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The ecological impact of dreissenid mussel (e.g., quagga and zebra) populations and their empty shells on native fauna in large rivers and lakes has been extensively studied. However, there is limited information on their effects in small wadable streams. Although established mussel populations in these systems are uncommon, their shells are found in high densities in benthic environments and may adversely impact stream communities. Shell densities were quantified using quadrats in two wadable streams to assess impacts on native benthic macroinvertebrates and fish. Eight reaches of each river were sampled, four with dreissenids and four without, totaling 16 locations. Macroinvertebrate and fish communities were characterized using diversity and environmental tolerance indices. Shell densities were significantly higher in dreissenid-invaded sites compared to sites with only native bivalves in both rivers. Dense shell beds had degraded biological conditions with fewer sensitive macroinvertebrates, but bed density did not affect overall macroinvertebrate or fish diversity. These findings differ from lake and large river studies, which found a greater impact of dreissenid shell deposition on macroinvertebrate and fish diversity than we observed in small wadable streams. Thus, a different approach to management and restoration may be necessary to maintain a natural community composition in wadable streams. [ABSTRACT FROM AUTHOR]

The trade-off between current and future reproduction remains a central issue for understanding the diversity of fish life-histories along a slow-fast continuum. Fish living in rivers of tropical oceanic islands generally have a fast type life-history, but variations in key reproductive traits can occur in response to spatial changes in selection pressures. Here, we investigated the reproductive strategies of two sympatric amphidromous gobies widely distributed in Caribbean streams, Sicydium plumieri (n = 308) and Sicydium punctatum (n = 383), along a river gradient of Guadeloupe Island. Beyond the new insights provided on the reproductive traits (ovarian organization, gonadal development, length at maturity, and spawning season), the histological observations of testes and ovaries revealed variation in reproductive strategies. Sicydium punctatum showed a time-minimizing strategy, featuring early reproduction, a high spawning frequency, an extended reproductive period, and a broad spawning area along the river course. Sicydium plumieri displayed a size-maximizing strategy, featuring a delayed maturity, lower spawning frequency, and a shorter reproductive period restricted to the upper reaches of rivers. We discuss the advantages provided by these two strategies in response to the spatial changes in predation and disturbance levels along the upstream–downstream continuum, which probably affects the survival rate and mortality risk before the first reproduction. [ABSTRACT FROM AUTHOR]

Climate change is a major concern for the future of marine Arctic food webs. Diet shifts of seabirds can be used as indicators of environmental changes such as species compositions of food webs. However, studies on diets are often laborious and costly, while research in vulnerable Arctic environments benefits from short visits for data collection that minimize disturbance to Arctic wildlife and the environment. DNA-metabarcoding techniques are rapidly developing and could be used as an effective method of monitoring diet choice of seabirds. We tested DNA-metabarcoding on seabird faeces collected during short visits of typically around 30 min at breeding colonies of black-legged kittiwake Rissa tridactyla (3 colonies), Brünnich's guillemot Uria lomvia (2 colonies) and little auk Alle alle (3 colonies). DNA metabarcoding based on COI and 18S of a limited number of faeces samples revealed a wide spectrum of fish species and crustaceans in the diets of these species, comparable with or even exceeding diversity in diet composition found in conventional, more invasive techniques where birds are shot or caught and handled to obtain samples. While previous studies on diet choice of little auk, a crustacean specialist, mainly report small fractions of unidentified fish remains, DNA metabarcoding of faeces revealed a large variety of pelagic and benthic fish species supplementing its diet. We conclude that DNA metabarcoding of seabird faeces can be an effective attribute to diet studies supporting our understanding of changes in numbers and distribution of Arctic seabirds and their marine environment. [ABSTRACT FROM AUTHOR]

The practice of hybridization is carried out globally in fish farms. Here, we present the first record of the parasitic fauna of hybrids among genus Colossoma and Piaractus in natural environments. We identified a total of 48 hybrids, nine F1 hybrids (nuclear DNA from both species present in the cross) and 38 advanced hybrids (nuclear DNA from one species), both from crosses between Piaractus brachypomus and Piaractus mesopotamicus, and one F1 "tambacu" corresponding to cross between Colossoma macropomum and Piaractus mesopotamicus. This is the first record of Anacanthorus penilabiatus, Anacanthorus toledoensis, Mymarothecium viatorum, Mymarothecium ianwhittington, Haementeria sp., Dadaytrema oxycephala, Rondonia rondoni, and Echinorhynchus gomesi parasitizing hybrids collected in a natural environment. With this, we expand knowledge about the diversity of fish and parasites in the upper Paraná River and warn about the risk that fish escapes can cause in the basin. [ABSTRACT FROM AUTHOR]

A 21-day continuous monitoring of a highly tridimensional forest of the black coral Antipathella subpinnata (Ellis and Solander 1786) was carried out in the NW Mediterranean Sea at 63 m depth using an autonomous lander to investigate the diel short-term dynamics of the vagile fauna associated to the forest. The survey allowed to assess several aspects of the forest attractiveness and its use, especially by the ichthyofauna, including (i) the diversity and shifts of the fish community inhabiting three layers of the environment (seafloor, canopy, water column) between four light phases (dawn, day, dusk, night), (ii) the diel rhythm in forest use of the red swallowtail perch Anthias anthias (Linnaeus 1758) and its sleeping behaviour in terms of fidelity towards resting sites, duration of rests, and awakenings triggers, and, finally, (iii) the influence of biotic and abiotic variables on the fish behaviour. Considering that, so far, only spot censuses have been carried out in these habitats, this study provides a dynamic approach to the study of biodiversity in temperate mesophotic coral forests and offers an insight into the functioning of these complex and vulnerable ecosystems. [ABSTRACT FROM AUTHOR]

In this study, we aimed to identify the factors that drive the patterns in beta diversity of fish assemblages on the beaches of the Volta Grande do Xingu, a river stretch under the influence of Belo Monte dam. Fishes were collected using a trawl net in 28 sandy beaches during the low water period of 2021 (each beach was sampled once during this period). Measurements of environmental variables were carried out on-site, while spatial variables were obtained using Asymmetric Eigenvector Maps (AEM). Using the Bray–Curtis dissimilarity index, we calculated beta diversity and conducted a distance-based redundancy analysis (db-RDA) with the dissimilarity matrix to assess its relationship between beta diversity and environmental and spatial variables. Additionally, we performed a variance partition to quantify the pure and shared contributions of the explanatory matrices to our response matrix. The results revealed low beta diversity among the sampled beaches, and that this beta diversity was explained in part by the spatial variables and pH. Our findings underscore the influence of spatial structure on the assembly of local communities, indicating that dispersion processes and spatial connectivity are relevant mechanisms that contribute to the beta diversity of beach fish communities under influence of a reduced flow by a Hydropower Plant. [ABSTRACT FROM AUTHOR]

Besides providing key ecosystem services, including improved water quality, coastal protection, and carbon sequestration, seagrasses are highly productive habitat-forming species essential in supporting fish diversity at the global level. In the Mediterranean Sea, seagrasses represent the main component of the sublittoral marine environment hosting a huge number of fish species that use this habitat for reproduction, foraging and/or refuge from predation. However, a complete synthesis of fish species observed in different seagrass habitats is still lacking at the whole Mediterranean basin scale, so hindering a thorough understanding of the main mechanisms involved in determining fish diversity patterns. We performed a systematic review by implementing a semi-automated, threshold-based filtering pipeline that allowed building up a dataset concerning all fish species reported in native Mediterranean seagrasses, including specific functional traits known to be involved with the potential use of seagrasses by fish. These data allowed to carry on a narrative synthesis on fish diversity in seagrass habitats, providing support to several assumptions repeatedly stated in literature but so far sustained mainly by local and fragmented data. Our findings suggested the onset of a general pattern in the occurrence of species, mostly based on life history and driven by body size and feeding habits. We evidenced unexpected knowledge gaps on the role of habitat heterogeneity and fish life stages in determining the presence and the potential use of seagrasses by species. In depth studies are therefore needed to better understand the mechanisms behind the structuring of fish communities, fundamental for the maintenance of marine biodiversity. [ABSTRACT FROM AUTHOR]

