Abstract:With the implementation of the 10-year Fishing Ban policy, the abundance of anadromous Coilia nasus has dramatically increased in the Changjiang River and the species has been redistributed to some traditional habitats. The Xiangjiang River is one of the main distribution waters of C. nasus in the Dongting Lake catchment. However, no anadromous C. nasus has been found in this river for several decades. To verify the distribution of anadromous C. nasus in this river after the Fishing Ban, microchemical analysis of otoliths was performed on a specimen collected from the Xiangying section of the Xiangjiang River on June 13, 2023. The results showed that the strontium-calcium ratio of otoliths of this individual could be divided into five stages, including S_I (1.37±0.60), S_III (2.80±0.16), and S_V (2.47±0.62) stages corresponding to freshwater habitats, while S_II (5.50±1.10) and S_IV (4.52±0.94) stages corresponded to estuarine water. In addition, some parts of the Sr/Ca ratios were greater than 7 in the S_II stage, indicating that it had once entered marine water. The corresponding Sr-content mapping analysis results also show blue, yellow-green, blue, yellow-green, and blue characteristics from the core to the edge of the water. All the aforementioned results reflect the characteristics of a typical anadromous C. nasus. To the best of our knowledge, this is the first study to confirm the distribution of anadromous C. nasus in the Xiangjiang River in the upper reaches of Dongting Lake by otolith microchemistry. This finding demonstrates the effect of the Fishing Ban policy in that anadromous C. nasus could migrate back to the Xiangjiang River through the Changjiang River and Dongting Lake from the sea. To continuously protect the migratory resources in Dongting Lake and its tributaries, as well as the stable effect of the Changjiang 10-year Fishing Ban policy, it is important not only to investigate the distribution of anadromous stocks and their key habitats in Dongting Lake and its tributaries but also to carry out urgent protection of the refunctioned key habitats.

Abstract:This study aimed to investigate the genetic structure and variability within the clearhead icefish (Protosalanx chinensis) population by developing 18 microsatellite (simple repeat sequence, SSR) primers for population genetic analyses. In total, 281 samples of P. chinensis were collected from four water systems and eight water bodies since 2016. The results were as follows: 172 alleles were detected, with an average of 9.6 alleles (N_a) ranging from 3 to 24; the number of effective alleles (N_e) ranged from 1.039 to 4.595, with an average of 2.384; the expected heterozygosity (H_e) ranged from 0.035 to 0.804, with an average value of 0.507; and the polymorphic information content (PIC) ranged from 0.034 to 0.775, with an average of 0.469. Notably, 10 of these loci exhibited high polymorphism with PIC values exceeding 0.5. Regarding population-level statistics, the average allele number (N_a) of the eight water populations was 3.389–5.389 and the average value was 4.375. The polymorphic information content (PIC) was 0.373–0.479, with an average value of 0.419. Analysis of Molecular Variance (AMOVA) showed that 84.54% of the total variation in P. chinensis came from within populations and 15.46% from genetic variation among populations. Additionally, a Principal Component Analysis (PCA) was conducted on eight geographic populations of P. chinensis, and all individuals were divided into three subgroups. Nei's genetic distance was employed to construct a UPGMA cluster tree, which classified the eight water bodies into two major branches. Among these, the five water groups of Lianhuan Lake displayed considerable diversity, with Nashidai (NS) and Talahong (TL) forming clusters that subsequently merged with Erbaguzi (EB). Similarly, Dalonghu (DL) and Amuta (AM) grouped, indicating that these five water bodies constituted independent entities within the Lianhuan Lake. Moreover, Xingkai Lake (XK) and Xinlicheng Reservoir (XLC) were grouped, followed by their combination with Taihu Lake (TH) as another unit. Research has shown that the northern population of P. chinensis maintains a high level of genetic diversity and exhibits significant genetic differentiation from populations in different water bodies. To safeguard and preserve population diversity, it is imperative to recognize and protect the distinct statuses of both the southern and northern water system populations. In particular, the preservation of Lianhuan Lake, which serves as the primary source of P. chinensis, is of paramount importance.

