Abstract:The national aquatic germplasm resources conservation area of Coilia nasus in the Anqing Section of the Yangtze River ("conservation area" for short) is located at the upper section of the migration interval of C. nasus, with a favorable ecological environment. To understand the current status of C. nasus resources, an investigation was conducted from April to July 2018. The results showed that C. nasus resource densities in the conservation area were (0.09±0.07) ind/(10⁴m³) and (4.46±3.43) g/(10⁴m³), and the dominant body length and weight of C. nasus were 250-300 mm and <50 g, respectively. Generally, C. nasus resource status in the conservation area was not optimistic, and C. nasus miniaturization was observed during the investigation. The temporal characteristics of C. nasus showed that the migration period was from early April to July in the Anqing section of the Yangtze River, and the peak period was from mid May to late June. Furthermore, C. nasus abundance showed an increasing trend in the late migration period. Spatially, C. nasus density in the core conservation area was higher than that in the experimental area. In addition, the gender and development stages of sampling results show that the ratio of males to females was 1.02:1, but the range was larger; the males developed earlier, and females developed later. The main development stage of testes and ovaries were III, and gonad development for stage V began in June. In this study, C. nasus with gastric contents of 6.38% were found. This study documented systematic C. nasus data in the Yangtze River pre-fallow reserve, which will provide an important basis for the recovery assessment of this species and conservation management in the future.

Abstract:DMRT1, an important member of the DMRT family, is mainly involved in sex determination and sex differentiation regulation in animals, but its expression characteristics and function are different in different species. In the present study, we analyzed Chlamys farreri Dmrt1 sequence characteristics using bioinformatics methods; determined Dmrt1 mRNA tissue distribution in adult gonad, adductor muscle, mantle, gill, and kidney tissue using semi-quantitative RT-PCR; and revealed its spatiotemporal expression pattern in C. farreri gonads using quantitative RT-PCR and in situ hybridization. The results showed that the deduced amino acid sequence of DMRT1 contained the conserved DM domain of the DMRT family; its mRNA was expressed exclusively in the gonads, and the mRNA levels in the testes were significantly higher than those in the ovaries, and it was the highest in the testis at the growing stage. Moreover, Dmrt1 positive signals were located in C. farreri germ cell cytoplasm. We suggested that Dmrt1 expression characteristics in C. farreri adult gonads is consistent with that in most animals, and may be involved in regulating C. farreri sex differentiation and testis development.

Abstract:The yellow drum (Nibea albiflora) is an important marine fish and has been cultured widely in Southeast China in recent years. To understand the gene homozygosity of meiotic gynogens of yellow drum, microsatellite markers (SSR) and amplified fragments length polymorphism (AFLP) markers were applied to identify gynogenetic diploid offspring and genetic analyze. The results showed:(1) no paternal specific alleles were found in all 4 SSR loci or amplification loci from five pairs of AFLP selective primers in the gynogenetic diploid family, indicating that all individuals in the gynogenetic diploid family were gynogens; (2) no completely homozygous loci were found in seven SSR loci in either gynogenetic diploid family or normal mating family. The average homozygosity of the gynogenetic diploid family was 0.382, 2.37 times that of the normal mating family (0.161). Homozygous loci in gynogenesis individuals was during 0-6, with their homozygous ratio of 0-85.7%, whereas the homozygous loci in normal individuals was during 0-4, with their homozygous ratio of 0-57.1%; (3) 182 clear bands were amplified from five pairs of AFLP selective primers, of which there were 21 paternal and 16 maternal specific bands. Among the 16 maternal specific bands, ten bands were heterozygous loci, and seven loci in the gynogenetic diploid family showed significant partial separation (P<0.05). The percentage of polymorphic bands in the gynogenetic and normal mating families were 14.7% and 20.3%, respectively; (4) based on SSR and AFLP markers, the gynogenetic diploid family had a higher genetic similarity to female parents than to the normal mating family, whereas the normal mating family had approximately the same genetic distance to both parents. The results showed that the genetic homozygosity of the meiotic gynogenetic diploid family was significantly higher than that of the normal mating family, and artificial induction of gynogenetic development is an effective way to promote gene homozygosity, since it can accelerate favorable homozygous gene fixation, and also accelerate harmful gene elimination; thus, effectively improve breeding efficiency.