Anthropogenic land use has caused a major crisis to the biodiversity of stream fishes in recent decades, especially with regard to biotic homogenisation. Understanding the response of stream fishes to anthropogenic land use will help to promptly implement effective conservation measures. In this study, we investigated the effects of agriculture on fish diversity in streams in the Wannan Mountains, China. We predicted that agriculture would influence fish diversity by affecting local habitat conditions. The results showed that habitat conditions (e.g. water temperature, water width, water depth) differed significantly between disturbed and reference sites. The disturbed sites had high species richness due to the addition of translocated species outpacing the loss of endemic species. Moreover, fish assemblages showed taxonomic differentiation accompanied by functional homogenisation, which mainly resulted from the addition of translocated species with redundant functional traits. However, the emergence of homogenisation shows a time delay. The biotic differentiation of fish assemblages in agroecosystems is temporary in the Wannan Mountains, and homogenisation may eventually develop as stress intensifies. Thus, it is urgent and necessary to take effective conservation measures to delay or prevent fish assemblages from worsening in agroecosystems before homogenisation develops. [ABSTRACT FROM AUTHOR]

The Ib River is an important tributary of the Mahanadi River. The aim of the present study was to establish a reliable barcoding reference database for fish in Ib River. A total of 134 specimens, belonging to 42 species within 32 genera, 18 families, and 11 orders, were subjected to PCR amplification of the target region of mitochondrial genome and sequenced. The average length of the 134 barcodes was 648 bp. The average K2P distances within species, genera, and families were 0.13, 9.94, and 16.79%, respectively. The average interspecific distance was approximately 76.46 times higher than the mean intraspecific distance. The Barcode Index Number (BIN) discordance report showed that 134 specimens represented 42 BINs, of which 13 were singletons, 29 were taxonomically concordant while no species taxonomically discordant in our dataset. The barcode gap analysis demonstrated that 100% of the fish species examined could be discriminated by DNA barcoding. These results provide new insights into fish diversity in the Ib River and can provide a basis for the development of further studies on fish fauna. [ABSTRACT FROM AUTHOR]

The combination of the physical structural heterogeneity of the environment, oceanographic characteristics, and the benthic assemblage composition structures the habitat, consequently shaping the associated diversity of fish. Understanding the spatial variability of fish assemblages and how it relates to environmental factors is essential to identify potential variables that determine spatial patterns and predict impacts on fish assemblage metrics, thus providing valuable information for management. Here, we investigated reef fish micro-scale spatial distribution around Alcatrazes Island in the subtropical region of the Southwest Atlantic, Brazil. Multivariate Regression Trees were fitted to explore the effects of structural heterogeneity, wave power, depth, water temperature, and benthic cover on the structure of reef fish assemblages, addressing composition, richness, density, biomass, trophic groups, mobility, and conservation status. Our results suggest that depth, turf, and coral cover were the main predictors of fish assemblages in rocky reefs at Alcatrazes Island, revealing five distinct fish assemblages with different habitat preferences. These results provide additional insights into the relationship between reef fishes and their environment, providing empirical evidence for decision-makers to implement spatially based management policies, especially to prioritize zones for conservation along the island. [ABSTRACT FROM AUTHOR]

Tropical ecosystems host a significant share of global fish diversity contributing substantially to the global fisheries sector. Yet their sustainable management is challenging due to their complexity, diverse life history traits of tropical fishes, and varied fishing techniques involved. Traditional monitoring techniques are often costly, labour-intensive, and/or difficult to apply in inaccessible sites. These limitations call for the adoption of innovative, sensitive, and cost-effective monitoring solutions, especially in a scenario of climate change. Environmental DNA (eDNA) emerges as a potential game changer for biodiversity monitoring and conservation, especially in aquatic ecosystems. However, its utility in tropical settings remains underexplored, primarily due to a series of challenges, including the need for a comprehensive barcode reference library, an understanding of eDNA behaviour in tropical aquatic environments, standardized procedures, and supportive biomonitoring policies. Despite these challenges, the potential of eDNA for sensitive species detection across varied habitats is evident, and its global use is accelerating in biodiversity conservation efforts. This review takes an in-depth look at the current state and prospects of eDNA-based monitoring in tropical fisheries management research. Additionally, a SWOT analysis is used to underscore the opportunities and threats, with the aim of bridging the knowledge gaps and guiding the more extensive and effective use of eDNA-based monitoring in tropical fisheries management. Although the discussion applies worldwide, some specific experiences and insights from Indian tropical fisheries are shared to illustrate the practical application and challenges of employing eDNA in a tropical context. [ABSTRACT FROM AUTHOR]

The Pama Croaker, Otolithoides pama, is an economically important fish species in Bangladesh. Intra-family similarities in morphology and typical barcode sequences of cox1 create ambiguities in its identification. Therefore, morphology and the complete mitochondrial genome of O. pama, and comparative mitogenomics within the family Sciaenidae have been studied. Extracted genomic DNA was subjected to Illumina-based short read sequencing for De-Novo mitogenome assembly. The complete mitogenome of O. pama (Accession: OQ784575.1) was 16,513 bp, with strong AC biasness and strand asymmetry. Relative synonymous codon usage (RSCU) among 13 protein-coding genes (PCGs) of O. pama was also analyzed. The studied mitogenomes including O. pama exhibited consistent sizes and gene orders, except for the genus Johnius which possessed notably longer mitogenomes with unique gene rearrangements. Different genetic distance metrics across 30 species of Sciaenidae family demonstrated 12S rRNA and the control region (CR) as the most conserved and variable regions, respectively, while most of the PCGs undergone a purifying selection. Different phylogenetic trees were congruent with one another, where O. pama was distinctly placed. This study would contribute to distinguishing closely related fish species of Sciaenidae family and can be instrumental in conserving the genetic diversity of O. pama. [ABSTRACT FROM AUTHOR]

Understanding consumer–resource interactions is essential for understanding the trophic dynamics of species-rich fish communities. Woodland et al. (Oikos 125:556–565, 2016) assumed that trophic position (TP) distributions of primary consumers and tertiary species are restricted versus intermediate consumers tending to be omnivores with broader TP distribution, where these omnivores often dominate the overall biomass. With rare evidence supporting this hypothesis in a river, we tested it in the species-rich Pearl River fish assemblage, China. Using bulk stable isotope (SI) approach (δ13C, δ15N), the TPs, SI distribution parameters, isotopic niche sizes (as standard ellipse areas, SEA) and interspecific niche overlap were calculated for the abundant fish species. Fishes of intermediate TPs (i.e. omnivores) had larger δ13C variance/ range, broader isotopic niches and higher niche overlap compared to fishes at low TPs and high TPs, indicating a higher degree of trophic redundancy among the omnivores, whereas high TP fish had narrower niche and lower niche overlap, indicating trophic partitioning among tertiary species. These omnivores at intermediate TPs between 2.4 and 2.8 dominated fish biomass. The results not only support the Woodland et al. (Oikos 125:556–565, 2016) hypothesis in the river, but also provide a novel explaining in how niche sizes and overlap vary by TP. [ABSTRACT FROM AUTHOR]

Citizen-collected data are used to describe ecological patterns and to obtain information about the distribution and trends of fauna and flora to inform management and conservation actions worldwide. However, considering the logistical and financial aspects, data should be collected in a cost-effective way. In addition, informed by the spatio-temporal distribution of observations, under-, and oversampled areas can be identified to guide future sampling efforts. Here, we classify 37,161 observations of South American Actinopterygii submitted to iNaturalist, occurring in both coastal and inland water bodies. We consider the status of the fish (live/dead), the characteristics (taxonomy and habitat) of the species and the circumstances of the observation (e.g., during fishing or diving). We test whether adding opportunistic observations increases species diversity, i.e., if observations of dead fish and fishing-related data add information to traditionally collected occurrence data (i.e. those of live fish observed during diving). Our dataset contained 2,377 species of 206 families, representing 24% of all South American ray-finned fish species. Dead individuals and observations related to fishing on average contributed 37% and 33% of annual observed species richness, respectively and added 151 unique species not recorded live or under circumstances not related to fishing. We found that for dead fish the rate of validation by peers and experts on the platform had been 20% lower compared to that of live individuals. We argue that recording organisms observed under different circumstances and in different conditions improves our knowledge of biodiversity. Demonstrating the value of all observations can encourage volunteers to make their data collection more inclusive. [ABSTRACT FROM AUTHOR]

