Abstract:The objective of this study was to obtain the tryptic albuminase gene EsTRY from Antarctic krill (Euphausia superba) by screening and cloning, construct the recombinant expression vector EsTRY-pCold-SUMO, realize the high efficiency of heterologous expression in Escherichia coli, and reveal the degradation activity of this enzyme on phthalate esters (PAEs). The gene of trypsin EsTRY of Antarctic krill is 1350 bp in length, encoding 449 amino acids, with a theoretical molecular weight (MW) of 47040.35 Da and a theoretical isoelectric point (pI) of 4.90. Structural analysis revealed the presence of a catalytic triad (Asp/Glu-Ser-His) and a substratespecific binding site, classifying EsTRY as a member of the serine protease family. The esterase activity of EsTRY was determined to be 18973 U/mL, with a specific enzyme activity of 5802.15 U/mg. The optimal reaction temperature was found to be 25 ℃, and the optimal pH was determined to be 7.0. Enzyme-catalyzed degradation experiments demonstrated that EsTRYpossessed the capacity to degrade phthalic acid esters (PAEs), with 13.2%, 34.4%, and 63.5% of the 1 mmol/L of PAEs being degraded within 15 min, respectively. Furthermore, 48.9% of 1 mmol/L DMP, DEP, DPRP, and DBP were degraded within 15 min, and the degradation rates reached 39.4%, 62.7%, 86.8%, and 98.7% within 5 h, respectively. In this paper, we investigated the degradation activity of EsTRY on PAEs, which provides a new potential tool for the biological management of plasticizer pollution, as well as a scientific basis for the efficient utilization and high-value exploitation of Antarctic krill. Key words: Antarctic krill; trypsin; heterologous expression; degradation of plasticisers

Abstract:The Chinese tapertail anchovy (Coilia nasus) is a typical anadromous fish species. Its spawning grounds are located in numerous river-connected lakes throughout the middle and lower reaches of the Yangtze River. Since the mid-20th century, the construction of embankments and sluice gates has disconnected most of these lakes from the main channel of the Yangtze River, preventing C. nasus from spawning and rearing offspring. In the Chaohu Lake, the primary river-connected channel has been equipped with sluice gates, resulting in the lake disconnected from the Yangtze River, and the population of C. nasus in Chaohu Lake being classified as landlocked. Although fish passages and boat sluice gates may still offer opportunities for migratory fish, no studies have yet investigated whether migratory C. nasus still exists in the lake. Investigating the ecological types of C. nasus in Chaohu Lake and tracing their origins can enhance our understanding of its migratory ecology and provide a more comprehensive view of lake connectivity, improving our ability to protect the ecology of Chaohu Lake. In July 2022, nine adult C. nasus samples were collected from Chaohu Lake in the Anhui Province, China. In this study, the otolith Sr/Ca ratio was analyzed using an Electron Probe Microanalyzer (EPMA) to determine the habitat history of C. nasus collected from Chaohu Lake. The ⁸⁷Sr/⁸⁶Sr ratio of otoliths was analyzed using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to trace the origin of some C. nasus individuals. The results showed that seven out of nine C. nasus individuals collected from Chaohu Lake exhibited low otolith Sr/Ca ratio profiles from the core to the edge. Change-point analysis revealed that the average values at different stages of these otoliths were all below three, indicating a freshwater life history. Moreover, the Sr/Ca ratio of individual 22CH03 exhibited a temporary increase exceeding 3, whereas the ⁸⁷Sr/⁸⁶Sr ratio of the individual remained stable at approximately 0.71053, confirming that this individual had a freshwater life history. In contrast, the otoliths of individual 22CH07 displayed sharp fluctuations in Sr/Ca ratios, rising to 5.37±0.57 after a low Sr/Ca ratio region near the core, and decreasing to less than 3 at the edge. This pattern indicated that the individual was born in freshwater, grew in the estuary, and returned to freshwater, reflecting a migratory life history. The ⁸⁷Sr/⁸⁶Sr ratios of the otoliths of 22CH07 were initially high at 0.71451, corresponding to the region with high Sr/Ca ratios and higher than the water of Chaohu Lake and its tributaries. This suggests that this fish originated from Poyang Lake. Subsequently, the ratio decreased to 0.70945, aligning with regions with high Sr/Ca ratios, indicating an estuary and nearshore life history. At the otolith margin, the ratio decreased to 0.71079, which was close to the background 87Sr/86Sr ratio of Chaohu Lake. These results indicated the presence of one anadromous C. nasus individual in Chaohu Lake, likely originating from Poyang Lake. This suggests that Chaohu Lake maintains connectivity with the Yangtze River to some extent. Additionally, owing to the small sample size of this study, further investigation is needed to determine whether an anadromous C. nasus population exists that is both born and reproduces in Chaohu Lake.

