Abstract:This study investigated the expression pattern of the cyp19a gene during gonad development in grass carp (Ctenopharyngodon idellus) and the expression responses of various sex-related genes after RNA interference-mediated silencing of the target gene. The full-length cDNA sequence of the cyp19a gene was cloned using RACE technology, and the expression patterns of the cyp19a gene in gonadal tissues at different developmental stages of grass carp as well as in various tissues of adult fish were detected using qRT-PCR technology. Synthetic cyp19a-dsRNA was injected ino female grass carp for RNA interference experiments, while an equal volume of physiological saline was injected into the control group. The expression levels of sex-related genes in gonadal tissues and serum sex steroid hormone concentrations were then detected. The results showed that the full-length cDNA sequence of cyp19a in grass carp is 2219 bp, encoding an open reading frame of 1554 bp, a 5' UTR of 48 bp, a 3' UTR of 617 bp, and 517 amino acids encoded. The expression level of the cyp19a gene was highest in the gonads, followed by muscle, brain, and heart tissues. In gonads at different developmental stages, the expression level of cyp19a in ovaries was significantly higher than that in testes (P＜0.05) and significantly increases during the sexually mature stage at 48 months old, indicating that this gene plays a crucial role in the development and maturation of ovaries in grass carp. Five days after injection of 5 μg/g of cyp19a-dsRNA for silencing interference, the expression level of cyp19a in the dsRNA-injected group was significantly reduced compared to that in the control female fish (P＜0.05). The silencing efficiency of the target gene was 59.72% at 1 day post-injection and gradually increased thereafter. Compared to the control female fish, the dsRNA-injected group showed significant upregulation of foxl2a and foxl2b expression levels (P＜0.05) and downregulation of amh expression levels (P＜0.05) at 1 to 3 days post-injection, while dmrt1 expression levels were not significantly changed (P＞0.05). By 4 to 5 days post-interference, the expression levels of foxl2a, foxl2b, dmrt1, and amh in the dsRNA-injected group gradually returned to levels close to those of the control female group (P＞0.05). Furthermore, the serum estradiol (E2) levels in the injected group were significantly decreased (P＜0.05) compared to those in the control female fish, while testosterone (T) levels were significantly increased (P＜0.05). In conclusion, the expression level of the grass carp cyp19a gene, which belongs to the gonad aromatase gene, was highest in ovarian tissues, increased significantly during the sexual maturity stage, and may positively regulate foxl2a and foxl2b expression by negative feedback expression of dmrt 1 and amh. These results suggest that cyp19a plays a pivotal role in the development of ovaries and the nervous system in grass carp.

Abstract:Glycogen serves as a crucial indicator for assessing the quality of oysters, and glycogen debranching enzyme (AGL) plays a pivotal role in glycogenolysis. The Jinjiang oyster (Crassostrea ariakensis), widely distributed along China’s coast, is highly sought after in the high-end market. However, the molecular mechanism of glycogen metabolism in the Jinjiang oyster has been inadequately investigated. This study aimed to explore the AGL gene expression during the proliferative stage by administering dsRNA, and subsequently to investigate the relationship between the mRNA expression and glycogen content, thereby elucidating the pivotal role of this gene in glycogen metabolism. First, bioinformatics tools were employed to analyze the AGL gene sequence. Subsequently, dsRNA expression vectors were constructed for inducing the dsRNA production by the HT115 (DE3) bacteria, which were then co-cultured with unicellular algae as attachment hosts. Finally, the bacterial-algal mixture was fed daily to the Jinjiang oyster for RNA interference (RNAi). Furthermore, on days 15 and 30 of RNAi treatment, gonadal tissues were collected for subsequent determination of glycogen content and gene expression analysis. In the control group, gonadal development was observed using tissue sections. The software SPSS 26 was employed to analyze the correlation between AGL gene expression and glycogen content in gonads as well as to determine differences in data. According to the findings, the coding region of the AGL gene had a sequence length of 4719 bp and encoded 1572 amino acids. It contained four structural domains and exhibited a predicted protein molecular weight of 178.23 kDa, a theoretical isoelectric point of 6.21, and an AGL sequence similarity with other selected species ranging from 49.59% to 97.26%. Phylogenetic analysis revealed that the C. ariakensis AGL gene was genetically most closely related to mollusks. Throughout the experimental period, gonads in the control group showed progressive development but remained in the proliferative stage. Following interference for 15 and 30 days, expression levels of the AGL gene were significantly lower (P＜0.05) while glycogen content was significantly higher (P＜0.05) in comparison to those in the control group. In addition, after RNAi for 30 days compared to 15 days, there was a significant increase (P＜0.05) in AGL gene expression accompanied by a significant decrease (P＜0.05) in glycogen content. Importantly, it was observed that there existed a highly significant strong negative correlation (P＜0.05) between AGL gene expression and glycogen content within C. ariakensis gonads. In this study, we successfully employed the RNAi technology to downregulate the gene expression of AGL in the Jinjiang oyster and observed corresponding alterations in glycogen content, thereby confirming the critical role of the AGL gene in glycogenolysis. By manipulating the gene expression to validate its function, it is anticipated that the artificial regulation of glycogen content and other quality traits can be achieved, ultimately enhancing oyster quality and increasing market value. The present study contributes to the comprehensive understanding of the AGL gene in oyster glycogen metabolism, thereby offering valuable insights for the exploration of novel technologies aimed at regulating glycogen content.