Abstract:This study was conducted to find out the effects of water temperature on the growth, antioxidant enzyme activity, and immune enzyme activity of juvenile sea cucumbers Holothuria scabra. We cultivated healthy individuals with an average body weight of (1.70±0.24 g) at three temperatures: low temperature at 23 ℃, control at 28 ℃, and high temperature at 33°C in temperature-controlled tanks for 30 d. The specific growth rate of H. scabra juveniles was measured every 10 d. Juvenile H. scabra body walls, coelomic fluid, intestines, and respiratory trees were collected to determine superoxide dismutase (SOD), catalase (CAT), alkaline phosphatase (AKP), lysozyme (LZM), and malondialdehyde (MDA) content. The results showed that: (1) The SGR_0-30 of the control group was significantly higher than that of the high-temperature and low-temperature groups (P＜0.05), and the high-temperature group exhibited a significantly higher value than that of the low-temperature group (P＜0.05), indicating that long-term low temperature had a greater impact on juveniles than long-term high temperature. (2) In the low-temperature group, SOD, AKP, and LZM activity and MDA content in the coelomic fluid were not significantly different from those in the control group at 0 d, and SOD, CAT, and AKP activity were significantly higher than those in the control group at 30 d (P＜0.05). SOD, CAT, and LZM activity, and MDA content in the body wall were not significantly different from those in the control group at day 0; however, SOD, CAT activity, and MDA content were significantly higher than those in the control group at day 30 (P＜0.05). All enzyme activities in the intestine were significantly higher than those in the control group at 0 d (P＜0.05), except for MDA content. Then, only MDA content was significantly higher that of the control group at 30 d (P＜0.05). All indicators in the respiratory tree were significantly higher than those in the control group at 0 and 30 d (P＜0.05). The results showed that the coelomic fluid and body wall of juvenile H. scabra needed to cope with oxidative stress caused by prolonged low temperatures, while the intestine had to deal with oxidative stress from short-term low temperatures, and the respiratory tree had to adapt to oxidative stress from both short-term and prolonged low temperatures. (3) In the high-temperature group, SOD, CAT, and AKP activity and MDA content in the coelomic fluid and body wall were significantly higher than those in the control group at 0 d (P＜0.05). No indicators showed significant differences from those in the control group at 30 d. CAT activity in the intestine was significantly higher than those in the control group on day 0 (P＜0.05), and all indicators were significantly higher than those in the control group on day 30 (P＜0.05). All indicators in the respiratory tree were significantly higher than those in the control group at 0 and 30 d (P＜0.05); CAT content and MDA content were significantly higher than that in the control group (P＜0.05). This suggests that the coelomic fluid and body wall primarily faced oxidative stress from short-term exposure to high temperatures, whereas the intestine and respiratory tree had to deal with both short-term and prolonged high-temperature stresses. (4) Antioxidant and immune enzyme activities in the four tissues of juvenile sea cucumbers were negatively correlated with SGR, indicating that the increase in antioxidant and immune enzyme activities conflicted with rapid growth, resulting in a significant decrease in SGR. In conclusion, both prolonged low and high temperatures generated oxidative stress in juvenile H. scabra, and juvenile H. scabra had greater adaptability to high temperatures.