Abstract:As one of the ecotypes of anadromous Coilia nasus, the freshwater resident Coilia nasus taihuensis is unable to conduct anadromous behavior due to the existence of physical barriers. C. nasus taihuensis can grow and reproduce independently in freshwater habitats such as Lake Taihu. Genetic differences in the genome have been demonstrated between anadromous C. nasus and non-anadromous C. nasus taihuensis due to geographical isolation and the significant difference in living environment. The genetic mechanisms related to environmental adaptation of C. nasus taihuensis were hindered by the lack of reference genomes. To conduct comprehensive and systematic analysis of the genomic characteristics of C. nasus taihuensis, a freshwater resident individual from Lake Taihu was selected as the experimental object. The first complete, gap-free reference genome of C. nasus taihuensis was constructed using a combination of PacBio (Pacific Biosciences) high-fidelity reads and ONT (Oxford Nanopore Technologies) ultra-long reads and Hi-C datasets. Based on a K-mer value of 21, we estimated the genome size as 612.76 Mb with a heterozygosity rate of 1.31%. The results of genome assembly showed a gap-free C. nasus taihuensis genome with an assembly size of 834.09 Mb. A contig N50 of 35.45 Mb was obtained through library construction, sequencing, assembly, chromosome mounting and gaps filling. Compared with the genome of cultured C. nasus, our gap-free genome substantially improved contiguity and completeness, where contig N50 increased from 1.6 Mb to 35.46 Mb. The integrity also increased from 87.1% to 91.9%, representing the highest quality genome. By Hi-C data, the assembled sequences were anchored and oriented onto all the 24 chromosomes with a total length of 829.28 Mb, covering 99.83% of the scaffold-level genome. After gap filling using ONT ultra-long reads, all 24 chromosomes were assembled without gaps, representing the highest assembly quality. BUSCO analysis based on the actinopterygii_odb10 database showed that 91.9% of the expected actinopterygii_odb10 genes (single-copy genes: 90%; duplicated genes: 1.9%) were identified as complete, suggesting that the assembled C. nasus taihuensis genome is highly complete. Furthermore, a total of 382.393 Mb of repetitive sequence, accounted for 45.85% of the genome. Using a combination of de novo prediction, protein homology and RNA-seq annotation, a total of 21730 protein-coding genes were identified. Approximately 99.71% (21666 genes) of the total predicted genes were assigned with at least functional annotation, showing a more complete annotation. Furthermore, the conservation synteny between C. nasus taihuensis and C. nasus was compared to validate the chromosome assembly, and the results showed that the genomic sequences of C. nasus and C. nasus taihuensis were highly consistent (96.95%). Such highly conserved synteny and strict correspondence of chromosome assignment indicated a close genetic relationship between the two ecotypes. The high-quality gap-free assembled genome of C. nasus taihuensis can provide material for studying the freshwater adaptability of C. nasus and accumulate basic data for further studies on the population genetics of C. nasus.