Abstract:Diptychus maculatus is a national second-class wild protected animal. Although artificial breeding and stock enhancement have been achieved, bottleneck problems such as genetic homogeneity still exist. Therefore, it is of great significance to conduct research on the relationships between the morphological traits and body weight of D. maculatus for the stable inheritance of excellent traits. In this study, 102 female and 104 male fish from the Muzart River were taken as the research objects. The body weight, 12 traditional morphological traits [total length (X₁), body length (X₂), body width (X₃), body depth (X₄), head length (X₅), snout length (X₆), eye diameter (X₇), interorbital distance (X₈), caudal peduncle length (X₉), caudal peduncle height (X₁₀), mouth cleft width (X₁₁), and mouth cleft height (X₁₂)], and 21 truss morphological traits [the distance from the tip of snout to the end of the end of the back of the head (X₁₄), the origin of the dorsal fin (X₂₃), the origin of the pectoral fin (X₂₂), the origin of the pelvic fin (X₂₄), the distance from the end of the head dorsum to the origin of the dorsal fin (X₁₅), the origin of the pectoral fin (X₂₅), the origin of the pelvic fin (X₂₆), the distance from the origin of the dorsal fin to the end of the dorsal fin base (X₁₆), the origin of the pectoral fin (X₂₇), the origin of the pelvic fin (X28), the origin of the anal fin (X₂₉), the origin of the ventral caudal fin (X₃₀), the distance from the end of the dorsal fin base to the origin of the dorsal caudal fin (X17), the origin of the pelvic fin (X₃₁), the origin of the anal fin (X32), the origin of the ventral caudal fin (X33), the distance from the origin of the dorsal caudal fin to the origin of the ventral caudal fin (X18), the origin of the anal fin (X₃₄), the distance from the origin of the ventral caudal fin to the origin of the anal fin (X₁₉), the distance from the origin of the anal fin to the origin of the pelvic fin (X₂₀), and the distance from the origin of the pelvic fin to the origin of the pectoral fin (X₂₁)] were measured. The effects of morphological traits on body weight were studied through correlation analysis, regression analysis, and path analysis. The results showed that: (1) The morphological traits that show a significant positive correlation (P＜0.05) with body weight as well as their numbers are different in Diptychus maculatus of different genders and ages; (2) Linear regression equations between morphological traits and body weight were established for male and female populations of Diptychus maculatus. The total determination coefficients (R₂ ) of these equations ranged from 0.946 to 0.993 for the female group and from 0.797 to 0.991 for the male group; (3) Path analysis showed that X₄, X₂, X₂₉, and X₂₄ have the greatest direct effects on the body weight of female fish aged 1+ to 4+ , with path coefficients of 0.615, 0.444, 0.550, and 0.603, respectively. Meanwhile, X ₂₇, X ₂, X ₂₉, and X1 have the greatest direct effects on the body weight of male fish aged 1⁺ to 4⁺ , with path coefficients of 0.439, 0.545, 0.439, and 0.640, respectively. This study enriches the relevant morphological data of D. maculatus and provides a basic theoretical basis for later breeding work.

