Abstract:To explore differences in the Coilia mystus populations of the Yangtze Estuary and its adjacent waters, 240 individuals were collected from four populations of Lyusi (Ls population), Chongming Island in Shanghai (Cm population), Zhoushan (Zs population) and Wenzhou (Wz population). Twenty-one morphological parameters of the sagittal otolith were measured by otolith measurements and the otolith frame method. Twenty morphological indices transformed from the 21 morphological parameters were analyzed by multivariate statistical analyses. Non-parametric tests showed that there were significant differences in 14 of the morphological indices among the 4 populations. Principal component analysis constructed 7 principal components of the otolith morphological characteristics, with a cumulative contribution rate of 81.79%. The overall shape of the otoliths was similar among populations, and the differences were mainly reflected in the local frame morphological indices. The discriminant equation of the 4 populations was constructed using the 9 parameters with the greatest contribution rates. The discriminant accuracy of the Wz population was highest (96.7%), followed by the Cm (66.7%), Ls (60.0%), and Zs populations (58.3%). Cluster analysis showed that the Cm and Zs populations were closest, followed by the Ls population, and the Wz population had the furthest distance. The shape of the sagittal otolith in the Cm population was similar to the Zs and Ls populations, and there were significant differences in the otolith morphology of the Wz population versus the other 3 populations. These results indicate that Wz is an ecological population. Therefore, the differences in otolith morphology between populations of C. mystus with short-distance migratory habits are related to their geographical distribution. Otolith shape varied little among geographically close groups with similar habitats but was larger in groups with geographic barriers and genetic differentiation. Variability in the size of the otolith is related to the degree of geographic isolation.

Abstract:Mandarin fish (Siniperca chuatsi), which are economically important in China, have a unique predatory habit. They feed on live bait and are only sensitive to moving targets, but have diverse and complex predatory behavior. This study aims to understand the unique predatory behavior of mandarin fish via the visual and lateral line sensory systems. Predatory behavior was studied using a high-speed camera and sensory inhibition techniques. Four experimental groups (vision only, lateral line sensation only, no vision or lateral line sensation, and control group) were created, and the predatory behavior was analyzed. Compared to other predatory fishes, the predatory behavior of mandarin fish is unique and complex. Four main movements were observed during predation:direct strike, tracking, caudal peduncle bend, and whole-body bend. The different predatory movements formed five patterns:direct-attack, track-catapult, track-deviate, catapult, and deviate types. The direct-attack, track-catapult, and catapult types were regulated by vision, while the track-deviate and deviate types were regulated by lateral line sensation. When both vision and lateral line sensation were available, the predation behavior was simplified but became complex and diverse when only lateral line sensation was available. Various mandarin fish predatory behaviors may account for its unique feeding habits and ensure a high success rate. These results allow a better understanding of the special predatory behavior of mandarin fish and provide a theoretical basis for improving the production process.

