Abstract:The breeding population of Eriocheir sinensis “Changdang Lake 1” were composed of two parallel breeding strains (strain A and strain B), which were resistant to high density and large size, respectively. To evaluate the breeding effect and genetic progress of the second generation of Eriocheir sinensis “Changdang Lake 1” in odd year population, juvenile and adult crab culture experiment was performed under the condition of ecological culture in outdoor pond. The experimental period lasted for approximately 20 months. During the experiment, multiple growth-proofing and gonadal developmental anatomies were combined with the final harvest size distribution. Compared with the unselected population, the growth performance, gonadal development, and culture effects of the two selected strains were comprehensively evaluated. The average body weight of the two selected strains in the juvenile and adult crab culture stages was always higher than that of the control group, and it was significantly higher than that of the control group in July and from September to November during the juvenile crab culture stage (P＜0.05). For adult crabs, the average body weight of strain B was significantly higher than that of the control group (P＜0.05) in October; however, the difference in the average body weights of the three groups in the other months were not significant (P＞0.05). For adult crabs, the peak periods of puberty molting in male and female individuals were from July 30th to September 10th, and August 20th to September 30th, respectively. The puberty-molting rate of the control group was slightly higher than that of the two selected strains. For the hepatosomatic index (HSI), the HSI of the males in the control group was significantly higher than that of the two selected strains on September 20th, while the HSI of the females in the two selected strains on November 10th was significantly higher than that of the control group (P＜0.05). The gonadosomatic index (GSI) of the two selected strains was similar to that of the control group, and the GSI of female strain B was significantly lower than that of the control group on November 10th (P＜0.05). For culture performance, the final average body weight and yield of the two selected strains in the juvenile and adult crab culture stages were higher than those of the control group (P＜0.05), and the final average body weight of strain B was slightly higher than that of strain A. The feed conversion rate (FCR) of the two selected strains in the juvenile and adult crab culture stages was lower than that of the control group (P＜0.05), and the FCR of strain A in the adult crab culture stage was significantly lower than that of the control group. The number of large-size juvenile crabs (≥15 g) and adult crabs (male≥200 g, female≥175 g) of the two selected strains was higher than that of the control group, while the number of small-size juvenile crabs (≤9 g) was lower than that of the control group. In summary, Eriocheir sinensis “Changdang Lake 1” strain A has the advantages of fast growth, high unit yield, and low FCR, while Eriocheir sinensis “Changdang Lake 1” strain B has the advantages of large average body weight, high proportion of large size crabs and late puberty molting. These two breeding strains have the potential for further breeding.

Abstract:Biofloc technology (BFT), which is a recirculating aquaculture system, can significantly enhance nutrients and waste recycling. In addition, heterotrophic microorganisms in the BFT system can convert nitrogenous waste and residual bait produced by the metabolism of the culture species into nutrients, thereby reducing feed requirements. BFT systems are divided into three types based on the circulation of nitrogen: chemoautotrophic, heterotrophic and photoautotrophic. Common bioflocs are mainly chemoautotrophic, and control toxic nitrogen through nitrification. Additional sugars were supplemented to increase the C/N ratio to synthesize the nitrogen source into the biomass through assimilation. The bioflocs of these two energy metabolic pathways have been extensively studied. However, algae often play a prominent role in natural biofloc communities that cannot be explained simply by chemoautotrophy and heterotrophy. Algae absorb CO₂ through photosynthesis to produce O₂ and organic matter that can be used by bacteria. Moreover, it can utilize nitrate produced by nitrite-oxidizing bacteria as a nutritional substrate to support their growth. Loach (Misgurnus anguillicaudatus) is an important freshwater species farmed in China. Traditional loach breeding techniques include pond, paddy, and cage farming. However, these farming methods rely on a substantial quantity of water to manage nitrogen-containing waste in the water body, which places great pressure on the environment and hinders the sustainable, eco-friendly development of aquaculture. To understand the breeding effects of nitrification and photoautotrophic bioflocs as compensatory nutrients, loach was grown in two types of