Search Results (44)

Introduction: Freshwater fish communities in Mediterranean basins have undergone profound changes over recent decades due to biological invasions, habitat alteration, and hydrological regulation. The Segura River basin (SE Spain), particularly in the Region of Murcia, represents a paradigmatic case of these transformations, with increasing pressures on native ichthyofauna and growing relevance for recreational fisheries. Objective: This study aims to provide an updated inventory of fish communities in the rivers and reservoirs of the Region of Murcia, assessing current composition, relative abundance, and conservation status. Methodology: Fish assemblages were surveyed during sampling campaigns conducted in autumn 2023, 2024 and 2025. Sampling sites included representative reservoirs and river reaches within the middle sector of the Segura River basin, focusing on areas of interest for recreational fishing. Passive fishing gears were used in reservoirs, while electrofishing was conducted in riverine habitats. Presence and relative abundance data were recorded for all detected taxa. Results: A total of 15 taxa were identified (8 in reservoirs and 15 in river reaches). Reservoir communities were almost entirely dominated by non-native invasive species, including Cyprinus carpio, Alburnus alburnus, Sander lucioperca, Micropterus salmoides, Lepomis gibbosus, and Gambusia holbrooki, with Luciobarbus sclateri as the only native species. Riverine sections of the main channel also showed a strong dominance of exotic taxa, with additional species such as Esox lucius, Oncorhynchus mykiss, Gobio lozanoi, and Pseudochondrostoma polylepis. Native species detected included L. sclateri (dominant), Anguilla anguilla, and Salariopsis fluviatilis, the latter showing a recent expansion likely linked to human-mediated introduction. Isolated tributaries hosted the most valuable assemblages, including populations of L. sclateri, Squalius tartessicus, and the endangered Valencia hispanica (recently unauthorized translocations into the Segura river basin). Conclusions: Current fish communities in the Region of Murcia reflect a marked ecological degradation compared to historical conditions, driven by the proliferation of non-native species and habitat alteration. Changes over the last 30 years have been particularly pronounced in reservoirs and regulated sections of the main river channel, where local extinction of the native S. tartessicus has also been detected. Only the headwaters of certain tributaries retain fish assemblages of notable conservation interest, highlighting their priority for management and protection. Full article

In the Iberian Peninsula, the rapid expansion of the invasive species Alburnus alburnus (bleak) has intensified its contact with several endemic cyprinid species, raising concerns about hybridization, introgression, and the loss of genetic diversity. Despite increasing evidence of hybridization, data remain limited for many Iberian River basins, where endemic species persist in fragmented and vulnerable habitats. The aim of this study is to assess the extent and spatial distribution of hybridization between the bleak and the following native cyprinid species, Anaecypris hispanica (jarabugo), Iberochondrostoma lemmingii (pardilla), Pseudochondrostoma willkommii (Guadiana nase), and Squalius alburnoides (calandino), across several rivers within the Guadalquivir Basin. To this end, Sanger sequencing will be performed on the mitochondrial cytochrome b gene (maternal lineage; approximately 1000 base pairs (bp)) and the nuclear β-actin gene (paternal lineage; approximately 950 bp) from individuals of all endemic species and the bleak. Parental species and putative hybrids were initially identified in the field using diagnostic morphological and meristic characters, including number of rays in the anal fin morphology, mouth position, and the number of lateral line scales. Molecular analyses will include haplotype network reconstruction and phylogenetic tree inference to evaluate relationships among individuals from different species and to assess lineage divergence. The results will allow us to: (1) detect hybrids between the bleak and endemic cyprinids, (2) identify hybridization events among endemic cyprinid species, and (3) evaluate the correspondence between diagnostic morphological and meristic traits and the molecular identification of hybrid individuals. Overall, these findings will provide key information for the conservation management of endangered Iberian freshwater fishes in the context of invasive species expansion and global change. Full article