Abstract:Takifugu rubripes is a fierce, benthic, carnivorous, and stenothermic fish species. With global warming, physiological reactions such as stress are more common, due to rising temperatures in factory cultures, which result in declined breeding benefits. Stress can disrupt intracellular homeostasis and cause changes in other physiological and immune responses. Temperature is an important environmental variable that affects immune responsivity in fish. Among temperature stressors, heat stress is considered the most basic mechanism of cell protection in animals. Increased body temperature due to changes in the environmental temperature is a natural physiological response in fish, so it is practical to study the response of the vital organs of fish under heat stress. Taurine promotes fish growth, improves immune ability and stress resistance, and is closely related to the physiological and nutritional status of aquatic animals under stress. To explore the relationships between taurine and acute heat stress tolerance in fish, three diets of 0% (T1, control), 1.0% (T2), and 5.0% (T3) taurine were fed to T. rubripes[initial body weight:(32.28±0.20) g] for 56 d. At the end of the breeding experiment, a high-temperature[(28±0.3)℃) stress test was conducted for 30 min, and the three experimental groups were analyzed for their liver transcriptomes by RNA-Seq. The differentially expressed genes (DEGs) were screened with a threshold criterion of P<0.05. In total, 167 DEGs were identified under acute heat stress among which 111 genes were up-regulated and 56 genes were down-regulated. Gene ontology (GO) enrichment analysis showed that most of the DEGs in the T3 vs T1 group were significantly enriched in the proteolysis, serine-type peptidase activity, serine-type endopeptidase activity, serine hydrolase activity, endopeptidase activity, L-amino acid peptidase activity, and peptidase activity pathways. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that most of the DEGs were involved in cell adhesion molecules and neuroactive ligand-receptor interaction pathways in T2 vs T1, while most of the DEGs were involved in the neuroactive ligand-receptor interaction and metabolic pathways in T3 vs T1. These results suggest that dietary taurine supplementation can change the temperature response of T. rubripes under acute heat stress and that the response varied with the amount of taurine. Real-time PCR (RT-PCR) was used to verify the transcriptome sequencing results, and the results showed similar expression patterns for 3 different genes in the RNA-seq and RT-PCR data. This indicates that the gene expression results of the transcriptome sequencing are credible. This study provides foundational information to further studying the effects of dietary taurine supplementation on the acute heat stress response in T. rubripes. This study also serves as an indicator of taurine's ability to resist heat stress.

Abstract:We systematically studied the reproductive characteristics and gonadal development of the threatened freshwater mussel Solenaia oleivora from the Huaihe River. This species is not only threatened, but it also holds important economic value in China. The results indicate that this mussel has a short-term incubation and spawns from March to early June, peaking from March to May. The youngest gravid female investigated was 2 years old. During the reproductive period, the female oocytes mature rapidly and release several times in one reproductive cycle. The inner and outer gills of the female could be utilized as the marsupia for fertilized egg incubation, which belongs to Tetragenae in Exobrandae. The total number of glochidia in the gravid female mussel is estimated to be 1.349 to 4.021 million for a single egg release event. Based on female gravidity and the ovary tissue sections, we confirmed that S. oleivora could release eggs several times in one reproductive cycle. There were no significant differences in the growth of males and females. The development of the ovary and spermary were synchronous and can be divided into the proliferating, growing, maturing, releasing, and recovering stages. Histological sectioning and scanning electron microscopy (SEM) showed that the oocytes are linked to the follicular wall through a stalk approximately 5 μm in diameter. There was no cell membrane on the surface of early oocytes < 20 μm in diameter, but a yolk-membrane was observed on the surface of late oocytes when the diameter was > 40 μm. SEM showed that the sperm had a long flagella (~40 μm long) and a bullet head and neck with a maximum width of~2 μm. There was a round micropyle (1 μm in diameter) on the surface of the fertilized egg, suggesting that sperm cannot completely enter the oocyte for fertilization. The results of this study provide a foundation for the artificial breeding of this mussel species in China and serve as an important reference for the breeding and conservation of other threatened or endangered freshwater mussels.