Abstract:Topmouth culter (Culter alburnus) is a large Cyprinidae fish, which occupies the top of the food chain in freshwater ecosystems and has a crucial contribution to the stability of aquatic ecosystems. Due to human activities, this species is facing the challenges of reduced natural resources and decreased genetic diversity within its population. Genetic diversity has direct impacts on growth, survival, and reproductive capabilities of fish. However, current genetic research on the cultured populations of C. alburnus is still insufficient. The importance of genetic resource conservation has not yet been fully recognized. In this study, whole genome resequencing (WGS) was used to conduct a comprehensive analysis of three cultured populations of C. alburnus from Taihu (TH), Qingyuan (QY), and Yangzhou (YZ) regions in order to evaluate the population genetic diversity level in these three regions, explore their genetic characteristics, and investigate the genetic differences among them. A total of 23156699 SNPs were identified, and SNP variants were mainly located in intergenic (47.21%) and intron (39.37%) regions. SNP markers in all three populations showed low polymorphism (PIC value ＜0.25). The TH population (0.1923) had the highest inbreeding coefficient, indicating a much higher degree of inbreeding than the QY (0.0631) and YZ (–0.0280) populations. Population structure analysis revealed that each of the three populations clustered into a branch; the TH population was separated into a distinct cluster derived from the common ancestor, whereas the QY and YZ populations may have been genetically influenced by multiple ancestral populations. The LD decay plot demonstrated that the TH population had the largest decay distance and slowest decay rate, whereas the YZ population showed a lower degree of linkage disequilibrium. Both genetic differentiation index (F_st) and gene flow (N_m) indicated that there was a certain degree of genetic differentiation among the three populations, and that the TH population was significantly differentiated from the other populations. Through selective scanning analysis based on nucleotide diversity (π) and fixation index of population genetic differentiation (F_st), with the QY and YZ populations as reference groups, a total of 572 and 602 selective genes were identified in the TH population, respectively. These genes are involved in biological processes such as energy metabolism, oxidative stress response, and inflammatory response. Selective signal detection results indicated that the most selected regions were located on chromosomes 3 and 7. Furthermore, the YZ population exhibited relatively high genetic diversity and showed a lower degree of domestication, whereas the TH population displayed the lowest genetic diversity and was strongly influenced by artificial selection. Our research provides basic data support for genetic studies and germplasm conservation management of C. alburnus cultured populations. This not only provides a reference for developing breeding selection strategies but also can help to formulate effective genetic resource conservation and culture management strategies.

Abstract:To investigate the effects of starvation and re-feeding on hepatic fatty acid composition and lipid metabolism in mandarin fish (Siniperca chuatsi), fish with an average body weight of (5.57±0.57) g were divided into three groups with three replicates in each group. The control group was fed live bait normally for 0 days (C₀), three days (C₃), six days (C₆), nine days (C₉), and 18 days (C₁₈). The starvation groups were deprived of food for three days (S₃), six days (S₆), or nine days (S₉), whereas the re-feeding groups were deprived of food for three days followed by normal feeding for 15 days (S₃R₁₅), six days followed by normal feeding for 12 days (S₆R₁₂), or nine days followed by normal feeding for nine days (S₉R₉). The experiment lasted for 18 days, during which changes in growth indices, hepatic fatty acid composition, and lipid metabolism gene expression were examined. The results showed that: (1) With prolonged starvation, body weight, liver weight, hepatosomatic index, and liver crude fat content in the starvation groups gradually decreased, significantly lower than those in the corresponding control group (P＜0.05). In the S₉ group, hepatocytes showed vacuolation, and cell boundaries became unclear. After re-feeding, there were no significant differences in body weight, liver weight, and hepatosomatic index (HIS) between the S₃R₁₅, S₆R₁₂, and C18 groups (P＞0.05), whereas body weight and liver weight in the S9R9 group were significantly lower than those in the C18 group (P＜0.05). Crude fat content in the S₃R₁₅ group recovered (_P＜0.05), whereas hepatocytes morphology in the S₉R₉ group was not fully recovered. (2) As starvation progressed, the relative contents of saturated fatty acid (SFA) (C16: 0, C 18: 0), monounsaturated fatty acids (MUFA) (C16: 1n-7, C18: 1n-9), and 20: 4n-6 in the liver of the starvation group gradually decreased, while the relative contents of polyunsaturated fatty