Abstract:Cyprinus carpio var. qingtianensis, commonly known as the Qingtian paddy field carp, is a key species in the Qingtian rice-fish co-culture system. However, the early developmental process has not been sufficiently studied, limiting a comprehensive understanding of its biological mechanisms. In this study, transcriptome sequencing was used to analyze the gene expression dynamics at six key developmental stages: gastrula (TS1), 6-somite (TS2), eye pigmentation (TS3), hatching (TS4), 12 h post-hatching (TS5), and 24 h post-hatching (TS6). In total, 31153 differentially expressed transcripts (DETs) were identified. GO and KEGG enrichment analyses revealed that differentially expressed genes (DEGs) in the TS2vsTS1 stage were mainly enriched in nucleic acid metabolism and cell cycle-related pathways, indicating active cell proliferation during the transition from the blastula stage to somite formation. In TS3vsTS2, upregulated genes were significantly involved in skeletal muscle development and aerobic metabolic processes, suggesting the establishment of muscular and energy metabolism systems. In TS4vsTS3, pathways related to cardiac muscle contraction, neural development, and sensory functions were prominently activated, reflecting functional maturation from organ formation to the pre-hatching stage. The number of DEGs in TS5vsTS4 and TS6vsTS5 was relatively low, mainly involving stress responses and immune functions, indicating a shift toward environmental adaptation after hatching. These results indicated that C. carpio var. qingtianensis follows a "framework first, acceleration later" developmental strategy, in which maternal factors continue to regulate embryonic development even after zygotic genome activation (ZGA). In terms of energy metabolism, Qingtian paddy field carp adapted to the hypoxic rice field environment by downregulating oxidative phosphorylation (OXPHOS) and activating the HIF-1 signaling pathway. Additionally, 16 transcripts related to hatching enzyme (HCE) expression were identified in cluster 6, with all but one annotated as hce1 and hce2, suggesting that hatching in the Qingtian paddy field carp is primarily mediated by HCE activity. This study provides new molecular insights into the early developmental regulation of C. carpio var. qingtianensis revealed its unique adaptations to the rice-fish ecosystem and lays a foundation for further investigation into its regulatory mechanisms.

Abstract:Hepatocyte nuclear factor 4 (HNF4) is a pivotal transcription factor that regulates lipid metabolism and the biosynthesis of long-chain polyunsaturated fatty acids (LC-PUFA) and plays a critical role in maintaining hepatocyte function. LC-PUFAs, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential for various physiological processes. However, most aquatic species exhibit limited biosynthetic capacity. Eriocheir sinensis, an economically significant crab species, serves as an important model for investigating lipid metabolism mechanisms in aquaculture. Despite its importance, the functional role of Hnf4 in crustaceans remains poorly understood. This study aims to elucidate the molecular characteristics and regulatory mechanisms of Hnf4 in E. sinensis. The full-length Hnf4 gene was cloned using rapid amplification of cDNA ends (RACE) technology, and its mRNA expression profile across multiple tissues was analyzed via quantitative polymerase chain reaction (qPCR). The full-length sequence of the Hnf4 gene in E. sinensis is 3554 bp, including a 5 ʹUTR of 569 bp, a 3ʹ UTR of 1179 bp, an ORF of 1806 bp, and Hnf4 cDNA encoding 601 amino acids. The overall average hydrophilicity and hydrophobicity of HNF4 protein is −0.177, indicating that the HNF4 protein in E. sinensis is a hydrophilic protein. Homology analysis revealed that the HNF4 of E. sinensis has high sequence and amino acid homology with crustaceans such as Procambarus clarkii, Scylla paramamosain and Portunus trituberculatus, and is clustered together with the HNF4 of Portunus trituberculatus and Procambarus clarkii in the phylogenetic tree. The qPCR results showed that Hnf4 was expressed in multiple tissues of E. sinensis, with the highest expression in the hepatopancreas. E. sinensis were treated with ds Hnf4, inhibitor BI-6015, and agonist Benfluorescex. After 24 h of treatment, hepatopancreatic tissue samples were collected to detect changes in the expression of lipid metabolism-related genes. The results showed that after injection of the inhibitor BI-6015 and interference of Hnf4 gene expression with dsRNA, the expression of Fas, Scd, Fad6, Fad9, and Elovl4 in the hepatopancreas of E. sinensis was significantly reduced. Meanwhile, the expression of Hsl was significantly upregulated (P＜0.05), whereas injection of the agonist Benfluorescex yielded the opposite result. This indicates that the Hnf4 gene plays a role in regulating lipid metabolism and LC-PUFA biosynthesis in E. sinensis. This study represents the first successful cloning of the Hnf4 gene in E. sinensis and demonstrates its regulatory role in LC-PUFA biosynthesis by modulating key lipid synthesis genes (Fas and Scd) and enzyme genes (Fad6, Fad9, Elovl4). The hepatopancreas has been identified as the primary site of Hnf4 activity, where its suppression leads to reduced fatty acid synthesis and enhanced oxidative metabolism. Notably, the relatively low expression of Hnf4 in the eyestalk of E. sinensis suggests potential species-specific regulatory mechanisms distinct from those observed in mammals. These findings provide valuable insights into the biological specificity of HNF4 and its physiological regulation of lipid metabolism in E. sinensis. Furthermore, they offer a theoretical foundation for elucidating the lipid metabolism network in crustaceans and for reducing the reliance of aquaculture on fish oil. Future research should focus on exploring the distribution of HNF4 subtypes and their interactions with other transcription factors.

