Abstract:As a transcription repressor, the bmi1b gene plays an important role in maintaining the self-renewal and proliferation of many stem cells. This study identified single nucleotide polymorphisms of bmi1b and conducted an association analysis with bighead carp (Hypophthalmichthys nobilis). The bighead carp bmi1b gene has 5800 bp in length including nine exons and eight introns; therefore, its amino acid sequence is evolutionarily conserved. The hypothalamus exhibited the greatest spatial expression of bmi1b in the tissues of adult bighead carp. During the embryonic development and larval stages of bighead carp, this gene was highly expressed from the unfertilized egg to the blastocyst stage, whilst its expression was significantly lowered after the gastrula stage. Two single-nucleotide polymorphism (SNPs), g. 5224 T＞A and g.5550 C＞T, were obtained at the 3′ UTR of bighead carp bmi1b by direct sequencing of polymerase chain reaction (PCR)-amplified products. The results from genotyping these two SNP loci in 169 fish from a multi-family population of bighead carp and their correlation with growth and body type highlighted three key findings: (1) g. 5224 T＞A was significantly associated with body weight and head height (P＜0.05); (2) g. 5224 T＞A was significantly associated with body height and head length (P＜0.01); and (3) g.5550 C＞T had no significant association with body weight and body type traits. Allele combination analysis of the two SNPs showed that the diplotype D2 (AT CC) was the dominant genotype combination and its mean body weight and size traits were significantly higher than other diplotypes. These results provide a valuable reference for further research on the function of the bmi1b gene in fish. Additionally, the SNP markers of the bmi1b gene and their dominant genotype show good potential in molecular breeding studies of growth and body type traits in bighead carp.

Abstract:The spotted scat (Scatophagus argus) is a valuable fish species in the southeast coastal areas of China. The female of this species grows at a comparatively more rapid pace than its male counterparts; as such, mono-female fingerlings may be used to improve production. In a previous study, the spotted scat was shown to possess an XX-XY sex-determination system. The truncate Dmrt1b and normal Dmrt1 are located on the X and Y chromosome, respectively; the male-specific Dmrt1 is the candidate sex determination gene. However, the lack of a rapid and accurate sex-specific marker has hampered the establishment of sex control during the breeding process, and investigations of sex determination and differentiation mechanisms in spotted scat. This study designed three pairs of sex-specific primers on Dmrt1/Dmrt1b according to published male and female genomic data on spotted scat using next-generation sequencing technology. The sex-specificity of these primers was validated using the polymerase chain reaction (PCR)-amplification in three male and female fish. All three markers were able to amplify the Y chromosome-specific band or the X and Y chromosome-specific bands. One pair of these primers, the Dmrt1-Marker-4-F/R, are a pair of co-dominant sex-specific primers located on the 3? untranslated region of Dmrt1. A single 593 bp-X chromosome-specific fragment was amplified in female fish using the Dmrt1-Marker-4-F/R primers, while the 593 bp-X and 693 bp-Y were specific fragments amplified in male fish. The Dmrt1-Marker-4-F/R were subsequently tested in three different geographic populations of spotted scat (213 tails in total) from the South China Sea; the results of the genetic sex were consistent with their phenotypic sex. This sex-specific maker confirmed that the spotted scat possesses an XX-XY sex-determination system. It also implied that developing sex-specific markers in the sex determination gene or candidate sex determination gene region is very effective. In addition, this pair of primers was able to amplify shorter length deoxyribonucleic acid (DNA) fragments extracted by a rapid DNA extraction kit. This study establishes a time-effective and straightforward method for rapid genetic sex identification in spotted scat, accelerating the development of sex control breeding in spotted scat. However, the XX fish lack Dmrt1, critical for testicular development and male reproduction; this means it is impossible to reverse the sex of the XX female to a functional neo-male and as such, a genetically all-female fingerling is currently unavailable. As the phenotypic XX-female is irreversible, it becomes a new bottleneck for the sex control breeding of spotted scat. The growth comparison experiment demonstrated that some XY male fish were observed to be growing at a more rapid rate than some of the XX females; the XY spotted scat is sexually reversible. This means that selective breeding and sex control technologies may be combined to produce fast-growing all-male spotted scat in future.