Whilst the importance of foundation species for biodiversity conservation has been largely acknowledged (e.g., coral and bivalve reefs, seagrass, kelp and rhodolith beds), the role of their associated species as secondary habitat engineers has just begun to be appreciated. Here, we evaluated whether secondary engineering of rhodolith beds by the sand tilefish Malacanthus plumieri influences the composition and β-diversity of benthic macroinvertebrates and reef fish assemblages. Our findings indicate that, by selecting, relocating, and rearranging rhodoliths into mounds, M. plumieri creates a distinctive habitat for macroinvertebrates and fishes. M. plumieri mounds increase fish abundance by 57% in rhodolith beds, with an 82% species turnover rate between mounds and non-mounded areas. In contrast, the macroinvertebrates in M. plumieri mounds are largely a subset of the species from non-mounded areas, with an 86% species nestedness rate. Despite decreasing the abundance of macroinvertebrates in the mounds by half, M. plumieri increases the heterogeneity and structural complexity of rhodolith beds, affecting the composition of associated fish assemblage at a larger spatial scale. Our results suggest that, by increasing the structural complexity of rhodolith beds and shaping their associated biodiversity, the abundance of M. plumieri mounds could be a useful proxy to define priority areas for conservation across the South Atlantic rhodolith beds, especially in the light of ongoing impacts related to offshore oil exploitation, overfishing and carbonate mining. [ABSTRACT FROM AUTHOR]

The classification of underwater fish species holds significant importance for fisheries management. Nevertheless, existing deep fish classification models require high computational resources, which hamper their deployment on underwater devices. Additionally, the complex underwater environment, the camouflaged appearance of fish, and the similarity among fish species pose challenges to the accuracy of lightweight fish classification models. To address the above issues, this paper proposes a novel two-tier knowledge distillation (T-KD) method to improve the accuracy and reduce the parameters of the underwater fish species classification models. Specifically, the T-KD involves the following key steps. Firstly, a new fish species dataset, Fish37, is constructed to augment the diversity of fish species present in existing datasets. Subsequently, we introduce a novel interlayer mapping similarity-preserving (IMSP), to facilitate the learning of richer discriminative features by capturing the mapping relationships between teacher and student network layers. Moreover, a new layer tail response (LTR) is proposed to mimic the predictions of the teacher network, efficiently improving classification performance and generalization capability. The proposed T-KD approach demonstrates remarkable performance in fish species classification, surpassing that of well-known lightweight models. The effectiveness of T-KD is extensively validated across various network depths, including ResNet and EfficientNet, and compared to other knowledge distillation methods like KD, PKT, RKD, and SP. Notably, T-KD outperforms MobileNetv3-large and obtains an impressive Top-1 accuracy of 97.20% on the Fish37 dataset only using about 1/15 model size of Vision Transformer. Furthermore, detailed generalization experiments are conducted to assess T-KD's performance on popular benchmark datasets, such as A_Large_Scale_Fish_Dataset, Fish4knowledge, WildFish and WildFish++. In conclusion, the results indicate the potential of the T-KD to facilitate underwater fish species classification with limited computational resources on underwater devices. This research also opens up promising avenues for the practical implementation of lightweight fish classification models. [ABSTRACT FROM AUTHOR]

Non-genetic sources of phenotypic variation, such as the epigenome and the microbiome, could be important contributors to adaptive variation for species with low genetic diversity. However, little is known about the complex interaction between these factors and the genetic diversity of the host, particularly in wild populations. Here, we examine the skin microbiome composition of two closely-related mangrove killifish species with different mating systems (self-fertilising and outcrossing) under sympatric and allopatric conditions. This allows us to partition the influence of the genotype and the environment on their microbiome and (previously described) epigenetic profiles. We find the diversity and community composition of the skin microbiome are strongly shaped by the environment and, to a lesser extent, by species-specific influences. Heterozygosity and microbiome alpha diversity, but not epigenetic variation, are associated with the fluctuating asymmetry of traits related to performance (vision) and behaviour (aggression). Our study identifies that a proportion of the epigenetic diversity and microbiome differentiation is unrelated to genetic variation, and we find evidence for an associative relationship between microbiome and epigenetic diversity in these wild populations. This suggests that both mechanisms could potentially contribute to variation in species with low genetic diversity. Species with low genetic diversity have limited capacity to adapt to environmental change. This study finds that the skin microbiome and non-genetic (epigenetic) modifications of the DNA represent additional sources of variation that could help low diversity fish survive environmental challenges. [ABSTRACT FROM AUTHOR]

Local and global ecological stressors are leading to increased documentation of phase shifts in coral reefs from healthy stony corals to macrophytes. In more rare cases, phase shifts result in sponge, zoantharian or other dominant species. In Ulithi Atoll, Federated States of Micronesia, we have documented an unusual phase shift from reefs with a diverse stony coral assemblage to reefs dominated by a single species of stony coral: Montipora sp.—a coral-to-coral phase shift. This monospecific type of reef lowers fish diversity and biomass, impacting both ecological integrity, and livelihoods of reef-dependent human communities. In this study, we used a genomic approach to characterize such a reef. We assembled a de-novo reference genome and used RAD seq data with thousands of SNPs to determine if different reefs result from sexual or asexual reproduction, if weedy Montipora fragments are transported between islands by human activities, and if there is evidence of natural selection on specific genotypes, thus favoring spreading success. We found that sexual reproduction is predominant in the focal species, that there is no evidence of human-mediated spread, and that some genomic regions might be under selection. While such results eliminate a number of spreading hypotheses, more precise dispersal maps will be important to determine the tempo and mode of 'invasion' of Montipora in Ulithi Atoll. This study shows that selection and adaptation may be contributing to the success of a stony coral (e.g., Phase shift). While a stony coral may be successful in a disturbed environment, it does not necessarily provide the type of habitat that is conducive to high fish biomass and coral diversity. These results serve as a cautionary tale for restoration efforts that focus on single species coral resilience rather than ecosystem function. [ABSTRACT FROM AUTHOR]

Seagrass habitats play a major role in fisheries productivity through nursery functions and feeding grounds for diverse fish species. However, little is known about the seasonal distribution of fish larvae at large spatial scales in coastal East Africa. We investigated drivers of the seasonal fish larvae abundance and composition in seagrass habitats in Kenya and Tanzania. We found a high diversity of fish larvae (54 families) inhabiting seagrass habitats that differed between sites and seasons. Fish larvae abundance were highest in Kenya, particularly during the northeast monsoon season. Overall, total larval abundances per site were low, reaching less than 190 individuals/100 m3 in Kenya and less than 40 individuals/100 m3 in Tanzania, likely related to the low productivity and strong hydrodynamic processes in this region. Our data suggests that most of the fish spawn year-round in these tropical waters as we did not find strong seasonal patterns. All sites had a high relative abundance of larvae from demersal spawning fishes, indicating that many fish species move to coastal sites for spawning. Primary productivity and dissolved oxygen, driven by hydrodynamics conditions are positively related to fish larvae productivity both in Kenya and Tanzania. These findings indicate that the occurrence of both resident and transient fish larvae in seagrass meadows is driven by strong hydrodynamic and tidal processes that transport fish larvae across adjacent habitats. [ABSTRACT FROM AUTHOR]

