Abstract:The upper reaches of the Yangtze River section from Yibin to Jiangjin are located in the upper reaches of the Yangtze River Rare and Endemic Fish National Nature Reserve (hereinafter referred to as “the Reserve”), which is a key protection area for rare and endemic fishes in China. With the successive development of hydropower stations at the lower reaches of the Jinsha River and the implementation of the “10-year fishing ban” policy, the structure and diversity of rare and endemic fish communities in this section of the river are expected to change. Therefore, conducting a comprehensive survey and assessment of rare and endemic fishes in this section of the river is necessary. In this study, we analyzed the inter-annual changes in the community structure of rare and endemic fishes in this section of the river based on the fish resources survey data from 2007 to 2021. We evaluated the diversity of rare and endemic fishes in this section of the river at different periods (before impoundment in Jinsha River Phase I, after impoundment, and early after the fishing ban) using eight indices in three dimensions: species diversity, taxonomic diversity, and functional diversity. The results showed that 29 species of rare and endemic fish belonging to three orders, six families, and 23 genera were identified during the 15 consecutive years of monitoring. Regarding ecological types, the rare and endemic fishes in this section of the river were mainly omnivorous or carnivorous fishes inhabiting the bottom, laying drifting eggs, and preferring flowing water habitats. Cluster analysis and non-metric multidimensional scale analysis (NMDS) showed that the rare and endemic fish communities for the different years could be divided into four groups with stress=0.09＜0.1 when the similarity level was 70%, and the ranking result was good.
The One-way ANOSIM test showed no significant difference in the community composition of rare and endemic fishes between the before-and after-impoundment periods, whereas significant differences were observed in community composition between the early fishing ban period and the before-and the after-impoundment periods (P˂0.05). The results of species diversity analysis showed that the Shannon-Wiener, Simpson, Margalef, and Pielou indices had different interannual trends, with ranges of 1.709–2.506, 0.729–0.906, 1.719–3.147, and 0.647–0.867, respectively. The mean taxonomic difference index (Δ+) and categorical difference variance index (Λ+) both showed that the early fishing ban > before the impoundment > after the impoundment. Functional diversity in different dimensions, such as motor, reproduction and feeding, showed some differences in different periods, with locomotion functional richness being higher at the early fishing ban, feeding function richness being higher after impoundment, and reproduction function richness being higher before impoundment. The uniformity of locomotion functional richness was significantly higher during the early fishing ban than that before and after impoundment. No significant difference was observed in the uniformity of feeding and reproduction functions in different periods. The dispersion of the functions was significantly higher at the beginning of the fishing ban than that before and after impoundment. Dispersion was significantly higher during the early fishing ban than before and after the impoundment. The results showed that the community structure and diversity of rare and endemic fish in the upper reaches of the Yangtze River are evidently affected by environmental factors such as hydropower development and fishing ban policy, and the relationship between diversity indices in different dimensions is complex, reflecting the adaptation and adjustment of fish communities under the changes of ecological environment. This study reveals the dynamic evolution law of the diversity of rare and endemic fish, which provides a powerful scientific basis for protecting and restoring the diversity of rare and endemic fish in this section and promotes the healthy and sustainable development of the Yangtze River ecosystem.

Abstract:Gymnodiptychus pachycheilus (248 individuals) were collected from the middle reach of Yalong River from October 2020 to May 2022 and used to study reproductive characteristics and assess its population growth potential. The results showed that the number of samples with phase-I and phase-II gonads was 66 and 143, respectively. No individual with phase-VI gonad was observed. The average gonadosomatic index (GSI) of male and female samples were (5.21±0.93)% and (4.75±0.87)%, respectively. The average egg diameter of the 24 female samples was (2.14±0.30) mm, and the spawning type of female G. pachycheilus belongs to the unimodal single spawning type. The average obsolute and relative fecundity of the female samples were (9054±2310) eggs and (6.56±0.69) eggs/g, respectively. A significant positive correlation was observed between absolute fecundity and standard length, body weight (P＜0.05). However, no significant correlation was observed between absolute fecundity, and gonad weight (P＞0.05). Of the 182 samples that could be sexed, the sex ratio was 1.49∶1(♀∶♂), and both the female and male samples presented the same minimum sexually mature age (4 years old). Furthermore, considering the constraints imposed by their biological characteristics and the detrimental impacts of habitat changes and human disturbances on population dynamics, the population growth potential of G. pachycheilus inhabiting the middle reaches of the Yalong River is limited, posing significant challenges for its future development.