Abstract:Brachymystax tsinlingensis (Li 1966) is a landlocked Salmonidae fish endemic to China. Based on long-term artificial breeding and resource conservation studies, it was found that B. tsinlingensis has obvious photophobic behavior and light-sensitive characteristics. To further understand the visual characteristics of B. tsinlingensis in different habitats, this study studied the second filial generation population (SFGP) [body weight: (51.50±10.86) g, body length: (15.40±0.75) g] and wild population (WP) [weight: (85.68±31.81) g, body length: (18.17±2.34) cm] of B. tsinlingensis under artificial breeding and natural environment. Traditional histological methods have been used to study the structural characteristics of the retina, and fluorescence quantitative PCR technology has been used to identify five key opsin genes that play a crucial role in visual formation: rhodopsin (RH1), rhodopsin-like pigments (RH2), short wavelength-sensitive pigments (SWS1), SWS1-like pigments (SWS2), and long wavelength-sensitive pigments (LWS). The results showed that there was no significant difference in the retina between SFGP and WP. The number of cones (C.) and outer nuclear layer (O.N.) in the retina of SFGP was significantly higher than that of WP (P＜0.01), and the number of ganglion cells (G.) was significantly higher than that of WP (P＜0.05). The relative expression level of RH1 in WP was significantly lower than that in SFGP (P＜0.01), and RH1 had the highest expression level among the five opsin genes in both populations. In cone opsin genes RH2, SWS1, SWS2, and LWS were significantly different; no significant difference in relative expression of RH2 was observed. The transcription levels of SWS1, SWS2, and LWS genes were significantly higher than those of WP (P＜0.01). The expression ratio of cone opsins in the SFGP was LWS＞SWS1＞SWS2＞RH2 from high to low, whereas that in the WP was LWS＞SWS2＞RH2＞SWS1. The expression of LWS was dominant in both populations, accounting for more than 60% of total expression. Five opsin mRNA were specifically expressed in the retinas of the two populations. This study indicated that both the SFGP and WP of B. tsinlingensis have strong photosensitive characteristics that can regulate the expression profile of opsin genes to trigger spectral sensitivity changes to cope with different habitats, and the performance characteristics of the SFGP are more significant. The exhibited photophobic behavior may be an adaptive strategy for different environments, and photosensitivity indicates that behavior depends largely on visual communication. The results of the present study provide a vital reference for the proliferation and maintenance of B. tsinlingensis.

Abstract:This study was conducted to explore the swimming ability of different species of juveniles under fasting stress. Herring (Mylopharyngodon piceus), grass carp (Ctenopharyngodon idellus), silver carp (Hypophthalmichthys molitrix), bighead (Aristichthys nobilis), crucian carp (Carassius auratus), long loach (Leptobotia elongata), loach (Misgurnus anguillicaudatus), and Taiwan loach (Paramisgumus dabryanus ssp.) were studied. The induced flow rate (U_ind), critical swimming speed (U_crit), and burst swimming speed (U_burst) were determined for different periods of fasting (0, 2, 5, 10, 15 d). For all the eight fish species, the following result is obtained: induced flow speed ＜ critical swimming speed ＜ burst swimming speed. The variation in the average induction flow rate ranges from (6.12–12.78) cm/s. Meanwhile, the induction flow rate of grass carp, silver carp, and bighead is close to and sensitive to the flow rate, and the induction flow rate is 4.75–7.75 cm/s. The swimming speeds of the eight fish species were significantly different (P＜0.05). Among the eight experimental fish, the critical swimming velocity and burst velocity were the highest for herring (121.65±3.19 cm/s, 143.48±5.77 cm/s), which were followed by that of long loach (85.08±3.23 cm/s, and 132.68±8.52 cm/s). The critical swimming velocity and burst swimming velocity of the Taiwanese loach were slower, which were (19.28±1.90) cm/s and (31.53±2.14) cm/s, respectively. The effect of fasting on the induced flow rate was not significant (P＞0.05); however, the critical swimming speed and burst swimming speed decreased linearly with fasting time, and the decrease in critical swimming speed was more significant than that in the burst swimming speed (P＜0.05). At 0 d and 2 d, the critical and burst speeds were significant (P＞0.05); at 5 d; after 5 d, the critical and burst speeds decreased by 13% to 51% and 9% to 39%, respectively. After 10 d of fasting, critical and burst swimming speeds decreased by 29%–70% and 20%–55%, respectively, with the most significant reduction in swimming speed during 10d fasting. Therefore, 10 d is a critical period that affects the swimming ability of fish. Fasting had no significant effect on the induced flow rate of juveniles; however, the critical swimming speed and burst swimming speed were significantly affected by the fasting time and a longer decrease in swimming ability. Moreover, the difference between critical and burst swimming speeds may stem from differences in energy expenditure between the different swimming modes.