bioflocs for 45 days. Growth performance, digestive enzyme activity, community structure of the water column, as well as gut microbiome and nutritional composition of the two types of flocs were compared. Nitrification and photoautotrophic groups significantly reduced the feed conversion rate compared with the clear water group. Meanwhile, the ABFT group exhibited an enhanced absorption of nitrate (40.93%) and phosphate (37.47%), compared with the BFT group. No significant differences was observed in feed conversion and specific growth rates, or mean final weight between the two groups. The mean final weight of both groups was reduced by 10% and no significant difference was observed in the final density of the nitrification group compared to that of the clear-water group. Nitrification and photoautotrophic bioflocs could provide 36.69±1.17% and 40.20±1.05% of crude protein, respectively. Photoautotrophic bioflocs increased crude fat content and promoted the conversion of saturated to unsaturated fatty acids. The higher protein and crude fat contents of the photoautotrophic group promoted the activity of trypsin and lipase in this group of loaches. Microbial community analysis showed that the addition of algae had no significant effect on the alpha diversity index of mature bioflocs at the phylum or genus level. The ingestion of bioflocs by loaches resulted in a significant decrease in the sobs index of the intestinal flora. The dominant intestinal flora in the nitrification group were Proteobacteria, Actinobacteria, and Chloroflexi, and those in the photoautotrophic groups were Proteobacteria and Cyanobacteria. Increased concentrations of Aeromonas were observed in the ABFT group at the genus level. The high abundance of Aeromonas may have disrupted the balance of the intestinal flora of loaches in the ABFT group, leading to a lower survival rate. Additionally, the bacterial flora detected in both the water and gut reflected the influence of bioflocs on the gut health of the loaches. By substituting a portion of the feed with nitrification and photoautotrophic biofloc, it is possible to partly reduce the feed and most of the water treatment costs, which in turn, lowers the feed conversion rate. Therefore, both types of flocs demonstrate practical value in the breeding of specific species such as loaches. This study establishes a theoretical basis for advancing the integration of specialized aquatic products with innovative farming models.

Abstract:Yellowfin tuna (Thunnus albacares) is an apex predator in marine ecosystems and plays a vital role in energy flow and nutrient cycling. This study aimed to investigate the dietary modifications of Pacific yellowfin tuna throughout ontogeny and variations in nutritional niches among different maritime regions. The fatty acid composition and properties of yellowfin tuna muscle were examined using specimens obtained from tuna fishing vessels operating in the eastern Pacific Ocean in 2019 and the western and central Pacific Ocean in 2021. Thirty-four fatty acids in yellowfin tuna muscle, including 16 saturated fatty acids (SFA), 8 monounsaturated fatty acids (MUFA), and 10 polyunsaturated fatty acids (PUFA), were identified. The SFA content of yellowfin tuna muscle was negatively correlated with the PUFA content, whereas the MUFA content was positively correlated with the PUFA content. Furthermore, a significant negative correlation was observed between SFA content and fork length, whereas both MUFA and PUFA content exhibited a significant positive correlation with fork length. Distinct variations were observed in the muscle fatty acid composition of yellowfin tuna inhabiting the western and central Pacific Oceans compared to those in the eastern Pacific Ocean, with an average compositional dissimilarity of 18.85%. Primary disparities were found in n-3 polyunsaturated fatty acids (n-3 PUFA), SFA, PUFA, C22∶6n3 (DHA), Cl6∶0, Cl8∶1n9, MUFA, C22∶6n3/C20:5n3 (DHA/EPA), C18∶0, and n-6 series of polyunsaturated fatty acids (n-6 PUFA). Principal component analysis showed that the higher the trophic level of yellowfin tuna, the higher the carnivorous ability of yellowfin tuna and the greater the contribution of organisms that feed on dinoflagellates and diatoms to the energy sources of yellowfin tuna. In contrast, yellow-fin tuna at lower trophic levels mainly feed on bacteria, terrestrial plants, and phytophagous copepods. Principal component regression analysis indicated that, as fork length increased, the nutritional level and carnivorous nature of yellowfin tuna also increased. Additionally, their feeding behavior progressively shifts from relying on crustaceans and cephalopods to organisms abundant in characteristic fatty acids, such as shrimp and teleosts. Compared to the yellowfin tuna inhabiting the western and central Pacific Oceans, those in the eastern Pacific Ocean exhibit a higher degree of carnivorous behavior and occupy higher trophic levels, with crustaceans contributing significantly to their energy intake.

