Abstract:Stock assessment and fisheries management need supporting data that can be collected through fishery-dependent or fishery-independent surveys. The main objective of cost-effective fishery-independent survey design is to collect high-quality data with limited survey cost, and optimization of survey design is often conducted to improve the sampling efficiency. In order to compare the performances of different sampling designs in a fishery-independent survey in estimating abundance indices of multiple target species, four fish species with different spatial distributions, including Larimichthy polyactis, Chaemrichthys stigmatias, Enedrias fangi and Conger myriaster were selected as target fish species. Relative abundance data collected from the bottom trawl surveys conducted in the offshore waters of Shandong Province in 2016-2017 were used to simulate the spatial distributions of relative abundance of target species using Kriging interpolation method. It is assumed that the interpolated relative abundance data were the ‘true’ distribution of four target fish species. The simple random sampling (SRS), the regular systematic sampling (SYS_r), the hexagonal systematic sampling (SYS_h), the stratified random sampling with strata defined by depth (StRS_depth), region (StRS_region), and depth and region (StRS_total) were chosen as the potential sampling designs for estimating abundance index of each fish species at different sample sizes from 20 to 200. The relative estimation error (REE) and relative bias (RB) were used to measure performances of different sampling designs. The accuracy change rate (ACR) less than or equal to 10% was set as the standard for determining the optimal sample size. Computer simulation study was used to compare the accuracy and the precision of different sampling schemes in estimating the abundance indexes. The results showed that the estimation accuracy of three sampling methods was different: simple random sampling < stratified random sampling < system sampling. Except for the systematic sampling, estimates of abundance indices of target fish species in other sampling methods were unbiased. The REE values of target species abundance index estimation in systematic sampling fluctuated irregularly with sample size increasing. The ACR was not suitable to determine the optimal sample size for systematic sampling design. The REE for the stratified random sampling was slightly higher than that of systematic sampling, but it showed higher stability. The stratified random sampling was the best sampling method. The stratified random sampling StRS_total could reduce the REE value compared with other two stratified sampling schemes. It was the best stratification scheme. The optimal number of stations for design StRS_total in four seasons could be set at 80. This study also offered references to determine the optimal sampling design for multispecies fishery-independent surveys in other waters.

Abstract:The off-flavor has always been one of the main factors affecting the quality and consumption behavior of aquatic products, which has long plagued aquaculture-related industries. Carrying out researches on the source, accumulation, detection, and prevention and control methods of off-flavour substances geosmin and 2-methylisoborneol (2-MIB) in aquatic animals is of great significance for improving the quality. This paper reviewed the sources of off-flavor coumpounds, including actinomycetes and cyanobacteria, then illustrated the accumulation pathway of off-flavor during culture as well. Recently, there have been different detecting methods to evaluate the content of off-flavor coumpounds in aquatic products. This review compared the physical, chemical and biological treatments to control the off-flavor problem, and in particular, the microbial control and ecological pond management methods are the most promising ways. This review summarized the relevant information to date and provides insights to improve quality of aquatic products and how biological treatment options can be implemented in treatment of off-flavor.

Abstract:Antarctic krill (Euphausia superba) is a key species in the pelagic ecosystems of the Southern Ocean, and is also an important fishing target in China’s distant-water fisheries. A full understanding of its spatial distribution characteristics can provide theoretical support for the sustainable exploitation and conservation of E. superba resources. Based on acoustic data collected by E. superba resource survey in the South Orkney Islands in summer 2018, the survey area was divided into 7 different spatial scales and the geo-statistical method was used to research the spatial heterogeneity of abundance of E. superba at different spatial scales. The result showed that: ① as the spatial scale increased, the nugget and nugget-sill ration gradually decreased, the partial sill and sill decreased first, then increased and went down again, and 40'×40' spatial scale had the biggest values; ② at different spatial scales, the semi-variogram was fitted by different models, spherical model had the best performance at 20'×20' and 50'×50' spatial scales, exponential model had the best performance at 10'×10' spatial scale, Gaussian model had the best performance at 30'×30', 40'×40' and 60'×60' spatial scales. And the fitted models showed the spatial auto-correlation was relatively strong; ③ the spatial structure of E. superba showed that, based on anisotropy, 50'×50' spatial scale had the minimum difference of fractal dimension values, 60'×60' spatial scale had the biggest difference of fractal dimension values. Based on isotropy, 60'×60' spatial scale had the minimum fractal dimension value, 50'×50' spatial scale had the biggest fractal dimension value. It is concluded that the abundance of E. superba in the South Orkney Islands had distinct spatial heterogeneity, a number of factors contributed to this phenomenon, including external factors such as ocean flow fields, the change of nutrient and thermocline caused by the exchange of water masses and internal factors such as behavior character of E. superba.

