Abstract:The changes in fish resources after the impoundment of the Three Gorges Reservoir have attracted considerable attention. To explore the fish assemblage structure and population dynamics of the major fish populations in the Three Gorges Reservoir, we sampled fish from the lower to upper sections of the reservoir from 2015 to 2016, and analyzed the age structures of 12 primary fish populations. A total of 89 fish species were identified, with 62, 62, and 85 species recorded in the lower, middle, and upper sections, respectively. Fish assemblages were dominated by Cyprinus carpio, Hemiculter spp., and Hypophthalmichthys molitrix in the lower section; Leiocassis longirostris, Pelteobagrus spp., Saurogobio spp., and Squalidus spp. in the middle section; and Rhinogobio spp. and Coreius spp. in the upper section. In contrast, fish assemblages exhibited spatial gradients from the perspective of settlement type, habitat use, and feeding habit. These populations were composed of ages 1–7 years, and 1–3 years individuals that dominated the populations with an average proportion of 88.51%. Our results revealed that the fish community showed spatially gradient changes, and the key fish populations tended to be of younger age. This study raises suggestions for the evaluation of the ecological effects of fishing ban and further fish resource management.

Abstract:To investigate the trophic structure characteristics of fish communities in Yangcheng Lake, resource surveys were conducted in summer (July), autumn (October) 2017, and spring (April) 2018, and the carbon (δ¹³C) and nitrogen (δ¹⁵N) values of fish communities and their trophic structure were analyzed using stable isotope technology. The results of the study showed that 42 species of fishes, belonging to 5 orders, 10 families, and 33 genera were collected from the lake. The mean values of δ¹³ , δ¹⁵N and trophic level of Yangcheng Lake fishes were (?24.85±1.77)‰, (15.34±2.19)‰, and 3.06±0.64, respectively, among which δ¹⁵N and trophic level showed significant differences (P<0.01) in fish feeding and seasonality, whereas the value of δ¹³C did not show significant differences (P>0.05). The Layman’s community-wide metrics showed that there were seasonal differences in the trophic structure of fish communities in Yangcheng Lake, wherein the trophic level length, basal food source, total ecological niche space, overall community density, trophic niche distribution range, and core ecological niche space of the fish in spring were greater than those in summer and autumn, with a high diversity of food sources and low degree of trophic redundancy. A gradual upward trend from summer to autumn in 2017 and then to spring 2018 was noted. This study initially constructed a continuous trophic spectrum of fish in Yangcheng Lake, enriching the study of the Yangcheng Lake ecosystem in terms of fish community trophic structure, with the aim of providing a reference for lake ecological management and sustainable fishery development.

Abstract:In order to understand the dynamic spatio-temporal characteristics of the phytoplankton community in the Danjiangkou Reservoir during high-level water storage, the species composition, density, biomass, and biodiversity of phytoplankton in the Danjiangkou Reservoir were investigated and analyzed during May, August and November, 2017, and its fish productivity was evaluated. The results showed that 114 genera (including varieties) of phytoplankton from seven phyla were recorded in the Danjiangkou Reservoir, among which Chlorophyta had the most species with 65. The average density and biomass of phytoplankton were 7.71×10⁶ ind/L and 3.37 mg/L. The total algae density of Chlorophyta, Cyanophyta, and Cryptophyta accounted for 86.31%, and each of them exceeded the density of diatom algae (accounting for 13.50%). The Margalef richness index (D_m) and the Shannon-Wiener diversity index (H′_N) of phytoplankton ranged mainly from 1 to 2, and the Pielou evenness index (J_N′ ) of phytoplankton mainly ranged from 0.4 to 0.7, with averages of 1.35, 1.78, and 0.58, respectively. The fish productivity of phytoplankton was 101.10 kg/hm² . Analysis of Similarities (ANOSIM), Permutational Multivariate Analysis of Variance (PERMANOVA), and Similarity Percentage Analysis (SIMPER) showed that there were significant seasonal differences in phytoplankton community structure in the reservoir area, which were caused by changes in the abundance of dominant species. There were no significant spatial differences in phytoplankton community composition, with a certain homogenization trend among the different reservoir areas. Compared with previous studies, our results showed that the density and biomass of algae in the reservoir had increased, the proportion of diatoms in the Danjiangkou Reservoir area had dropped obviously, and Cyanophyta and Chlorophyta algae had become the main species in the reservoir area. All phytoplankton biodiversity indexes were at a relatively lower level, which indicates that the phytoplankton community structure is simple and unstable. These results could serve as an essential scientific basis for optimizing the ecosystem structure and function of the Danjiangkou Reservoir, as well as its ecosystem health management.