Abstract:To study the spatio-temporal distribution and seasonal variation of resource density of Oratosquilla oratoria in Hangzhou Bay and its adjacent waters, single bottom trawl surveys and environmental data collection were conducted in March (winter), May (spring), July (summer), and November (autumn) in 2014. The spatial distribution characteristics of resource density, seasonal variation of barycenter, and body mass were analyzed, and the relationship between resource distribution and environmental factors was analyzed using GAM model. The results showed that the average resource density of Oratosquilla oratoria in Hangzhou Bay and its adjacent waters showed a changing trend of autumn＞winter＞spring＞summer, with the average resource density of 20.40 kg/km² in autumn being the highest, and 10.09 kg/km² in summer being the lowest, which was more than twice that of summer. The Oratosquilla oratoria resources were mainly distributed on the offshore side of the island chain formed by Zhoushan island-Qushan island-Sijiaoshan-Huaniao Mountain, while the distribution of the Oratosquilla oratoria was relatively small on the coastal side near the mouth of Hangzhou Bay. The center of gravity of its resource density was located at a water depth of 30–40 m, and the overall trend was from south to north, from outside to inside. The average body mass of Oratosquilla oratoria individuals showed the order of summer＞winter＞spring＞autumn, and no significant difference was observed in body mass between different seasons. GAM model analysis showed that season, bottom salinity, and bottom chlorophyll significantly affected the resource density of Oratosquilla oratoria. The bottom salinity was the most significant factor affecting the distribution of Oratosquilla oratoria, and the average bottom salinity of Oratosquilla oratoria occurence showed the trend of summer＞winter＞spring＞autumn. This study provides technical support for revealing the spatio-temporal distribution and seasonal variation of the resource density of Oratosquilla oratoria in Hangzhou Bay and its adjacent waters. It also provides guidance for effectively managing and rationally utilizing Oratosquilla oratoria resources in this area.

Abstract:The Yarlung Zangbo River, one of the largest rivers on the Tibetan Plateau, is a hotspot for biodiversity conservation efforts. Schizothorax curvilabiatus is mainly distributed in the waters of the lower trunk and tributaries of the Yarlung Zangbo River, and it is a representative fish of the lower basin. Recently, geological disasters and human activities have caused severe damage to the habitat of the Schizothorax curvilabiatus, leading to a decline in its resources. Consequently, conducting relevant studies to protect the germplasm resources of Schizothorax curvilabiatus is urgently required. In this study, SLAF-seq was used to develop SNPs. Genetic diversity was calculated using a script provided by Beijing Biomarker Technologies Co., Ltd; paired F_ST values between populations were calculated in Stacks; linkage disequilibrium analysis was performed by Plink; phylogenetic analysis, Admixture population structure analysis, and principal component analysis were used to classify the genetic structure of Artemia; and the TreeMix (v.1.13) software was used to calculate the level of gene flow in the populations. A large number of SNPs were identified in Schizothorax curvilabiatus populations. Overall, the genetic diversity of Schizothorax curvilabiatus was small, with MTXG having the highest genetic diversity. Recent geological events, such as weir collapses and earthquakes, have significantly impacted stock levels. Overfishing and biological invasions have also impacted stock levels. Human activities such as engineering construction and sand mining have altered the localized aquatic ecosystem of the river and reduced the population size of