Abstract:To understand the community structure and seasonal dynamics of gastrointestinal helminths of native fishes in Lake Chugutso, Tibet, four seasons of sampling investigation were conducted in September (Autumn) and December (winter) 2018, March (spring) and June (summer) 2019. Two native fish species, Gymnocypris waddellii and Triplophysa stewartii, were collected, which were different from the original records. Five different gastrointestinal helminths were found in G. waddellii, including Parabreviscolex niepini, Neoechinorhynchus sp., Alloclonium sp., Contracaecum sp., and Streptacera sp., Their morphological characteristics were described, and structure diagrams of some species were drawn. We found that the gastrointestinal helminth composition of G. waddellii in Chugusto Lake was regimal and most are widespread parasites, where birds play an important role in their transmission. The Shannon-Wiener diversity index for gastrointestinal helminths of G. waddellii was 0.70-1.27. Compared with the species number and diversity index of gastrointestinal helminths in lakes and reservoirs from other regions of China, they were relatively abundant species and showed a high community diversity, although there were fewer native fish species in Chugusto Lake. The Berger-Parker dominance index was 0.38-0.76, and nematodes were the dominant group. The numbers of nematode population dynamics showed certain seasonality:the highest abundance in autumn and lowest in summer, with a decrease in winter, and increase in spring. It is possible that the nematode population dynamics is related to water temperature, number of intermediate hosts, nematode life cycle, and fish host behavior during the breeding period. The infection rates of digenea, cestodes, and acanthocephalans were <10% in four seasons, and the mean abundance was also low. Freezing temperatures and hypothermia in winter may limit the number of intermediate host populations, and result in low infection rates and mean abundance of gastrointestinal parasites. No gastrointestinal helminths were found in T. stewartii, which was possibly related to the differences of gastrointestinal space size, food intake, and fish host habitat. The purpose of this study was to provide a theoretical basis for further understanding the parasite composition and characteristics in Tibet and the coevolution of parasites and fish hosts in the Qinghai Tibet Plateau.

Abstract:To study the physiological performance of Nile tilapia (Oreochromis niloticus) under long term nitrite exposure stress, five different treatments of nitrite concentration groups (control, 0.03, 0.06, 0.12, and 0.23 mmol/L) were set to assess the effects of the physiological, biochemical, metabolic function, and non-specific immune response in blood and liver tissue of juvenile tilapia under 21 days of nitrite exposure treatments. The results showed that the white blood cell count in the blood increased slightly with the increasing nitrite nitrogen concentrations, whereas the red blood cell count and hemoglobin concentration decreased significantly (P<0.05). Serum glucose concentration, alanine aminotransferase, aspartate aminotransferase activities, and K⁺ concentration in juvenile tilapia increased significantly with increasing nitrite nitrogen concentrations (P<0.05), whereas triglycerides, total cholesterol, total protein, Na⁺, and Cl^- concentration, and superoxide dismutase, alkaline phosphatase, and lysozyme activities, and immunoglobulin concentrations showed an inverse trend with increased nitrite nitrogen (P<0.05). The hepatic expression of non-specific immune factors HSP70, Il-1β, IL6, and TNFα mRNA levels was significantly improved by increased nitrite nitrogen concentrations (P<0.05), whereas LYS mRNA expression decreased. The results suggested that long-term exposure of low nitrite nitrogen concentrations (0.06-0.23 mmol/L) could lead to dysfunction of blood physiology, metabolism, and immune response in tilapia, and furthermore the hepatic non-specific immune gene expression could be affected. Data from this study will be useful to further understand nitrite ion toxicity mechanisms in the tilapia, and thereby help to establish a safe range of nitrite nitrogen in tilapia aquaculture.

Abstract:New Zealand black abalone Haliotis iris is an important aquatic species with high nutritional value and a bright shell. Since initial research was found to possibly effectively enrich aquaculture species in China, there has been much scientific interest in this species. Limited studies have been conducted on the tolerance and physiological response of H. iris to desiccation during long-distance transportation, and these studies are important for subsequent experiments and breeding. To investigate H. iris tolerance to desiccation at different temperatures, physiological experiments were carried out in New Zealand in November 2019. Variations in H. iris respiratory metabolism and immunity were monitored. The results showed that the desiccation tolerance of H. iris decreased with higher temperatures. The half-lethal time (LT₅₀) under 4, 10, and 15℃ were 48.80, 33.75, and 23.20 h, respectively. During the experiments, cytochrome oxidase (CCO) activity decreased from 11.45-12.70 U/mg at 0 h to 1.43-1.83 U/mg, the CCO activity of the experimental group with high temperatures decreased rapidly, and the minimum value of CCO activity in each experimental group was significantly lower than that in the control group (P<0.05). However, fumarate reductase (FRD), lactate dehydrogenase (LDH), and nitric oxide (NO) activity increased in the beginning and then decreased. Catalase (CAT) and superoxide dismutase (SOD) only showed synergy in the 4℃ experimental group, and SOD of the other two experimental groups were not activated. Malondialdehyde (MDA) content increased from 2.71-3.01 μmol/mg at 0 h to 8.62-9.10 μmol/mg, the MDA content of the experimental group with high temperatures reached the maximum value early, and the content was significantly higher than that of the control group (P<0.05). The results implied that H. iris could tolerate desiccation by maintaining aerobic respiration and glycolysis to some extent. Thereafter, the metabolic system was disordered, and a large amount of lactic acid was accumulated. Desiccation also lead to the disturbances of immune-related functions, which affected H. iris survival under other combined stresses. This study explored the physiological response of H. iris under conditions of desiccation, and the results provided a basis for further research. Methods to maintain the physiological state of H. iris during long-distance transportation should be investigated in the future.