Introduction: Studying the structure and dynamics of living communities is essential from both ecological and wildlife management perspectives. Objective: The main objective of this study was to analyze the fish community structure inhabiting different river sections across several basins in the Mediterranean area. The data collected here contributed to: (i) creating a regional and national reference inventory to assess ichthyological biodiversity; (ii) generating digital cartographic information on species distribution and potential habitats; and (iii) providing scientific data to update national legal protection for governments. Methodology: Fish assemblages were monitored using electrofishing, which ensures reproducible data and long-term comparability. The study period extended until autumn 2025, with intensive sampling at 30 sites across major water bodies in the Valencian Community and selected rivers in Mijares, Turia, Jucar and Palancia basins. Results: The results reveal notable ichthyological richness in the studied basins (Turia, Júcar, Palancia, Mijares), with 12 native species identified. Cyprinidae and Leuciscidae were the most representative families, both in species number and spatial distribution, consistent with their dominance in Mediterranean river systems. Areas with the highest species richness corresponded to the middle and lower river sections and to ecologically valuable coastal wetlands. However, the study also detected 10 invasive alien species, representing 45% of the total fish fauna recorded. This high proportion reflects the significant ecological alteration affecting rivers and wetlands in these basins and underscores the urgent need for management actions to limit the spread of invasive species and reduce their impact on native biodiversity. The most widespread IAS were the bleak (A. alburnus), mainly in the Júcar basin, and the mosquitofish (G. holbrooki), predominantly in coastal wetlands. Conclusions: This study contributes directly to updating the Atlas of Ichthyofauna of the Valencian Community, providing a robust and current information base to support environmental decision-making at regional and national levels. The findings highlight the importance of strengthening proactive conservation measures, particularly in areas where biodiversity is most vulnerable. Full article

To address cryodamage in Culter alburnus sperm, this study evaluated the effects of trehalose supplementation in a conventional cryomedium (D-15 + 10% ethylene glycol). Six experimental groups were established: fresh sperm (G1), a conventional cryomedium (G2), groups supplemented with 10, 100, or 200 mmol/L trehalose (G3–G5), and a control group with extender only (G6). The group with 100 mmol/L trehalose (G4) was associated with improved post-thaw motility parameters (activation rate, movement time, and lifespan) and higher antioxidant (superoxide dismutase and catalase) and energy metabolism (ATPase, succinate dehydrogenase, lactate dehydrogenase) enzyme activities. Ultrastructural damage in G4 included partial plasma membrane rupture and mitochondrial swelling, while G6 exhibited additional damage features including membrane disintegration, mitochondrial disruption, and flagellar fracture. Proteomic analysis revealed that, compared to G1, G4 exhibited higher abundance of proteins (e.g., Histone H2A, cytochrome c oxidase, profilin) involved in structural integrity and energy homeostasis, whereas G6 showed signatures of oxidative stress and metabolic dysfunction (lower abundance of NADH dehydrogenase and higher abundance of calcium-transporting ATPase and glutathione S-transferase). In conclusion, 100 mmol/L trehalose was associated with improved cryopreservation outcomes, and the proteins identified provide a basis for further investigation. This approach offers a framework for refining germplasm conservation strategies in aquaculture. Full article

Ongoing urbanization continuously reshapes water quality, habitat structure, and biological communities in river ecosystems; however, its impacts on host-associated microbial communities remain poorly documented. The fish gut microbiota, a critical interface between the aquatic environment and host physiology, is widely recognized as an integrative indicator of both environmental change and host ecological traits. This study established a continuous urbanization gradient along Shanghai’s Suzhou River, spanning from suburban areas through the outer and inner ring roads to the city center. Five common wild fish species (Coilia nasus, Hemiculter bleekeri, Culter alburnus, Acheilognathus macropterus, and Pseudorasbora parva) were collected, and their gut microbiota were characterized via high-throughput 16S rRNA gene sequencing. Significant variation in OTU richness, alpha diversity, and community structure was observed across urbanization gradients and among fish species. Principal coordinate analysis revealed that samples from suburban areas were structurally distinct from those collected in other zones, whereas inner-ring and urban-core areas exhibited substantial compositional overlap. Taxonomic analysis revealed that Firmicutes and Pseudomonadota dominated all samples; however, their relative abundances and genus-level composition varied considerably among fish species and across the urbanization gradient. PICRUSt-based functional prediction indicated that metabolic pathways predominated, particularly those involved in global and overview maps, carbohydrate metabolism, amino acid metabolism, energy metabolism, and metabolism of cofactors and vitamins. Collectively, these findings demonstrate that fish gut microbial communities exhibit spatial structuring along the urbanization gradient, with species-specific responses linked to ecological traits. This study provides valuable data on host-associated microbial communities in urban rivers and offers a reference for incorporating microbial indicators into urban water ecological assessments. Full article