Abstract:Cyclina sinensis and Anadara broughtonii are economically important bottom-sowing farming shellfish in China. Understanding their food sources can help quantify the interaction between shellfish and shallow sea aquaculture ecosystems and provide data support for the construction and screening of suitable bottom-sowing shellfish varieties for shallow sea comprehensive aquaculture models. In the present study, stable isotope and high-throughput sequencing technologies were used to determine the food composition characteristics of C. sinensis and A. broughtonii cultured in bottom sowings, and the differences and influencing factors of the food sources of the two shellfish were analyzed. Samples were collected from the bivalve culture area (BA) and bivalve kelp polyculture area (BKA) in Sanggou Bay in September 2021. The results showed the following: (1) The food sources of C. sinensis and A. broughtonii include phytoplankton, zooplankton, kelp detritus, shellfish biodeposition, seagrass detritus, C₄ plants, and terrestrial sediments. Among them, phytoplankton were the main food source of C. sinensis and A. broughtonii (accounting for 40.4%–79.6%). Zooplankton are the second food source and the contribution rate of zooplankton to A. broughtonii (35.6%–37.3%) was significantly higher than that of C. sinensis (13.3%–15.9%). There were regional differences in the contribution rates of shellfish biodeposition and kelp detritus to the food of C. sinensis and A. broughtonii. The contribution rates of shellfish biodeposition to C. sinensis and A. broughtonii in the BA were 2.0% and 7.4%, respectively. The contributions of shellfish biodeposition to C. sinensis and A. broughtonii in the BKA were 5.1% and 4.3%, respectively. The contribution rates of kelp detritus to C. sinensis and A. broughtonii in BA were 0.7% and 2.9%, respectively, and those to C. sinensis and A. broughtonii in BKA were 3.4% and 2.1%, respectively. (2) The main component in the stomach contents of C. sinensis was chlorophyta (the proportion reached 56.55%), followed by streptophyta (44.35%); the main component in the stomach contents of A. broughtonii was chlorophyta (47.27%), followed by chordata (30.3%). This was closely related to the feeding mechanisms of the two shellfish species and their physiological structures. The feeding mechanism of filter-feeding shellfish includes active and passive mechanisms, both of which are related to feeding organs. However, C. sinensis have water pipes that extend their feet and pipes before they are exposed, relying on the inlet and outlet pipes for feeding and excretion. A. broughtonii does not have water pipes and is selectively fed through gill filaments. There were also differences in the gill structures of the two shellfish. Different physiological structures lead to differences in feeding behavior between two shellfish species in the same culture area. The eukaryotic composition of the stomach contents of the two shellfish species was predominantly phytoplankton and came mainly from the bottom seawater; this was in agreement with the stable isotope results. (3) In BA and BKA, the contribution of organic matter (biodeposition and kelp detritus) produced by the raft culture to A. broughtonii was higher than that to C. sinensis. The contribution of kelp detritus to C. sinensis in BA was higher than that to A. broughtonii. From the perspective of food source structure, both A. broughtonii and C. sinensis can be used as bottom-sown shellfish in the comprehensive aquaculture area of Sanggou Bay, and C. sinensis is more suitable for bottom sowing in areas with algal cultures.