Abstract:This study comprehensively analyzed the complete sequence of the mitochondrial genomes of 13 species in Palinuridae. The results showed that the length of the mitochondrial genome is 15470 to 16105 bp, and the A+T content is 62.63% to 67.11%. Analysis of the ratio of the number of non-synonymous substitutions per nonsynonymous site (Ka) to the number of synonymous substitutions per synonymous site (Ks) showed that the Ka/Ks ratio of 13 protein-coding genes (PCGs) in the mitochondria of ten Panulirus species in Palinuridae were much lower than one; this demonstrated strong purification options. In the analysis of different sites, we found that the nd5, nd4, and rrnL genes were ideal molecular markers. Codon usage analysis showed that the encoded amino acid preferences were similar. This study also adopted more systematic and comprehensive maximum likelihood (ML) and Bayesian inference (BI) methods to construct a phylogenetic tree. The results showed that the Sagmariasus first began to differentiate, and Panulirus clustered into one branch joining the Linuparus/Puerulus as sisters. The Bayesian molecular clock estimation results showed that species in Palinuridae may have originated in the Triassic, and then further differentiated into lobster species with modern characteristics. This study provides reliable molecular markers for the rapid identification of lobsters, and provides a theoretical basis to analyze the genetic diversity of lobsters.

Abstract:Temperature and salinity are common and important environmental factors in aquaculture; the fluctuation of these parameters may cause a large amount of reactive oxygen species (ROS) accumulation in organisms, which can be toxic to cells. As such, antioxidant capacity needs to be increased in order to remove excessive ROS and protect against cell damage. The antioxidant system is composed of enzymatic and non-enzymatic components, which play an important role in antagonizing and removing ROS in aquatic fauna; this system includes superoxide dismutase (SOD) and catalase (CAT). Additionally, malondialdehyde (MDA), one of the products of lipid peroxidation (a reaction related to oxidative stress), is often used as an evaluation index. Palaemon gravieri is a common cheap shrimp in the East China and Southern Yellow seas; there are limited studies on the effects of temperature and salinity on Palaemon gravieri. To understand the effects of water temperature and salinity on Palaemon gravieri, this study investigated the survival rate and antioxidant capacity of Palaemon gravieri under sudden temperature and salinity changes and different heating rates. The sudden change of temperature experiment consisted of one control group (temperature: 22.0 ℃; salinity: 25), four treatment groups (14.0, 18.0, 26.0, and 30.0 ℃; salinity: 25), and three groups for the different heating rate experiments (2.0, 4.0, and 6.0 ℃/d; salinity: 25). The sudden change of salinity experiment consisted of one control group (salinity: 25; temperature: 22 ℃), and four treatment groups (salinity: 15, 20, 30, and 35; temperature: 22.0 ℃). The total antioxidant capacity (T-AOC), and the superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) activities in the hepatopancreas were detected. The results showed that the survival rate had significantly decreased (P＜0.05) only when the temperature increased from 22.0 to 30.0 ℃. At 96 h, the survival rate was ＜50.00%; however, the sudden change in salinity had no significant effect on the survival rate. In the different temperature rise experiments, there was no significant difference in survival rate between the 4.0 ℃/d group and the other two groups; however, there was a significant difference in survival rate between the 2.0 and 6.0 ℃/d groups (P＜0.05), and the half survival temperature was 31.6 ℃ based on the change in the 2.0 ℃/d survival rate. The activities of the three antioxidant enzymes and the MDA content was observed to gradually rise, and this accelerated with an increase to the heating rate. The change of temperature rising rate was found to not affect the maximum SOD and CAT during heating, while the maximum T-AOC and MDA increase with the heating rate. In the sudden change of temperature experiment, the activities of three antioxidant enzymes and the MDA content had initially increased, then decreased to the control level; the exception to this was T-SOD, which did not decrease to the control level at 96 h. In the sudden change of salinity experiment, the T-SOD and CAT activities initially decreased, then increased, and finally decreased. By contrast, the activity of T-AOC and the MDA content initially increased, then decreased; at 96 h, the MDA content was lower than that of the control group. These results indicate that changes in temperature and salinity may cause significant changes in the antioxidant capacity in the body. In addition, changes in temperature had a significant effect on the shrimp survival rate compared to salinity; the effect of temperature increase was more significant than that of temperature decrease. This study advances research on the stress resistance of shrimp and the culturing of Palaemon gravieri.

