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The Yarlung Tsangpo River on the Tibetan Plateau provides a unique natural environment for studying fish evolution and ecology. However, the genomes and genetic diversity of plateau fish species have been rarely reported. Schizopygopsis younghusbandi, a highly specialized Schizothoracine species and economically important fish inhabiting the Yarlung Tsangpo River, is threatened by overfishing and biological invasion. Herein, we generated a chromosome‐level genome of S. younghusbandi and whole‐genome resequencing data for 59 individuals from six locations of the river. The results showed that the divergence time between S. younghusbandi and other primitive Schizothoracine species was ∼4.2 Mya, coinciding with the major phase of the Neogene Tibetan uplift. The expanded gene families enriched in DNA integration and replication, ion binding and transport, energy storage, and metabolism likely contribute to the adaption of this species. The S. younghusbandi may have diverged from other highly specialized Schizothoracine species in the Zanda basin during the Pliocene epoch, which underwent major population reduction possibly due to the drastic climate change during the last glacial period. Population analysis indicated that the ancient population might have originated upstream before gradually adapting to evolve into the populations inhabiting the mid‐stream and downstream regions of the Yarlung Tsangpo River. In conclusion, the chromosome‐level genome and population diversity of S. younghusbandi provide valuable genetic resources for the evolution, ecology, and conservation studies of endemic fishes on the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Endemic fish species have long supported the livelihoods of local communities in the Rufiji River Basin (RRB). However, destructive fishing practices have led to a concerning decline in endemic fish stocks. To assess these changes, this study employed key informant interviews, focus group discussions (FGDs), and fishery surveys to assess the historical and contemporary distribution of endemic fishes within the RRB. DNA barcoding was also used to verify species identities. Out of 37 reported fish species, 33 species (54.55% endemic and 45.45% exotic to RRB) were confirmed through DNA barcoding and morphological characteristics. About 5 species including, Heterobranchus longifilis, Citharinus congicus, Labeo congoro, Mormyrus longirostris, and Labeobarbus leleupanus were rarely found in the field, despite being classified as Least Concern by IUCN. Additionally, five species that were reported to be present in the RRB by experienced fishers were not captured during sampling. This highlights the need for validation of the existence of such species through eDNA metabarcoding. Moreover, due to the rarity of some species in the area, their IUCN assessment should be revisited. [ABSTRACT FROM AUTHOR]

Some East Asian rivers experienced repeated rearrangements due to Indian–Asian Plates' collisions and an uplift of the Tibetan Plateau. For the upper Changjiang (Yangtze/Jinsha River), its ancient south-flowing course and subsequent capture by the middle Changjiang at the First Bend (FB) remained controversial. The DNA of freshwater fishes possess novel evolutionary signals of these tectonic events. In this study, mtDNA Cyt b sequences of endemic Schizopygopsis fish belonging to a highly specialized grade of the Schizothoracinae from the eastern Tibetan Plateau were used to infer the palaeo-drainages connectivity history of the upper Changjiang system. Through phylogenetic reconstruction, a new clade D of Schizopygopsis with three genetic clusters and subclusters (DI, DII, DIIIa, and DIIIb) were identified from the upper Yalong, Changjiang, and Yellow Rivers; the Shuiluo River; the FB-upper Changjiang; and the Litang River; respectively. Ancient drainage connections and capture signals were indicated based on these cladogenesis events and ancestral origin inference: (1) the upper Yalong River likely acted as a dispersal origin of Schizopygopsis fish to the adjacent upper Yellow and Changjiang Rivers at ca. 0.34 Ma; (2) the Litang River seemed to have directly drained into the upper Changjiang/Yangtze/Jinsha River before its capture by the Yalong River at ca. 0.90 Ma; (3) the Shuiluo River likely flowed south along a course parallel to the upper Changjiang before their connection through Hutiao Gorge; (4) a palaeo-lake across the contemporary Shuiluo, Litang, and Yalong Rivers was inferred to have served as an ancestral origin of clade D of Schizopygopsis at 1.56 Ma. Therefore, this study sheds light on disentangling ambiguous palaeo-drainage history through integrating biological and geological evidence. [ABSTRACT FROM AUTHOR]

In the present study, we provide a checklist of the predators that may impact the population of the critically endangered Mandra shemaya (Alburnus mandrensis Drensky, 1943). This endemic fish only inhabits the basin of Mandra Lake in the Burgas district (SE Bulgaria) and data on its biology are scarce. We have confirmed the presence of the Mandra shemaya in Mandra Lake for the last six years (including 2024) and provided an analysis on the potential predatory pressures on A. mandrensis. The recently recorded presence of a highly invasive piscivorous predatory fish in Mandra Lake is considered potentially dangerous for the sustainability of native fish species. [ABSTRACT FROM AUTHOR]