Abstract:The diversity of fish communities in artificial reefs has attracted considerable interest. Previous studies have primarily focused on species-level assessments, often overlooking variations in functional traits across species, including morphology, physiology, and reproduction. To deepen our understanding of community differences and aid in fish resource conservation, this study examined species diversity indices and functional diversity indices encompassing 12 functional traits. We analyzed data from four seasonal surveys of fishery resources and environmental variables conducted between July 2020 and April 2021 in the Fuhan National Sea Ranch Demonstration Area. Our study explored the spatial and temporal variations in fish community diversity and their correlation with environmental factors. We found significant seasonal changes in both species and functional diversity indices in the artificial reef area, whereas only functional diversity indices varied in the control area. Additionally, we observed marked spatial changes in the Pielou evenness, Simpson diversity, functional evenness, and functional dispersion indices. Spearman correlation analysis indicated that functional richness was significantly correlated with the number of species and Margalef richness index, whereas functional evenness was significantly associated with the number of species and Pielou evenness index. The community-weighted mean (CWM) index illustrates spatial and temporal shifts in the dominance of specific traits within fish communities. Redundancy analysis indicated that transparency and inorganic nitrogen were significant drivers of species diversity indices, whereas pH, inorganic nitrogen, dissolved oxygen, and transparency substantially influenced the functional diversity indices. Thus, our study highlights the complementary roles of traditional species diversity and functional diversity indices in characterizing the intricacies of fish community dynamics. Our findings suggest that the spatial and temporal patterns of fish community diversity are largely shaped by fish migration, habitat complexity, and seasonal variability in environmental factors.

Abstract:To analyze the reef-tending behavior and spatial distribution of rocky reef fishes under different aperture shapes and sizes, the behavioral effects of artificial reefs with different aperture shapes (diamond, circle, square) and sizes (2.5, 5, 7.5, 10 cm) on juvenile Acanthopagrus latus were observed and analyzed. LoliTtrack Version 5 was used to analyze the mean velocity, mean acceleration, mean turning speed, percentage of activity time, and mean distribution coordinate position of juvenile A. latus. The results showed that there was a significant increase in the mean distribution rate of juvenile A. latus in the reef area after being placed in the artificial reef, and the juveniles had the highest mean distribution rate at (27.32±4.93)% in the artificial reef area in the diamond opening experimental group, followed by the square and circular opening experimental groups, which had rates of (25.48±3.41)% and (19.83±5.59)%, respectively. In addition, the highest mean distribution rate of A. latus juveniles in Zone VI was found in the experimental group with 7.50 cm openings at (29.18±4.75)%; the second highest mean distribution rate in Zone VI was found in the experimental groups with 2.50 cm and 5.00 cm openings at (23.45±3.86)% and (23.04±5.51)%, respectively; and the lowest mean distribution rate was found in the group with 10.00 cm openings at (21.17±4.93)%; followed by square and round openings at (25.48±3.41)% and (19.83±5.59)%, respectively. was the lowest with (21.17±5.14)%. In terms of locomotor ability, the mean speed, mean acceleration and percentage of activity time of juvenile A. latus showed highly significant differences between the experimental group of the artificial reef model and the blank control group, with the mean speed increasing from (1.12±0.34) m/s in the blank control group to (1.53±0.64) m/s; mean acceleration increasing from (29.54±9.51) m/s in the control group to (40.47±17.53) m/s; and percentage of active time increasing from (77.13±12.66)% in the blank control group to (83.36±12.40)%. The mean speed, mean acceleration, mean turning speed, and percentage of activity time of juvenile A. latus differed significantly among the reef model treatment groups. The lowest mean velocity, mean acceleration, and percentage of active time were (0.81±0.31) m/s, (20.85±8.38) m/s² , and (67.44±17.45)%, respectively, for the reef model with a diamond-shaped opening and 7.5 cm opening size, which was the least active; whereas the highest mean turning speed was found in (56.79±22.80) deg/s. No significant difference was found in the mean distribution coordinate positions. The study showed that after adding the artificial reef model, the A. latus larvae had the greatest mean distribution rate as well as the lowest degree of activity for the reef model with a diamond-shaped opening and an opening size of 7.50 cm and that this artificial reef model was the most effective in attracting A. latus larvae. This preliminary study investigated changes in the reefing behavior of juvenile A. latus on different types of reefs. The results of this study can provide a theoretical basis and reference for the selection and design of species-specific proliferating artificial reefs.