Abstract:Within a polyculture system of Portunus trituberculatus and Penaeus japonicas (SC), Sinonovacula constricta with low density (SCC₁), medium density (SCC₂) and high density (SCC₃) were raised to construct an integrated aquaculture system of Portunus trituberculatus, Penaeus japonicus, and Sinonovacula constricta, respectively. Monthly samples from the aquaculture system were collected from July to December 2020 to analyze the phytoplankton community structure during aquaculture. Canonical correspondence analysis (CCA) and redundancy analysis (RDA) were used to analyze the relationship between the phytoplankton community structure and environmental factors. The results showed that there were six phyla, 54 genera, and 81 species during aquaculture; species abundance relating to class in descending order was: Bacillariophyta＞Pyrrophyta＞Cyanophyta＞Chlorophyta＞ Euglenophyta＞Cryptophyta. Among them, there were 30 dominant species, mainly including Cyclotella sp., Synedra acus, Stauroneis anceps, Phormidium tenus, Oscillatoria tenuis, and Euglena sp.. Phytoplankton density ranged from 2.23×10⁵ ?28.06×10⁵ cells/L, the biomass was 0.06?21.37 mg/L, the Shannon-Wiener diversity index was 0.90?2.42, the Pielou evenness index was 0.31?0.78, and the Margalef richness index was 1.00?2.08. The diversity of phytoplankton was high and this community was stable. The CCA and RDA results showed that water temperature, transparency, and salinity were the main environmental factors affecting the integrated aquaculture systems of Portunus trituberculatus. When the medium (75.0 kg/hm² ) and high densities (112.5 kg/hm² ) of Sinonovacula constricta were mixed in the polyculture system of Portunus trituberculatus and Penaeus japonicus, there was good diversity in the phytoplankton community. Such diversity may achieve the balanced development of phytoplankton and enhance the anti-interference ability of the culture system. This diversity is beneficial to the stability of the comprehensive polyculture system of the Portunus trituberculatus pond.

Abstract:This article preliminarily discusses the effects of perfluorooctane sulfonate (PFOS) on the acute lethality and metabolism of Macrobrachium rosenbergii juveniles using a hydrostatic toxicity experiment and non-targeted metabonomics. Additionally, a chronic toxicity experiment was used to analyze changes to antioxidant enzyme activities in the gills, hepatopancreas, and gastrointestinal tract of juvenile shrimp under PFOS stress (0.1, 1, 5 ng/mL). The results showed that the 96 h half-lethal concentration of PFOS stress on Macrobrachium rosenbergii was (0.68±0.22) mg/L, and the safe concentration was 0.068 mg/L. Following 24 h of PFOS stress (20 ng/mL), 30 metabolic compounds with significant differences were identified in the gills of juvenile shrimps, 19 significantly differential metabolic compounds were identified in the hepatopancreas, and 24 metabolic compounds with significant differences were identified in the gastrointestinal tract. These metabolic compounds with significant differences were involved amino acid metabolism, fatty acid metabolism, and phospholipid metabolism. Under chronic PFOS stress, different exposure times and concentrations of PFOS may affect the activities of malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and acid phosphatase (ACP) of Macrobrachium rosenbergii. There were also differences in the effects of phosphatase (ACP) activity, the activities of SOD, CAT, and ACP were inhibited, and the MDA content increased with prolonged exposure time. In summary, it is speculated that PFOS can cause oxidative damage to the gills, hepatopancreas, and gastrointestinal tissues of juvenile shrimp, it also affects the physiological metabolism of Macrobrachium rosenbergii. The results provide basic data and a reference to explore the toxic effects of PFOS on aquatic organisms.