Sandy beaches have experienced substantial human modifications worldwide for centuries. Yet, sandy beaches are known as nursery areas for coral reef fishes. Due to global and local stressors, the degradation of nurseries such as the sandy beaches may have wide reaching consequences for the resilience of reef fishes. In our study, the impact of erosion vs. accretion phenomena was highlighted on coral reef fish community in Guadeloupe in comparing the abundance and diversity of juvenile fish between two nearby beach sites (one that undergoes accretion and the other one that undergoes erosion since the 1950s). The main result showed that a significant retreat of sandy beach along the entire coastline, by bringing out an old reef, could create new habitats, favorable to the settlement of fish juveniles. This result is surprising when considering that erosion negatively affects coral reefs through the sedimentation, deterioration of water quality, and loss of habitat. [ABSTRACT FROM AUTHOR]

There is an interest in mono-sex fish production in a variety of aquatic species, particularly to achieve higher growth, limit unwanted reproduction, increase survival, prevent sexual/territorial behavior, avoid size diversity in fish harvest, and reduce environmental risks from escape into the wild. In this project, rainbow trout (Oncorhynchus mykiss) larvae (15 days old) were fed diets containing 75 mg letrozole kg−1, 150 mg letrozole kg−1, 70 mg 17α-methyltestosterone kg−1, 140 mg 17α-methyltestosterone kg−1, 200 mg Tribulus terrestris extract kg−1, 400 mg T. terrestris extract kg−1, 200 mg Asparagus racemosus extract kg−1, 400 mg A. racemosus extract kg−1, 200 mg combination of both extracts in equal proportions kg−1, and 400 mg combination of both extracts in equal proportions kg−1. The control group was fed basal diet for 120 days. The fish were then fed a commercial diet until approximately 11 months of age. At the end of the experiment, the growth, survival rate, and percentage of male, female, and intersex fish were evaluated. The results showed that the groups with 17α-methyltestosterone (70 and 140 mg kg−1 diet), letrozole (150 mg kg−1 diet), and a combination of T. terrestris and A. racemosus extracts (400 mg kg−1 diet) had a higher percentage of induction of masculinization than the other groups (P < 0.05). In general, letrozole and a mixture of T. terrestris and A. racemosus extracts are recommended as alternatives to 17α-methyltestosterone. [ABSTRACT FROM AUTHOR]

For shallow lakes, the most dramatic ecosystem shift is that from a clear-water, macrophyte-dominated regime to a turbid, phytoplankton-dominated regime. Whereas many studies have focussed on the factors that trigger such shifts, it is still unclear how these changes shape fish diversity. In the present study, we characterised the fish communities taxonomically and functionally in Lake Taihu, China, along a spatial gradient of habitat types, i.e. algal-dominated, macrophyte-dominated, open-lake and aquaculture conversion zones. Random Forests regression was then applied to examine how fish diversities were related to environmental conditions. Our results showed that the taxonomic and functional composition of the fish community varied among different habitat regimes. Macrophyte and water quality were identified as the most important factors affecting the fish diversity indices. Habitats with a high macrophyte biomass and low nutrient concentration supported higher functional diversity. Moreover, our analysis revealed that although functional diversity indices were strongly correlated with species richness, they appeared more sensitive to changes in habitat conditions. Overall, our study highlights the importance of macrophyte-dominated state in maintaining fish diversity in freshwater ecosystems and provides new insight into how functional diversity can improve our understanding of the response of biodiversity to ecological processes. [ABSTRACT FROM AUTHOR]

The heterogeneity of urban landscapes has effects on the environmental characteristics and fish composition of individual urban streams, even within a single water system. It is, therefore, imperative to assess the influence of physiochemical properties on urban streams by analyzing the spatial distribution of fish communities at the local scale. However, conventional fish surveys encounter time and labor constraints when selecting and surveying dense sampling points under 2 km in stream networks. In this study, environmental DNA (eDNA) metabarcoding was used as an innovative survey methodology to identify the effects of land use and stream order on fish composition and tolerance guild in an urban area. The eDNA sampling was conducted in 31 sites of the Anyang stream network in Korea, including part of the stream undergoing ecological restoration. The eDNA survey detected 12 of 17 species (70.6%) that appeared in the historical data, and 12 of 18 species (66.7%) identified in a conventional field survey with kick nets and casting nets. The proportions of urban area, forest and grassland were positively correlated with abundance (p < 0.05) and richness (p < 0.05) in multiple regression analyses, while the proportion of agricultural area showed a negative correlation (p < 0.05). For abundance, richness, and diversity within the fish community from first- to third-order streams, there was a significant decrease in sensitive species (p < 0.05) alongside a significant increase in tolerant species (p < 0.01) across all three indices. The results of this study highlight variations in fish composition across sites within the local scale of the urban stream network, underscoring the need for detailed monitoring to understand the ecological function of urban streams. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) is pervasive in urban environments with well described effects on animal melatonin profiles, behavior, fecundity, cognition, and predation. However, its potential effects on higher levels of biological organization, such as biotic communities, are not fully understood. We investigated the effects of ALAN on fish assemblages in 20 lit-unlit reaches across 10 sites in Columbus, Ohio, USA across two years. Our results show that light trespass into urban streams is approximately doubled during leaf-off in winter months (1.97 lx ± 0.28) compared to leaf-on in summer months (1.00 lx ± 0.19), highlighting the important interceptive effect of canopy coverage in headwater systems. There were no differences in fish assemblages (i.e., abundance, relative abundance, biomass, diversity, guild composition) between lit and unlit reaches (> 100 m apart). Species richness and α-diversity (Hill numbers) scaled positively with mean stream depth. Nutrient concentrations were negatively related to mean fish mass and fish assemblage diversity. Species richness scaled negatively with total phosphorus and α-diversity scaled negatively with orthophosphate. Our results imply that the relatively low-levels of ALAN observed in canopied streams may exert only subtle effects on small stream fish assemblages, which are difficult to detect amongst the multiple, confounding stressors impacting these relatively species-poor, urban systems. Experimental approaches or large-scale manipulative studies may be necessary to isolate the effects of ALAN on streams and fish in urban contexts. [ABSTRACT FROM AUTHOR]

Fishes are relevant indicators of reefs' conservation status due to the wide variety of functions they perform in the ecosystem. Natural and anthropogenic-induced threats are causing declines in biomass and diversity locally, with immediate effects on trophic structure and ecosystem function. This study evaluated the spatial variation of species richness and the alpha and beta functional diversity of fish assemblages across the Mexican Tropical Pacific (MTP). Visual fish censuses were performed in nine localities between 2012 and 2020. The results showed that species richness and functional diversity of the reef-associated fish assemblage vary at different spatial scales (local and regional), with the highest variability on the local scale. The functional richness and functional divergence presented high values in most localities. On their part, functional beta diversity among regions was low, with almost no functional turnover, while higher trait turnover was observed among localities. This study complements taxonomic diversity metrics by identifying differences due to local conditions, with human intervention as a critical factor. Therefore, it provides information tools that can help improve the management of marine communities subjected to distinct types and degrees of intervention in the MTP. [ABSTRACT FROM AUTHOR]

Functional diversity has proven to be more responsive than traditional taxonomic diversity to alterations for a wide set of communities, especially in aquatic ecosystems. Habitat alterations are among the most relevant causes of biodiversity loss in freshwater ecosystems, nevertheless their effect on functional diversity has been scarcely investigated so far. In this study, functional diversity of fish communities in the River Po basin, north Italy, were related to habitat quality at different spatial scales. Land use and riparian vegetation were identified as the most influent factors on freshwater fish functional diversity. On the other hand, habitat descriptors at smaller scale did not influence functional diversity of fish. The evidenced responses were driven by the contribution of exotic species, which maximized ecological niche occupancy, either by exploiting increased habitat heterogeneity or by interaction with native species. Moreover, traits filtering, disadvantaging large predators such as salmonids, was also observed in the studied communities, but likely this effect was related to other factors than habitat alterations. Overall, this study confirms that land use changes can be considered as valid proxies for anthropogenic alterations. Moreover, possible effects at ecosystem level, also related to the spread of exotic species, could be hypothesized, giving that traits mostly influencing the observed patterns of diversity in communities were related to trophic niche, a factor that has been associated with crucial processes like nutrient cycling or energy transfer. [ABSTRACT FROM AUTHOR]