Abstract:Macroalgae that grow naturally on the artificial rafts of shellfish culture, have attracted much attention due to their high coverage, high biodiversity, and large biomass, as well as the following ecologica side effects of the formation of amphipods such as Gammaridea and Caprellidae, and the microbial on the leaves communities. In order to understand the characteristics of the species composition, distribution pattern and seasonal variation of macroalgae in the mussel raft culture area, the epiphytic macroalgae adhere to the mussel rafts around Gouqi Island in spring (May), summer (August), and autumn (November) of 2018, and winter (February) of 2019 were sampled and analyzed. The results showed that 49 species of epiphytic macroalgae belonged to 11 orders, 20 families, and 33 genera. In terms of seasonal variation, the number of species was the highest in autumn (29 species), the lowest in spring (20 species), with an average of 23 species; the seasonal variation of average biomass was the highest in summer (5529.40 g/m²), and the lowest in autumn (2340.45 g/m²). The annual average value was 3455.06 ±1480.40 g/m²; the horizontal distribution of species number and biomass were gradually decreasing from the inside to outside of the culture zones; the highest index of epiphytic macroalgae diversity (H') was in autumn (2.30). The lowest was in summer (1.87), the annual average was 2.07 ±0.18; there were 13 dominant species in the epiphytic macroalgae community, the highest in autumn (8 species) and the lowest in summer (5 species), with an average of 6 species. The dominant species that existed throughout the year were Jania adhaerens and Hypnea boergesenii; among the dominant epiphytic macroalgae, the maximum and minimum niche breadth occurred in autumn, they were Hypnea boergesenii (2.214) and Sargassum horneri (0.739); the maximum and minimum values of niche overlap occurred in autumn, and they were Sargassum horneri-Gracilaria textorii (0.861) and Grateloupia turuturu-Sargassum horneri (0) respectively. The present study has shown that the existence of large-scale raft culture can prolong the growth period of red algae such as Grateloupia livida and Hypnea boergesenii, and broaden the habitat range of brown algae such as Sargassum horneri, thus changing the community structure of macroalgae in the culture area, which is conducive to maintaining a higher level of annual primary productivity and the production of macroalgae debris in the sea area, and providing new ideas and important scientific basis for the construction of seaweed beds in the process of marine ranch construction.

Abstract:In order to study the effect of light color on behavior response, plasma cortisol and blood biochemical indicators of O. mykiss, light stripes of white, red, yellow, blue and green, were respectively laid at the bottom of the tank center at a intensity of 56.9 lx. In each experiment, 10 healthy and lively fish were placed on the same side of the tank to observe the times of O. mykiss crossing the light curtain in the tank. Each experiment lasted for 1 hour. The number of times of fish passing through the light curtain was observed and recorded every 10 minutes, no matter whether it was the first crossing or repeated crossing. Before each experiment, a control group was carried out, that is, a light stripe was laid without turning on the light, and then experiments were carried out in sequence under white light, red light, yellow light, blue light and green light. The experiment was repeated three times for each light color. Blood samples were collected after the fish were exposed to light for 1 hour. Plasma levels of cortisol, total protein (TP), albumin (ALB), triglyceride (TG), total cholesterol (TC), aspartame aminotransferase (AST) and alanine aminotransferase (ALT) under different light colors were determined by enzyme-linked immune reaction kit (ELISA). The results showed as follows: (1) The number of times of O. mykiss crossing the light curtain under yellow and white light conditions was significantly lower than that of the control group and the other three light colors (P<0.05), there was no significant difference between red light, blue light, green light and control group (P>0.05). (2) The plasma cortisol concentration in yellow light condition was significantly higher than that in control group and the other four light colors (P<0.05), there was no significant difference between the control group and the other four light colors (P>0.05). (3) There were significant differences in TP, ALB, TG, TC, AST and ALT among five light colors (P<0.05). This study indicated that the O. mykiss was more adapted to blue light and green light, and had a certain avoidance reaction to yellow and white light, and the effect of yellow light was the strongest, which was consistent with the concentration of cortisol; the O. mykiss adapted to different light color changes through active physiological regulation. In conclusion, green light could be used in O. mykiss production to reduce the stress response. Yellow light stresses fish and is unsuitable for O. mykiss farming, but could be designed as underwater lamp for fishing or preventing fish from escaping from cage. Long-term experiments should be carried out to study the effects of different light colors on behavior, growth, physiological responses of O. mykiss.