Abstract:The effects of herbicide pollution on the marine environment and aquatic product quality and safety has been of great concern. To explore the effects of metolachlor pollution on shellfish cultivation in the Yellow River Delta, the effects of different mass metolachlor concentrations on gill and hepatopancreas antioxidant enzyme activities and tissue structure of Mactra veneriformis were investigated. Additionally, the tissues at different times during the exposure and elimination phases were determined. Superoxide dismutase (SOD), catalase (CAT) activity, variations in malondialdehyde (MDA) content, and changes to the microstructure of tissues were observed. The results showed that metolachlor induced or inhibited anti-oxidase activity under differing metolachlor concentrations. It was found that 10 μg/L of metolachlor significantly increased SOD activity in gill tissue, and different concentrations of metolachlor inhibited CAT activity in the gill and hepatopancreas. Metolachlor at 0.5 and 2.5 μg/L caused irreversible oxidative damage to SOD and CAT in the gills; the SOD and CAT activities in the gills of the 10 μg/L metolachlor concentration group was restored to the level of the control group during the elimination phase. The SOD and CAT activities in the hepatopancreas of the three concentrations groups were restored to or close to the level of the control group during elimination phase. Compared with SOD, the CAT activity was more susceptible to exogenous stimulation and was inhibited; this may be related to the sensitivity and mechanism of action of the two enzymes. After eliminating drug stress, the MDA content in the gills and hepatopancreas of all concentration groups had returned to or was lower than that of the control group. This suggests that the effects of metolachlor stress on lipid peroxidation in the gills and hepatopancreas of Mactra veneriformis may be reversible. Metolachlor stress induced gill filament enlargement, ciliary shedding, epithelial cell damage, and digestive canal damage; the dose-time effect of two types of tissue damage was evident. However, the effect of drug stress on antioxidant enzymes in tissues did not exhibit a significant dose-effect; this does not correspond to tissue structure damage. It is speculated that there was insufficient damage caused by drug stress to breakdown the antioxidant enzyme system. Different concentrations of drug stress activated various antioxidant enzymes to maintain the physiological balance of the body; this aspect requires further investigation. The results of this study offers a reference for the risk assessment of marine ecosystems and and achieving a controllable level of quality in shellfish aquaculture in tidal areas.

Abstract:Free-living zooxanthellae, much like symbiotic zooxanthellae, contribute to maintaining the health of the coral community. Previous studies have shown that Symbiodinium sp., a free-living zooxanthellae, exhibits different responses to various phosphate concentrations in terms of growth and alkaline phosphatase activity. To understand how Symbiodinium sp. responds to dynamic changes in dissolved inorganic phosphorus (DIP), we carried out comparative analyses on the transcriptome of this dinoflagellate under two different initial phosphate concentrations in 0, 5, and 10 d. Initial phosphate concentrations of 0.15 and 35 μmol/L were designed based on the phosphate concentration of an F/2 medium typically used in laboratory culture and a low average phosphate concentration of the East China Sea in recent years, respectively. The de novo assembly results showed that 231 642201 Transcripts and 80955 Unigenes were obtained; a total of 4407 (5.44%) Unigenes were co-annotated in the NR, gene ontology (GO), Kyoto encyclopedia of genes and genomes (KEGG), evolutionary genealogy of genes: non-supervised orthologous groups (eggNOG), SwissProt, and protein families (Pfam) databases. In addition, 27 236 (33.64%) Unigenes had significant matches in the NR database. All Unigenes annotated in the NR database were selected for annotation in the GO database. As such, a total of 23998 (29.64%) Unigenes were mapped into three categories: molecular function, cellular population, and biological process. Among the annotations in the GO database, there were 13 sub-categories of molecular functions, 16 sub-categories of cellular components, and 19 sub-categories of biological processes. The eggNOG functional analysis results showed that 45387 (56.06%) Unigenes were divided into 25 categories according to their functional characteristics. The largest category was post-translational modification, protein turnover and chaperone (3704, 8.16%), followed by signal transduction mechanism (3272, 7.21%), translation, ribosomal structure and biological development (2091, 4.61%), extracellular structure (168, 0.37%), nuclear structure (78, 0.17%), and cell movement (24, 0.05%). To obtain the differentially expressed genes related to phosphorus utilization, transcriptome data from five experimental groups were compared and analyzed. The results suggest that there were three phospholipase A2 genes, two phospholipase B genes, one phospholipase C gene, three phospholipase D genes, two alkaline phosphatase, genes, four acid phosphatase genes, three inorganic phosphate transporter genes, two sodium-dependent phosphate transporter genes, and three mitochondrial phosphate transporter genes that were differentially expressed. According to the genetic expression profile of the differentially expressed genes, it was hypothesized that the free-living Symbiodinium sp. may continue growing under low phosphorus stress by enhancing its ability to transport inorganic phosphate into cells and utilizing organic phosphorus via phosphatase. This study improves the current understanding on the survival mechanism of zooxanthellae in oligotrophic seas. The findings pave an avenue to uncover the molecular regulation mechanism of Symbiodinium sp. in response to different phosphate concentrations.