Quantifying trophic relationships within and between species in terms of trophic position, ontogeny and trophic diversity provides information on community-level structure and function. Little attention has been focused on examining the trophic structure and temporal changes of communities in freshwater-marine coupled systems in the subarctic and associated impacts of anthropogenic activity on trophic interactions. Therefore, the objective of this study was to quantify the trophic position of mobile consumers (15 species in total) within the lower Churchill River area (Churchill, Manitoba, Canada), examine trophic position variation in relation to ontogeny, and measure the trophic diversity of a fish assemblage before (1993–1995) and after (2019–2020) the installation of the Churchill River weir in the late 1990s. We used stable isotopes (δ13C and δ15N) to quantify individual and group-level variation in trophic position of thirteen fish species and two seal species and also assessed six community-level metrics of a three fish species assemblage between time periods. Overall, species that mainly foraged on freshwater resources occupied lower trophic positions than species that mainly consumed marine resources. Trophic position increased with fish age only in cisco, fourhorn sculpin, Greenland cod and northern pike. A temporal shift from a trophically diverse to a more trophically redundant fish assemblage occurred between 1993–1995 and 2019–2020. As a result, these predator species now play similar trophic roles. Information on the long-term change in trophic structure of this sub-Arctic estuarine system may help with understanding how anthropogenic activity and climate change have influenced the trophic diversity of a fish assemblage inhabiting this system. [ABSTRACT FROM AUTHOR]

Drifting marine debris has been shown to host associated biological communities and facilitate their dispersal. Little is known about how biota engage with, and are transported by, this debris. This study characterizes debris-associated communities and explores the role of plastics in transferring fishes to new geographic regions. ~ 1500 underwater photographs were reviewed from five cruises during 2018–2020: one between Japan and Hawaii encompassing the Western and Eastern Pacific Ocean (Group I), and four passing through the North Pacific Garbage Patch in the Eastern Pacific Ocean (Group II). Debris properties were recorded and 13 associated fish species from 43 debris items were identified. Fish communities around marine debris have low diversity, individual debris items have highly dissimilar species compositions, and species composition is affected by horizontal debris item size. Debris items in Group I have significantly higher fish species diversity and differ in community composition from Group II. Four taxa (Abudefduf vaigiensis, Histrio histrio, Oplegnathus punctatus, and Petroscirtes spp.) were observed surviving east of the Hawaiian Islands, where they have not been previously reported. Marine debris is found to be a mobile natural habitat substitute that can facilitate long-distance species dispersal. While natural flotsam has long been a potential vector, long-lived and increasingly abundant plastic debris may set the stage for altering fish biogeography. [ABSTRACT FROM AUTHOR]

This study investigates the fish assemblage in a temporarily-closed sandbar estuary along India's west coast, across different zones and seasons. Moderate species diversity (54 species), low species abundance, varying fish diversity from lower to upper estuarine gradient (higher counts in lower zones, and decreasing from middle to upper zones), and higher prevalence of marine migrants (estuarine use) and piscivorous species (feeding mode) were the significant characteristics of the estuary. Distinct spatial, seasonal, and estuarine mouth state-based variations were recorded in the estuary, based on diversity indices and count of taxa. Peak diversity and abundance were noted during the pre-monsoon, and during the open mouth state of the estuary. The entire estuarine gradient is anthropogenically impacted by a multitude of stressors, except at the estuarine mouth region, which is favored by marine connectivity. The fish assemblage structure in Poonthura estuary (PE) has thus far remained unaffected by anthropogenic disturbances. Nevertheless, growth and nursery function of the estuary have been significantly compromised. The predominance of juvenile fish in the ecosystem, and prevailing anthropogenic stressors from point and non-point sources underscore the necessity for long-term maintenance of the population of coastal species, as well as a need for developing and implementing urgent management strategies for this fragile ecosystem. [ABSTRACT FROM AUTHOR]

The Media Luna spring, Mexico, is the main reservoir of the endemic and endangered fish Ataeniobius toweri. In the last decades, the ecosystem has been modified by tourism, and the habitat has changed for this species. Therefore, for better conservation management of the natural fish population, it is necessary to understand its abundance status and suitable habitat conditions, in ecological and spatial scenarios, on a temporal scale. In the present study, we modeled A. toweri's ecological responses and spatial distribution for adult and juvenile life stages, in three summer periods (years 1999, 2009, and 2019). As habitat variables, we used water depth and underwater coverage. Ecological response curves were obtained from a Generalized Linear Model; distribution models were obtained with DOMAIN. In the modeling evaluation, for the Linear Regression Model, we obtained true statistical skills metric > 0.30 and, for DOMAIN, an area under the curve (AUC) > 0.70 with an AUC ratio > 1.00. In general, as the summer periods progressed, we found the highest probability of occurrence (P > 0.20) and distribution (P > 0.60) in areas with conditions of large coverage of underwater vegetation, in the first 1.5 m of depth, and near the shores of the spring. Also, the variations of relative abundance were always observed at sites with these habitat conditions. Thus, we concluded that our models had the performance to discern between suitable and unsuitable habitat conditions for A. toweri, and that areas with little or no anthropogenic pressure are more important for this species. [ABSTRACT FROM AUTHOR]

Human activities are one of the main causes of biodiversity loss and the reduction of ecosystem services. These activities, together with seasonality and the associated ecological and physicochemical changes, are the main modulators of fish communities in subtropical streams. Using data from 62 streams from Uruguay, we analyzed the effect of environmental variables on several attributes of fish community structure. First, we evaluated the effect of climatic seasonality on fish biomass, density, mean body length and weight using a paired t-test. Secondly, we analyzed the relationship between seasonality, environmental variables (environmental degradation, watershed area, and habitat diversity), and species richness with fish biomass using a linear mixed model. Fish biomass and density were higher in summer meanwhile, mean length was higher in winter. We found a humped relationship between biomass and environmental degradation in winter and summer, with low biomass in sites with high and low quality. Our model shows that species richness increase generates an increase in biomass, with the magnitude of this increase being greater during winter. In view of this results, we highlight that the humped pattern founded in our work should have special management attention to avoid misinterpretation of biomass increases caused by environmental degradation. [ABSTRACT FROM AUTHOR]

Anthropogenic alterations have paramount impacts on the alpha and beta diversity of aquatic resources, and fishes are predominantly susceptible to such impacts. Mahanadi River, one of the major peninsular rivers of India, has abundant fish resources, which play a significant role in supporting the fishers' livelihoods. The exploratory study in the river conducted for three consecutive years recorded 148 species under 53 families. Cyprinids dominated the fish diversity with 41 species, followed by Bagrids (9) and Sciaenids (7). One hundred-one species under 29 families were reported from the freshwater stretch. With a total of 111 species reported under 48 families, the estuarine and tidal freshwater stretch was more speciose, due to marine migrant species which advent the estuarine and tidal freshwaters stretch for breeding and feeding purposes. Tikarpara, a conserved site within a sanctuary, was the most species-diverse as well as a species-even site. The study also recorded the extension of the distributional range of 3 fish species and also 4 exotic species from the river. The seasonal variations in diversity indicated that the deviations were not prominent in freshwater sites, whereas in tidal brackish water sites, species richness was relatively higher in post-monsoon, and species evenness was higher during monsoon. Taxonomic distinctness test showed that the average taxonomic distinctness was high for tidal estuarine locations as they harbour taxonomically distant fishes. The hierarchical clustering of sites showed the inordinate effect of river gradient and fragmentation on the fish community structure. Analyzing the key drivers of the assemblage structure of the entire river, salinity was the major deterministic factor, and within the freshwater stretch, the major influences were depth, transparency, and specific conductivity. The study concluded that, despite all of its ecological stresses, Mahanadi still supports rich fish diversity, yet there is a notable shift in the fish community structure. There is a need for integrating molecular and morphological tools for the taxonomic revision of many genera and species for proper in situ and ex situ conservation measures and to formulate future biodiversity management plans addressing to reduce the impacts of the ecological threats. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) analysis is a promising method for monitoring marine biodiversity. However, it is necessary to verify whether eDNA analysis provides an accurate measure of biodiversity in species-rich ecosystems such as coastal waters as part of a long-term monitoring campaign. Therefore, both an underwater visual census (UVC) and eDNA metabarcoding were conducted monthly from June 2018 to May 2019 to investigate fish diversity off the coast of Nodaedo Island, Tongyeong, South Korea. A total of 16,036 fish were observed in the UVC and classified into 69 species. Perciformes was the most dominant group with 31 species. eDNA metabarcoding identified 68 operational taxonomic units and 738,217 reads, encompassing 18 orders, 42 families, and 68 species. The Gobiidae family was the most dominant taxon with five species. The UVC was able to detect species that were otherwise not identified using eDNA due to the low number of individuals or analytical limitations, while eDNA metabarcoding was suitable for detecting smaller species, pelagic species, and those that inhabit microhabitats. Our findings demonstrated that these two methods can be used to complement each other and gain insights into the structure of fish communities in various coastal environments. Though eDNA metabarcoding represents a fast and efficient method for surveying fish species diversity in coastal waters, it should be carefully compared with other traditional survey methods to ensure that it is suitable as an effective complementary measure. [ABSTRACT FROM AUTHOR]