Abstract:Shijiu Lake is the only river-connected lake in the lower reaches of the Yangtze river. To determine the status of its fish resources, this study used multi-mesh gill nets and customized series cage pot to collect fish in the Shijiu Lake in the season from January 2017 to March 2018, and analyzed the fish community structure and seasonal changes in the Shijiu Lake. Our subsequent results showed that a total of 36 species of fish were collected, belonging to 28 genus, 7 families and 6 orders, among which Cyprinidae was the most common, accounting for 69.4% of the total species. The fish species were primarily sedentary, omnivorous, and pelagic fish with 25 small fish accounting for 69.44% of the total species. Toxabramis swinhonis, Coilia nasus, and Carassius auratus were the dominant species of the Shijiu Lake throughout the year. In addition to the dominant species throughout the year, the seasonal unique dominant species are Pseudorasbora parva in spring, Culter alburnus and Hemiculter leucisculus in summer, Pseudobrama simoni in autumn and Hemiculter bleekeri in winter. The relative density and biomass of fish showed marked seasonal variation, but the variation trend was the same: winter > spring > autumn > summer. The Margalef richness index R ranged from 2.28 to 3.17. The variation range of Shannon-Wiener diversity index H'_N and Pielou evenness index J'_N based on individual number was 1.24-2.14 and 0.14-0.34, respectively. The variation range of Shannon-Wiener diversity index H'_W and Pielou evenness index J'_W based on biomass was 1.64-2.51 and 0.21-0.49, respectively. All indexes were significantly higher in summer than those in other seasons, except H'_W in summer and autumn (P<0.05). The results showed that the fish species diversity of the Shijiu Lake were low. This study complements the basic data of fish community research in the Yangtze River-connected lake, and has a certain significance for the protection of fish diversity in the middle and lower reaches of the Yangtze River.

Abstract:Fish are important consumers in the food web of lakes. Fish can have different diets and can therefore occupy multiple trophic levels in the food web, thereby strongly affecting aquatic organisms and environment through trophic cascade. In the present study, we first summarize the key mechanisms and methods of biomanipulation by regulating fish assemblage. We also consider the example of Kuilei Lake, a shallow lake located in the middle and lower reaches of the Yangtze River, to elaborate on the ecological effects of integrated biomanipulation, which combines the enhancement and release of planktivorous, carnivorous, and detrivorous fish species and the removal of omnivorous fish species. Our results demonstrated the positive effects of integrated biomanipulation in optimizing the fish assemblage, water quality, and submerged plant in such a shallow lake. In conclusion, the study summarizes the impact of fish community regulation in optimizing lake ecosystems and provides new ideas and means for lake restoration.

Abstract:From 2019 to 2020, a large number of Coilia fish samples were collected during a fish resource survey carried out in Poyang Lake, Jiangxi Province, China. Morphological and molecular biological methods were used to identify these samples. Of the 112 randomly measured samples, the supermaxilla was significantly longer than the head, and the ratio of the supermaxilla/head was 1.00 to 1.46, with an average of 1.17±0.07. D-loop sequence and Cyt b sequence analysis was used to compare 22 samples, and the results confirmed that the collected samples were Coilia nasus. The microchemical characteristics of five otolith samples were measured, and the results showed that the ratio of strontium to calcium (Si/Ca) of the otoliths was greater than 3, indicating that the samples were anadromous C. nasus. In 2019 and 2020, the catch per unit effort of C. nasus in the Poyang Lake reached 8.1 ind/d and 142 ind/d, respectively. This increase is significant compared with historical data. The recovery of C. nasus resources in Poyang Lake shows that the Fishing Ban in the Yangtze River and the C. nasus fishing permit cancellation achieved positive results. Additional investigation of the spawning grounds and habitat protection are recommended to further promote the recovery of C. nasus resources in the Poyang Lake.