Abstract:To scientifically implement conservation actions (ten-year fishing ban) on fish biodiversity in the Yangtze River, it is necessary to understand the dynamic changes in fish resources. Through a combination of literature review and field surveys, this study conducted a quantitative analysis of the changes in body length of representative Yangtze River fish since the 1980s and explored the indicative role of these changes in resource recovery. The research results showed that: 1) analysis of body length changes in seven typical fish species in the Yichang River section over the past 10 to 40 years revealed these changes are closely related to biological characteristics; high resource base values, wide-ranging feeding habits, low age of sexual maturity, and strong fecundity were associated with greater increase in body length after the fishing ban; 2) analysis of the body length of fish communities in the four waters of the Yichang reach, Jinsha River, Chishui River, and Dongting Lake over the past 20 to 40 years shows that changes can be roughly divided into three stages: decline, fluctuating increase, and obvious increase. This corresponds well with the progress of the fishing ban. 3) The average body length of Coreius heterodon and dominant fish communities in the Yichang River section is positively correlated with the catch per unit fishing effort (correlation coefficients are 0.66 and 0.88 respectively), indicating that the fish body length is closely related to resource abundance. 4) The analysis and prediction of the body length of the fish community in the Yichang River section based on the logistic curve showed that the value would reach 1.22 by 2030, which is close to the characteristic value in the 1980s. This suggests that fish resources in the river section can be restored to the resource levels of the 1980s by 2030. This study found that changes in fish body length in natural waters are closely related to the health status of populations and communities and have a positive effect on resource abundance and changes. The body length of fish can be used as an important reference indicator for routine monitoring of fish resources in the Yangtze River.

Abstract:The Yarlung Zangbo River is the largest river on the Tibetan Plateau in China. It nurtures a variety of endemic, rare, and valuable species and is a key area for global biodiversity research. However, in recent years, other natural disasters, such as mudslides within the Yarlung Zangbo River Grand Canyon (above the Motuo reach), have led to a serious decline in fishery resources in the mainstream. Benthic macroinvertebrates are an important component of river ecosystems; however, their biodiversity has not been investigated properly, and most studies are clearly inadequate at the spatial and temporal scales. To characterize the benthic macroinvertebrate community structure of the Motuo reach of the Yarlung Zangbo River Grand Canyon in Tibet, the species composition in the Motuo reach and its affiliated tributaries were investigated in October-November 2022 (autumn) and April-May 2023 (spring), and the spatial and temporal distributions of their community structure and diversity were analyzed. The results showed that 52 species of benthic macroinvertebrates, belonging to 3 phyla, 3 classes, 10 orders, and 30 families, were collected in spring and autumn. Compared with the results of a previous study, the number of benthic macroinvertebrate species was greatly reduced. Among these, aquatic insects are dominant (50 species). In addition, the dominant species in spring were Baetis sp.1 and Lepidostoma sp., whereas Baetis sp.1 and Potamyia sp. were dominant in autumn. The macrobenthic community composition differed somewhat between spring and autumn (P＜0.001). The total average abundance of benthic macroinvertebrates in the basin was 6.67 ind/m² and the total average biomass was 0.04 g/m² in autumn. Meanwhile, the total average abundance in spring was higher than that in autumn (at 8.71 ind/m² ), and the total average biomass was 0.04 g/m² . Macrobenthic biodiversity showed some differences in both the main streams and tributaries during the different seasons (P＜0.01), which may be related to water quantity and habitat stability. Natural disasters, such as mudslides, are the most significant cause of such consequences. Compared with published data (2015‒2016) and combined with the current status of water environmental factors, the dominant species of macrobenthos have significantly changed, and the total abundance and biomass of species have significantly decreased, indicating that the habitat of aquatic organisms was disturbed after the disaster. The results of this study help map the current status of benthic macroinvertebrate resources in the Motuo reach of the Yarlung Zangbo Grand Canyon in Tibet after the 2017 mudslide and provide a reference basis for biodiversity conservation in plateau regions. However, it is necessary to conduct correlation analyses in conjunction with several environmental factors to identify the key factors influencing differences in the macrobenthic community structure in subsequent studies.