Abstract:Eriocheir sinensis is one of the most widely commercially cultured crabs which is generally cultured in the ponds mainly fed with formula feed, frozen fish and mixture with formula feed and frozen fish. However, high-density pond culture and feeding frozen fish with unstable source and imbalanced nutrition bring many problems such as severe diseases outbreaks and variable quality of crabs, water pollution and so on. Therefore, to study the effect of formula feed and frozen fish on the breeding performance and nutritional status of the crabs, this experiment analyzed the growth performance, gonadal development and nutrient composition of monocultured crabs by continuous sampling, and further compared the final body weight (FBW), weight gain rate (WGR), specific growth (SGR), survival rate (SR) and molting intervals (MI). The results showed that: ① In terms of SR, the formula feed group was significantly higher than those of the frozen fish group, while there was no significant difference in the FBW, WGR, SGR and MI between the two groups. At different molting stages, the boby weight of the formula feed group was smaller than the frozen fish group, and the differences between the two groups after the third molting was significant; the WGR was different between the female and male crabs, and the WGR of formula feed group in the female crab was significantly smaller than that of the frozen fish group after the second molting, while the male crabs in the two stages after the first and fourth molting were significantly larger than those of the frozen fish group. ② The hepatopancreas indices (HSI) were 3.59% and 4.45% in the formula feed and frozen fish groups, respectively, while the gonadosomatic indices (GSI) were 3.20% and 2.25%, respectively; and the HSI and GSI had no significant differences in the two groups. ③ In terms of muscle amino acid content, the total amino acids (∑TAA), total essential amino acids (∑TEAA) and total flavor amino acids (∑FAA) in the formula feed group were significantly smaller than those of the frozen fish group; From the perspective of a single amino acid, the lysine and arginine contents of the formula feed group were significantly smaller than those of the frozen fish group, while the content of proline was significantly greater in formula feed than that in the frozen fish group. ④ In terms of muscle fatty acid content, the highly unsaturated fatty acids (∑HUFA) and DHA+EPA contents of the formula feed group were significantly higher than those of the frozen fish group; In addition, the contents of C16:1 and C18:1n-9 in the monounsaturated fatty acid (∑MUFA) were significantly smaller in the formula feed group than those of the frozen fish group, but in the polyunsaturated fatty acids (∑PUFA), the contents of ARA and DHA of formula feed group were significantly higher than those of the frozen fish group. This study has shown that the formula feed group is close to the frozen fish group in the growth performance and muscle quality of the Chinese mitten crab, but the gonadal development and SR of the crabs fed with formula feed are better than the frozen fish group under the monomer culture conditions. So formula feed has more development advantages in aquaculture.