Abstract:The largefin long barbel catfish (Hemibagrus macropterus) is an economically important fish species in China. Although breakthroughs have been made in the artificial breeding technology of H. macropterus, obstacles such as imperfect broodstock cultivation and low fertilization rates remain. Therefore, it is essential to strengthen research on the reproductive biology of broodstocks of this species. In this study, morphological measurements, histological analysis of ovarian tissues, and enzyme-linked immunosorbent assay (ELISA) of serum were performed to investigate the annual changes in ovarian development and sex steroid hormone levels in female large fin long barbel catfish broodstocks under artificial breeding conditions. The fish used in this study were cultured at the Changshou Experimental Farm of the Chongqing Fishery Sciences Research Institute. From October 2023 to August 2024, 40 female H. macropterus broodstock were sampled every three months with 10 fish sampled in each sampling month. The body weight and total length of H. macropterus used in the experiment were 122.20 to 494.50 g and 26.20 to 44.0 cm, respectively. Individually sampled fish were anesthetized using 100 mg/L MS-222, and their body weight and total length were measured. Blood samples were collected from each fish via caudal venipuncture and allowed to coagulate at 4 ℃ for 12 h. Serum was obtained by centrifugation at 3000 g for 10 min. The ovary samples were dissected and weighed, and the anterior, middle, and posterior parts were immersed in Bouin’s solution for histological analyses. Commercial ELISA kits were used to measure estradiol (E2) and testosterone (11-KT) levels in serum. The results showed that the gonadosomatic index (GSI) of female H. macropterus broodstocks varied between 0.57 and 12.16 throughout the year, reaching its peak (12.16 ± 0.67) in May when they entered the breeding season. In August, the GSI value decreased, and the ovaries began to degenerate. From November to February of the following year, the GSI were not significantly changed compared with that of August, and kept at a low level ranging from 0.57 to 0.82. Based on their morphological characteristics, oocytes in the ovaries of the sampled fish were divided into six stages (I~VI): immature oogonia (I), primary growth (II), cortical-alveolar (III), vitellogenic (IV), mature (V), and degeneration (VI). By comparing the proportion of oocytes in each sampling month, ovarian development was classified into four stages: the initial development stage (November; dominated by stage II and III oocytes), pre-breeding stage (February; with the highest area ratio of stage III oocytes), breeding stage (May; oocytes from stages II to VI occurred simultaneously with stage V oocytes occupying the highest area proportion), and degeneration stage (August; mostly stage II and III oocytes). In the May spawning season, the expression level of E2 in the serum of H. macropterus broodstocks peak at 301.15 pg/mL and then decreased significantly in the subsequent degeneration stage in August. Conversely, the 11-KT content was the highest in August (135.00 pg/mL), which was significantly different from that in the other three sampling months (P＜0.05). These results indicate that the female large fin long barbel catfish belong to the single spawning type, with only one peak in the annual GSI, and the breeding season begins in May. The levels of hematological sex steroid hormones are closely related to the stages of ovarian development and can be used as important indicators to assess the ovarian developmental status of cultured H. macropterus. The results of this study provide a reference for further research on the reproductive regulation of large fin long barbel catfish broodstock and for improving the efficiency of artificial breeding of this species.