Abstract:Utilizing the basic biology data of Hemiculter bleekeri collected from October 2019 to September 2020 in Zhushan Lake, this study aimed to explore the population parameters of H. bleekeri in the Zhushan Lake and to thereby evaluate the utilization of resources using Electronic Length Frequency Analysis I (ELEFAN I), based on the length of frequency data and length-based Bayesian biomass (LBB). The results show that the length range of H. bleekeri is 44.17–181.87 mm; the weight range is 0.88–70.30 g; the relationship between body length and body weight can be expressed as W=9.0×10^–5L^3.0707(R2 =0.8775, n=805); and the growth equation of body length and weight can be described respectively as: L_t=194.25×[1–e^{–0.36(t+0.46)}], W_t=95.74×[1–e^{–0.36 (t+0.46)}] ^3.0707. According to the estimation by ELEFAN I, the relative natural mortality is M/K=2.28; the relative fishing mortality is F/K=4.50; the relative total mortality is Z/K=6.78; and the exploitation rate is E=0.66. According to the estimation by LBB, M/K, F/K, Z/K, and exploitation rate E are 1.88, 5.78, 7.64, and 0.76, respectively. The results of this study can not only fill the knowledge gap regarding the population growth characteristics and resource utilization of H. bleekeri in Zhushan Lake, but also provide a basis for scientific management of fishery resources in Taihu Lake.

Abstract:To study the changes in food web structure in the process of ecological restoration of Yidian Lake, this study was conducted in the experimental area of the Shihoudian lake by planting submerged plants to build artificial fish nests. Based on the investigation data of fish resources and ecological environment of Shihoudian Lake in 2019, the structure and energy flow characteristics of the two regional ecosystems were compared and analyzed using Ecopath with the Ecosim software and ecosystem energy channel model. The results showed that the trophic level of the same fish species in the experimental area was slightly lower than that in the control area. The niche of the same species in the ecological restoration area was lower than that in the control area. Meanwhile, there were more consumers in the former food chain, such as catfish (Siluriformes), mandarin fish (Siniperca chuatsi), Wuchang bream (Megalobrama amblycephala), and grass carp (Ctenopharyngodon idellus). Complex structure suggest a stable food web. In addition, the energy conversion efficiency among the trophic levels in the experimental areawas was higher than that in the control area. The total energy conversion efficiency (2.5%) in the experimental area was higher than that in the control area (1.7%); the connection coefficient (0.22) in the experimental area was slightly lower than that in the control area (0.27); the system omnivorous index (0.15) was higher than that in the control area (0.14); and the Finn’s cycle index and average path length (0.61 and 2.08, respectively) in the experimental area were lower than those in the control area (1.73 and 2.20, respectively). The overall characteristics of the two regional ecosystems showed that the structure of the food web in the experimental area was more complex, the energy transfer efficiency was improved, and the ecosystem was more perfect. However, the length of nutrient flow through the food chain in the experimental area was shortened, and the proportion of material recycling was decreased. At the same time, the production was greater than the respiration in the experimental area. Thus, further implementation of restoration measures for fish resources would be conducive to development of the ecosystem in the experimental area.

Abstract:To explore the current status of the Weishui Reservoir ecosystem and the ecological capacity of Hypophthalmichthys molitrix and Aristichthys nobilis, we used data from the fishery resource survey in July 2020 (summer), September 2020 (autumn), and January 2021 (winter) to establish an Ecopath model. The Ecopath model of the Weishui Reservoir consisted of 15 functional groups, and the fractional trophic levels ranged from 1 to 3.336. The keystones were Siniperca chuatsi and Culters, and the results indicated that their two niches, which included Hypophthalmichthys molitrix, Aristichthys nobilis, and Hemiculter leucisculus highly overlapped. The Finn cycling index (FCI), system connectance index (CI), and omnivory index (SOI) of the Weishui Reservoir were 11.35, 0.351, and 0.099, respectively, indicating that the Weishui Reservoir had a higher material recycling ratio than other lake and reservoir ecosystems, and that its functional groups had more closely and complexly connected relationships. The total system throughput (TST) of the ecosystem of the Weishui Reservoir was 44254.860 t/(km²·a), and the ratio of the total primary production to the total respiration (TPP/TR) was 1.394, indicating that the overall scale of the system was appropriate and was approaching a mature development stage. The biomasses of Hypophthalmichthys molitrix and Aristichthys nobilis in the Weishui Reservoir were 2.117 t/(km² ·a) and 16.577 t/(km² ·a), respectively, and their ecological capacities were 30.169 t/(km² ·a) and 236.217 t/(km² ·a), respectively.