Abstract:Conger myriaster is a fish of high economic and nutritional value in China. It is distributed throughout the Yellow Sea, East China Sea, and Bohai Sea. There have been few studies of this species, focused mainly on fishing, feeding ecology, resource distribution, breeding, and genetics. To explore the relationships between the morphological traits and body weight of C. myriaster, the body weight (Y) and 11 morphological traits were measured, including the total length (X₁), snout-vent length (X₂), tail length (X₃), head length (X₄), snout length (X₅), eye length (X₆), head length behind the eye (X₇), length before the first dorsal fin (X₈), trunk length (X₉), head width (X₁₀), and the interorbital space (X₁₁). The direct and indirect effects of the morphological traits on body weight were studied by correlation and path analyses. A stepwise regression method was used to establish a regression equation in which the morphological traits were independent variables and the body weight was the dependent variable. The best curve models of 4 morphological characters and body weight were obtained by curve fitting. There was a positive correlation between the morphological traits and body weight of C. myriaster, and the correlation coefficients reached extremely significant levels (P<0.01). The correlation coefficient of snout-vent length (X₂) and body weight was the largest (0.970), snout-vent length (X₂) had the largest direct effect on body weight (0.450), and head width (X₁₀) had the largest indirect effect (0.431) on body weight through the snout-vent length (X₂). The direct determinate coefficient of snout-vent length (X₂) on body weight was the largest (0.203) and the largest joint determinate coefficient was for snout-vent length (X₂) and head width (X₁₀) (0.172). The multiple regression equation of the morphological traits and body weigh was Y=-113.859+6.481X₂+49.213X₆+ 11.514X₇+20.145X₁₀ (R²=0.954). The best-fitting models of snout-vent length (X₂), head length behind the eye (X₇), and head width (X₁₀) on body weight were the exponential functions, and the model equations were Y=1.466e^0.287X, Y=1.435e^1.328X, Y=1.970e^1.974X, respectively. The best fit model of eye length (X₆) and body weight was linear, and the equation was Y=-77.460+222.093X. Snout-vent length (X₂) and head width (X₁₀) were the main selective characteristics of C. myriaster, and eye length(X₆) and head length behind the eye (X₇) were auxiliary selective characteristics. These results provide valuable information and a theoretical basis for C. myriaster selection.

Abstract:Black bream (Megalobrama terminalis) is an important economic fish species in the genus Megalobrama in China. Historically, it extensively distributed in many river basins. However, overfishing and pollution had a great impact on its germplasm resources. Nowadays, the fish species exists only in the Qiantang River, Jinshahe Reservoir and Heilong River. The black bream population in the Heilong River is endangered, only dozens of individuals of black bream can be found per year near Fuyuan City (134°28' E, 48°37' N), which is located in Heilongjiang Province. Our team successfully achieved the artificial propagation of the species in 2018 and 2019. To improve artificial propagation and seedling cultivation techniques, information on embryonic and early larval development is required. In this research, the morphological characteristics and development time for embryonic and early larval development of black bream in the Heilong River were observed and described. The chorion-free fertilized eggs were cultured in Holtfreter's solution, and the embryonic development stages of gastrointestinal stage and subsequent stages were observed. Under a water temperature of (23.5±1.0)℃, it required 30 h 10 min for the embryonic development process. The process includes 7 main development stages (prophase of cleavage stage, cleavage stage, blastocyst stage, gastrula stage, neurula stage, organ formation stage and hatching stage), and 25 specific developmental periods. The average total length (TL) of newly hatched larvae were (4.33±0.16) mm, and the yolk sac was completely absorbed at 144 h after hatching (HAH) at a controlled temperature of (25.5±1.0)℃ when larvae total length reached (7.73±0.20) mm. Early larval development can be divided into 5 periods (eye pigmentation increasing period, body pigmentation increasing period, air bladder appeared period, air bladder inflated period, yolk sac absorbed completely) according to the pigmentation in eye and body (mainly in head, neck, back and digestive tract), and the change of air bladder and yolk sac. Black bream had no feeding behavior before the air bladder was inflated (at 96 HAH). The larvae are suitable to be transferred to ponds for summerling cultivation in the period between 96 HAH and 144 HAH.