acids (PUFA) (C18: 2n-6, C20: 5n-3, C22: 6n-3) gradually increased. In the re-feeding group, the relative contents of all fatty acids were recovered to the levels of the C18 group, except for C20: 5n-3 and C 22: 6n-3, which were significantly higher than those in the C₁₈ group (P＜0.05). (3) As the duration of starvation increased, the relative expression levels of fatty acid synthase (fasn), acetyl-CoA carboxylase (acaca), peroxisome proliferator-activated receptor gamma (ppar-γ), and elongation of very long-chain fatty acids protein 6 (elovl6) significantly decreased, whereas the relative expression levels of carnitine palmitoyltransferase 1Ab (cpt1ab) and acyl-CoA oxidase 1 (acox1) significantly increased (P＜0.05). After re-feeding, the relative expression levels of fasn and ppar-γ in all re-feeding groups, acox1, cpt1ab, and elovl6 in the S3R15 group, and acox1 in the S₆R₁₂ group were recovered (_P＜0.05). These results indicate that MUFA and SFA are primarily utilized in the liver of mandarin fish under starvation conditions, whereas SFA, MUFA, and PUFA contents could be recovered after re-feeding. Starvation promotes lipolysis and inhibits lipogenesis, whereas re-feeding can recover normal lipid metabolism. This research provides fundamental data on the physiological mechanisms of nutritional regulation during starvation in mandarin fish.

Abstract:Thiamine is a water-soluble vitamin essential for the growth and development of organisms and usually functions as the coenzyme participating in the metabolic processes of nutrients in the body. Protein is a necessary nutrient for human growth and the main source of energy. Therefore, this study was carried out to investigate the relationship between nutrient levels and protein content in shrimps as well as optimize the nutrient ratio in diets to promote shrimp growth performance and improve the utilization rate of feed protein, while also paying attention to reducing pollutants such as ammonia nitrogen generated in the breeding process to effectively reduce the environmental burden on the aquatic environment. To investigate the growth performance and protein utilization of white shrimp diets with different combinations of dietary proteins and thiamine, eight isoenergetic experimental diets with two protein levels (37% and 42%) and four thiamine-supplemented levels (0 mg/kg, 20 mg/kg, 40 mg/kg, and 80 mg/kg) were designed and fed to juvenile shrimps with an initial weight of (0.44±0.05) g for eight weeks under freshwater conditions. Two weeks before the end of the experiment, feces were collected for the detection and analysis of apparent digestibility of nutrients. Before the end of the experiment, the shrimps were subjected to 12-hour fasting, followed by weighing and counting after removal from the net cage to calculate the survival rate (SR), weight gain rate (WGR), specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), and protein deposition rate (PDR). Twelve whole shrimps and hepatopancreas were collected from each cage to assess the composition of whole shrimps and digestive enzymes (protease, lipase, and amylase). After the weighing was completed, the remaining shrimps were returned to the corresponding cages for continuous rearing. After a stabilization period of three days, an ammonia nitrogen excretion experiment was carried out to determine the variations in the ammonia excretion rate of shrimps eight hours after satiation. The results showed that dietary protein and thiamine levels affected the FBW, WGR, and crude protein content of whole shrimps. The growth performances of shrimps fed with high-protein diets were significantly better than those of shrimps fed with low-protein diets (P＜0.05). With the increase of thiamine level in the diets of the same protein level, the FBW, WGR, and crude protein content in whole shrimps initially increased and then decreased. Compared with that of 0 mg/kg thiamine group, the shrimps of 40 mg/kg thiamine displayed significantly higher FBW, WGR, and crude protein content in whole shrimps (P＜0.05). The shrimps fed with diets with thiamine displayed significantly higher SGR, PER, PDR, hepatopancreatic amylase, protease activities, and apparent dietary digestibility of protein and lipids (P＜0.05). The PER, PDR, amylase activity, and the apparent digestibility of protein and lipids of the shrimps fed with low-protein diets were significantly higher than those of shrimps fed with high-protein diets (P＜0.05). The ammonia excretion rate of the shrimps first decreased and then increased with the increase of dietary thiamine level. Regression analysis showed that the optimal dietary thiamine supplementation was 45.14 mg/kg with dietary protein content of 42% and 49.53 mg/kg with dietary protein content of 37%. In conclusion, appropriate levels of dietary protein and thiamine enhance shrimp growth performance by improving the digestive enzyme activities and apparent digestibility while reducing nitrogen excretion. Furthermore, the optimal dietary thiamine level required for maximum shrimp growth decreases as the dietary protein level increases.