Abstract:This study aimed to explore the distribution patterns of the phylogenetic structure of fish communities and the maintenance mechanism of fish diversity at different spatio-temporal in the Yellow River estuary and its adjacent waters and discuss the main influencing factors affecting community assembly. This study focused on the fish communities in the whole area of the Yellow River estuary and its adjacent waters and used the net relatedness index (NRI) to analyze the spatio-temporal changes in the phylogenetic structure of the fish community, considering the phylogeny of fish species based on data collected from different surveys. The surveys were conducted in June, July, August, and October 2013; and February, April, and May 2014 in the Yellow River estuary and its adjacent waters from 2013 to 2014 The results showed that in the whole area of the Yellow River estuary and its adjacent waters, community structures in February and April 2014 were phylogenetically overdispersed, and competitive exclusion may be the main influencing factor in community assembly. Meanwhile, in other months, the community structures were phylogenetically clustered, and habitat filtering may be the dominant factor in the community assembly of fish assemblages. The fish communities were phylogenetically clustered, and habitat filtering might have played a major role in the phylogenetic structure of fish communities at each station throughout the year, except for the phylogenetic structure of fish communities at stations near the estuary, which showed that phylogenetic overdispersion and competitive exclusion played a dominant role. The NRI of fish communities among different stations varied slightly each month, and the community structures at most stations were phylogenetically clustered in different months, except for February and April 2014, indicating that habitat filtering was the main driving factor. Fish communities have different species compositions and phylogenetic structures at different spatiotemporal scales in the Yellow River estuary and its adjacent waters. Habitat filtering played a dominant role in phylogenetic structure at large spatio-temporal scales, whereas competition exclusion was the main driving factor in the phylogenetic structure at small spatio-temporal scales.

Abstract:The genus Lucifer is a type of macro-planktonic crustacean and serves as a food for various fish species. Some Lucifer species can be an indicator species for fishing grounds. Utilizing data from six sampling investigations conducted annually from 2016 to 2021 in the Pearl River estuary during August, this study investigated the relationship between the distribution characteristics of Lucifer hanseni and water masses and explored the adaptability of L. hanseni to temperature and salinity. The results showed that the average abundance of L. hanseni varied from 9.26 to 31.09 ind/m³ , with the index of clumping between 57.00 and 236.32, indicating a strong spatial aggregating distribution. According to K-means cluster analysis of water temperature and salinity, the survey region could be divided into three water masses: runoff, brackish-mixed and high-salinity water. L. hanseni is mainly assembled in the south area of Lantau islands, which is characterized by high salinity, and spread northerly to the runoff and brackish-mixed water. The spread range, with the northernmost distribution area near Humen, was determined by the strength of high-salinity water and the abundance of L. hanseni. L. hanseni was generally recognized as a warm water species, which is corroborated by the results of this study. The average abundance and number of distribution stations of L. hanseni in each investigation were significantly positively correlated with the average sea surface temperature. Previous studies presented varying results on the salinity adaptability of L. hanseni. L. hanseni was previously regarded as a nearshore-, offshore-, or estuarine low-salt species. In this study, positive correlations were observed between the abundance of L. hanseni and sea bottom salinity (SBS) in most surveys. The highest abundance was consistently noted within the salinity range from 29.5 to 31.0, implying that the distribution pattern of L. hanseni was closely related to SBS in the Pearl River estuary during the summer. In conclusion, L. hanseni was a nearshore species.