Abstract:Salinity is an important environmental factor that affects the physiological activities of fish. In order to investigate the changes of gene expression level in Nibea japonica, an economic marine fish treated by acute salinity stress, the transcriptomes of muscle tissues under different salinity conditions were sequenced based on the Illumina HiSeq^TM 2500 high-throughput sequencing platform and the data were analyzed by bioinformatics tools in this study. A total of 46 379 598 (5.27 Gb), 36 130 844 (4.87 Gb) and 38 715 820 (5.53 Gb) clean reads were obtained in the high salinity group (HS), the low salinity group (LS) and the control group (C), respectively. 91 667 transcripts were assembled and 61601 unigenes were spliced after removing redundancy. Compared with the control group, 2 230 and 1 377 differential expression genes (DEGs) were up-regulated, while 1 959 and 2 447 DEGs were down-regulated in the high salinity group and the low salinity group, respectively. Six DEGs were randomly selected for quantitative real-time PCR (qRT-PCR), and the results were consistent with the RNA-seq. 21 and 41 ion channel genes were obtained from all significant DEGs in high salinity group and low salinity group, respectively. Fourteen of 15 shared genes showed the same trend. By contrast, 6 and 10 ion transporter genes were acquired from the significant DEGs of two groups. The results of GO functional enrichment showed that the DEGs were significantly enriched in proteasome and complement activation, and KEGG pathway enrichment suggested that the DEGs were enriched in binding, catalytic activity, signal transduction and catabolism. The results indicated that the salinity adaptation of N. japonica is a complex process involving multiple tissues and genes. Besides the change of ion channels and ion transporters, the change of salinity also affects the protein degradation and immune system. The findings will provide important references for further study on the regulation mechanism of salinity adaptation and breeding of N. japonica.

Abstract:Aeromonas hydrophila is one of the main opportunistic pathogens in aquaculture. Quinolones are one of the main fishery antibiotics. However, the frequent and unreasonable use of quinolones has led to the emergence of bacterial resistance. The research on the molecular characteristics of quinolone resistant plasmid of Aeromonas spp. is still in the initial stage. In this study, to investigate the relationship between endogenous plasmids and quinolone-resistant phenotype of A. hydrophila isolates, a plasmid termed pAhW39, from a quinolone-resistant A. hydrophila strain W39 which was isolated from a diseased Megalobrama amblycephala from a fish farm in Xiantao, Hubei Province, was cloned and characterized. pAhW39 was 6 739 bp long, had a GC content of 46.13%, and contained four putative open reading frames (ORFs) (nspv, nspV-like, repB and qnrS2). The GC content of pAhW39 was lower than the GC content of the currently published A. hydrophila chromosomal DNAs which ranged from 60.1% to 62.0%, suggesting a possibility that the plasmid pAhW39 might originate from other strains through the horizontal transfer of plasmids. nspV and nspV-like encoded type II endonucleases NspV and NspV-like, respectively. The repB encoded a replication protein RepB and qnrS2 encoded a quinolone resistance protein QnrS2 which usually confers increased resistance to quinolones. pAhW39 was stable in A. hydrophila strain W39 in the absence of selective pressure. Compared with plasmid pAhW39 elimination strain W39-C, the minimum inhibitory concentrations of nalidixic acid and ciprofloxacin against strain W39 were increased 16-fold and 8-fold, respectively, indicating that the plasmid pAhW39 containing qnrS2 might mediate the resistance of strain W39 to quinolones. Comparative genomics analyses revealed that the plasmid pAhW39 had 99.9% DNA sequence identity over its whole length with the plasmid pAER-e58e from Aeromonas sp. strain ASNIH2 isolated from wastewater from a hospital in Maryland, USA. The result implied that plasmid pAhW39 (or pAER-e58e) was widespread and stable, and reminded us that the existence of plasmid-mediated quinolone resistance in Aeromonas spp. in fish might cause a more widespread dissemination of resistance to quinolones in aquaculture. This should attract more attention.