Abstract:In order to investigate the occurrence and sources of floating Sargasssum horneri in the coastal waters of Gouqi Island. This study used the raft attachment and benthic S. horneri in Gouqi Island as the research object. Based on the growth, vesicle formation time, and biomass change rules of the attached S. horneri, the occurrence time, biomass, and floating path of the S. horneri were analyzed from the source. The findings indicate the following: (1) The formation time of floating S. horneri from raft attachment is 5–6 months earlier than that from benthic sources, and that approximately 99.12% of the biomass of floating S. horneri in the coastal waters of Gouqi Island likely originates from raft-attached S. horneri, whereas only 0.88% of the biomass originates from benthic S. horneri. (2) The number of floating S. horneri strains formed after the raft-attached S. horneri detached from the attachment base was approximately 22×10⁶ , with a biomass of about 141938 t. The biomass of floating S. horneri solely from raft attachment on Gouqi Island accounts for 23.36% of the total biomass of floating S. horneri in the East China Sea, whereas the benthic S. horneri comprises 0.21%. (3) Based on the biomass of attached S. horneri in various regions of China, the timing of floating S. horneri occurrences, tidal currents, and the influence of the Yangtze River environment on the floating pathways of S. horneri, two potential sources of floating S. horner in China were identified. The northern source is located near the Liaodong Peninsula and Shandong, whereas the southern source is situated south of the Yangtze River estuary. These findings not only provide a reference for analyzing the sources and occurrence potential of floating S. horneri in the coastal waters of Gouqi Island but also offer some basis for tracing the origins of the “Golden Tide”.

Abstract:Pond culture and rice-crab co-culture are currently the two main culture modes for the Chinese mitten crab (Eriocheir sinensis) in China. Due to the large differences in the aquaculture environments of paddy fields and ponds, there may be significant differences in greenhouse gas (GHG) emissions and their influencing factors. Therefore, research on the differences in GHG emissions under different culture modes is urgently needed. In this experiment, the pond culture and rice-crab co-culture modes were used as the research objects, and CH₄ and N₂O emission fluxes were collected and measured using a static box-gas chromatography method, along with the related environmental factors, at 10-day intervals between 9:00 a.m. and 11:00 a.m. on sunny days from June 7 to September 27, 2023, with a view to exploring the characteristics of the GHG emissions and their influencing factors under the two modes of aquaculture. Based on the results, the integrated warming potential of the two modes of river crab culture was calculated. The results showed that N₂O emission in the rice-crab co-culture mode was 2.8 times higher than that in the pond culture, with a fluctuation range of 34.94−126.90 μg/(m² ·h) and a mean value of (85.41±5.78) μg/(m² ·h), whereas CH₄ emission was 1.19 times higher than that in the pond culture, with a fluctuation range of 1.32−39.50 μg/(m² ·h) and a mean value of (13.69±1.42) μg/(m² ·h). The Global Warming Potentials (GWPs) of pond culture and rice-crab cultivation were (10.73±1.16) t/hm² and (13.07±1.62) t/hm2 , respectively, and the emission peaks of both modes occurred during the high temperature period of August. Multiple stepwise regression showed that the CH4 emission in the pond culture mode was mainly affected by water temperature and total nitrogen (TN), while the N₂O emission was mainly affected by nitrate nitrogen (NO₃ ⁻ -N); the CH₄ emission in rice-crab culture mode was mainly affected by total phosphorus (TP) content, while the N₂O emission was mainly affected by dissolved oxygen (DO) and water temperature. In summary, the rice-crab cropping mode significantly increased the GHG emissions and GWP of CH₄ and N₂O during the cultivation of the Chinese mitten crab, probably due to the fact that the GHG emissions under the rice-crab cropping mode were mainly caused by the rice emissions, and that there was a huge space for GHG emission reduction in the rice-crab cropping mode. This study provides data support for greenhouse gas emission of Chinese mitten crab under different culture modes as well as a theoretical basis for the promotion and demonstration of rice-crab co-culture mode.