Live fish transport easily induces severe physiological stress, marked by pronounced oxidative damage and significant mortality, leading to substantial economic losses annually. Here, we evaluated the effects of taurine intake on alleviating stress response during transportation of Culter alburnus. Juvenile fish were fed diets containing 0 (control), 0.5, 1.0, 1.5, or 2.0 g/kg taurine for 8 weeks before undergoing 12 h of simulated transport. The results showed that taurine supplementation significantly improved growth performance in a dose-dependent manner. During transportation, the deterioration of water quality and the damage of gill tissue decreased with the increase in concentration. The determination of catalase (CAT), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) showed that 2.0 g/kg taurine improved antioxidant capacity. The high-concentration taurine group enhanced the activities of immune enzymes such as acid phosphatase (ACP) and alkaline phosphatase (AKP), while the activity of total nitric oxide synthase (T-NOS) was inhibited. The antioxidant immune effect of the 0.5 g/kg and 1.0 g/kg concentration groups was not obvious. Transcriptome analysis revealed that 2.0 g/kg taurine enhanced the antioxidative stress capacity of C. alburnus by upregulating the expression of immune-related genes (TLR5, Il12b) and activating the Toll-like receptor signaling pathway as well as the cytokine–cytokine receptor interaction pathway. These findings demonstrated that dietary taurine improved resilience to transport stress in C. alburnus. Full article

Aiming to understand the genetic diversity of Culter and Cultrichthys fishes in West Dongting Lake following the implementation of fishing ban, this study analyzed the genetic diversity and phylogeny of five Cultrinae species based on mitochondrial Cytb and COI gene sequences. For Cytb, 50 haplotypes were identified with high overall genetic diversity (H_d = 0.954, π = 0.04765, K = 53.506). Similarly, COI yielded 48 haplotypes (H_d = 0.950, π = 0.03251, K = 36.414). Interspecific comparisons revealed that Culter mongolicus and Culter alburnus exhibited the highest genetic diversity, while Cultrichthys erythropterus showed the lowest. Demographic inferences from neutrality tests and mismatch distribution analyses differed between markers. Based on Cytb, populations of C. erythropterus and C. oxycephaloides appeared to be at neutrality, whereas C. mongolicus, C. alburnus, and C. dabryi significantly deviated, suggesting historical expansion. Mismatch distributions supported recent expansion in C. mongolicus and C. dabryi. In contrast, COI-based neutrality tests indicated expansion in C. mongolicus, C. alburnus, and C. dabryi, with mismatch results confirming this signal for C. dabryi. The negative values of Tajima’s D and Fu’s Fs observed across all five species reflect an accumulation of low-frequency alleles within populations, which may indicate a recent rapid demographic recovery. These findings provide genetic evidence that the genetic diversity of these Cultrinae species has likely been recovering since the fishing ban took effect on 1 January 2020. Further conservation strategies are therefore recommended to promote population recovery and enhance genetic diversity. Full article

Culter alburnus (topmouth culter, TC) is extensively distributed in various rivers and lakes in China. As a widely adaptive fish species, they have significant economic value and special ecological roles. Intergeneric hybridization is a pivotal strategy for generating novel hybrid lineages and species. In a previous study, we obtained an improved bisexual hybrid culter, BTBTF₁, derived from the hybrid lineage of Megalobrama amblycephala (blunt snout bream, BSB, 2n = 48, ♀) × Culter alburnus (2n = 48, ♂). In this study, we established an improved hybrid culter lineage by the self-crossing of BTBTF₁ and evaluated the biological characteristics regarding cytology, morphology, and genetics. DNA content and chromosome analyses confirmed that BTBTF₁-F₂ was a diploid lineage (2n = 48), with morphological traits exhibiting intermediate values between parental species, except for significantly TC-biased full-length-to-body length (FL/BL) and body length-to-head length (BL/HL) ratios (p < 0.05). ITS sequencing analysis revealed that BTBTF₁-F₂ inherited ITS1 sequences from BSB and TC. The global methylation level in BTBTF₁-F₂ was substantially reduced compared to progenitors, characterized by elevated full and diminished hemimethylation states. Transcriptomic analysis identified 7877 differentially expressed genes (DEGs), displaying 9.05%/8.30% maternal (BSB)-dominant and 17.01%/18.95% paternal (TC)-dominant expression patterns in BTBTF₁ and F₂. Remarkable intergenerational similarity in phenotypic and molecular profiles, coupled with bidirectional inheritance of progenitor characteristics, confirmed BTBTF₁-F₂ as a genetically stable allodiploid lineage. Remarkably, methylation patterns, and DEG expression collectively demonstrated significant TC-oriented bias (p < 0.05). This study reports a novel stabilized allodiploid culter lineage after a comprehensive assessment at cytology, morphology, and genetic levels, and provides new insights into genetic bias in hybrid progeny. 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

