Search Results (164)

Due to overfishing, eutrophication of rivers and lakes, and irrational stocking practices, the diversity of wild native carp populations has declined, leading to germplasm degradation and a decrease in fish quality, thereby affecting the sustainable development of fisheries. In this study, a novel hybrid crucian carp lineage (designated LWR) was successfully established via distant hybridization using Dongting Lake crucian carp (LC, ♀) and Hefang crucian carp (WR, ♂) as parental stocks. Systematic analyses were conducted on the morphology, ploidy, fertility, growth performance, survival rate, and molecular genetics of LWR. The results reveal that LWR is an allodiploid (2n = 100), with a chromosome number identical to that of its parents. Gonadal development in the hybrid progeny (LWR) was normal, with both sexes being fertile and reaching sexual maturity at one year of age. Morphologically, LWR exhibited intermediate traits with a paternal bias, characterized by a deep-bodied and elongated shape. In terms of growth performance, LWR displayed significant heterosis (approximately 145% and 271% higher than the body weight of the maternal parent at 6 months and 1 year). Molecular genetic analysis indicated that the 5S rDNA sequences of LWR were predominantly inherited from the paternal parent WR, with insertions, deletions, recombination, and mutations detected. The mtDNA sequences exhibited 99.78% similarity to those of the maternal parent LC, following maternal inheritance with sporadic nucleotide variations. These findings offer a new paradigm for hybridization and a theoretical foundation for the improvement and sustainable utilization of indigenous crucian carp germplasm resources, the selective breeding of improved aquaculture strains, and the sustainable development of fisheries. Full article

Ecosystems can undergo abrupt, often irreversible transitions between alternative states—phenomena termed critical transitions or regime shifts—with profound consequences for biodiversity, ecosystem services, and human well-being. Early warning signals (EWSs) derived from time-series analysis offer the prospect of anticipating such transitions before they occur, potentially enabling preventive management intervention. This review provides a comprehensive synthesis of EWS methods for ecological systems, encompassing theoretical foundations, statistical indicators, empirical applications, and emerging methodological frontiers. We examine the dynamical basis of EWS in critical slowing down theory, wherein systems approaching bifurcation points exhibit characteristic statistical signatures including rising autocorrelation, increasing variance, and spectral reddening. We present a systematic overview of proposed indicators discuss moving-window frameworks for their computation, and critically evaluate preprocessing requirements and sensitivity to analytical choices. Empirical applications across major ecosystem types—including lakes, coral reefs, grasslands, forests, and marine fisheries—reveal both successes and limitations, with EWS performance depending critically on data quality, transition mechanism, and system-specific dynamics. We address recent advances including machine learning approaches, non-equilibrium thermodynamic indicators, multivariate extensions, and the important distinction between bifurcation-induced, noise-induced, and rate-induced tipping. We conclude with recommendations for specialists, emphasizing the integration of EWS within broader monitoring frameworks, systematic sensitivity analysis, and the interpretation of indicators as probabilistic assessments of changing resilience rather than deterministic predictions of imminent collapse. Full article

The present study incorporates age- and length-based methods to estimate the stock status of Nile tilapia (Oreochromis niloticus) in the inland fisheries of Lake Nasser, Egypt. In 2021, a total of 570 specimens were sampled to determine the length–weight relationships, condition factor, maturity schedules, age structure and growth parameters. The age estimations were quite accurate, suggesting a lifespan of 5 years. Females attained 50% maturity at a length of 27.85 cm and age of 2.30 years, while males attained maturity at 29.93 cm and 2.45 years. The von Bertalanffy model best described growth parameters using the Bayesian approach. Length-based reference points produced from aLBI indicate a close association between length at initial maturity (L_mat = 29.3 cm) and optimal harvest length (L_opt = 30.8 cm). The Froese indicators indicate that all the proportions of mature fish (P_mat = 44.8%), fish of optimum size (P_opt = 35.6%), and big spawners (P_mega = 18.1%) were below sustainability targets. The results indicate that non-selective fishing gear is responsible for growth and recruitment overfishing by harvesting fish at, or below, maturity. The integrated Bayesian–aLBI approach offers a rigors and transparent assessment for inland fisheries with limited data and support for size-based management actions to rebuild the Nile tilapia stock in Lake Nasser. Full article