Abstract:Marine ranching, through the establishment of artificial reefs and mariculture facilities, effectively promotes the proliferation of marine organisms in an area. It is a promising strategy for enhancing the carbon sink function of fishery ecosystems, thereby contributing significantly to climate change mitigation. Currently, most research on carbon sequestration in marine ranching focuses on artificial reef areas, but studies on the carbon sequestration potential of different functional zones across the entire system remain limited, especially regarding their dynamic changes at high spatial and temporal resolutions and their relationship with environmental factors. Therefore, this study integrated in situ sampling with satellite remote sensing and conducted multi-seasonal and multiple-cruise surface water sampling to analyze chlorophyll-a concentration (Chl-a), sea surface temperature (SST), and other environmental factors. Comparisons between Chl-a, SST data, and remote sensing products validated the applicability of satellite data for monitoring long-term marine trends. The Vertically Generalized Production Model (VGPM) was used to estimate the net primary productivity (NPP) of phytoplankton, quantifying their carbon sequestration capacity and analyzing the spatiotemporal variations of Chl-a concentration and phytoplankton carbon sequestration across different functional zones. The Generalized Additive Model (GAM) was applied to examine the relationships between environmental factors and carbon sequestration intensity and to assess the impact of marine ranching on the carbon sink capacity. Additionally, by comparing the changes in Chl-a concentration before and after the construction of marine ranching, this study further analyzed its impact on the regional carbon sink capacity. The results showed that: (1) The trends of Chl-a concentration and sea surface temperature observed in both remote sensing and in situ data were largely consistent, validating the reliability of using remote sensing data to assess long-term trends in marine environments. (2) Following the establishment of the marine ranching, Chl-a concentration exhibited significant seasonal and spatial variability, characterized by an “M”-shaped double-peak pattern, with peaks occurring during the summer-to-fall and winter-to-spring transition periods. The overall Chl-a concentration was significantly higher than both pre-establishment levels and those in the control area. (3) Carbon sequestration intensity also showed notable spatiotemporal distribution differences, featuring a pronounced peak in summer (June). The overall carbon sequestration intensity was significantly higher than that of the control area, with a total annual carbon sequestration of 1.85×106 kgC, indicating that marine ranching contributes significantly to enhancing the regional carbon sink capacity. (4) In the optimal GAM model, pH, silicate, dissolved oxygen, salinity, and latitude were identified as significant factors influencing carbon sequestration intensity. Notably, silicate promoted carbon sequestration within a certain concentration range. This study emphasizes the important role of artificial reefs and aquaculture infrastructure in enhancing carbon sequestration by promoting phytoplankton growth and altering hydrodynamic conditions. The findings suggest that future research should focus on optimizing marine ranching practices to maximize carbon sequestration effects. Future studies should explore the interactive effects of multiple environmental factors, examine the roles of different functional zones within marine ranching, and develop improved management strategies to enhance the carbon sink functions of these ecosystems. Furthermore, the integration of satellite remote sensing with in situ sampling provides a comprehensive approach to understanding the spatiotemporal dynamics of carbon sequestration in marine ecosystems. This method enables high-resolution monitoring of carbon fluxes, making it an important tool for assessing the effectiveness of marine ranching and its contribution to the global carbon budget.

Abstract:The aims of this study were to investigate the habitat suitability and spatiotemporal variations of Hexagrammos otakii in the coastal waters of Dalian, identify the relationship between its resources and environmental factors, and provide a basis for habitat conservation and the selection of its release areas. Based on fishery survey data collected from May to October during 2015–2023, this study investigated the habitat suitability using synchronously-obtained sea-bottom environmental factors, including depth, temperature, salinity, dissolved oxygen, and chlorophyll-a concentration. A single-factor suitability index was established by combining the catch abundance of H. otakii (as a dependent variable) and five environmental factors (as independent variables) to analyze the relationship between the distribution of suitable habitats and environmental factors. A habitat suitability index model was built for each month based on the weights of the environmental factors derived from a boosted regression tree model to explore the spatiotemporal variation in habitat suitability for H. otakii. The distribution of suitable habitats for H. otakii varied by month. In the Bohai Sea area near Dalian, suitable habitats induced a north-to-south migration from May to October. In the Yellow Sea area near Dalian, suitable habitats induced H. otakii migration from nearshore to offshore and from west to east toward the waters around the Dachangshan and Haiyang islands from May to July, and then they reversed their migration back to the nearshore areas of southern Dalian City and Lvshun from August to October. Overall, the area of suitable habitats for H. otakii in the Yellow Sea near Dalian and its proportion within the studied sea area were higher than those in the Bohai Sea. This study explored the distribution and changes in the habitats of H. otakii, the optimal release times, and suitable waters for their release. These findings provide a scientific basis for the conservation and enhancement of H. otakii resources and to optimize stock enhancement strategies.