Grass carp (Ctenopharyngodon idella) is one of the most economically important cyprinid species cultured in China. The diploid gynogenetic grass carp (2nGGC, 2n = 48) was generated from the hybrid of female grass carp (GC, 2n = 48) and male topmouth culter (TC, 2n = 48, Culter alburnus). This study obtained the full-length transcriptome of 2nGGC from five tissues using Pacific Biosciences (Pacbio) single-molecule real-time long-read isoform sequencing. Following the mapping of long reads to GC and TC reference genomes, a total of 1848 fusion isoforms were identified. Among them, 775 were distributed across different genomes, indicating that chimeric DNA fragments of TC were embedded in the 2nGGC genome. After removing the fusion genes and redundant isoforms, 107,721 full-length transcripts were obtained from 2nGGC, providing important full-length reference sequences for further research. Finally, comparative analysis of homologous gene variation identified 34 fragments in 2nGGC containing recombinant SNPs derived from both GC and TC. These results provide evidence that natural gynogenesis represents a form of “micro-hybridization” characterized by heterogeneous DNA fragments, distinct from traditional hybridization involving chromosome-level recombination. These findings offer valuable reference for fish genetic breeding. Full article

Fish morphological traits are increasingly recognized as sensitive bioindicators of aquatic ecosystem quality. This study investigated the associations between dominant meristic traits, which are a subset of morphological features of six common freshwater species, Alburnus alburnus, Perca fluviatilis, Abramis brama, Rutilus rutilus, Scardinius erythrophthalmus, and Carassius carassius, and chemical parameters of water in the regulated ecosystem of the Styr River, Ukraine. Water quality was evaluated using biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), dissolved oxygen (DO), nutrients, solids, pH, and water quality classes (WQC). Meristic traits of fish were analyzed through frequency analysis of species (FAS) and the Zakharov scoring method (ZSM), while hierarchical cluster analysis (HCA) and neural networks (NN) were applied to detect associations between meristic traits of fish and water chemical parameters. Results revealed that overall water quality corresponded to WQC I–II (clean to moderately polluted), although COD consistently exceeded permissible limits. Key meristic traits, including fin rays, scales, and gill rakers, showed significant sensitivity to environmental variability, with species-specific responses reflecting ecological adaptation. The integrative use of WQC, FAS, ZSM, HCA, and NN demonstrated the potential of meristic traits to serve as reliable indicators of ecological integrity in freshwater systems. Full article

The Xingkai Lake topmouth culter (Culter alburnus) is an endemic, economically valuable fish in Heilongjiang that is highly sensitive to ammonia. However, the systemic effects of acute ammonia stress on its liver have not been determined. The objective of this study was to elucidate the changes in and relationships among stress biomarkers, antioxidant defense mechanisms, apoptosis indicators, and histopathological alterations in the liver of C. alburnus, a fish species native to Xingkai Lake, China, under acute ammonia exposure. Guided by the findings of a 96 h-LC₅₀ assay, the researchers subjected the fish to 48 h of acute exposure at specified total ammonia nitrogen (TAN) concentrations of 30 mg/L, 36 mg/L, and 40 mg/L. A comprehensive assessment of physiological and biochemical markers, including cortisol (COR), blood ammonia (Amm), blood glucose (Glu), aspartate aminotransaminase (AST), alanine aminotransaminase (ALT), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA), revealed pronounced physiological stress and oxidative damage, particularly in the high-concentration groups. The physiological effects of ammonia exposure on C. alburnus showed a clear concentration and time dependence. Notably, elevated ammonia levels significantly upregulated apoptosis-associated genes such as P53, Bax, and Caspase-3. These findings were further substantiated by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assays and histopathological examinations. Overall, the study demonstrated that acute ammonia exposure exerted substantial impacts on the physiological, biochemical, and genetic expression profiles of C. alburnus in Xingkai Lake, leading to sustained stress and oxidative damage, especially at elevated concentrations (30–40 mg/L). Full article