Abstract:As an important apoptosis-regulating gene, Bcl-2 gene plays an important role in endogenous apoptotic pathways. In this study, Pinctada fucata martensii Bcl-2 gene (Pm Bcl-2-like) was cloned by rapid-amplification of cDNA ends (RACE) technology and its characteristics was analyzed by bioinformatics methods. The expression levels of PmBcl-2-like in different tissues, development stages and by immune stimulation were analyzed by quantitative real-time PCR (qPCR). The results showed that the full length of PmBcl-2-like cDNA was 2180 bp, the length of open reading frame was 1650 bp, and it encoded a total of 549 amino acids and the molecular weight was 21.62 ku. Domain prediction showed that PmBcl-2-like contained BH1-4 domains which are typical domains of Bcl-2 family. Multiple sequence alignment and phylogenetic tree analysis showed that PmBcl-2-like was highly conservative and had high similarity with Bcl-2 of other species in phylogenetic tree. Quantitative real-time PCR results showed PmBcl-2-like was expressed in all the tested eight tissues of P. fucata martensii, with the highest expression in the gill, followed by the gonad, and with the lowest expression in the mantle central. At different developmental stages, the expression of PmBcl-2-like was higher in the embryonic stage and the highest in the fertilized egg stage. After being stimulated by LPS, the expression of PmBcl-2-like reached the maximum at 24 h, and then decreased to the minimum at 72 h, with the maximum being about 2.5 times of the minimum. After PGN stimulation, the expression of PmBcl-2-like reached the highest at 6 h and the lowest at 48 h, and the highest was about 7.28 times of the lowest. After Poly: IC stimulation, the relative expression reached its maximum at 3 h, and decreased to its minimum at 12 h, and the maximum was 6.49 times of the minimum. This study suggests that PmBcl-2 -like may play an important role in the development and immune defense response of P. fucata martensii.

Abstract:China owns the largest eel culture industry in the world. Since 1990s, "mucus sloughing and hemorrhagic septicemia disease" has become one of the main epidemic diseases of cultured juvenile eel, with typical symptoms of "mucus sloughing", "red head" and "hemorrhagic septicemia", and high morbidity and mortality. The disease could also be found in adult eels with typical symptoms of "hemorrhagic septicemia", resulting in a huge number of deaths, and enormous economic losses to the industry. Cultivation experience showed that the disease might be caused by viral pathogen. We had Anguillid herpesvirus 1 (AngHV) isolated from the clinical samples of the disease. Further pathogenicity and epidemiological analysis showed that AngHV was the pathogenic agent of eel "mucus sloughing and hemorrhagic septicemia disease". A rapid and sensitive detection method for AngHV is of great significance for the early diagnosis, prevention and control of AngHV disease. Real-time fluorescence quantitative PCR (qPCR) method has been widely used in pathogen detection. To establish SYBR Green Ⅰ qPCR method for detection of AngHV, the sequence of AngHV ORF49 was amplified by PCR and cloned into pET-32a vector to construct the standard plasmid pET-32a-ORF49. Primers were designed according to ORF49 sequence, and a SYBR Green Ⅰ qPCR method was developed for AngHV detection using serially diluted standard plasmid as templates, then the sensitivity, repeatability, specificity and application effects of the method were evaluated. The results showed that the cycle threshold value(C_T) of the qPCR assay had a good linear relationship with the copy number of the standard plasmid, the correlation coefficient (R²) of the obtained standard curve was 0.999, and the amplification efficiency was 100.855%. The melting curve analysis showed that there was only one melting peak with Tm values of 88.34-88.95 ℃. Amplication specificity analysis indicated that the method could specifically detect AngHV, and had no amplification of Cyprinid herpesvirus 3 (CyHV-3), Rana grylio virus (RGV) and Eel iridovirus (EIV). The coefficient of variation within and between groups was less than 1% and 2%, respectively, which indicated that the method was repeatable. The qPCR method could detect a minimum of 10 viral copies with higher sensitivity than conventional PCR method which has detection limit of 1 000 copies. Application analysis indicated that AngHV could be detected in the main tissues of AngHV infected Anguilla anguilla with 5.70×10⁷ copies in gill, 1.91×10⁶ copies in mucus, 1.31×10⁶ copies in fin, 3.31×10⁴ copies in heart, 1.75×10⁴ copies in intestine, 1.25×10⁴ copies in kidney, 6.51×10³ copies in skin, 6.26×10³ copies in muscle, 6.13×10³ copies in brain, 2.48×10³ copies in liver and 1.81×10³ copies in spleen. The amounts of virions in gills, fins and skin mucus were significantly higher than those in other tissues. The positive detection rate of the qPCR method for the 25 suspected Anguilla spp. "mucus sloughing and hemorrhagic septicemia disease" samples was 96%, while that of the conventional PCR method was only 76%. In conclusion, the established SYBR Green I qPCR method has high sensitivity, strong specificity and good repeatability, and can be used for rapid and quantitative detection of AngHV, which would be helpful for the prevention and control of Anguilla spp."mucus sloughing and hemorrhagic septicemia disease".