Abstract:The body wall is the main edible part of the sea cucumber (Apostichopus japonicus). The body wall proportion (the proportion of body wall weight to total weight, BWP) is an important economic trait and acts as an important indicator for assessing the quality of sea cucumber. Studying the genetic regulatory mechanisms of BWP can provide a scientific basis for sea cucumber breeding. To screen for candidate functional genes and molecular markers related to BWP, 250 randomly selected sea cucumber individuals from the same breeding batch and in the same culture environment were used to measure individual body wall proportions. After sorting by BWP, the top 10% (25 individuals) with the highest BWP and the bottom 10% (25 individuals) with the lowest BWP were assigned to the H and L groups, respectively. Using whole-genome resequencing and selection sweep analysis, the selected regions were screened, genes and key pathways were excavated, and single nucleotide polymorphism (SNP) loci and dominant genotypes related to BWP were determined. A total of 7398410 high-quality SNPs were obtained from the whole-genome sequencing. Analysis of the population genetic structure showed no obvious difference in genetic structure between the two groups. Based on the selection sweep analysis of Fst and Pi, 524 and 484 selection regions were screened in the high and low BWP groups, respectively, and annotated to 214 and 193 candidate functional genes, respectively. Pathway enrichment analysis obtained 1199 predicted GO categories and 44 KEGG metabolic pathways, among which four significantly differentially enriched pathways related to BWP were identified: metabolic pathways, fatty acid elongation, fatty acid metabolism, and mucin-type O-glycan biosynthesis. Through retrieval and analysis of functional genes, five functional genes possibly related to high BWP, ELP2, TPRA1, G2E3, TIE1, and DOCK1, were screened. Furthermore, 28 SNP loci within these five related genes were screened and four dominant genotypes related to BWP were obtained. The results provide basic data for exploring the genetic regulation mechanism of the BWP of Apostichopus japonicus and lay a foundation for the development of molecular-assisted selection technology and genomic breeding chips. Relevant research results also provide a basis for the selective breeding of high-quality Apostichopus japonicus varieties.

Abstract:The roles of α-ketoglutarate (AKG) as a supplementary additive have been proved in improving the growth performance and immune response of several carps, while its effects are rarely studied on repairing oxidative damage in target organs of aquatic organisms in carbonate-alkaline environments, as well as the regulation of intestinal microbiota. As a prominent freshwater economic aquaculture species within the Chinese fishery industry, crucian carp (Carassius auratus) has good attributes of swift growth and robust adaptability, making it an ideal model for probing into the saline-alkaline adaptation mechanism of freshwater fishes. This study explored the mechanisms by which AKG modulates antioxidant enzymes, digestive enzymes, and intestinal microbiota in crucian carp under carbonate-alkaline stress. Using biochemical analysis and 16S rRNA sequencing, five experimental groups were established: a freshwater control group (group C), two carbonate-alkaline exposure groups (20 mmol/L NaHCO3, group T; 40 mmol/L NaHCO3, group F), and two AKG supplementation groups (20 mmol/L NaHCO3, group TA; 40 mmol/L NaHCO3, group FA). The experimental crucian carp were exposed to 20 and 40 mmol/L NaHCO3 for a period of 30 days. Finally, six biochemical indicators and intestinal microbiota of the experimental carps were measured and then analyzed with GraphPad Prism 9.0, principal co-ordinates analysis (PCoA), and linear discriminant analysis (LDA). The results showed that with increasing carbonate-alkaline concentration, the activities of superoxide dismutase (SOD) and catalase (CAT) significantly decreased, while malondialdehyde (MDA) content increased. Moreover, the activities of digestive enzymes (amylase, AMS; trypsin, CHY; lipase, LPS) in the intestine were also significantly declined. However, after the exogenous addition of AKG, both antioxidant and digestive enzyme activities were notably restored, and MDA content significantly decreased. As shown in PCoA, there were some differences in clustering degree between carbonate-alkaline exposure groups (groups T and F), AKG supplementation groups (groups F and FA) and control group (C). Compared with the group C, the abundance of Proteobacteria increased significantly in the groups T and F, while the abundance of Firmicutes decreased. The dominant genera in the groups T and F were Sphingomonas and Shewanellaceae, respectively. In contrast, in the AKG-supplemented groups (groups TA and FA), the abundance of Proteobacteria decreased substantially, and Firmicutes considerably increased. The dominant genus in the group TA shifted to Bacillus, while Shewanellaceae remained dominant in the group FA. According to KEGG function prediction, the functions of the intestinal microbiota were mainly involved in multiple physiological processes such as energy metabolism, amino acid metabolism, carbohydrate metabolism, nucleotide metabolism, signal transduction, lipid metabolism, replication and repair, immune system and immune disease. In summary, this study demonstrated that carbonate-alkaline exposure destroyed the antioxidant defense system in the intestine of crucian carp, leading to oxidative stress, while reducing the abundance of beneficial intestinal microbiota. AKG can enhance the antioxidant enzymes of crucian carp by neutralizing excess oxygen radicals and inhibiting lipid peroxidation. Owing to the improvement of the absorption and transport of nutrients, the digestive enzyme activity of crucian carp was intensified. Furthermore, AKG regulates the composition of beneficial intestinal flora by means of providing energy support. In conclusion, supplementing with AKG effectively alleviates the toxic effects of carbonate-alkaline environment.