Extant 'fishes' belong to jawless, cartilaginous, actinopterygian, or sarcopterygian fish lineages. They comprise a non-monophyletic group of vertebrates from which tetrapods are excluded, and they are therefore paraphyletic. Recent advances in whole-genome sequencing have shed light on phylogenetic relationships, divergence times among major fish lineages, and the molecular basis of phenotypic diversity. This review encompasses the diversity of extant fishes and explores the variation in genomic organization and its evolutionary origins. This review begins with evaluating available genomic sequence resources with a focus on literally complete ('telomere-to-telomere') sequencing. Next, it discusses among-lineage variations in genomic contents, considering karyotype reports, genome sizes, and whole-genome duplication events. Additionally, we investigate three families of protein-coding genes, visual opsins, aquaporins (Aqps), and Hox genes, as they offer insights into morphological and physiological differences among major fish lineages. Overall, our technical basis of analyzing fish genomes and the knowledge of genomic organization provide valuable insights into our vertebrate-wide understanding of how molecular mechanisms specifying variable phenotypes are encoded in genomic sequence information. [ABSTRACT FROM AUTHOR]

The fish community of the Scotia Sea is diverse and plays key roles in Antarctic food webs and biogeochemical cycling. However, knowledge of the spatial and community structure of their early life stages is limited, particularly in the region surrounding the South Orkney Islands. Here we examine the structure of the early life stage fish community in the epipelagic using data from a basin-scale survey conducted in early 2019, which sampled the top 200 m of the water column. 347 early life stage fish from 19 genera were caught in 58 hauls. A third of all specimens belonged to the genus Notolepis and the nine most common genera comprised over 90% of specimens. Cluster analysis revealed five distinct groupings, the most common were a group dominated by pelagic and shelf slope genera (Notolepis, Muraenolepis and Electrona) found mainly in oceanic waters (depth ≥ 1000 m), and a group dominated by species with demersal or benthopelagic adults (Chionodraco, Chaenocephalus and Nototheniops) found mainly in shelf waters. Bottom depth was the main environmental determinant of community structure, separating the diverse on-shelf assemblage at the South Orkneys from the less species-rich community of widespread oceanic taxa. Our results indicate the highest diversities of early life stages of endemic fish occur on the shelf and near-shelf areas. Dedicated monitoring is recommended to understand the seasonal differences in larval community assemblages and the implications of early life stages fish bycatch within the krill fishery. [ABSTRACT FROM AUTHOR]

Resident salt marsh fishes consume a diversity of intertidal benthic prey whose abundances may be affected by anthropogenic stressors. A generalist feeding strategy in which diet closely matches the benthic community could allow these fishes to flexibly track changes in prey availability, whereas selection for particular prey may put these fishes at risk if preferred resources decline, especially as warming water temperatures increase metabolic demand. This study detected differences between the diet of adult mummichogs (Fundulus heteroclitus) and the benthic prey community at salt marshes along Hoffler Creek in southeastern Virginia, USA, in May through August of 2 years. Polychaetes made up 74.8% of benthic samples but were only 33.9% of benthic prey items identified in diet samples. Compared to benthic samples, mummichog diet contained higher percentages of small arthropods, including ostracods, copepods, amphipods, and Diptera larvae, with substantial variation across months and sites. Consumption of large numbers of arthropods by some individual fish suggests they were taking advantage of patchily abundant prey. Despite these differences, mummichog diet reflected major temporal and spatial patterns in the benthos, including increased consumption of polychaetes in late summer and of ostracods at the upstream site in 2017. These results suggest that mummichogs are not uniformly generalist in their diet but that they may still be fairly robust to variation in prey availability due to their ability to consume large numbers of abundant prey on a small spatial scale and to track changes in the most abundant prey categories through time. [ABSTRACT FROM AUTHOR]

Aquatic animals are very precious to humans because they provide food sources. In order to satisfy the growing demand for food over the past few decades, there has been a significant rise in the widespread application of pesticides. Surface runoff transports pesticide residues into the aquatic environment, where they pose a threat to the plants and animals that live there. The rise in the human population is accompanied by an accompanying rise in the toxicity of pesticides. The toxicity of pesticides causes damage to the aquatic food chain by decreasing the amount of oxygen that is dissolved in water bodies and contaminating the water. The contaminated water causes harm to the algal component, plankton, and benthos, which in turn causes harm to the water quality and fish diversity. Additionally, the polluted water reduces the abundance of aquatic species. This assessment places particular emphasis on the influence that pesticides have on the quality of water and the biodiversity of aquatic environments. All aquatic organisms, and fish species in particular, are extremely vulnerable to the toxicity of pesticides. Organs such as the liver, kidneys, and gills, as well as the nervous system, are the primary targets of the toxic effects that pesticides have on fish. Because humans use fish species for food, exposure to pesticides can cause a variety of health problems. The primary objective of this study is to draw conclusions regarding the effect that the application of pesticides had on the aquatic ecosystem as well as biodiversity. [ABSTRACT FROM AUTHOR]

Hypoxic aquatic environments have increased in recent decades mainly by human activities that generate pollution. The objective of this work was to study the influence of the discharge of sewage effluents from Chascomús city on the concentration of dissolved oxygen (DO) in the Girado stream and its connection with Chascomús lake and analyze the impact on fish biodiversity. Four sites were selected to measure DO and temperature weekly for one year: discharge of sewage effluent, union of the sewage effluent with the Girado stream, Girado stream and Chascomús lake. Also, ichthyological samplings were carried out in a presumed hypoxic zone and a normoxic zone of the Girado stream. The results showed that there were two hypoxic zones corresponding to the sewage effluent and the union of the effluent with the Girado stream (~3 mg l−1). Also, two normoxic zones were identified, the course of the Girado stream and the union with Chascomús lake (~ 8 mg l−1). In these areas the water temperature varied according to the seasonality of the region (from 10 to 30 °C) without differences between zones. It is important to note that these areas received a constant flow of sewage effluent from Chascomús city (~ 885,600 l per day). In the fish sampling carried out in the 4 seasons of the year, 14 typical species of the Pampas lakes were captured with species more tolerant to low DO. Pejerrey were captured in a small number in both sites but with no signs of abnormalities in the gonads. [ABSTRACT FROM AUTHOR]