Abstract:Dongping Lake, located downstream of the Yellow River, serves as a crucial flood storage reservoir and is the final reservoir of the Eastern Route of the South-to-North Water Transfer Project. To explore the current status of fish diversity and community characteristics in Dongping Lake, this study employed environmental DNA (eDNA) technology and compared the results with traditional net fishing surveys. This study elucidates the diversity of the fish community in Dongping Lake and discusses the feasibility of long-term monitoring using eDNA technology. The results revealed that the eDNA technology detected 23 species belonging to 23 genera, 7 families, and 5 orders. Further analysis indicated that the Shannon-Wiener diversity index had an average value of 1.04, ranging from 0.21 to 2.36. The average Pielou evenness index was 0.54, with values ranging from 0.29 to 0.81. The average Margalef richness index was 0.75, varying from 0.13 to 2.09. Analysis of similarities (ANOSIM) tests suggested no significant differences in diversity indices between the lake area and river channels. Non-metric multidimensional scaling (NMDS) analysis revealed four distinct cluster structures in the fish community of Dongping Lake, categorized as coastal, lake center, and two riverine types, with significant overall differences (R＜1, P＜0.05). The traditional net fishing survey captured 24 fish species belonging to 21 genera, 6 families, and 4 orders, with 18 species detected using both methods. Cypriniforms were the most abundant among the fish species detected using both methods. This study demonstrated a high similarity (62.06%) in species composition between eDNA technology and traditional net fishing surveys. Geographically, the fish community in Dongping Lake exhibited distinct distribution patterns from the Liuchang River along the coastline of Dongping Lake, north of the lake center, to the Xiaoqing River, indicating a north-south difference in the overall fish community. The results of this study confirm the feasibility of using eDNA technology for monitoring fishery resources in Dongping Lake, effectively supplement fish resources monitoring means. This study provides valuable data and technical references for the management and conservation of fishery resources in the Dongping Lake.

Abstract:Antarctic krill (Euphausia superba) is a keystone species in the Southern Ocean ecosystem, and its physiological processes across all life history stages are closely related to sea ice dynamics. The rapid warming of the Antarctic Peninsula and the southward shift in krill distribution range have garnered attention regarding the response of Antarctic krill to sea ice dynamics. The population structure of the Antarctic krill affects the Southern Ocean ecosystem at multiple trophic levels. Achieving a thorough understanding of the Antarctic krill population structure necessitates additional understanding of the replenishment, growth, and reproduction of this species. In this study, we used an open-access database to calculate five indices that reflect the population structure of Antarctic krill in the Bransfield Strait, that is, recruitment index, average length of larval, female, and male individuals in the population, and the ratio of females in the population, and developed a generalized additive model to analyze the effects of sea ice area within the Bransfield Strait and the other three areas adjacent to the Bransfield Strait, water depth, seafloor complexity, and daily index of the southern annular mode (SAM) on krill population dynamics. Since changes in sea ice and SAM have delayed impacts on Antarctic krill, this study proposes lag times of 0, 30, 60, and 90 d for both sea ice dynamics in the four areas and SAM. The results indicate that the increased sea ice area in the Bransfield Strait in the winter of the previous year promoted an increase in the recruitment index. Furthermore, aside from the sea ice area in the Strait, the Weddell Sea predominantly influenced the average lengths of juvenile and male Antarctic krill in the Bransfield Strait. The impact of sea ice area may be due to the fact that the Antarctic krill population in Bransfield Strait originates from the northwest Weddell Sea. The average length of male krill and krill juveniles exhibited a significant negative correlation with the sea ice area in the northwest Weddell Sea 60 d prior. This demonstrates the complexity of the influence of sea ice on average Antarctic krill length. The correlation between the Antarctic krill recruitment index and SAM was significantly positive on both the current day and 60 d prior. This finding contradicts previous studies that suggested that the positive effect of SAM was detrimental to Antarctic krill juvenile survival and resulted in a reduced density of Antarctic krill juveniles. This may be because positive SAM enhances upwelling and increases productivity, providing more food for juvenile Antarctic krill, leading to an increase in the recruitment index. Another possibility is that the effect of SAM on krill is regionally variable. As seafloor complexity increased, the Antarctic krill recruitment index decreased significantly. This may be because complex water depths imply a complex hydrological environment that is not conducive to the survival of Antarctic krill with poor swimming abilities. The influence of sea ice and circulation in the northwest Weddell Sea on Antarctic krill in the Bransfield Strait and the complex relationship between Antarctic krill and SAM require further study to better understand the effects of sea ice changes on Antarctic krill in the local and surrounding waters of the Bransfield Strait and its response to climate change.