Abstract:To investigate variations in cold-water fish muscle quality under different growing environments and their causes, this study focused on masu salmon (Oncorhynchus masou) as a target object. Samples were collected from migratory and landlocked triple, breeding and non-breeding group masu salmons. The appearance, texture, nutritional composition, and omics features of the back muscles of masu salmon were compared. Results showed that the fracture, gumminess, and water- holding capacities of the masu salmon triple group were significantly higher than those of the migratory, breeding, and non-breeding groups (P＜0.05). The adhesive force, shear force, and cohesiveness of the triple group were significantly lower than those of the migratory, breeding, and non-breeding groups (P＜0.05). The pH of the triple-breeding group was significantly lower than those of the breeding and non-breeding groups (P＜0.05). The hardness of the migratory group was significantly higher than that of the non-breeding group (P＜0.05). The redness of the triple-breeding group was significantly higher than those of the migratory, breeding, and non-breeding groups (P＜0.05). The crude fat and water content of the masu salmon triple group were significantly higher than those of the migratory, breeding, and non-breeding groups (P＜0.05). The crude protein and ash content of the migratory group were significantly higher than those of the landlocked triple, breeding, and non-breeding groups (P＜0.05). The TAA, EAA, and DAA contents of the migratory masu salmon were significantly higher than those of the landlocked masu salmon (P＜0.05) and showed significant differences between the groups (P＜0.05). The contents of saturated fatty acids (∑SFA), monounsaturated fatty acids (∑MUFA), and polyunsaturated fatty acids (∑PUFA) of the landlocked masu salmon were significantly higher than the migratory masu salmon (P＜0.05), and the triploid group was highest. The eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) contents of the triploid group were significantly higher than those of the migratory, breeding, and non-breeding groups (P＜0.05). The fiber diameter of landlocked masu salmon was significantly larger than that of migratory masu salmon (P＜0.05). The results showed that the protein and amino acid contents of landlocked masu salmon were slightly lower than those of migratory masu salmon. However, landlocked triploids were better than migratory and other breeding groups in terms of muscle texture, color, fatty acid composition, and muscle fiber structure. These results provide a scientific basis for variety breeding optimization, differentiated breeding, and functional feed development in cold-water fish.

Abstract:To understand the effects of the complex current environment created by different obstacles on the swimming ability of fish, juvenile black carp (Mylopharyngodon piceus), Chinese barb (Spinibarbus sinensis), and long-finned kissing fish (Rhinogobio ventralis) were used as target species. Critical swimming speeds and changes in induced current speeds were measured by placing round, square, and semi-circular barriers in the swimming flume. The results showed that there was no significant difference (P＞0.05) between the critical swimming speeds of juvenile black carp under no obstacle and semicircular obstacle. The critical swimming speeds were significantly reduced (P＜0.05) under cylindrical and square obstacles, with U^a _crit reduced by 36.3% and 15.6%, and U^r _crit reduced by 34.9% and 15.3%, respectively. The U^r _crit of juvenile Chinese barb was (15.20±0.84) BL/s under square, which was 12.7% (P＜0.05) lower compared to the control group (17.42±0.55) BL/s. The critical swimming speeds of juvenile long-finned kissing fish were significantly lower than those of the group with no obstacle in all the three types of obstacles (P＜0.05). The effect was most pronounced in the group with a round type obstacle U^a _crit and U^{r crit} were (62.83±7.52) cm/s, (8.17±0.73) BL/s. There was no significant difference in the induced flow velocity of juvenile black carp and Chinese barb with no obstacle and different types of obstacles (P＞0.05). The induced flow velocity of juvenile long finned kissing fish was significantly different (P＜0.05) under round and square type of obstacles. The flow-sensing velocity ranges for the three species were as follows: Ua ind from 1.60 cm/s to 5.20 cm/s, and U^r _ind from 0.17 BL/s to 0.62 BL/s. In the same obstacle environment, the U^r _crit and U^r _ind values of juvenile Chinese barbs were significantly higher than those of juvenile black carp and long-finned kissing fish. The critical swimming speeds of all the three experimental fish species were higher than their flow-sensing velocities. This study found that obstacles and their types significantly affected the critical swimming ability of fish, whereas the impact on flow-sensing velocity was significant only among different species. These results provide a reference for fish habitat and fishway design.