Schizothorax curvilabiatus, thus leading to an overall low genetic diversity of the Schizothorax curvilabiatus in the lower reaches of the Yarlung Zangbo River. Schizothorax curvilabiatus populations showed a low to moderate degree of genetic differentiation. The lower reaches of the Yarlung Zangbo River are characterized by considerable differences in elevation, which may act as a barrier to geographic dispersal and promote differentiation among populations of the Schizothorax curvilabiatus. Unexpectedly, MTLD and MTXR were the furthest apart but had the smallest FST within the Motuo population. Excluding the absence of gene flow and common ancestry between the two populations, we hypothesized that this was due to the local effect of genetic drift, which led to the convergence of genetic structure between the two populations and minimized FST. The LD results indicated that the Motuo populations were subjected to greater natural positive selection, and their ability to adapt to the environment was stronger, while the Palong and Chayu populations were subjected to relatively less natural positive selection. The results of the phylogenetic tree, Admixture, and principal component analysis showed that the Schizothorax curvilabiatus in the lower reaches of the Yarlung Zangbo River belong to the same taxon. TreeMix results showed that the optimal number of gene flow was two, both occurring in the Mutuo populations. Geological disasters have decreased the resources available to Schizothorax curvilabiatus, resulting in smaller populations. Additionally, Schizothorax curvilabiatus migrate over long distances and have limited movement patterns, which restricts inter-individual gene flow. This study provides a database for the conservation and exploitation of the germplasm resources of the Schizothorax curvilabiatus in the Yajiang River Basin.

Abstract:Portunus trituberculatus is widely distributed in the coastal waters of China and is currently facing high fishing pressure. To protect and sustainably utilize the fishery resources of P. trituberculatus, this study was conducted based on survey data from an offshore trawl survey in Zhejiang Province in April (spring) and November (autumn) from 2020 to 2022. The spatial distribution characteristics and the relationship between Portunus trituberculatus and marine environment were analyzed using global autocorrelation analysis, hot spot analysis, and the geographical weighted regression (GWR) model. The results showed that the spatial autocorrelation in spring ranked from small to large in the order of 2020, 2022, and 2021, and that in autumn ranked from small to large in the order of 2022, 2021, and 2020. In 2021 and 2022, the spatial aggregation degree of P. trituberculatus in spring was higher than that in autumn, whereas that in 2020 was lower than that in autumn. The local autocorrelation showed that the distribution of hot spots in spring and autumn was regular. In spring, P. trituberculatus mainly concentrated around the waters near the northwest of the Zhoushan Sea area at coordinates 121.7°–122.5° E, 30.7°–31° N, whereas in autumn, it concentrated around the northeastern part of the Zhoushan Sea area at coordinates 122.5°–123.25° E, 30°–31° N. The GWR model showed that environmental factors had spatial non-stationary effects on resource distribution of P. trituberculatus during different seasons. The spatial heterogeneity degree of environmental factors on resource distribution of P. trituberculatus spring was in the order of bottom sea dissolved oxygen (SBD)＞bottom sea temperature (SBT)＞bottom sea salinity (SBS). The spatial heterogeneity in autumn was in the order of SBT＞SBD＞SBS. This study contributes to understanding the spatial distribution of P. trituberculatus in offshore waters of Zhejiang, thereby providing a scientific foundation for the management of fishery resources.