Geological events can have a major effect on the genetic structure and differentiation of fish populations. The relative importance of key geological events on the distribution and genetic structure of endemic fish of the genus Discogobio in the Yunnan–Guizhou Plateau has not yet been evaluated. Studies of the phylogeography of Discogobio fishes could provide insights into spatial and temporal changes in their population size, dispersal history, and extent of geographical isolation, and the data acquired in such studies can be used to aid their conservation. Here, we used single‐nucleotide polymorphisms (SNP) to characterize the phylogeography of Discogobio fishes. Our analysis supports the endemicity of Discogobio. However, Discogobio samples from different regions contained multiple ancestral components, including admixed and diversified genetic components. This might stem from polymorphism of the ancestors themselves or the infiltration of genes caused by hybridization between Discogobio species. We estimated that the most recent common ancestor (MRCA) of Discogobio fish in the Central Yunnan Basin was approximately 4.63–3.83 million years ago (Ma). We also inferred that the evolution of Discogobio in the Central Yunnan Basin was closely related to the expansion and contraction of the lake basin around 2.59–0.13 Ma. We proposed measures that could be implemented to conserve remaining populations and their corresponding habitats to prevent further declines and preserve the biodiversity of this unique genus. [ABSTRACT FROM AUTHOR]

The Chesapeake Logperch, Percina bimaculata, is a small fish endemic to the upper Chesapeake Bay drainage with a range significantly reduced by water quality and habitat degradation. It was described by Haldeman in 1842 and 1844 from the Susquehanna River, Pennsylvania, synonymized with the Logperch (Percina caprodes) by Jordan in 1877, and redescribed by Near in 2008. It is extirpated from the Potomac River drainage and extant in a portion of its historic range within the Susquehanna River drainage of Pennsylvania and Maryland in the United States of America. We reviewed available historic field survey information and defined the likely extent of the historic distribution of P. bimaculata and its change in response to historic environmental perturbations. We performed fisheries surveys during 2004–2023 to fill data gaps and to define the current distribution and abundance in the Susquehanna River drainage within Pennsylvania. Our surveys utilized electrofishing gears, electrified benthic trawls, and seines. Our surveys targeting P. bimaculata on the Susquehanna River and tributaries from York Haven to Holtwood, Pennsylvania, combined with available fisheries surveys conducted by others, confirm it was extirpated from that portion of the drainage. We documented the continued usage of Conowingo Pond, Susquehanna River, and tributaries below Holtwood by populations known to exist in historic field surveys. These populations appear to have been stable since at least the 1960s based on historic data and our current surveys. We documented previously unknown populations in the Octoraro Creek drainage, Octoraro Reservoir, and Muddy Run Pumped Storage Facility. Habitat utilization observations during our surveys indicate that clean sand, gravel, rubble, boulders, and large woody debris are preferred substrates. In the lower Susquehanna River and two tributaries, P. bimaculata has demonstrated a plasticity of habitat usage by continuing to occur in environments converted into impoundments by dams. In these impoundments, shorelines and connections with clean tributaries containing preferred substrates appear to be important given their utilization by P. bimaculata during our surveys. It is our opinion that the Susquehanna River and tributaries above Holtwood once again constitute suitable habitats. Conservation efforts focused on reintroductions, water quality, habitat, and connectivity have the potential to increase the extent of occurrence, abundance, and security of P. bimaculata. [ABSTRACT FROM AUTHOR]

Channel constructions significantly impact river hydrodynamics, subsequently influencing river ecosystems. To mitigate the negative influence of channel construction and protect fish habitat, it is essential to evaluate fish habitat suitability through the integration of hydrodynamic and habitat models. This study models channel constructions on both the left and right riverbanks to evaluate habitat suitability for Four Major Chinese Carps and the Chinese sturgeon. Initially, flow velocity, water depth and grain size are simulated, followed by an assessment of habitat conditions using the Habitat Suitability Index (HSI) for three distinct construction strategies. Results reveal that constructing channels on the left bank mitigates adverse effects on fish habitat, while constructions on the right bank and both riverbanks lead to habitat degradation. Long‐term effects on riverbed elevation and fish habitat suitability post‐construction were also investigated. Notably, the Four Major Chinese Carps consistently demonstrate greater suitability for the studied river, regardless of flow rate or construction strategies, in comparison to the Chinese sturgeon. These findings underscore diverse responses to channel construction, providing valuable insights for identifying critical habitat areas for endemic fish conservation. This research presents a robust framework for assessing fish ecology in river systems, offering support for conservation decision‐makers. [ABSTRACT FROM AUTHOR]