Abstract:This study was conducted in April 2022 (spring), June 2023 (summer), October 2023 (autumn), and January 2024 (winter) to understand the relationship between fish community structure and diversity as well as environmental factors in the Henan section of the Yellow River (Hongnongjianhekou, Qinglongjianhekou, Nancun, Shuangmacun, Tongshuling, Yiluohekou, Liuyuankou, Naoli, Tianranwenyanqukou, and Jindihekou). Using the obtained data, fish community structural characteristics, spatial and temporal distribution patterns, and their relationship with environmental factors were analyzed. A total of 16556 individuals belonging to 47 species, 40 genera, 15 families, and five orders were collected, among which, there was one species of fish under state secondary protection and five exotic fish species, accounting for 2.1% and 10.6% of the total species, respectively. According to the index of relative importance (IRI), the dominant fish species were small fishes, such as Parabramis pekinensis, Rhinogobius giurinus, Cyprinus carpio, Pseudobrama simoni, Hypophthalmichthys molitrix, and Hemiculter leucisculus. The average Margalef richness, Pielou evenness and Shannon-Wiener diversity were 3.01±0.68, 0.56±0.16, 2.49±0.77, respectively. The abundance/biomass comparison curve showed that the fish communities in Nancun, Tongshuling, Naoli, and Jindihekou were relatively stable, whereas those in Hongnongjianhekou, Qinglongjianhekou, Shuangmacun, Yiluohekou, Liuyuankou, and Tianranwenyanqukou were seriously disturbed. Cluster and non-metric multidimensional scale ranking (NMDS) analyses showed that the fish communities in Henan section of the Yellow River could be divided into three groups: those in Hongnongjianhekou and Qinglongjianhekou belong to one group; those in Naoli, Tianranwenyanqukou, Jindihekou, Nancun, Yiluohekou, and Liuyuankou belong to one group; and those in Shuangmacun and Tongshuling belong to one group. RDA analysis showed that permanganate (CODMn) and suspended substance (SS) were the main environmental factors affecting the differences of fish community structure in the Henan section of the Yellow River. These results show that, compared with the historical data, the fish community structure in the southern section of the Yellow River has obviously changed, alien species have increased, indigenous fish have decreased, and individual fish tend to be smaller and younger.

Abstract:Docosahexaenoic acid (DHA) (22:6n-3) is an n-3 (omega-3) long-chain polyunsaturated fatty acid (LC-PUFA) that has attracted much attention in recent years. It is indispensable in the brain and visual development of infants and young children and has many physiological functions, such as the regulation of blood lipids, inhibition of tumor growth, and prevention of Alzheimer’s disease. Fish are an important source of DHA in humans. However, with the decline of wild-capture marine fisheries and the increasing aquaculture production, the proportion of DHA obtained from farmed fish is projected to increase significantly. Recent studies suggest that genetic manipulation or selective breeding can enhance endogeous DHA biosynthesis in farmed fish by targeting key regulatory factors, potentially reducing dietary fish oil reliance while increasing DHA content in muscle. During the biosynthesis of LC-PUFAs, elongation of very long-chain fatty acids (Elovl) and fatty acid desaturases (Fads) play important roles by extending the carbon chain and introducing double bonds, respectively. This article provides an overview of the DHA biosynthesis pathways in fish and the Elovl and Fads gene family members that play key roles at various nodes, and explores the division of labor, functional compensation, and diversity of these genes. The different regulatory modes of transcription factors on the key enzyme genes mentioned above and their effects on DHA biosynthesis were analyzed at the promoter level. This article provides a theoretical reference for genetic improvement and precision breeding of the DHA content trait in farmed fish using techniques such as gene editing or molecular module design.