Abstract:This experiment was conducted to investigate the effects of dietary mulberry leaf flavonoids on growth performance, serum biochemical parameters, antioxidant indices and anti-hypoxic stress ability of Litopenaeus vannamei. A total of 960 L. vannamei individuals (initial body weight:1.32±0.01 g) were divided into 6 groups, with 4 replicates per group and 40 shrimp per replicates. Six diets were formulated to contain 0 mg/kg, 10 mg/kg, 50 mg/kg, 100 mg/kg, 150 mg/kg, and 300 mg/kg diet of mulberry leaf flavonoids. The trial ran for 50 days. The survival rate, growth related indicators, serum biochemical indexes, antioxidant index and resistance to hypoxia stress were determined. The results indicated that:(1) there were no significant differences in the survival rate (SR), weight gain rate (WGR), specific growth rate (SGR), or feed conversion ratio (FCR) among the groups (P>0.05). WGR was highest in the 50 mg/kg group, 6.76% higher than the control group. (2) There were no significant effects on whole-body composition (P>0.05). (3) Adding 150 mg/kg and 300 mg/kg of mulberry leaf flavonoids to the diet significantly increased the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in the serum of L. vannamei (P<0.05). (4) Adding 10–300 mg/kg of mulberry leaf flavonoids to the diet significantly increased the total antioxidant capacity (T-AOC) in the serum and liver, and significantly decreased the malondialdehyde (MDA) and lipid peroxide (LPO) contents in the liver of L. vannamei. Adding 50 mg/kg mulberry leaf flavonoids significantly increased glutathione peroxidase (GSH-Px) activity in the serum (P<0.05). (5) After 2 h of hypoxic stress, the cumulative mortality of the 10 mg/kg and 50 mg/kg groups were significantly lower than the control group, and after 4 h, the cumulative mortality of the 10 mg/kg, 50 mg/kg, and 100 mg/kg groups were significantly lower than the control group (P<0.05). In conclusion, the evaluative index of T-AOC in the serum and regression equation analyses showed that the optimal supplemental level of mulberry leaf flavonoids in the diet of L. vannamei was 56.18 mg/kg. Adding 10–100 mg/kg mulberry leaf flavonoids to the diet improved the anti-hypoxic stress ability of L. vannamei.

Abstract:Chinese mitten crab, Eriocheir sinensis, is an important aquaculture species in China. Large amounts of adult E. sinensis appear in the market in autumn, but the prices are much higher before the National Day (Oct. 1st). To promote rational consumption and comprehensively evaluate the edible yield and quality of E. sinensis, this study used a pond-rearing experiment (planted with Elodea nuttallii) to obtain adult E. sinensis according to the ecological and healthy culture methods. Dissection and biochemical composition analyses were conducted to systematically explore the edible yield, proximate composition, and fatty acid and free amino acid contents of adult E. sinensis tissues. Regardless of gender, the hepatosomatic index (HSI) and gonadosomatic index (GSI) differed significantly between September and October (P<0.05), but there were no differences in meat yield (MY), total edible yield (TEY), or condition factor (CF) (P>0.05). The HSI value was higher in September than in October, and the values of the other indicators were higher in October. No significant different parameters (P>0.05) were obviously observed in proximate composition between September and October, but the moisture and lipids in the hepatopancreas, lipids in the gonads, and moisture and proteins in the muscles of females differed significantly (P<0.05). Proteins, lipids, and ash in the gonads and lipids in the muscles of males were also significantly different (P<0.05). As for fatty acid, one fatty acid in the hepatopancreas of adult E. sinensis differed between September and October (P<0.05), two fatty acids in the gonads differed between September and October (P<0.05), and eleven fatty acids in the muscles differed between September and October (P<0.05). As for free amino acid, only one amino acid in the gonads of adult E. sinensis differed between September and October (P<0.05), and three amino acids (Tau, Ala, Leu) differed in the male muscles (P<0.05). In summary, the GSI, MY, TEY, and CF values of adult E. sinensis were higher in October than in September, and there were some differences in proximate composition. There were small differences in the fatty acid and free amino acid contents of the gonads, but larger differences in the fatty acid contents of the muscles. Overall, the edible yield and quality of adult E. sinensis were better in October than in September, which is important for the comprehensive evaluation and rational consumption of Chinese mitten crab.