Digestive tract structure is a key indicator of fish health and environmental adaptation, while seasonal dynamics of the gut microbiota reflect host responses to environmental changes. In this study, the digestive tract microstructure of Hypomesus nipponensis from Bosten Lake was characterized using H&E staining and scanning electron microscopy, followed by 16S rDNA gene V3-V4 region sequencing and analysis of the gut microbiota in spring, summer, and autumn. The results showed that the esophageal mucosa of H. nipponensis is a stratified columnar epithelium, with abundant gastric glands, and the circular muscle layer of the stomach caeca is significantly thickened (244.84 ± 49.01 μm). The pyloric caeca resemble the gut in structure; both are covered with dense microvilli on the luminal surface. Collectively, these features constitute the structural basis for its carnivorous diet. Microbiota analysis revealed that the diversity of gut microbiota fluctuated significantly with season: the Chao, Ace, and Sob indices in spring (144.63 ± 30.27) were significantly higher than in summer (82.13 ± 21.45) and autumn (83.25 ± 15.30) (p < 0.001), with no significant difference between summer and autumn (p > 0.05). The dominant marker genera of H. nipponensis in spring, summer, and autumn were Bacillus (31.60%), Clostridium (32.20%), and Sarcina (29.32%), respectively. This study describes the adaptive characteristics of the digestive tract structure and feeding habits of H. nipponensis and reveals the seasonal changes in its gut microbiota. Importantly, since the digestive tract structure data were collected only in summer, the direct relationship between the structure and seasonal microbial dynamics cannot be determined, and multi-season histological sampling is needed for further investigation. Nevertheless, these findings provide preliminary morphological and microbiological references for the ecological adaptation of this species in Bosten Lake and offer a scientific basis for water resource management in this area. Full article

Water scarcity is an increasingly pressing global concern, making the sustainable development of water resources a critical priority. Revered as the “Sacred Sea,” Lake Baikal holds the largest volume of freshwater in any single lake in the world, with exceptional water quality, conferring it with considerable global strategic importance. This study reviews the hydrological dynamics of Lake Baikal, including water level fluctuations and runoff patterns, and examines water resource utilization (including virtual water and long-distance diversion), along with its potential, challenges, and associated ecological risks, in an integrated manner. Previous studies reveal an interannual cycle of fluctuating water levels, with annual peaks typically occurring between September and October. Outflow runoff closely depends on lake water levels, while inflow runoff exhibits considerable variability. The Selenga River, the largest tributary originating from the Mongolian Plateau, significantly influences the lake’s hydrology and ecological integrity. Current water uses primarily include domestic supply, regional industry, and fisheries, while agricultural water use is relatively limited and mainly occurs within tributary catchments. Emerging options, such as virtual water trade, may offer relatively more manageable alternatives to large-scale transboundary water transfers in certain contexts. Given the multiple disturbances and potential impacts on the Lake Baikal ecosystem, this study advocates prioritizing ecological protection in water resource utilization and underscores the necessity of comprehensive, system-level assessments prior to any water extraction or diversion activities. Full article

The increasing consumption of fish has raised public health concerns regarding fish-borne zoonotic helminths (FBZHs), which are recognized as significant food-borne parasites worldwide. In freshwater environments, Clinostomum complanatum, Opisthorchis felineus, Pseudamphistomum truncatum, Dibothriocephalus latus and Eustrongylides excisus are of particular concern in Italy and neighbouring countries. This study aimed to assess the prevalence of these FBZHs in five commercially and ecologically relevant freshwater fish species from Lake Varese, a heavily anthropized and understudied basin in northern Italy. A total of 59 fish were examined via necropsy and stereomicroscopic inspection of skeletal muscles. Only Eustrongylides spp. larvae were detected, with a prevalence of 16.9%. Molecular analysis (ITS region) identified them as E. excisus. This study reports, for the first time in Western Europe, E. excisus in Sander lucioperca (p = 12.5%) and Esox lucius (p = 8.3%). The highest prevalence occurred in Silurus glanis (p = 37.5%), followed by Perca fluviatilis (p = 25.0%), while Tinca tinca showed no infection. These findings confirm that among the FBZHs considered, E. excisus is currently present and expanding both in host range and geography in Italian lakes, underscoring the need for updated epidemiological data to support risk assessment, food safety and zoonotic parasite control in freshwater fisheries. Full article