Abstract:Palaemon annandalei is a small commercial shrimp species in China. Palaemon annandalei is mainly distributed in the Yellow Sea, East China Sea, and western coast of the Korean Peninsula. Since P. annandalei is the dominant macroinvertebrate species in northern Hangzhou Bay, this species plays an important role in marine ecosystem balance in this area. Hangzhou Bay is a traditional feeding and spawning ground for many fishes, such as Collichthys lucidus and Coilia mystus. Palaemon annandalei is also one of the prey items of C. lucidus in nor-thern Hangzhou Bay, and is important for C. lucidus growth and breeding. Based on data from 12 set-net surveys in northern Hangzhou Bay in February, May, August, and November 2018, power function, relative body weight, one-way ANOVA, and covariance analysis were applied in this study to analyze the body length-weight relationships (LWR) and relative fatness of P. annandalei. The results showed that the impact of seasonal changes on P. annandalei body length and weight compositions was statistically significant. Mean body length and body weight decreased from spring to winter, and seasonal changes on P. annandalei mean body length and weight was statistically significant (P<0.05). The condition factor (a) of LWR was highest in summer and lowest in winter, and firstly increased, then decreased from spring to winter. The allometric factor (b) of LWR was highest in winter and lowest in summer, which presented opposite trends to a. Covariance analysis showed that a and b was not significantly different between spring and summer (P>0.05), and all the other seasons had significant differences between each other (P<0.05). The relative fatness of P. annandalei increased from spring to autumn, reaching a maximum in autumn, then decreased to the minimum in winter. A one-way ANOVA showed that relative fatness was not significantly different between spring and summer (P>0.05), and all the other seasons had significant differences between each other (P<0.05). The research indicated that seasonal changes on a and b of LWR of P. annandalei in northern Hangzhou Bay were statistically significant, and the changes on a and b of LWR was mainly affected by predation, fishing pressure, and environmental factors.

Abstract:Length frequency distribution and mean length data are often used to estimate parameters of growth and mortality of fish stocks, as they are relatively easy to obtain from fishery-independent surveys for most fish species and can provide insights into the dynamics of fish populations, especially for data-poor or -limited fisheries. A lack of smaller size classes of fish populations may represent recruitment deficiencies, whereas a lack of larger size classes might indicate high mortality of adult individuals of fish stock. Precise and accurate estimates of population parameters are critical to ensure rational fish stock assessment and management. The performance of a survey sampling design might vary with different size structure indices, including length frequency distribution and mean length. To provide high quality length data for supporting fishery resource assessment and scientific management, the performances of the number of survey stations for estimating Enedrias fangi length frequency distribution and mean length were evaluated using computer simulations based on the original data collected from bottom trawl surveys in October 2016, and January, May, and August 2017 in the southern waters off Shandong Peninsula. The dispersion index (DI) was calculated to reflect E. fangi size composition variability within survey stations to identify the factors that influence sampling efficiency. Large DI values implied that length samples were evenly distributed among all size bins, whereas a DI close to zero indicated all observations were skewed into relatively few size bins. The sum of absolute difference (SAD) and relative estimation error (REE) were used to measure the performances (accuracy and precision) of different numbers of stations in estimating the target size structure indices. The results showed that the E. fangi length frequency distribution DI ranged from 0 to 0.91 in four seasons, whereas the DI of most stations was between 0.75 to 0.91. The number of sampling stations could be reduced so that the sampling efficiency could be improved. In general, SAD and REE showed similar trends, decreasing with sample sizes initially and then becoming stable after certain sample sizes during all four seasons, which implied that the length data estimation precision improved with an increased number of sampling stations. The optimal number of sampling stations varied with target indices. The optimal sample size was 20 stations for estimating length frequency distribution and 30 stations for estimating mean length. This study identified the accepted optimal sample sizes to estimate length frequency distribution and mean length and could provide a technical reference for fishery-independent surveys to estimate the size structure index.