Abstract:UV sex-chromosome system exhibits unique evolution and genetic features during the haploid stage of the life cycle in some algae and bryophytes. In this study, a bacterial artificial chromosome (BAC) library was constructed from the female gametophytes of Saccharina japonica. The library, contained a total of 31 872 BAC clones with an average insert size of 115 kb as revealed by pulsed-field gel electrophoresis. It covered 6.57-fold of the estimated haploid genome equivalents. To evaluate the quality of this library, one pair of primers was designed on the basis a female-specific marker FRML-1488 to screen positive BAC clones harboring this specific marker by PCR amplification. Four positive clones were obtained, demonstrating that the possibility of selecting any gene from the library was 99.86%. A randomly selected BAC clone (638-C12) was sequenced by Roche454 pyrosequencing method. Total 10 contigs were assembled and the gaps were further filled by PCR amplification. Finally, a full-length fragment was assembled with the length of 86 996 bp. It was located in Scaffold285 of the kelp genome by blast, and it accounted for 22.4% of this scaffold in length. This well-matching result pointed out that the insert in BAC clone 638-C12 was from the kelp genome. Sequence analysis showed that a large number of repetitive sequences including microsatellites, satellites and retrotransposons (Copia) were found upstream of the female-specific marker FRML-1488. Since sex-determining region (SDR) is characterized by high proportion of repetitive sequences associated with non-combination, the insert of BAC clone 638-C12 might be involved in the SDR of S. japonica U chromosome. This study is the first report on the application of BAC library in map-based cloning of sex-related sequences in S. japonica, which contributes to comprehensive understanding of sex chromosome structure and the sex determination mechanism of this kelp.

Abstract:The increase of canvas area not only promotes the net mouth opening, but also increases the overall resistance of the net. In order to understand the relationship between canvas area and net performance, 7 groups for model test were designed, the ratio of canvas area/net resistance (K) was used as an indicator for net performance. The 7 groups were divided into two parts according to research objective, (1) 5 groups within 7 groups were chosen to study the effect of the canvas areas on net performance, which the canvas areas increased gradually, but the canvas width/length ratio was similar; (2) 4 groups within 7 groups were chosen to estimate the effect of the canvas width/length ratio on the research result of part (1). The results show that: when the current speed was 0.24 m/s, the K rose with the canvas area increasing, but the rise rate slowed down gradually, as the canvas area was close to 0.288 m², the K was close to the peak; when the current speed was more than 0.4 m/s, the K was a constant, and the correlation between k and canvas area was not obvious. So when the canvas area was close to 0.288 m², the matching coefficient (P) of canvas area and net size was close to 0.072, the stow net can keep good performance under different current conditions. The effect of aspect ratio of canvas on K trend was not obvious. The power function relation was found between net resistance with canvas area and current speed, and the empirical formula was expressed as F=334.32×A^0.5×V ^1.61. As a common sense, the matching coefficient (P) and net resistance were affected by multiple factors, not only by canvas area and current speed. So the results were suitable for using in similar condition. If the conditions were different obviously, the coefficient and formula should be modified. The above findings can be used for the performance improvement of canvas spreader stow nets.

Abstract:Gonatopsis borealis is a cold water cephalopod species which is extensively distributed in the northwest Pacific Ocean between 37°-55°N, and is rich in resources with a good development potentiality. The beak is an important feeding organ of cephalopods, pigmentation is one of the important changes in the growth of the beak, and its pigmentation characteristic is an important material to study the feeding ecology of cephalopods. In this paper, the characteristics of pigmentation stages in the beak were studied, which would provide the basis for the study of fishery ecology of G. borealis. We measured and identified the samples by basic fishery biology data including mantle length (ML), body weight (BW), sex and sexual maturity, divided the pigmentation stages based on Hernández-García's method, researched whether there were gender differences in pigmentation stages, and established the growth models between the beak pigmentation and ML, BW, sexual maturity and the external morphological parameters of 268 beaks of G. borealis collected in the Northwest Pacific Ocean from September to November of 2018 by Chinese jigging fishing fleets. The results showed that the stage 6 and 7 were the dominant pigmentation stages accounting for 91.11% of the total samples. There was no significant sexual difference in the relationships between beak pigmentation stages and ML, BW and morphological parameters including Upper hood length (UHL), Upper crest length (UCL), Upper rostrum length (URL), Lower hood length (LHL), Lower crest length (LCL) and Lower rostrum length (LRL) of beaks based on analysis of covariance (ANCOVA). The correlation analysis indicated that the pigmentation degrees of beak were highly significantly correlated with ML and BW. The beak pigmentation degrees had a positive relationship with ML, BW and morphological parameters of beaks, and the coefficient of association were 0.9800, 0.6715, 0.7615, 0.9165, 0.9188, 0.6772, 0.8071 and 0.9153, and there was also a positive relationship with sexual maturity. The pigmentation degrees of beak of G. borealis had a positive relationship with ML, BW, sexual maturity and morphological parameters of beaks, and increased with the growth of individuals and seemed to reach the maximum from September to November.