Abstract:To provide technical guidance and a theoretical basis for the sustainable development of Coilia nasus resources in Dongping Lake, this study estimated the growth and death parameters of C. nasus using ELEFAN_GA technology and fitted the Von Bertalanffy (VBGF) growth equation based on the length and mass data of C. nasus obtained from a gillnet survey in Dongping Lake from 2021 to 2023. The yield per recruitment (YPR) and spawning stock biomass per recruitment (SSBPR) models based on body length structure were constructed to assess the resource dynamics and management strategy of C. nasus in Dongping Lake. The results show that the body length of C. nasus ranges from 4.9 to 26.2 cm, with an average body length of (12.2±2.4) cm. Meanwhile, the body weight ranged from 1.1 to 51.8 g, with an average weight of (6.6±4.5) g. The ELEFAN_GA method based on Bootstrap was used to estimate the parameters, and the result revealed that the growth parameters infinite length of C. nasus was 31.65 cm (L_∞), with a growth parameter of 0.66 (K). Meanwhile, the theoretical starting age of growth (t₀) was −0.23, with a growth amplitude of 0.65 (C), and the annual fastest growing time of 0.40 (t_s). The total coefficient of mortality was 2.71 (Z), with the coefficient of natural mortality at 1.074 (M), and the coefficient of fishing mortality at 1.641 (F). The exploitation rate was determined to be 0.604 (E), and the optimum catchable size was 9.15 cm (L₅₀). The results of the YPR model showed that with the increase of F, the YPR value first increased and then decreased, and the biological reference points F_0.1 and F_max were 0.978 and 2.204, respectively. The results of the SSBPR model show that with an increase in fishing intensity, the SSBPR shows a downward trend. The current fishing intensity was between F_20% (2.848) and F_40% (1.065), which was slightly greater than that of F_35% (1.286). In conclusion, the growth of C. nasus in Dongping Lake shows obvious seasonal changes compared with other geographical populations, and the differences in the biological parameters of C. nasus in Dongping Lake reflect the spatial heterogeneity of its growth process. The maximum K value indicates that C. nasus in Dongping Lake can grow to an infinite length in the shortest time, indicating that Dongping Lake is rich in bait. However, the high exploitation rate and low optimum catchable size indicate that C. nasus in Dongping Lake is currently in an overexploited state. The SSBPR curve shows that the current fishing intensity is less than the limit value of F_20% and slightly less than the biological reference point of F_35%. The schedule of closed fishing season in Dongping Lake is from April 1st to August 31st each year. According to the fitting results for the growth parameters and SSBPR, a closed fishing season was relatively reasonable (only for C. nasus). To ensure the sustainable use and achieve a balance between ecological and economic benefits of C. nasus in Dongping Lake, maintaining the sustainable development of fishery resources can be achieved by increasing the mesh size and optimum catchable size while appropriately reducing the number of fishing vessels to alleviate fishing intensity.