Abstract:The ecological niche is widely used to study species relationships, biodiversity, and community structures. It is also an important method to evaluate inter-and intra-species competition and the status of a population in the community. To understand the community structure and interspecific relationships of fishes in the saltmarsh wetlands of the Yangtze Estuary (YE), this research examined the IRI (index of relative importance), mean clumping index, niche breadth, and niche overlap in the YE using fyke net data from May to October 2019. Ten dominant fish species were collected in three seasons, among which Liza haematocheila, Lateolabrax maculatus, and Odontamblyopus rubicundus were three co-dominant species. Among the 10 dominant fishes, the temporal niche breadth varied from 0.11 to 1.70; Odontamblyopus rubicundus (1.70) had the highest temporal niche breadth, and Larimichthys polyactis (0.11) had the lowest. The spatial niche breadth varied from 0.57-1.53; Liza carinatus (1.53) had the highest spatial niche breadth, and Larimichthys polyactis (0.57) had the lowest. The temporal niche overlap of the dominant fishes varied from 0 to 0.99; 34 species pairs (75.56%) overlapped, while 6 species pairs (13.33%) did not overlap. The spatial niche overlap varied from 0.20 to 0.98; 36 species pairs (80.00%) overlapped, but 2 species pairs (4.44%) did not. The temporal and spatial niches of the dominant fishes in the salt marsh wetlands had distinct seasonal dynamics. Most of the species pairs had spatiotemporal niche overlap (73.33%), and 48.89% of the species pairs reached significant ecological niche overlap, indicating similarities in the spatiotemporal distributions of the dominant fishes in the saltmarsh wetlands. However, competition for the spatial and temporal resources was not the decisive factor affecting the community structure. In conclusion, this research suggests similar spatial and temporal distributions for the dominant fishes in the saltmarsh wetlands, reflecting the competitive relationships between fishes for the utilization of the temporal and spatial resources. Nonetheless, this competition did not affect the fish community structure. The differences in resource utilization may be related to the individual fishes' habits and environment. Further studies of the trophic niches of fish in the saltmarsh wetlands of the Yangtze Estuary are required to better understand the mechanisms of fish habitat selection and biodiversity maintenance.

Abstract:Albacore (Thunnus alalunga) is a migratory pelagic species, and its spatio-temporal distribution is vulnerable to environmental variation. Thus, a better understanding of the environmental effects on the albacore habitat is of great scientific importance. We used information from the albacore logbooks of mainland China commercial longline vessels and the oceanographic environmental data in the area of 140°E-130°W, 0°-50°S for the South Pacific fishing season (from May to August) from 2015 to 2017 to analyze the response curves of the environmental factors affecting albacore catch per unit effort (CPUE) and the contribution rate of the environ­mental factors through a maximum entropy model (MaxEnt). We also explored the potential albacore habitat in the main 2017 fishing season and assessed the prediction accuracies compared to the actual catch data. The results showed that:(1) the optimal range of environmental factors were homologous:28.4-30.6℃ of sea surface temperature, 13.2-17.6℃ of sea temperature at 300 m depth, 35.6-36.7 of sea surface salinity, -1.6-5.8 m/s of northward sea surface wind north of 25°N, and 17.8-23.4℃ of sea surface temperature, 12.2-16.9℃ of sea temperature at 300 m depth, 35.2-36.0 of sea surface salinity, -0.7-4.9 m/s of northward sea surface wind north of 25°S. (2) The environmental factors (sorted by importance) north of 25°S were sea surface temperature (31.3%), sea temperature at 300 m depth (30.1%), sea surface salinity (29.2%), and northward sea surface wind (9.4%); north of 25°S, the environmental factors were sea surface temperature(60.7%), sea surface salinity (22.4%), northward sea surface wind (10.6%), and sea temperature at 300 m depth (6.3%). The most important environmental factor north of 25°S was sea surface temperature (over 60%, on average), which was more significant than the same variable north of 25°S. The importance of the first three environmental factors was similar north of 25°S (approximately 30%, on average). (3) The overall prediction accuracy was 30%-85%; the prediction accuracy of the medium potential habitat was relatively high, while prediction accuracies for the high and low potential habitats were low, as a result of the model and limited data.