Abstract:Laizhou Bay is located in the southern part of the Bohai Sea, and is one of three major bays in the Bohai Sea. Laizhou Bay contains many species of crabs and is an important spawning and feeding ground for commercial crab species such as Portunus trituberculatus and Charybdis japonica. In recent years, the ecosystems and marine living resources in Laizhou Bay have been greatly affected due to the overexploitation of fisheries. Compared to the severe decline of economic fish resources, the decline in crab resources has been relatively slow, and the importance of these crabs in the ecosystem has been gradually increasing. Investigating the interannual variation of crab community structure and its influencing factors in Laizhou Bay provides a scientific basis for the rational utilization of crab resources. This study reports on the interannual variation and influencing factors of the summertime crab community structure in Laizhou Bay, based on bottom-trawl survey data from 2010 to 2019. This includes a description of the species composition, dominant species, biodiversity indices, community structure, and environmental factors affecting crab communities. Of the 16 crab species reported from this area during summer from 2010–2019, 14 occurred in 2011, although this reduced to seven in 2017; there were two to four dominant species per year. The average number of crab species decreased by 0.31 each year; the biomass and mantissa of crabs had initially decreased, then increased. Charybdis japonica and Portunus trituberculatus are the important dominant species in Laizhou Bay, the former being the first dominant species in 10 y and the latter being the dominant species in 8 y. The crab diversity index decreased significantly from 2014 to 2015. Crab assemblages in different years were divided into four groups: A (2010), B (2011, 2014, 2015), C (2012, 2013, 2018, 2019), and D (2016, 2017). The permutational multivariate analysis of variance test demonstrated that the crab community structure significantly differed between the four groups. The similarity percentages breakdown (SIMPER) analysis showed that characteristic species for different community groups were Charybdis japonica, Portunus trituberculatus, and Philyra carinata. The average dissimilarity between groups A and D was the largest (48.45%), and the main discriminating species were Dorippe japonica, Charybdis japonica, and Eucrate crenata. The average dissimilarity between groups A and B was 38.1%, and the main discriminating species were Dorippe japonica, Eucrate crenata, and Hemigrapsus penicillatus. Other discriminating species for different community groups were Heikeopsis japonicus, Raphidopus ciliatus, and Philyra carinata. Redundancy analysis showed that bottom sea chlorophyll, benthos biomass, and the Oceanic Ni?o Index were the key environmental factors affecting the interannual variation of crab community structure. The crab community structure was greatly affected by petroleum in 2011, as a result of the Penglai 19-3 oil spill accident. The strong El Nino event had a significant impact on crab community structure in 2014 and 2015, leading to a significant decrease in crab biomass and biodiversity in Laizhou Bay.