Catfish is a major commercial and subsistence species in Malawi, making its sustainability vital for local livelihoods and food security. However, limited evidence exists on the long-term biological and economic depletion of commercial catfish stocks. This study assessed the depletion status of the catfish fishery in the southeast arm of Lake Malawi using secondary catch and effort data from 2000 to 2023 obtained from the Malawi Department of Fisheries, and price and cost data obtained from the field study. Applying the bioeconomic Gordon–Schaefer model, the study estimated biological depletion and economic depreciation to quantify resource losses and evaluate the fishery’s sustainability. Constant and periodic harvesting strategies were examined to determine sustainable harvest thresholds. Results show that depletion occurred in 15 of the 24 years analysed, with a cumulative biomass loss of 446.1 tonnes and an estimated total depreciation of about MK 1.5 billion. These findings indicate exploitation beyond sustainable levels both biologically and economically, threatening stock recovery, long-term productivity, and economic viability. The study highlights the value of bioeconomic modelling in fishery assessment and underscores the urgent need for improved management, including strengthened monitoring, effort regulation, and enhanced enforcement, to ensure sustainable utilisation of catfish resources and protect dependent livelihoods. Full article

Yangtze finless porpoise (Neophocaena asiaeorientalis) is the only extant cetacean species in the Yangtze River, a national first-class protected wild animal in China, and a key indicator reflecting the health status of the Yangtze River ecosystem. Environmental changes can induce adaptive trophic responses in animal communities; thus, clarifying the dynamic interactions between fish assemblages and dietary shifts in the Yangtze finless porpoise after the fishing moratorium is critically important. In this study, fishery resources in Poyang Lake were surveyed using triple-layer composite gill nets and cage traps, with samples collected and analyzed accordingly. A total of 81 fish species belonging to 8 orders and 16 families were recorded. Following the fishing ban, the abundance of small-bodied fish species (e.g., Hemiculter bleekeri, Carassius auratus) decreased, while the proportion of piscivorous species among the top ten dominant fish increased from 40% to 60%. DNA barcoding was used to analyze gastric contents of 10 dead porpoises found post-moratorium, and the results were compared with pre-ban data. Gastric content analysis identified 11 prey taxa, and comparative analysis demonstrated that prey selectivity was closely correlated with local prey availability. Concomitant with the structural reorganization of the fish community in Poyang Lake during the early stage of the fishing ban, the Yangtze finless porpoise exhibited adaptive dietary shifts toward benthic and small-bodied fish species, suggesting a potential linkage between these ecological responses. These findings provide direct implications for formulating targeted conservation strategies for this endangered cetacean and highlight the necessity of protecting small and benthic fish populations to ensure their long-term survival. Full article

Sapanca Lake is a tectonic freshwater lake ecosystem whose water balance and ecological integrity are increasingly threatened by urbanization, pollution, climate change, and declining water levels. To assess recent changes in the fish community, length–weight relationships (LWRs), condition factors (CFs), sex ratios (F/M), and standing stock biomass estimates were determined for eight fish species (Blicca bjoerkna, Scardinius erythrophthalmus, Carassius gibelio, Esox lucius, Silurus glanis, Perca fluviatilis, Abramis brama and Cyprinus carpio) sampled between December 2024 and April 2025. According to standing stock biomass assessments, Cyprinus carpio showed the highest biomass (297.67 tons), while Abramis brama had the lowest (22.72 tons). Most species showed positive allometric growth (b > 3), suggesting generally favorable feeding conditions. In contrast, the main predatory species, E. lucius (b = 2.89) and Silurus glanis (b = 0.21), exhibited negative allometric growth, likely due to limitations in food availability and prey abundance. The CF values were generally >1, indicating good physiological status; however, lower CF values in A. brama (1.18) and B. bjoerkna (1.19) suggest species-specific ecological limitations. Sex ratio analysis revealed pronounced female dominance across species, ranging from complete female dominance (F/M = 1/0) in Carassius gibelio to a female-biased ratio of 1/0.04 in Scardinius erythrophthalmus, likely driven by seasonal sampling effects, sex-specific behavior, and species-specific reproductive strategies. Overall, the results indicate increasing trophic imbalance and ecological stress in Sapanca Lake, emphasizing the need for standing stock biomass assessments and ecosystem-focused fisheries management in tectonic lakes under hydrological pressure. Full article