Abstract:To investigate the morphometric differentiation of Harpadon nehereus from coastal areas of China, multivariate mathematical-statistical analysis of 29 meristic characters (199 individuals) of eight H. nehereus populations were conducted by traditional morphological and geometric framework methods. Principal component analysis (PCA) was used to construct seven principal components (PC), with a cumulative contribution ratio of 71.481%. The scatter-plot of the principal components showed that the characteristics of the Zhoushan and Chaozhou populations were different from the others. PC1 reflected differences in the anal fin size and the oblique distance of fish body between the ventral and anal fins. PC2 accounted for the distance between the eyes and the mouth crack length. A one-way analysis of variance (ANOVA) indicated no significant differences in the mouth crack length/head length (MCL/HL), the origin of the adipose fin to the origin of the pelvic fin/body length (D₃-D₈/BL), the origin of the anal fin to the origin of the dorsal fin/body length (D₅-D₆/BL), or the terminus of the anal fin to the terminus of the adipose fin/body length (D₇-D₁₀/BL). Phylogenetic analyses showed that the Zhoushan population clustered in the outermost layer of the tree, followed by the Haikou and Qingdao populations. Stepwise regression analysis was used to select 9 character values of the greatest effects to establish the discriminant formula. The discriminating accuracy of the Qingdao population was 100%, and the comprehensive discrimination rate was 66.9%. The results showed there were some morphological differences among different populations of H. nehereus. The body length, anal fin position and head shape were the dominant characteristics to distinguish them. However, these differences had no corresponding relationships with geographical distribution. It was speculated that the frequent communication between different populations made the morphological differences less affected by geographical distance, and environmental factors may be the main reason.

Abstract:The neon flying squid (Ommastrephes bartramii) is an ecologically and economically important squid species extensively distributed in the North Pacific Ocean. O. bartramii are short-lived (one year) species, so the abundance and distribution of this species are extremely sensitive to climatic and environmental variability. To evaluate the impacts of strong El Niño events on the O. bartramii stock in the Northwest Pacific Ocean and to examine O. bartramii fishing ground variations under anomalous climate conditions, we analyzed and compared the catch per unit effort (CPUE), catch, fishing effort, and latitudinal gravity center (LATG) of the fishing ground in 2008 and 2015 using data from the Squid-jigging Science and Technology Group of Shanghai Ocean University. The fishing ground in the Northwest Pacific Ocean lies between 36°-48°N and 150°-170°E. Three critical environment variables, the sea surface temperature (SST), anomalies in the sea surface height (SSHA), and the photosynthetic active radiation (PAR), were also examined and incorporated into a habitat suitability index (HSI) model to compare habitat quality between 2008 and 2015. The results showed that the CPUE in 2015 with the strong El Niño event was much lower than that in 2008 with normal climatic conditions. The LATG in 2015 tended to move to the southern waters of the fishing ground. Moreover, the suitable areas of SST and PAR significantly decreased in 2015, leading to a dramatic decrease in suitable habitat. The latitudinal positions of the preferred SST and PAR for O. bartramii moved southward in 2015, resulting in a southward shift in the suitable habitat. Our findings suggest that the strong 2015 El Niño event impacted the spatial and temporal characteristics of the O. bartramii fishing ground in the Northwest Pacific Ocean. The environmental conditions in 2015 were not suitable for O. bartramii growth, and the suitable habitats decreased and moved to the south. This led to low squid abundance and a southward shift in the O. bartramii fishing grounds. Future investigations into the impacts of El Niño events should consider the intensity of the anomalous events.

Abstract:Illex argentinus is a short-lived and economically important squid species inhabiting shallow waters in the southwest Atlantic Ocean. The annual production of I. argentinus fluctuates and varies between years. Complex oceanographic structuring due to the confluence of the Malvinas cold current and the Brazilian warm current in the southwest Atlantic Ocean is a crucial factor driving the spatial and temporal variations in I. argentinus resources. The marine environmental conditions have profound effects on the biological characteristics of I. argentinus, influencing the early life history, population structure, reproduction, age and growth, and trophic level. Also, the abundance and spatial distribution of I. argentinus are sensitive to meso-scale oceanic environmental changes and large-scale climate variability, so squids respond quickly to climatic and environmental variations. This study suggests that the biological factors and internal dynamic processes of the population and the abiotic factors at various spatio-temporal scales need to be considered when evaluating the effects of the environmental factors on I. argentinus. To provide a scientific basis for the development and management of I. argentinus resources, an individual-based model of I. argentinus life history and the oceanographic processes should be developed.