence for a natural population, a genome-wide association study (GWAS) to identify those loci associated with the rotten body disease resistance was performed in this work. A total of 3000 fish from 6 sub-populations were collected, and 270 phenotypic extremes were selected for genotyping. Two analysis models were employed to verify the accuracy and reliability of GWAS results. 2,019,067 SNPs were remained, and 14 SNPs were finally identified to be correlated with disease resistance, explaining phenotypic variance ranging from 5.4% to 9.2%. Within these regions, 5 candidate genes, NF-κB1, UBXN1, PTX3, DAB2IP and CYR61, which were involved in NF-κB signaling pathway, suggested the importance of NF-κB signaling pathway in the disease resistance. These results showed the complex polygenic architecture in large yellow croaker resistance against parasite scuticociliate. It also provided valuable foundation for future marker-assisted selection breeding of large yellow croaker against scuticociliate.

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

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.

Health risk assessment of heavy metals in marine fish to the population in Zhejiang, China

Environmental pollution with toxic metals can lead to the possible contamination of the marine fish. We investigated the levels of As, Cd, Cr, Hg and Pb in 652 marine fish samples (15 species) collected from coastal areas of Zhejiang, China and estimated their health risk. Mean concentrations of As, Cd, Cr, Hg and Pb were 0.783, 0.009, 0.114, 0.031, 0.043 mg/kg wet weight. The average estimated daily intakes (EDIs) for As, Cd, Cr, Hg and Pb were 1.214, 0.014, 0.177, 0.048 and 0.067 μg/kg bw/day. The risk assessment at mean exposure level showed that there was no health risk associated with these elements through consumption of marine fish. However, potential health risk may exist for high exposure consumers considering the possible contamination of As and Hg. Given that the different levels of certain elements in marine fish in China, this study provides a scientific basis for food safety assessment and suggestions for risk management.