Abstract:From 2020 to 2024, a fish survey was conducted in four sections (i.e., Luoguhe Village, Kaikukang, Huma, Heihe) and several tributaries in upper reaches of the Heilongjiang River. According to the survey statistics, 67 fish species live in these areas, consisting of 8 orders, 14 families, and 49 genera. Among them, 39 species belong to the Cyprinidae family, accounting for 58.21% of the total species number and making this family the biggest one in the fish community. Eight species belong to the loach family, contributing to 10.45% of the total species number and making it the second biggest family. Additionally, seven of the 67 fish species have been recognized as endangered species, including the national first-class protected wild animal Huso dauricus, the national second-class protected wild animal Acipenser schrencki, Brachymystax lenok, Hucho taimen, Lampetra japonica, Lampetra reissneri and Thymallus tugarinae; Furthermore, Lampetra japonica is a newly recorded species in the upper reaches of the Heilongjiang River. In the autumn of 2020, species diversity index (Hʹ) ranged from 1.81 to 2.47 for the fish community in the upper reaches of Heilongjiang Province, while its richness index (Dʹ) and evenness index (Jʹ) ranged from 1.52 to 2.78 and 0.60 to 0.74, respectively. Fish composition of the study areas varied with space and season, with the Heihe River section having the highest fish species richness and relatively high dominant species abundance. Meanwhile, fish species composition in the Heihe River section differed a lot between spring and autumn. These results provide fundamental information for the protection, management, and utilization of fish resources in the upper reaches of the Heilongjiang River.

Abstract:Juvenile flower ginseng Stichopus monotuberculatus are highly sensitive to environmental changes and anthropogenic stimuli, resulting in significant stress and high mortality during transportation of hatchery-reared juveniles. Developing an effective anesthetic method can alleviate stress responses and reduce mortality during transport. This study compared the anesthetic effects of five commonly used aquatic anesthetics, i.e., clove oil, 2-phenoxyethanol, magnesium sulfate, MS-222, and magnesium chloride, on juvenile Stichopus monotuberculatus. A behavior-based evaluation method for anesthetic and recovery stages was established, dividing the entire process into six phases: light anesthesia, moderate anesthesia, deep anesthesia, light recovery, moderate recovery, and full recovery. The results showed that clove oil, magnesium sulfate, and magnesium chloride effectively anesthetized juvenile Stichopus monotuberculatus. Clove oil at a concentration of 0.2 mL/L exhibited the best anesthetic effect, whereas concentrations of 0.02 mL/L and 0.04 mL/L significantly improved survival rates during prolonged transportation. Clove oil at 0.5 mL/L induced the shortest anesthesia duration of (6.04±1.24 min). Using magnesium sulfate at 0.05 mol/L resulted in the slowest time to achieve deep anesthesia [(34.13±3.77) min], while magnesium chloride at 0.05 mol/L produced the fastest full recovery of (10.01±1.36) min and magnesium sulfate at 0.25 mol/L produced the slowest time to full recovery [(60.39±5.28) min]. High concentrations of magnesium chloride and magnesium sulfate caused no significant changes in the body length of juvenile Stichopus monotuberculatus before and after anesthesia, whereas MS-222 and 2-phenoxyethanol were ineffective as anesthetics. This study identified clove oil at a concentration of 0.02 mL/L as the most suitable anesthetic for juvenile Stichopus monotuberculatus, ensuring effective recovery and high survival rates after 60 hours of long-distance transport. These findings provide critical technical support for the safe transportation of juvenile Stichopus monotuberculatus over long distances.