Many species within the family Moronidae possess biological traits that facilitate their success as invasive species in freshwater ecosystems. In Iowa, USA, non-native Yellow Bass (Morone mississippiensis) have expanded their range into at least 19 glacial natural lakes, yet their trophic interactions in these complex systems remain poorly understood. From 2018 to 2020, we evaluated the open-water diet composition of 1300 Yellow Bass across six Iowa natural lakes to quantify diet composition, feeding intensity, and ontogenetic dietary shifts. While zooplankton numerically dominated diets across most systems (>80% by number) biomass was driven primarily by benthic invertebrates and fish. Feeding intensity was not uniform, characterized by a distinct suppression of foraging during late spring followed by intense feeding in early summer. Overall, we found that Yellow Bass foraging is highly plastic but heavily constrained by spatial (lake identity, season, and year) and biological (ontogeny, age, and sex) filters. Spatial heterogeneity was the primary driver of diet composition ${(R}^2=0.407)$, with individual lakes explaining the largest portion of variance ${(R}^2=0.126)$. The interaction between lake size and population history ${(R}^2=0.054)$ was also significant, highlighting that the ecological impact of Yellow Bass is context-dependent, differing among established populations in small lakes versus recent invasions in large lakes. We identified distinct ontogenetic breakpoints at 114 mm and 252 mm; fish < 114 mm were obligate zooplanktivores, while significant piscivory was restricted to large adults (>252 mm). These results suggest that the successful colonization of Yellow Bass is supported by high dietary plasticity, which may lead to intensive resource competition with native juveniles. Our findings provide a critical baseline for fisheries managers to assess the ecological risks associated with Yellow Bass expansion and emphasize the importance of monitoring trophic shifts to preserve the integrity of native fish communities in the Midwest. Full article

Shoreline variations in closed-basin lakes are closely linked to hydrological fluctuations and long-term changes in water balance, making them important indicators of environmental change. This study analyzes historical shoreline dynamics in Lake Van (Türkiye), the world’s largest soda lake, and provides scenario-based shoreline projections for 2032 and 2042 to support hydrological assessment and water-related management. Multi-temporal Landsat satellite images from 1982, 1992, 2002, 2012, and 2022 were processed using the Digital Shoreline Analysis System (DSAS 5.0) to quantify shoreline retreat and accretion, while future shoreline positions were estimated using the Kalman filter model. The results show pronounced spatial variability, with the most significant shoreline retreat observed in the Çelebibağ and Karahan regions, where sediment supplied by major inflowing streams contributes to shoreline instability through reworking and redistribution rather than stable accretion. Net shoreline movement values reached −2580.1 m for erosion and up to 1700 m for accretion. Model projections indicate an increasing trend of shoreline retreat by 2032 and 2042, accompanied by localized accretion zones. These hydrological-driven shoreline changes have potential implications for littoral habitats, water–land interactions, and human use of the shoreline, including fisheries infrastructure. The study demonstrates the value of integrating remote sensing and statistical forecasting for monitoring shoreline dynamics in closed-basin lake systems. Full article

The status of the fishery resources in Poyang Lake, China, during periods of abnormal drought was examined using a comparative analysis of data from four fishery resource surveys performed during 2022 and 2023, in the first half (April–June) and the second half (September–November) of each year. A total of 91 fish species (11 orders, 17 families, 54 genera) were collected, with Cyprinidae accounting for 54.95% of the total species and Megalobrama skolkovii, Aristichthys nobilis, and Hypophthalmichthys molitrix as the dominant species. The Shannon-Weiner diversity, Pielou evenness, Simpson diversity, and Margalef richness indices were 3.30, 0.73, 0.95, and 6.93, respectively. The corresponding catch per unit effort (CPUE) values of the fish were 5.49 kg·(1000 m²·h)⁻¹, 4.45 kg·(1000 m²·h)⁻¹, 3.03 kg·(1000 m²·h)⁻¹, and 2.75 kg·(1000 m²·h)⁻¹, showing a clear decreasing trend across the successive sampling periods. The abnormal drought did not cause significant differences in the number of fish species and diversity indices (p > 0.05), but altered the fish community structure, characterized by reduced dominance of small, sedentary, and herbivorous fish, and led to a significant decline in CPUE (p < 0.05). This demonstrates that abnormal hydrological regimes can undermine the effectiveness of the 10-year fishing ban and threaten the recovery of fishery resources in river-connected lakes. Full article