Abstract:The increasing fishing effort of the crab pot fishery in the East China Sea has resulted in considerable pressure on swimming crab Portunus trituberculatus resources. Thus, there is an urgent need to implement conservation measures to release juvenile crabs from fishing pots to increase recruitment. In this study, sea trials were carried out to assess the effect of increasing mesh size on fishing efficiency and analyze the mesh size selectivity of crab pots for P. trituberculatus through a comparison experiment. Additionally, the effect of soak time and available population on the selective properties of mesh size was discussed based on the mixed effect model. The results showed that there were significant differences in P. trituberculatus carapace width (CW) distribution caught between the control pot with 32.0 mm mesh size and experimental pots with 52.3 mm and 59.7 mm mesh sizes. No significant difference in relative fishing power between control and experimental pots was detected according to the model fit of the catch frequency in the SELECT analysis model. The average CWs of P. trituberculatus with 50% probability of being retained (CW₅₀) were 86.9 mm for the pot with 52.3 mm mesh size and 90.9 mm for pot with 59.7 mm mesh size, whereas the selection ranges (SR) of CW were 15.9 mm and 9.2 mm, respectively. The finding that the P. trituberculatus experimental pot CW₅₀ was considerably smaller than the minimum landing size set by Zhejiang Province fishery regulations indicated that it may be impractical to effectively release undersized crabs by simply relying on increased mesh size in crab pot fisheries. The results of the mixed effect model showed that the influence of soak time and available P. trituberculatus population on size selectivity of the pots was not significant in this study.

Abstract:To verify the resistance coefficient used in numerical simulations and experimental models of hexagonal and square opening artificial reefs, an experimental model and numerical simulations were used to measure and calculate the resistance coefficients of the two methods at four different opening rates (γ_ty=0.0625, 0.14, 0.25 and 0.39) in hexagonal opening and square opening artificial reefs with four kinds of flow angles of attack (θ=0°, 15°, 30°, and 45°). The results showed that (1) in both the numerical simulation and the experimental model, the resistance of artificial reef models decreased with the increase in opening rate. The resistance of reef models can be changed by changing the angles of attack. In addition, the artificial reef model resistance reached a maximum at θ=30° at four angles of attack. (2) In both the numerical simulation and the model experiment, when θ=15°, 30°, and 45°, the resistance coefficient increased with an increase of opening rate in an obvious linear relationship, and the resistance coefficient reached its maximum when θ=30°. (3) The relative error of resistance between the numerical simulation and the experimental model resistance ranged from 0.12% to 17.18%, with an average error of 7.43%; the relative error of resistance coefficient ranged from 0.03% to 14.64%, with an average error of 5.26%. The resistance and coefficient of resistance error were below 20%. The correlation coefficients, R, between the experimental model and the numerical simulation for resistance and resistance coefficients were 0.99 and 0.80, respectively (P<0.001), showing a strong correlation. Therefore, it is feasible to use numerical simulation to study the hydrodynamic performance of artificial reefs.

Abstract:Streptococcus agalactiae is an important pathogen associated with humans, animals, and fishes. Recently, it has spread globally, resulting in great economic losses in tilapia industries. The phosphotransferase system (PTS) is regarded as the "nervous system" of bacteria. The effect of the EIIB protein of cellobiose-PTS (cel-PTS) on S. agalactiae virulent strain virulence is limited, but it could potentially effect that of the attenuated strain; however, the specific mechanism is still unclear. Therefore, it is necessary to clarify the expression patterns of virulence-related genes regulated by the EIIB protein. In the previous study, the cel-EIIB gene deletion of the S. agalactiae virulent strain was constructed by homologous recombination technology. In this study, the cel-EIIB gene deletion of the S. agalactiae attenuated strain was obtained using a similar method. Zebrafish were infected with a S. agalactiae virulent strain, attenuated strain, and their cel-EIIB gene deleted strains, respectively. The results showed that S. agalactiae attenuated strain virulence was significantly stronger after cel-EIIB gene deletion, whereas S. agalactiae virulent strain virulence was only slightly reduced. It was confirmed by PCR detection that the deletion of cel-EIIB could cause cel-EIIA of the cel-PTS system, DltR and CiaH of the two-component signal transduction system (TCS), and sodA, cpsD, and cpsG of virulence genes showed opposite expression patterns in virulent and attenuated strains. In addition, the expression of RgfC, DltS, and CsrR of TCS and cspA and pavA of virulence genes were not affected in the mutant of the virulent strain, but up-regulated significantly in the mutant of the attenuated strain. It is speculated that the increased virulence of the S. agalactiae attenuated strain was related to the up-regulation of the expression of these virulence-related genes. To summarize, the EIIB protein may negatively regulate the virulence of attenuated strains by regulating the expression of the above virulence-related genes.