Abstract:Recent evidence suggests that climate change affects the biodiversity, structure, and function of marine ecosystems, a phenomenon known as marine ecosystem transition. Climate change is expected to increase the frequency of regime shift phenomena, and it often interacts with fishing, contributing to these shifts in marine ecosystems. The ecosystem of the South China Sea lies at the intersection of the north-south air flow, with the Pacific Ocean to the east and the Indian Ocean to the west. It is located at the confluence of Walker Circulation patterns influenced by the Indian and Pacific oceans and is the most complex region in the global climate system and the most sensitive region for large-scale air-sea interaction. Currently, most studies on the response of the fishery ecosystem to climate change in the South China Sea focus on the species level, with a few studies on the fishery ecosystem. Therefore, this study examined the long-term changes in the fishery ecosystem structure in the South China Sea. The study aimed to explore the dominant and main driving factors that promote these long-term changes and support the management and sustainable development of fishery resources within this ecosystem. This study obtained catch data of each species in the South China Sea fishery ecosystem from 1950 to 2019 based on Sea Around US and screened and preprocessed the data. The nutrient levels for various species were obtained from the preprocessed biodiversity database in Sea Around US and were categorized into five functional groups: medium pelagics, small pelagics, medium demersals, shrimps, and medium reef assoc. fish based on previous studies. The optimum temperatures for these species were sourced from previous studies, FishBase and SeaLifeBase, and were classified into three thermal groups: warm-, temperate-, and cold-water species. Using the catch data of different functional and thermal groups, the long-term change characteristics of fishery ecosystem structure in the South China Sea from 1950 to 2019 were systematically determined by multivariate statistical analysis (serial T-test, cumulative sum method, principal component analysis, and temporal cluster analysis), to determine the occurrence of regime shifts. The results showed that the catch in the South China Sea gradually increased, with China’s catch accounting for the largest portion. Since 1981, the number and power of motorized fishing vessels in the South China Sea have increased steadily and stabilized after 1990, whereas the number and tonnage of non-motorized fishing vessels have notably decreased. The regime shift of the fishery ecosystem in the South China Sea occurred in the mid-1980s, mid-1990s, and early 2010s, effectively reflecting the fishing conditions of those periods. However, climate change is a notable contributor to regime shifts in fishery ecosystems. In future studies, factors such as climate change and fishing should be considered comprehensively to explore the leading factors affecting changes in the South China Sea fishery ecosystem and provide a basis for formulating fishery management policies.

Abstract:Increasing global temperature is causing water temperatures to increase, potentially leading to metabolic disorders in fish. The Xingguo red carp (Cyprinus carpio var. singuonensis) is an economically important fish in China; however, studies on its adaptation mechanism to high temperatures are relatively few. To analyze the changes in physiological regulation under heat stress, the present study simulated an acute high-temperature environment and cooling environment, and gill tissues of Xingguo red carp at different temperature levels (28 ℃ and 38 ℃) were examined. The results of enzyme activity indices showed that malondialdehyde (MDA) increased significantly and catalase (CAT) content decreased significantly after high temperature stress, whereas no significant difference was observed in glutathione peroxidase (GSH-PX) and superoxide dismutase (SOD). The SOD content decreased significantly after cooling, and the rest of the indicators were not significantly different. Using transcriptome sequencing analysis, 2643 differentially expressed genes (DEGs) were screened for differential genes between the high-and normal-temperature groups, of which 1,401 DEGs were upregulated and 1,242 were downregulated in Xingguo Red Carp. A total of 2396 DEGs were screened to compare the cooled and high-temperature groups, including 936 upregulated DEGs and 1460 downregulated DEGs. In comparing the cooled and normal-temperature groups, a total of 908 DEGs were screened, of which 300 DEGs were upregulated and 608 DEGs were downregulated. Meanwhile, the activation and involvement of DEGs in immune and apoptosis-related pathways were identified using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, such as endoplasmic reticulum protein processing, IL-17 signaling pathway, NF-κB signaling pathway, p53 signaling pathway, and apoptosis. Within these pathways, key signaling factors such as HSPs, IL-1β, IL-8, p53, Caspase-3, and HIF-1α showed different expression trends. The results showed that Xingguo red carp responds to high-temperature stress stimuli during high temperature stress by positively upregulating gene expression. However, the expression of Xingguo red carp immune-related genes and pathways were downregulated or suppressed, leading to suppression of the immune system, while apoptosis regulation was blocked, preventing the effective removal of abnormal and damaged cells. Furthermore, no signs of hypoxia existed. Following cooling recovery, the stress of the Xingguo red carp decreased. The immune response of Xingguo red carp was activated, and the inflammatory symptoms were reduced, but they did not recover completely. The symptoms of hypoxia returned to normal. These two levels were used to systematically investigate the physiological regulation mechanism of Xingguo red carp in high temperature environment. This study provides valuable information on how aquatic species adapt to high-temperature environments.