Context: Alterations of landscapes and riverscapes by humans have fundamentally altered patterns in freshwater biodiversity throughout the world's aquatic systems. Past research has demonstrated precipitous declines in small- and medium-sized streams, with much less attention given to patterns and drivers of fish biodiversity in larger riverine systems. Objectives: By examining alpha and beta diversity of fishes in the middle and lower reaches of the Yangtze River, China, we aimed to address the following question: What is the role of river–lake connectivity, wetland extent, and human stress factors (e.g., urbanization, fishing pressure, navigation, and shoreline modifications) in shaping fish alpha (species richness) and beta (species nestedness and turnover) diversity? Methods: We examined associations among three classifications of fish assemblage data (i.e., all species, nonmigratory species, and migratory species) sampled along gradients of river–lake connectivity (i.e., Dongting and Poyang lakes), wetland extent, and a suite of human stress factors (urbanization, fishing pressure, navigation, shoreline modification). We conducted redundancy analyses and distance-based redundancy analyses to facilitate mechanistic interpretations of the associations between the explanatory variables and fish alpha and beta diversity. Results: Longitudinally from the middle to the lower reaches of the Yangtze River, fish alpha diversity showed marked decreases while fish beta diversity increased. River segments with greater levels of human impact were generally associated with reduced fish species richness, while segments with higher wetland extent and greater river–lake connectivity tended to support greater species richness. River–lake connectivity, wetland extent, and fishing pressure largely influenced total fish beta diversity. Species nestedness was primarily associated with amount of wetlands, and exhibited the strongest associations with nonmigratory fish species. Turnover was primarily associated with river–lake connectivity (mainly Poyang Lake), especially for migratory species. Conclusions: Our analyses demonstrate the roles of river–lake connectivity, wetland extent, and human stress factors in shaping patterns of alpha and beta diversity for migratory and nonmigratory fishes in the middle and lower reaches of the Yangtze River. Fish diversity conservation in this large river ecosystem calls for protecting hydrological connectivity and wetland habitats, along with reducing fishing pressure. Results from this study will help better inform fish conservation efforts in the Yangtze River and have implications towards other large river systems of the world. [ABSTRACT FROM AUTHOR]

Medicinal leeches are known to primarily inhabit shallow parts of wetlands, which have unique physical, chemical, and biological properties that differ from the main bodies of water in these areas. However, limited research has been conducted on fish diversity and abundance in these habitats. This study aimed to investigate the fish diversity and abundance in the wetlands surrounding Lake Eğirdir (Turkey), where medicinal leeches are known to be present, and discuss the importance of conserving these habitats. Common diversity indices were used to estimate species richness, abundance, and biomass. A total of 416 fish from six species (Aphanius anatoliae, Carassius gibelio, Gambusia holbrooki, Pseudophoxinus egridiri, Pseudorasbora parva, and Seminemacheilus ispartensis) were sampled. The results showed that the species richness was lower in the studied wetlands (six species) compared to the lake itself (13 species), with the dominant species in terms of abundance and biomass being G. holbrooki (44.95%) and C. gibelio (33.46%). The presence of invasive and endemic species plays an important role in shaping the diversity and abundance of the fish community. The study found that there is compatibility between fish diversity and medicinal leeches in wetlands, and that fish species and their sizes provide feeding opportunities in favor of medicinal leeches. The wetlands also provide a protected area for the conservation of two IUCN red-listed fish species (P. egridiri and A. anatoliae). Thus, the study highlights the importance of conserving these habitats for maintaining the ecological unity, harmony, and sustainability of both medicinal leeches and fish populations. [ABSTRACT FROM AUTHOR]

Current status and distributional patterns of fish fauna of Pir Panjal Himalayan region are poorly explored, and research on habitat ecology and species composition along different habitat of river Poonch is still deficient. The current study was undertaken to update the status and distributional pattern of ichthyofauna of this river. The study was conducted from June 2017 to December 2019. A total of 25 fish species were documented from different sampling sites, which belong to four orders, six families and fifteen genera. The Renyi diversity profiles show that the lower and middle stretch had rich species diversity as compared to the upper stretch, with highest at Sher-e-Kashmir Bridge (lower stretch) and lowest at Bufflaiz (upper stretch). The Principal Component Analysis (PCA) results show a considerable variation in the total fish species composition as well as the water quality parameter among the studied sites. The distributional pattern of fish species showed significant variation in their dominance with respect to different sampling sites, indicating the supremacy of the family Cyprinidae (64%) followed by Sisoridae (16%) then by Cobitidae (8%). In contrast, the other three families, Nemachalidae, Salmonidae and Mastacembelidae, contribute only (4%) each, respectively. Significant variation in abundance of the species was recorded across all the site, as the least number of species have been encountered from Bufflaiz and the highest was recorded at the Sher-e-Kashmir bridge site. About 16% species were found common to the entire habitat, while 32% species were restricted to only single habitat. The result of the current study will provide the information needed for freshwater fish resource protection in river Poonch and a reference for promoting the conservation and management of fish diversity of the river. [ABSTRACT FROM AUTHOR]

Headwater streams, located upstream of the river network, play a crucial role in river ecosystems. However, the increasing conversion of natural habitats into agricultural land leads to extensive alterations in landscape composition, posing serious threats to natural stream ecosystems and biodiversity. This research focuses on the headwater streams of the Xin'an River in the Wannan Mountains, China. The study merged information on habitat conditions from two types of habitats (disturbed and natural segments) to evaluate the impact of agricultural land use on the beta diversity of fish assemblages. The results indicated that the disturbed segments exhibited intermediate land-use intensities, slightly higher habitat heterogeneities, and a higher number of native invasive species compared to the natural segments. Differences in local-scale habitat conditions and regional-scale land use drove the species composition discrepancy (taxonomic beta diversity) between disturbed and natural segments. This study provides evidence of how agricultural land use impacts fish assemblage diversity in headwater streams and underscores the significance of sustainable management and conservation for preserving endemic assemblages in these streams. [ABSTRACT FROM AUTHOR]

The Zig-zag eel (Mastacembelus armatus) is an economically important species in southern China. Its natural resources have declined year by year due to overfishing. Understanding its genetic diversity and population structure is very important for resource conservations. Here, we first successfully developed 28 polymorphic microsatellite markers for zig-zag eels and ten of them were used to examine the genetic diversity and differentiation of 7 populations collected from the major river systems of south China. In total, 224 alleles were found with the 10 microsatellite loci in 7 populations, ranging from 4.6 (Nandujiang: NDJ) to 11.1 (Xijiang, XJ), with an average of 8.871 alleles. The average observed and expected heterozygosity ranged from 0.550 (NDJ) to 0.964 (Yuangjiang, YJ) and from 0.537 (NDJ) to 0.775 (Tanjiang, TJ), respectively. The average polymorphism-information content ranged from 0.472 (NDJ) to 0.757 (TJ). Hardy–Weinberg equilibrium test results revealed the loci showed differing deviation in different populations. In total, low level of genetic diversity was only found in HJ (Hanjiang) and NDJ populations. Besides, evidence of recent bottleneck was found in the HJ populations. Analysis of molecular variation showed that the percent variation within individuals (75.00%) was higher than that among populations (25%). In addition, population structure and the pairwise FST revealed that there was low differentiation among XJ, TJ and YJ populations. These data provide important genetic resources for understanding the population differentiation and facilitating genetic conservation and utilization of this species. Article highlights: A total of 28 polymorphic microsatellite markers were successfully developed for zig-zag eels. Low level of genetic diversity was only found in HJ and NDJ populations. Low differentiation was found among XJ, TJ and YJ populations. [ABSTRACT FROM AUTHOR]

Co-occurring biodiversity and global heating crises are systemic threats to life on Earth as we know it, especially in relatively rare freshwater ecosystems, such as in Iran. Future changes in the spatial distribution and richness of 131 riverine fish species were investigated at 1481 sites in Iran under optimistic and pessimistic climate heating scenarios for the 2050s and 2080s. We used maximum entropy modeling to predict species' potential distributions by hydrologic unit (HU) occupancy under current and future climate conditions through the use of nine environmental predictor variables. The most important variable determining fish occupancy was HU location, followed by elevation, climate variables, and slope. Thirty-seven species were predicted to decrease their potential habitat occupancy in all future scenarios. The southern Caspian HU faces the highest future species reductions followed by the western Zagros and northwestern Iran. These results can be used by managers to plan conservational strategies to ease the dispersal of species, especially those that are at the greatest risk of extinction or invasion and that are in rivers fragmented by dams. [ABSTRACT FROM AUTHOR]