Abstract:In recent years, China has been increasing the input of fishery technology, but the performance of China's fishery technology efficiency and whether the structure of fishery factor input is reasonable deserve attention. In this paper, CD stochastic frontier production function was used to analyze the structure of fishery factor input and fishery technical efficiency through 232 sets of panel data from 29 provinces from 2012 to 2019. The results showed: ① the flexibility of labour, aquaculture area, the vessel power and fish fry showed a trend of increase, but in addition to the fish fry, the contribution of labour, aquaculture area, and the vessel power are negative, moreover the input of labour, aquaculture area, and the vessel power are excessire; ② China's fishery returns to scale are low, the utility of returns to scale has not yet been realized, the production efficiency is low, and the input of fishery technology factors is insufficient; ③ China's fishery technical efficiency is lower than that of other agricultural industries, but the fishery technical efficiency shows an increasing trend. The technical efficiency of coastal areas is greater than that of inland areas. Research shows that low technical efficiency of fishery is correlated with factor input synergy, and unreasonable factor allocation is the main reason for low technical efficiency, so factor input synergy can promote the improvement of production efficiency.

Abstract:This research was conducted to explore the population dynamics and stock status of Saurogobio dabryi in the lower reaches of the Jialing River. A total of 256 individuals of S. dabryi were collected in the lower reaches of the Jialing River (Hechuan section) from 2015 to 2016. Growth parameters and stock status of S. dabryi population were estimated by using the Fista II Software. The length-weight relationship was W=7.5×10⁻⁵×L^2.58 (R²=0.7311, n=256), and the Von Bertalanffy growth equation was fitted as L=173.81[1−e^{−0.73(t+0.23)}], where L_∞=173.81 mm, K=0.73, t₀=−0.23. The exploitation rates of the S. dabryi population were 68% and 69% in 2015 and 2016 respectively, exceeding the theoretical maximum exploitation rate (42%), based on the Yield per Recruit model (YPR), which indicated that the S. dabryi population was overexploited. The S. dabryi in the lower reaches of the Jialing River demonstrated negative allometric growth pattern, and r-selection life strategies. Recruitment to the population mainly occurred from April to June, and was unimodal. The population was dominated by younger and small sized individuals. Abundance had been declining due to overfishing and reduction of natural recruitments to the population.

Abstract:Aquaculture is one of the important ways to utilize alkali-saline water or land effectively. It is important to clarify the physiological and molecular mechanisms of fish alkali-saline adaptation, which is the prerequisite to breed new varieties for aquaculture in alkali-saline water with middle or high alkalinity. This paper summarized the advances of research of physiological and molecular mechanisms in several representative fish species inhabiting alkali-saline lakes around the world, including tissues micro-changing, plasma iono-osmoregulation, ammonia nitrogn metabolism, acid-base regulation, hormone regulation and genome adaptations. Based on these latest advances, we consider that the alkali-saline tolerant fish have evolved characteristics of strong phenotypic plasticity, complexity and integrity due to living in extreme hypersaline-alkali habitats for a long time. It is suggested that the research of correlation exploration should be extended to the determination of causality at gene level, through systematically integrating the information of physiology, phenotype, behavior and various omics, which will promote the research of the mechanisms of alkali-saline adaptation molecularly and evolutionarily for alkali-saline tolerant fish in the future.