Abstract:This study aimed to explore the effects of a notable increase of suspended sediment content in aquaculture water on the immune and antioxidant capacity of rainbow trout as well as the microbial community on the body surface. The sediment from the Yellow River was used and maintained suspended using the pump pool cycle and blower aeration method. Three suspended sediment content gradient groups of 0, 1000, and 10000 mg/L were set up for the rainbow trout acute stress test. The activity changes of alkaline phosphatase (AKP), lysozyme (LZM), total superoxide dismutase (T-SOD), peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) in serum were detected continuously after stress culture, as well as the differences of skin and gill microbial communities after 7 days of stress culture. The results showed that the activity of AKP and LZM in the rainbow trout serum significantly changed within 3–6 h after the acute increase of sediment content, but then the stable state was gradually restored. T-SOD and POD decreased and increased, respectively, within 24 h of sediment stress, but they all returned to a steady state after 48 h. CAT increased significantly after stress, with no significant dependence on sediment content. MDA decreased significantly after stress, and it was dependent on sediment content. On the body surface of rainbow trout, Bacteroidetes and Proteobacteria were the dominant bacteria groups; however, the number and richness of microorganisms in the skin mucus were significantly higher than those in the gill tissue. The tissues sites tested revealed a significant increase in the relative abundance of Acidovorax, Pseudomonas, and Chryseobacterium compared to the control group under suspended sediment stress (P＜0.05). The relative abundance of Sphingobacterium decreased significantly (P＜0.05). The results above indicate that the acute stress of suspended sediment can disrupt the immune and antioxidant capacity of rainbow trout in a short period and increase the harmful microorganisms on their body surface.

Abstract:Exosomal miRNAs are crucial in regulating the immune response of vertebrates. This study explored the function of exosomal miRNAs in the immune response of Pinctada fucata martensii by injecting poly(I:C) and PBS into the blood sinuses of the adductor muscle of P. f. martensii to stimulate an immune response, followed by the analysis of differentially expressed exosomal miRNAs in the hemolymph. The study aimed to predict their target genes and the immune-related signaling pathways regulated by exosomal miRNAs, providing preliminary insights into their roles in the immune response of P. f. martensii. The results showed that the hemolymph exosomes of P. f. martensii are spherical or nearly spherical vesicles with intact membrane structures and clear contours, ranging in size from 75 nm to 150 nm. A total of 101 miRNAs were identified in the PBS and poly(I:C) groups, of which 76 were known miRNAs. In the poly(I:C) group, seven miRNAs were significantly upregulated, and five miRNAs were significantly downregulated compared to the PBS group. These differential miRNAs were associated with 570 target genes. KEGG enrichment analysis identified immune-related signaling pathways, including “Acute myeloid leukemia” “JAK-STAT signaling pathway” and “Chemokine signaling pathway” metabolism-related pathways such as “Glycerolipid metabolism” “Purine metabolism” and “Arginine and proline metabolism,” as well as endocrine-related pathways such as “Relaxin signaling pathway” “Prolectin signaling pathway” and “Insect hormone biosynthesis” (P＜0.05). Notably, eight miRNAs, including novel_mir2, novel_mir22, miR-2b_5, and miR-279, were found to regulate immune-related signaling pathways and influence the immune response of P. f. martensii by modulating metabolism through FOXO coupling. This study suggests that hemolymph exosomal miRNAs in P. f. martensii coordinately respond to poly(I:C) stimulation by regulating immune, metabolic, and endocrine processes, providing foundational data for further research into the roles of exosomal miRNAs in the immune response of shellfish.