Abstract:To estimate the early stage fish resources of four major Chinese carp species and the effects of ecological regulation on fish reproduction, we collected samples of fish eggs and larvae from the Honghu section of the Yangtze River from May 2014 to July 2016. A total of 56 fish eggs and 74815 larvae were collected. Hypophthalmichthys molitrix accounted for 69.64% and 75.73% of the total numbers, respectively. From 2014 to 2016, we estimated there were 1.11×10⁸ , 0.95×10⁸ , and 0.94×10⁸ ind eggs of the four major Chinese carps drifted through the Honghu section, respectively; meanwhile, there were 7.63×10⁸ , 15.36×10⁸ , and 27.64×10⁸ ind larvae, respectively. Larval density was significantly and positively correlated with water flow, water temperature, and water level (P＜0.01). The GAM model indicated that the density of the larvae showed an upward trend, which was followed by a slight decrease within the water temperature range of 18.1–26.6 ; ℃ overall, it was significantly positively linearly correlated with flow. Compared to the previous century, the resource quantity of the four major Chinese carp in the Honghu reaches of the Yangtze River decreased; however, the location of their spawning grounds did not change significantly. Ecological regulation promoted the reproductive activities of the four major carp species in the Honghu reaches; however, the effect was weaker than that in the Yidu and Jingzhou reaches, which are closer to the dam. It is recommended that important spawning grounds be demarcated and labeled and that publicity and protection be strengthened.

Abstract:This study investigated the application prospects of environmental DNA (eDNA) technology for studying the species diversity of cetaceans. It involves extracting eDNA from water samples in the Xisha sea area using universal primers for amplification targeting cetacean mitochondrial 12S rRNA and 16S rRNA. High-throughput sequencing was conducted. The results were combined with visual observation data to discuss the potential of eDNA technology in cetacean species diversity studies. These results indicated that the 4 universal primers were effective for cetacean identification. Using these primers, 5 cetacean species were detected in samples from 19 stations in the Xisha sea area. The identified species included the pan-tropical spotted dolphin (Stenella attenuata), spinner dolphin (Stenella longirostris), Fraser's dolphin (Lagenodelphis hosei), Eden's whale (Balaenoptera edeni edeni), and short-finned pilot whale (Globicephala macrorhynchus). The cetaceans observed during sampling included the pantropical spotted dolphin, spinner dolphin, and Risso's dolphin (Grampus griseus). The dominant species detected by both methods were consistent, and the environmental DNA (eDNA) technology identified species that were not visually observed. The detection results of primers Cet-12S and Marver3 covered 5 cetacean species and 17 sites where cetaceans were detected, indicating that the combined use of primers targeting different gene segments is advantageous for improving detection effectiveness. There were no significant differences among the 4 primers in terms of the detected cetacean sequences and number of species. Cet-12S exhibited the highest proportion of cetacean sequences and species, accounting for 33.0% and 21.1% of the total population, respectively. In contrast, the other primers detected much lower proportions of cetacean sequences and species, ranging from 0.2% to 0.6% and 2.0% to 4.1%, respectively. In addition, the number of nonspecifically amplified sequences and species detected by Cet-12S was significantly lower than that of the other 3 primers, indicating its high specificity as a universal primer for cetacean eDNA. Compared to visual observation, eDNA technology has advantages such as high sensitivity, efficiency, and cost-effectiveness, making it well suited for studying the species diversity of cetaceans. This study enhanced our understanding of cetacean species diversity in the Xisha Sea area, offering technical insights for cetacean conservation and research.