Abstract:The jumbo flying squid, Dosidicus gigas, is an economically important squid species with a short life cycle. It is widely distributed in the Eastern Pacific Ocean and is exploited by international fishing vessels, such as those from Peru, Chile, and China. The inter-annual catch of D. gigas fluctuated significantly from year to year and was closely related to environmental changes and climate variability. Previous studies have found that fluctuations in the catch of this squid are associated with local environmental conditions such as sea surface temperature, current, and food density. However, this species exhibits vertical migration, and changes in the water temperature at different depths tend to have a significant impact on their resource abundance and habitat distribution. Therefore, to evaluate the impact of vertical water temperature on the habitat changes of D. gigas in the Southeast Pacific Ocean off Peru, a habitat suitability index model (HSI) was established. This model utilized the fisheries data of D. gigas in the spring and summer seasons off Peru from 2006 to 2015 (September to February of the next year), combined with the vertical water temperature data at depths of 0 m, 50 m, 100 m, and 150 m, to analyze the spatial and temporal distribution of the fishery and habitat of D. gigas off Peru. Fisheries data were obtained from the National Distant-Water Fisheries Data Center of China. By calculating the percentage of HSI in suitable habitats and validating the model with data from 2014-2015, the habitat model based on the vertical water temperature factor and the arithmetic mean method could better simulate HSI values. The results of the spatial correlation analysis showed that the water temperature at each water layer off Peru was negatively correlated with habitat suitability. Changes in catch per unit effort and suitable habitat area for D. gigas were relatively minor, with no significant inter-annual or inter-monthly differences, and a significant positive correlation was observed between them. However, significant inter-annual and inter-monthly changes were observed in the gravity center of the fishing effort and habitat of D. gigas, which showed a similar tendency to move in a southeastern direction. Moreover, a significant reduction was observed in the area of suitable habitats in spring compared to summer. The monthly and inter-annual changes in the longitudinal and latitudinal gravity centers of the fishing grounds of D. gigas were consistent with the spatial distribution of the habitat. A significant positive correlation was observed between these two variables. This study demonstrated a close correlation between the abundance of D. gigas and the extent of suitable habitat. Significant inter-annual and inter-monthly variations in the suitable habitat of D. gigas were identified, serving as a crucial factor in the spatial and temporal distribution variations of D. gigas off Peru. This finding suggests that vertical water temperature should be considered when evaluating the habitat changes of D. gigas in the Southeast Pacific Ocean off Peru.

Abstract:To explore the relationship between the microbial community structure of the skin mucosa of Chinese sturgeons and plate discoloration disease, this study analyzed the structural characteristics of the microbial communities of the dorsal plate and trunk skins of healthy and diseased Chinese sturgeons using Illumina high-throughput sequencing. A total of 3406 operational taxonomic units (OTUs) were identified in the skin mucosa from the four sources. Compared to Chinese sturgeons in the healthy group, the number of OTUs in the dorsal plate skin in the disease group decreased by 84%, and that in the trunk skin decreased by 55%. At the phylum level, the composition of the dominant bacteria in the dorsal plate and trunk skins of Chinese sturgeons in the healthy group was relatively similar, with Proteobacteria, Firmicutes, and Bacteroidetes being the main bacteria, accounting for more than 75%. Bacteroidetes were highly enriched in the dorsal plate and trunk skins of the disease group; the relative abundance of the former increased from 11.15% to 67.99%, and the relative abundance of the latter increased from 20.28% to 53.48%. At the genus level, the relative abundances of Flavobacterium in the dorsal plate and trunk skins of the disease group were 42.83% and 21.78%, respectively, which were higher than that of the healthy group (4.20% and 16.92%, respectively). The relative abundances of Chryseobacterium in the dorsal plate and trunk skins of the disease group were 23.34% and 27.65%, respectively, which were higher than that of the healthy group (0.33% and 2.16%, respectively). Diversity analysis showed significant differences in the Chao and Shannon indices between the skin mucosa of Chinese sturgeons in the healthy and diseased groups (P＜0.01). The significant difference analysis showed that Flavobacterium Chryseobacterium, Acidovorax and Hydrogenophaga were significantly upregulated in the disease group (P＜0.05). This study showed that compared with the healthy Chinese sturgeon group, the number of OTUs in the dorsal plate and trunk skins of the diseased Chinese sturgeon group as well as the richness and diversity were significantly reduced (P＜0.01). Flavobacterium and Chryseobacterium of Bacteroidota were highly enriched in the skin mucosa of Chinese sturgeons in the disease group, and may be the main pathogenic bacteria of this disease.