Background: Deforestation is a widespread disturbance for neotropical freshwater ecosystems. While biodiversity declines have been associated with deforestation, its functional consequences for stream and river fish faunas remain poorly understood. In this study, we explored how deforestation affects the different facets of the functional structure of fish communities inventoried using environmental DNA metabarcoding in 64 river and 35 stream sites of French Guiana. Specifically, we investigated how functional richness, divergence, evenness and identity of fish faunas are affected by deforestation. Results: We showed that anthropogenic disturbances in French Guiana are modifying the functional diversity of freshwater fish communities. These disturbances not only affected the amount of functional traits held by the communities but also the identity of the traits and the internal structure of the functional space. Consequently, different facets of the functional diversity supported by fish assemblages were altered. In streams, deforestation did not affect the overall diversity of traits but reduced functional redundancy, underlined by a shift in functional identity towards assemblages dominated by pelagic detritivores. In contrast, river fish faunas experienced a decline in functional richness, paired with shifts in functional identity and a loss of fish species with extreme functions. Conclusions: The response to deforestation differed between streams and rivers, but it supports the hypothesis that deforestation is linked to functional changes in fish assemblages. By diminishing the range of the functions in rivers or by jeopardizing the redundancy of functions in streams, deforestation could severely hamper the functioning and stability of neotropical freshwater ecosystems. [ABSTRACT FROM AUTHOR]

The Three Gorges Reservoir is one of the largest reservoirs in the world. Previous studies uncovered longitudinal changes in fish assemblages among riverine, transitional, and lacustrine zones, but whether they vary at small-scale habitats and how tributaries contribute to fish conservation is poorly understood. We selected three neighboring tributaries with different habitat characteristics within and among tributaries and hypothesized that the small-scale habitat heterogeneity within or among tributaries could shape spatial and temporal variation in fish assemblages. We analyzed spatial (among tributaries, pelagic versus benthic, lower versus upper reach) and seasonal patterns of fish assemblage and their relationship with the environment. Piscivorous, limnophilic, and mid-pelagic species dominated the fish assemblage in different habitats. Fish assemblage structure varied spatially between lower and upper reaches and among tributaries. Fish assemblages also varied seasonally, mainly related to environmental variability (i.e., water depth, water temperature, pH, specific conductivity, riparian slope, and vegetation coverage). Catch per unit effort was similar between pelagic and benthic habitats but exhibited horizontal and seasonal changes. The most influential environmental variables were water depth, water temperature, dissolved oxygen, and pH. Our results supported the hypothesis, and indicated that we should protect tributaries that provide important areas for fish diversity in large reservoirs. [ABSTRACT FROM AUTHOR]

The fish communities in the Yangtze River (YR) basin is in a degraded state due to the influence of human factors. Here, we used environmental DNA (eDNA) metabarcoding technology to conduct a survey on the fish diversity in the upper reaches of the YR from Jiangjin to Fuling to search for better monitoring methods. We set up 12 sampling sites in this river section, collected 36 environmental samples, and obtained 5,067,423 valid sequences. After conducting an annotated comparative analysis utilizing the NCBI public database, a total of 104 freshwater fish species were identified, belonging to 8 orders, 24 families, and 72 genera. This included six nationally protected fish species, as well as endemic, introduced, and previously unrecorded species within this basin. The results of this survey indicate a trend toward miniaturization of species and a decline in endemic fish species as well as an increase in exotic fish species in the region, which implied the fish communities in the upper YR region remains in a degraded state. However, the species composition at the family level has remained relatively stable over the past decade. Furthermore, the diversity analysis revealed that fish composition and diversity exhibit variability across different locations. [ABSTRACT FROM AUTHOR]

This study was conducted to clarify the relationship between fish species composition and environmental factors at various scales in river estuaries in the Japanese archipelago. The estuaries harbor diverse fish species composition due to their complex topography, varied climatic zones, and ocean currents. Non-hierarchical cluster analysis classified the fish species composition of 100 river estuaries (58 families, 152 species, and 486,356 individuals) into five groups. The highest number of species was confirmed in the group of river estuaries located in southwestern Japan and flowing into the inner bay (55.1 ± 9.6 species), characterized by an abundance of the number of Gobiidae species. In contrast, the species number was the lowest in the groups consisting of river estuaries that primarily belong to the northern Japanese archipelago (15.3 ± 3.3 species) that were characterized by an abundance of the number of cold-water fishes such as Salmonidae, Pleuronectidae, and Osmeridae. The highest fish species diversity was confirmed in the groups consisting of river estuaries flowing into the inner bays of southwestern Japan, which had a large tidal range (344 ± 132 cm), suggesting that the large tidal differences create a diverse tidal flat environment that supports fish species diversity. These results indicate that regional species diversity and geographical factors influence the classification of fish fauna. In northeastern Japan, the classification was influenced by geographic area and associated water temperature changes, whereas in southwestern Japan, tidal differences and wave effects could be more important. Understanding the factors that influence the fish species composition of a target river is fundamental to estuarine conservation, and the findings of this study provide basic knowledge for conservation. [ABSTRACT FROM AUTHOR]

Globally, small temporarily closed estuaries are the least considered for fisheries assessment and management due to a low scientific priority and regional importance. However, these ecosystems are highly exposed to anthropogenic pressures and may deteriorate without assessing its aquatic resources. In this study, fish diversity and guild structure of Chettuva—a temporarily closed tropical estuary in the western coast of India—was investigated. A total of 70 fish taxa belonging to 32 families were recorded with the quantitative predominance of families; Mugilidae, Cichlidae, and Leiognathidae. Family Carangidae had the highest species diversity (seven species), followed by Clupeidae and Mugilidae (five species). Ecological guild assessment revealed that the immigrating marine fish species (marine estuarine opportunist (34 species) and marine estuarine dependent (13 species)) dominated the guild structure over the estuarine resident species (seven species). The marine species were found all along the saline gradient and throughout the sampling period indicating the salinity ingress towards the estuarine zone throughout the year. Carnivores and omnivores were the major feeding mode functional guilds in terms of diversity, whereas detritivores dominated in numerical abundance throughout the salinity gradient. The major environmental drivers of the fish assemblages in the estuary were salinity and chlorophyll a. The distribution of freshwater fishes and estuarine resident species was connected with the rising primary productivity as the majority of fishes rely on the algae for feeding, whereas marine estuarine dependent and marine estuarine opportunist species occurred in areas with the highest salinity concentrations. [ABSTRACT FROM AUTHOR]

Climate change is perhaps the greatest threat to coral reefs worldwide. However, there is spatial variation in the extent and severity of this disturbance, with offshore and well-managed reefs presumed to be less vulnerable to anthropogenic disturbance. Here, fish and benthic communities at the offshore and well-managed reefs of Apo Reef Natural Park, Philippines, were examined during a bleaching disturbance in 2016 and reassessed 2 (2018) and 3 years (2019) after using scuba surveys. Results showed that benthic communities varied more strongly with year attributed to changes in the benthic cover of coral. These changes were influenced by site, with some sites experiencing coral loss of 41–48%, while other sites exhibited minimal changes. Site differences in coral loss may be associated with coral cover, with sites that had high coral cover prior to bleaching incurring larger loss of coral cover. Fish communities varied more with sites and was associated with differences in the predominant benthos. The stability of fish communities with year despite coral loss may be attributed to the minimal loss of coral cover at some sites. For sites that experienced high losses of coral cover, the presence of alternative and deeper habitats may have provided shelter and food for more mobile fishes maintaining taxonomic composition within sites. This study shows that bleaching disturbance circumvents effective management, but impacts are variable even at small (≤ 3 km) spatial scales. Benthic community composition and presence of alternative habitats potentially alleviate the negative impacts of bleaching on reef fish diversity and abundance. [ABSTRACT FROM AUTHOR]