Abstract:Domoic acid (DA) is a shellfish neurotoxin mainly produced by the diatoms of some species of Pseudo-nitzschia and Nitzschia in the ocean. To date, most reports on DA have focused on its effects on mice, humans, birds, and other animals, and have revealed that DA causes neurotoxicity in mammals. Although some studies on invertebrates have been reported, most have only reported the concentration of DA in various tissues of shellfish, which are important top predators. Few studies have reported the toxicological effects of DA on the shellfish themselves. Scallops, as invertebrates, lack adaptive immunity and mainly rely on an innate immune system for defense. Acid phosphatase (ACP) and lysozyme (LZM) are important lysosomal enzymes that are involved in humoral immune responses. Superoxide dismutase (SOD) catalyzes the dismutation of superoxide anions into H₂O₂ and O₂^- (disproportionation) to prevent lipid peroxidation. This process plays a very important role in biological defense. Glutathione, as an antioxidant, exhibits antioxidant effects by scavenging reactive oxygen species and protecting the sulfhydryl (-SH) group in bio-macromolecules. Glutathione S-transferase (GST) can catalyze the binding of GSH to electrophilic intermediate metabolites, thus reducing the toxicity associated with endogenous or exogenous poisons. This process plays an important role in the detoxification system. Therefore, in this study, in order to reveal DA exposure-induced toxicity on the immune and antioxidant system of scallops, the bay scallop (Argopecten irradians) was exposed to different concentrations (0, 10, 50, and 100 ng/mL) of DA and the SOD activity and GSH content in its hemolymph, and the relative expression levels of related genes (Cu/ZnSOD, MnSOD, GST, and ACP), were measured. The results showed that LZM activity significantly increased in the 10 and 50 ng/mL DA-treatment groups. The expression of ACP was upregulated at 6 and 12 h and was significantly downregulated at 24 h. These results suggest that low and medium concentrations of DA could momentarily stimulate the immune responses of the bay scallop. However, SOD activity was inhibited after exposure to 10, 50, and 100 ng/mL of DA (6-24 h exposure), and the relative mRNA expression of Cu/ZnSOD and MnSOD were also regulated. DA may inhibit SOD activity and affect it by disturbing the related mRNA expression at the gene level. Moreover, the GSH content significantly increased, and GST was significantly upregulated following DA exposure, indicating that the glutathione system was involved in resistance against DA toxicity. Generally, DA exposure could inhibit SOD activity. Short-term treatment with a lower concentration can stimulate the immune responses, while long-term treatment at high concentrations would cause immune fatigue. However, the bay scallop could resist the toxicity of DA by increasing the level of GSH in its hemolymph and by expressing GST. Thus, this study preliminarily revealed the effects of DA on immunity, antioxidant capacity, and the detoxification mechanisms of bivalves such as scallops.

Abstract:Small pelagic fishes are an important fishery resource in the Pacific Ocean. Generally, they have the characteristics of a short life cycle, fast growth rate, and high clustering, etc. Their resources fluctuate significantly from year to year and are affected by climate-ocean changes. In this study, the characteristics of the key climate-oceanic indexes, such as El Niño/La Niña-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Kuroshio-Oyashio (KR-OY) and their influence on habitat environment and fish resource variations were reviewed, focusing on six main small pelagic fishes, including saury (Cololabis saira), skipjack (Katsuwonus pelamis), chub mackerel (Scomber japonicus), anchovy (Engraulis japonicus), jack mackerel (Trachurus japonicus), and sardine (Sardina pilchardus). The climate-oceanic changes that directly influence migration distribution and resource abundance of small pelagic fishes and indirectly delay the influence on parental reproduction and spawning, larval and juvenile survival rate, and resource fluctuation were summarized. The review included the following suggestions:(1) the construction of a biomass dynamic model by adding parameters, such as population dynamic processes, fishing mode coefficients, and natural mortality rates based on several climate-ocean indexes to reveal the influence of climate-ocean change on fishery resource quantity; (2) analyzing the effects of large-scale ocean currents and mesoscale vortexes on small pelagic fish based on physical ocean models and spatially coupled hydrodynamics models, combined with other major north Pacific climates such as North Pacific Oscillation (NPO), North Pacific Gyre Oscillation (NPGO), and Arctic Oscillation (AO).