Abstract:Bottom trawls with large mesh sizes in the forefront section are commonly used to target the largehead hairtail (Trichiurus lepturus), which is one of the most ecologically and economically important fish species in marine capture fisheries in China. In this study, the size selectivity of four diamond-mesh codends with mesh sizes of 30, 35, 40, and 45 mm was tested using the covered codend method in pair trawls with large mesh sizes at the forefront section of the South China Sea. The experimental codends were termed D30, D35, D40, and D45 according to their mesh sizes. Catch data were analyzed using the double-bootstrapping technique to account for uncertainties from both within- and between-haul variations, compare the size selectivity of tested codends, and estimate the exploitation pattern indicators for largehead hairtail. The results demonstrated that by increasing the mesh sizes of the codends, the 50% retention length (L50) of the largehead hairtail increased, whereas the capture probability and exploitation pattern indicators for undersized individuals decreased. For instance, the L50 was 12.22 cm for the D30 codend, and increased to 13.24 cm for the D45 codend. The retention proportion of undersized individuals was 57.10% for the D30 codend and decreased to 40.06% for the D45 codend. The differences in the L50 and exploitation pattern indicators between the tested codends were not statistically significant. Differences in the retention probability of undersized individuals in some length ranges between the codends were statistically significant. Considering that the mesh size used in trawling fisheries is usually small, often close to 30 mm, our results demonstrated that increasing the mesh size from 30 to 40 or 45 mm would improve size selectivity for the target species. The L50 values increased, whereas the retention probability of the undersized largehead hairtail decreased. However, the size selectivity of the codend with a mesh size of 40 mm (D40), currently regulated by the government, was poor for the target species under the management regulation scenarios of the minimum landing size (23.0 cm). Consequently, over 93% of the largehead hairtail were undersized and thus discarded. This finding suggests that more selectivity studies are needed to further improve the selective properties and achieve sustainable development of the bottom trawl fishery. Additionally, research on the minimum landing size for largehead hairtails is warranted to supplement the minimum mesh regulations in the South China Sea.

Abstract:The sampling trawl of Quantitative sampling of larval and juvenile fish is advantageous for assessing dynamic changes in fishery resource replenishment and population numbers. It provides a basis for decisionmaking to further enhance the sustainable use of fisheries resources. In this study, a flume tank experimental method was employed to investigate the hydrodynamic performance variations of a frustum-type depressor for sampling trawls with different inclined positions (inward, outward, and tilted). Furthermore, numerical simulations using OpenFOAM were employed to analyze the alterations in the flow field around the depressor at different positions. The results showed that the sinking coefficient of the depressor initially increased and then decreased with increasing angle of attack and heel angle, and both reached their maximum values at a heel angle of 5°. The maximum values for inward and outward inclined were 1.75 and 1.77 (α=25°), respectively, and the maximum values for tilt were both 1.78 (α=25°). The drag coefficient gradually decreased with increasing heel angle and increased with increasing angle of attack. The ratio of the sinking force to drag initially increased and then decreased with increasing angle of attack and heel angle. The maximum values were reached at heel angles of 20° and 10° for inward and outward inclined, with values of 3.73 and 3.76, respectively (α=20°). The maximum values were reached at a heel angle of 5° for tilted, with values of 3.67 and 3.71, respectively (α=20°). The pressure center coefficient remains relatively constant at different angles of attack. C_pc gradually increases with increasing heel angle, while C_pb remains constant with increasing heel angle. The flow velocity on the outer side of the depressor decreased gradually as the heel angle increased. Under outward inclination, the boundary layer separation point on the depressor gradually moved toward the leading edge of the plate. In both forward and backward inclination states, the flow velocity decay region at the rear of the depressor gradually expanded as the heel angle increased. This study elucidates the hydrodynamic performance variations of the depressor under different inclination states, providing a scientific basis for further rational installation and adjustment of the working positions of the depressor.