Abstract:To investigate the impact of varying protein levels in feed on the growth performance, ovarian amino acid and fatty acid composition, gonad development, and serum hormone deposition of pengze crucian carp (Carassius auratus var. Pengze) broodstock, 135 broodstock with an average initial weight of (256.30±4.70) g were randomly selected for the experiment. These fish were then divided into three groups, each with three replicates and 15 individuals in each replicate. Fish and soybean meals were the primary protein sources, while corn starch was used to adjust the protein gradient, with dietary vitamin E content at 0 mg/kg (68.1 mg/kg), 400 mg/kg (462.3 mg/kg), and 1600 mg/kg (1655.8 mg/kg). The experiment was conducted for 60 days. No significant difference was observed in the growth, survival rate, and weight gain rate of Pengze crucian carp (P＞0.05). The fattening degree showed a significant increase and a stable trend with the increase in vitamin E in the feed. The gonadal index of the 400 mg/kg group was significantly higher than that of the remaining two groups (P＜0.05), and the egg diameter and number of eggs conceived showed an increasing trend and a decrease with an increase in vitamin E (P＞0.05). In the liver, vitamin E content in the 1600 mg/kg group was significantly higher than that in the remaining two groups (P＜0.05). In the ovaries, the vitamin E content in the 400 and 1600 mg/kg groups was significantly higher than that in the 0 mg/kg group (P＜0.05). The addition of vitamin E significantly increased the total amount of essential amino acids in the ovary (P＜0.05). Valine, isoleucine, threonine, lysine, and the total essential amino acids in the 400 mg/kg group were significantly higher than those in the 1600 mg/kg group (P＜0.05). Histidine, glutamic acid, and total amino acids were significantly higher in the 1600 mg/kg group than in the remaining two groups (P＜0.05); however, no significant difference was observed in the total non-essential amino acids between the groups (P＞0.05); seven saturated fatty acids, four monounsaturated fatty acids, and eight polyunsaturated fatty acids were detected in the ovaries of the various groups (P＜0.05). Polyunsaturated fatty acids, C18:3n6, and ΣPUFA were significantly lower in the 1600 mg/kg group than in the remaining two groups (P＜0.05), whereas DHA and Σn-3PUFA peaked in the 400 mg/kg group and were significantly higher than those in the 0 mg/kg group (P＜0.05), but did not differ significantly from the 1600 mg/kg group (P＞0.05). In the serum, CAT, ACP, and VTG were significantly higher in the 400 and 1600 mg/kg groups than in the 0 mg/kg group (P＜0.05), and MDA was significantly lower (P＜0.05), while T-AOC and LZM reached their peaks in the 400 mg/kg group and were significantly higher than that in the 0 mg/kg group (P＜0.05). In the liver, the SOD activity peaked in the 400 mg/kg group and was significantly higher than that in the 0 mg/kg (P＜0.05), and MDA activity decreased significantly with increasing feed vitamin E levels (P＜0.05). In conclusion, the addition of 400 mg/kg vitamin E in the diet significantly increased the gonad index and vitamin E content in the ovary of Pengze crucian carp, which was beneficial to the deposition of amino acids and fatty acids and increased the immune and antioxidant enzyme activities in serum and liver, thereby improving the gonadal development of Pengze crucian carp.

Abstract:The extensive use of antibiotics in industrial and agricultural activities has resulted in environmental deterioration, drug residues, bacterial resistance, and imbalanced microbial structure in the marine environment, affecting the function of the marine ecosystem. To understand the seasonal distributions of microbial communities and resistance genes in the sea area of Changli County, Qinhuangdao City, metagenomic sequencing technology was used to sample and analyze the seawater, sediments, and intestinal contents of the local fish, Synechogobius hasta. The microbial composition of the seawater samples in Changli County was mainly bacterial. Proteobacteria was the most dominant bacterial phyla, with Photobacterium being the most abundant genus. The main types of antibiotic resistance genes in seawater were APH2_IIa, vanXYG, OXA_325, and TriC, whereas in sediments were bcrB, vanHO, adeS, and EreA. Meanwhile, the main types of antibiotic resistance genes in the intestinal contents of the Synechogobius hasta were msrE, emrK, and QnrB4. Network analysis revealed that microbial genus level in the sea area was highly associated with antibiotic resistance genes, and the main genera were multi-resistant strains. The efflux pump of antibiotics is the main antibiotic resistance mechanism in this microbial community. The scallop farming area in Changli County is rich in antibiotic resistant bacteria and genes, which align with the commonly used antibiotic categories in aquaculture production. Enhancing the continuous monitoring of antibiotic-resistant bacteria and genes in the aquaculture area is urgently required.