Abstract:Silver and bighead carp (Hypophthalmichthys molitrix and Aristichthys nobilis) are typical filter-feeding fish that are important species for the implementation of water purification fishery, and scientific stocking based on the ecological capacity of the proliferating species can ensure the implementation effect of water purification fishery. To ensure the implementation of water purification fishery in the Taihu Lake, we constructed an Ecopath model comprising 16 functional groups. This model was based on the survey data of fishery resources and the ecological environment of the Taihu Lake in 2017–2018. Relevant data was collected using Ecopath with Ecosim 6.6 to estimate the ecological capacity of silver and bighead carp in the Taihu Lake and to investigate the effects of changes in silver and bighead carp biomass on the overall characteristics of the Taihu Lake ecosystem. The results showed that the current biomass of the silver and bighead carp was 10.21 t/km² , which increased 5.054 times to reach an ecological capacity of 51.6 t/km² . It is showed that there is still great potential for the growth of the silver and bighead carp. Total primary production/total respiration decreased from 2.548 to 2.23 (change of 0.318). Connectance index, system omnivory index, Finn’s cycling index, and Finn’s mean path length exhibited fewer changes. Silver and bighead carp exert less impact on the ecosystem structure when they reach the ecological capacity, but nevertheless help the ecosystem to mature. Further analysis shows that when Coilia nasus is controlled at 9.49 t/km² , the biomass capacity of the silver and bighead carp could increase to 206.4 t/km² , and when the silver and bighead carp reach their ecological capacity, the ecosystem will become more stable.

Abstract:为了探讨大型河流中的 eDNA 监测效率, 以长江为大型河流的代表, 以鱼类为水生生物的代表, 分析传统捕捞监测和 eDNA 监测结果的差异, 研究 eDNA 监测技术对长江武汉江段鱼类组成的监测能力、监测效率、平行样设置等问题。结果显示: (1) 用 1 对 eDNA 宏条形码引物(mlCOIintF/jgHCO2198R)共监测到 89 种鱼类, 其中 30 种可与历史捕捞调查记录互相确认, 另外 59 种需要更完善的条形码数据库来解决序列比对注释问题; (2) 9 月在武汉监测断面, 可用单引物(mlCOIintF/jgHCO2198R) eDNA 监测到的物种最优估计约 99 种, 单样品 eDNA 监测的鱼类物种检出能力约为 26 种, 检出效率约为 25.8%; (3) 在 80%的检出度目标下, 需要约 10 个平行样, 在 95%的检出度目标下, 需要约 17 个平行样。本研究在长江武汉江段鱼类 eDNA 监测效率和平行样设置的相关量化结果可为长江其他断面及其他大型河流的 eDNA 监测提供量化参考。同时, 本研究表明, 更完善的 DNA 宏条形码数据库和合适的平行样设置是未来 eDNA 监测作为常规监测手段进行运用的前提。

Abstract:Mandarin fish (Siniperca chuatsi) is a top predator in the freshwater ecosystem, and also a traditional fishery target in China. Over the years, due to the excessive interference of human activities, the natural resources of mandarin fish in large water bodies such as lakes and reservoirs have sharply declined. As an important measure for the conservation and restoration of aquatic biological resources, stock enhancement has been carried out in a large number of countries worldwide. In recent years, a series of basic research studies on stock enhancement of mandarin fish have been carried out, which has effectively improved this comprehensive benefit. This paper summarizes the stock enhancement technology of mandarin fish based on a reasonable stocking size, release season, release site, and release numbers. The latest progress in the effect evaluation of mandarin fish stock enhancement on three aspects of economic benefit, ecological effect, and social benefit are systematically reviewed. The future research direction is also highlighted which provides a reference for stock enhancement of mandarin fish in China.