Abstract:This study analyzed the population structure and growth characteristics of chub mackerel (Scomber ja-ponicas) based on its reproductive stocks samples collected in the central East China Sea from March to April in 2021. This analysis was undertaken using otolith interpretation, growth back-calculation, and growth equation fitting. The results showed that there was no significant difference between male and female individuals in the reproductive stock of Japanese mackerel (F=0.376, P=0.54＞0.05). The age structure of male and female was 1?7 years old and the dominant age group was 1?2 years old, accounting for 73.63% of the population. The number of females was more than that of males at three years old and below. For individuals older than three years old, the number of males and females was essentially the same, although the females were lacking in old age individuals. The relationship between fork length and body weight was: W=0.8837×10^–6FL^3.474. A linear functional relationship was the optimal solution for the relationship between fork length and otolith radius; this relationship was FL=184.09R–112.73. The fork length and age data of four models were used to fit three back-calculation models; von Bertalanffy, Gompertz, and Logistic. Among them, the von Bertalanffy equation of the Dahl-Lea model had the lowest AIC and BIC; as such, this model was selected as the best growth equation. The von Bertalanffy fork length growth equation was FLt=427.18 [1?e^{–0.23(t+2.5)}], and the body weight growth equation was Wt=1187.20× [1?e^{(–0.23(t+2.5)}] ^3.47. Following the second derivation test, the age of the inflection point was 2.91 years old, the corresponding inflexion body weight and fork length were 365.03 g and 304.09 mm respectively. These values may be used as an important references for the formulation of Scomber japonicus catch specifications in future.

Abstract:Historically, the chub mackerel (Scomber japonicus) has had stable spawning grounds in the offshore water of Yantai-Weihai, China; these spawning grounds have not received considerable attention in recent years. Data on chub mackerel eggs collected from monthly field surveys carried out from April to September in 2020, was used to establish a generalized additive model based on Tweedie distribution (Tweedie-GAM, generalized additive models). This model was used to evaluate the effects of environmental factors on the abundance of chub mackerel eggs. The spatio-temporal pattern of chub mackerel eggs and major habitat factors was plotted to interpret its optimal spawning habitat using the Kriging interpolation method. The distribution and biological characteristics of zero-year-old chub mackerel were also investigated to interpret their early life history parameters. The results indicate that the spawning period of chub mackerel extends from April to July, predominantly concentrated from late May to late June. The main spawning grounds spanned the area between 121°30′?122°15′ E and 37°30′? 38°00′ N. Surface seawater temperature (SST), anchovy (Engraulis japonicus) eggs abundance, ocean current velocity, and surface seawater salinity (SSS) were significant factors affecting the abundance of chub mackerel eggs, with an explained deviance of 54.6%, 17.8%, 4.0%, and 1.7%, respectively. Suitable spawning habitat in the offshore waters of Yantai-Weihai consisted of areas with an SST between 16.3?21.8 ℃, an SSS between 32.1?32.9, and low ocean current velocity, and high anchovy egg abundance. In conclusion, the offshore waters of YantaiWeihai still provide stable spawning grounds for chub mackerel; it is one of the most important spawning grounds for this population in the Yellow and East China seas, and its spatio-temporal distribution is closely related to environmental factors.

Abstract:Based on the survey data of bottom trawl fishery resources in Zhoushan fishing grounds and adjacent sea areas in spring (April) and autumn (November) from 2016 to 2019, we analyzed the spatial and temporal distribution characteristics of biomass resource density of small yellow croaker (Larimichthys polyactis) in this sea area, and used two-stage generalized additive model to study the environmental factors affecting its spatial and temporal distribution. The results showed that the density of small yellow croaker resources showed obvious seasonal changes, and it was significantly higher in spring than in autumn. The main factors affecting the resource density of small yellow croaker in this sea area are season, water depth and bottom water temperature. Small yellow croaker is mainly distributed in the range of 19 to 66 m water depth and the range of 11?22 ℃. With the increase of water depth, the resource density of small yellow croaker shows an upward trend, and the resource density is the highest near the water depth of 60 m. The resource density showed a downward trend at 16 ℃ centigrade to 20 ℃, and the resource density was high at 12?16 ℃. This result reveals the influence of seasonal variation of water depth and bottom water temperature in the sea area on the density distribution of small yellow croaker resources, and provides basic data for further understanding of its spatial distribution and quantitative management of resources.