The novel hybrid fish BTB, derived from crossing blunt snout bream (Megalobrama amblycephala, BSB) and topmouth culter (Culter alburnus, TC), exhibits markedly hypoxia tolerance in aquaculture. In this study, hypoxic treatment experiments confirmed that, comparing to its original parent BSB, the tolerance to low oxygen of BTB increased by 20.0%. Furthermore, a comparative analysis of the transcriptome and metabolome was performed using gill tissues from BTB exposed to normoxic and hypoxic conditions. Under hypoxic conditions, BTB displayed adaptive modifications in gill lamellae and hemocytes. Transcriptomic profiling identified 789 differentially expressed genes (DEGs), with 298 upregulated and 491 downregulated, enriched in pathways including apoptosis, NK cell-mediated cytotoxicity, MAPK/TNF/Toll-like receptor signaling, and HIF-1/FoXO signaling pathways. Twelve hypoxia-related candidate genes (egln3, im_7150988, znf395a, hif-1an, mknk2b, pck2, ero1a, igfbp-1a, vhl, bpifcl, egln1a, and ccna1) were screened and validated as potential contributors to hypoxia tolerance. Metabolomics analysis revealed a total of 108 differential metabolites (78 upregulated and 30 downregulated), predominantly linked to Arginine and proline metabolism, Ether lipid metabolism, Arachidonic acid metabolism, and Glycerophospholipid metabolism. Association analysis of transcriptomics and metabolomics revealed that the DEGs and DMs were enriched in the pathways of glycerophospholipid metabolism, ether lipid metabolism, arachidonic acid metabolism, and arginine and proline metabolism. In summary, BTB exhibited relatively high hypoxia tolerance, and 12 candidate genes related to hypoxia tolerance were identified. These findings laid a foundation for further investigation into the mechanisms of hypoxia tolerance improvement in hybrid fish. Full article

Danube Delta (DD), an ecologically vulnerable site, together with fish populations, which are significant food resources, are largely exposed to heavy metal contamination. This study was developed in the Babina–Cernovca sector of DD in September 2023. Zinc (Zn), and iron (Fe) were identified in water, while copper (Cu), iron (Fe), and manganese (Mn) were in sediments (mud). Proximate composition of the muscle tissues of eight fish species identified in the area was assessed. The muscle was also tested to identify heavy metals contamination. The contamination degree was assessed using bioaccumulation and bioconcentrations factors. The relation between nutritional parameters and metals was tested using bivariate and multivariate analyses. Samples were analyzed by specific laboratory tests, and data were processed using ANOVA, Spearman correlation, Principal Component Analysis (PCA), and hierarchical clustering. S. erythrophthalmus, C. gibelio, and A. alburnus have the highest metal bioaccumulation capacity, exhibiting species-specific accumulation patterns. PCA and clustering analysis reflect the influence of species and environmental factors on heavy metal accumulation in fish tissue. The study integrates the heavy metals content with nutritional parameters in fish muscular tissue, using bivariate and multivariate analysis for assessing fish vulnerability to heavy metals exposure in the Danube River. Full article

Olfaction plays a crucial role in fish feeding behaviors and ecological adaptation. However, systematic studies on its transcriptional regulation and molecular evolutionary mechanisms in herbivorous and carnivorous fishes remain scarce. In this study, we analyzed four Xenocyprididae species: two herbivorous (Ctenopharyngodon idella and Megalobrama amblycephala) and two carnivorous (Elopichthys bambusa and Culter alburnus), using olfactory rosette transcriptome sequencing and cross-species comparisons. The number of unigenes per species ranged from 40,229 to 42,405, with BUSCO completeness exceeding 89.2%. Functional annotation was performed using six major databases. Olfactory-related candidate genes were identified based on Pfam domains (7tm_4) and KEGG pathways (ko04740), revealing 8–19 olfactory receptor genes per species. These candidate genes were predominantly enriched in the olfactory transduction and neuroactive ligand–receptor interaction pathways. A total of 3681 single-copy orthologous genes were identified, and their expression profiles exhibited clear interspecific divergence without forming strict clustering by dietary type. High-threshold differentially expressed trend genes (|log₂FC| ≥ 4) were enriched in pathways related to RNA processing, metabolite transport, and xenobiotic metabolism, suggesting that the olfactory system may participate in diverse adaptive responses. Ka/Ks analysis indicated that most homologous genes were under purifying selection, with only 0.87–2.07% showing positive selection. These positively selected genes were enriched in pathways related to immune response and neural regulation, implying potential roles in adaptive evolution associated with ecological behavior. Furthermore, the olfactory-related gene oard1 exhibited Ka/Ks > 1 in the E. bambusa vs. C. idella comparison. qRT-PCR validation confirmed the reliability of the RNA-Seq data. This work is the first to integrate two complementary indicators—expression trends and evolutionary rates—to systematically investigate the transcriptional regulation and molecular evolution of the olfactory system in Xenocyprididae species under the context of dietary differentiation, providing valuable reference data for understanding the perceptual basis of dietary adaptation in freshwater fish. Full article