Effective fisheries management relies on accurate stock assessments to ensure sustainable exploitation and long-term ecosystem stability. Fisheries from the Nile Delta lakes of Egypt—comprising Manzala, Burullus, Edku, and Mariout—are economically critical, collectively contributing about 40% of the nation’s total capture fisheries and are facing severe anthropogenic challenges. This study assessed the stock status of 10 key fish species and two crustacean species from these four Nile Delta lakes by determining their life history parameters and exploitation levels. The analysis included estimation of the Length–Weight Relationship (LWR), von Bertalanffy Growth Function (VBGF) parameters, instantaneous mortality coefficients (Z, M, F), and the exploitation ratio (E). Asymptotic total length (L∞) varied widely, ranging from 10.47 cm for Portunus pelagicus to 86.78 cm for Clarias gariepinus (in Lake Manzala). The growth coefficient (K) spanned from 0.31 yr⁻¹ (C. gariepinus) to 1.79 yr⁻¹ (Metapenaeus stebbingi), reflecting diverse life history strategies. The key finding, based on the Gulland criterion, is that all commercial stocks examined in the Nile Delta lakes are currently subjected to severe overexploitation, with the exploitation ratio (E) consistently exceeding the optimal threshold of 0.5. These results underscore the urgent need for adaptive management strategies, including stricter gear regulations and improved fisheries monitoring, to ensure the sustainability of these vital resources. Full article

Linear mixed-effects modeling has been used to characterize fish growth changes over time, but early studies did not fully consider the implicit relationship among the three major factors of fish age, year-class, and sampling year in model development. Our objective is to resolve this issue and develop a linear mixed-effects model to clearly assess how lake trout (Salvelinus namaycush) growth has responded to the ecosystem regime shift in Lake Huron. We found that, from the late 1970s through the early 2000s, lake trout weight-at-age in northern Lake Huron had large variation with no apparent temporal trend, whereas the weight-at-age in southern Lake Huron steadily declined but remained larger than that in northern Lake Huron. The difference between northern and southern Lake Huron almost disappeared prior to the 2003 collapse of alewives, which accelerated the weight-at-age declines during the 2000s in both regions. By 2010, lake trout growth had a modest recovery and then stabilized. Our model fitted and explained variation in lake trout weight-at-age between years, regions, and recruitment origins, with the fixed age effect representing the general growth trajectory, the fixed year effect as the year-specific growth index, and the random year-class effect as the cohort-specific growth index. Full article

Standardized fishing gear represents a common fisheries management intervention, yet its effectiveness in multi-species freshwater ecosystems remains insufficiently assessed. This study presents the first application of the Length-Based Bayesian Biomass (LBB) method to systematically evaluate the stock status of eight major commercial fish species in Xingkai Lake (located within China). Length-frequency data collected in 2019 (marking the policy initiation) and 2024 (after five years of implementation) were used to estimate key population parameters and exploitation indicators. The results revealed that the four species (Carassius gibelio, Acheilognathus macropterus, Hemiculter lucidus, and Hemiculter leucisculus) recovered to healthy status (B/B_MSY ≥ 1.0), demonstrating the policy’s effectiveness for small-bodied, fast-growing species. In contrast, three species (Chanodichthys abramoides, Chanodichthys mongolicus, and Chanodichthys erythropterus) remained grossly overfished (B/B_MSY < 0.5), while Culter alburnus experienced increased fishing pressure, indicating limited efficacy for larger, slow-growing species with collapsed initial stocks. Although the mesh size increase facilitated recovery of specific populations, fisheries resources in Xingkai Lake continue to face overfishing pressure. Management strategies lacking an ecosystem perspective may not only fail to achieve conservation objectives but could also trigger ecological risks. This study underscores that ecosystem-based management is essential for sustainable management of multi-species fisheries. Full article