Stocking density has a significant influence on animal homeostasis, and so is a crucial factor in the management of organisms in captivity and an important role in ex situ conservation of endangered species. Hypancistrus zebra is an endemic fish species from the Xingu River, Brazil—considered Critically Endangered since the early 2000s due to fishing pressure and, more recently, due to habitat changes resulting from the construction of the Belo Monte Hydroelectric Dam. The implementation of appropriate management in captivity is of utmost importance for its conservation, particularly in enhancing ex situ breeding techniques. This study aimed to evaluate the growth of juvenile H. zebra in aquaria with three different stocking density levels. The juveniles were distributed between three treatments, each with three replicates. We found no correlation between biomass and aquarium volume. The highest correlation coefficients were found between growth rates and densities related to the number of individuals per shelter area. Mortality rate was directly related to the initial number of fish in the aquariums, with larger populations showing higher mortality rates. The treatment with lower stocking density displayed the highest growth rate, while the treatment with higher density had the lowest growth rate, with a 23.38% difference between them. [ABSTRACT FROM AUTHOR]

Cryonotothenioids constitute a subgroup of notothenioid fishes endemic to the Southern Ocean that are specialized to exist in a narrow range of near-freezing temperatures. Due to the challenges of reliably collecting and maintaining larval cryonotothenioids in good condition, most thermal tolerance studies have been limited to adult and juvenile stages. With increasing environmental pressures from climate change in Antarctic ecosystems, it is important to better understand the impacts of a warming environment on larval stages as well. In this study, we determine the critical thermal maxima (CTmax) of cryonotothenioid larvae collected in pelagic net tows during three research cruises near the western Antarctic Peninsula. We sampled larvae of seven species representing three cryonotothenioid families—Nototheniidae, Channichthyidae, and Artedidraconidae. For channichthyid and nototheniid species, CTmax values ranged from 8.6 to 14.9 °C and were positively correlated with body length, suggesting that younger, less motile larvae may be especially susceptible to rapid warming events such as marine heatwaves. To our knowledge, this is the first published test of acute thermal tolerance for any artedidraconid, with CTmax ranging from 13.2 to 17.8 °C, which did not correlate with body length. Of the two artedidraconid species we collected, Neodraco skottsbergi showed remarkable tolerance to warming and was the only species to resume normal swimming following trials. We offer two hypotheses as to why N. skottsbergi has such an elevated thermal tolerance: (1) their unique green coloration serves as camouflage within near-surface phytoplankton blooms, suggesting they occupy an especially warm near-surface niche, and (2) recent insights into their evolutionary history suggest that they are derived from taxa that may have occupied warm tide-pool habitats. Collectively, these results establish N. skottsbergi and larval channichthyids as groups of interest for future physiological studies to gain further insights into the vulnerability of cryonotothenioids to a warming ocean. [ABSTRACT FROM AUTHOR]

The primary objectives of this study were to advance understanding of the morphological intricacies exhibited by the endemic fish species Delminichthys ghetaldii, commonly known as the Trebinje minnow, and to determine intraspecific morphological variability. The study involved the examination of 76 mature specimens collected since 2018 from five distinct karst fields located within the Dinaric region of Eastern Herzegovina, Bosnia and Herzegovina. A comprehensive analysis of 22 morphometric and 8 meristic characteristics was conducted to unravel the underlying patterns of variation. Discriminant function analysis was employed for the thorough investigation of the morphometric traits, whereas canonical correspondence analysis was applied to scrutinize the meristic traits. The discriminant function analysis yielded noteworthy outcomes, revealing substantial differentiations across 17 morphological characteristics within samples from diverse karst fields. Furthermore, it revealed notable dissimilarities in four morphometric characteristics when data including both male and female specimens were examined. Remarkably, these analyses showed that Delminichthys ghetaldii specimens inhabiting the Popovo karst field exhibit significant morphological disparities compared to those in the other fields. Conversely, individuals from the Fatničko karst field showed a pronounced morphological affinity with their counterparts from the Mokro karst field. Intriguingly, a resemblance in morphometric characteristics was noted between Delminichthys ghetaldii inhabitants of the Dabarsko karst field and those from the Ljubomirsko karst field. The assessment of osteological meristic characteristics across samples from the five distinct karst fields, as well as the differentiation between male and female specimens, did not reveal any statistically significant distinctions. [ABSTRACT FROM AUTHOR]

The Yarlung Zangbo River is a river with abundant hydropower resources but fragile biodiversity in China. As an important benchmark for both research and ecological management, there is still a lack of knowledge about the swimming ability of fishes in the Yarlung Zangbo River. The induced flow velocity (Uind), critical swimming speed (Ucrit), and burst swimming speed (Uburst) of five Schizothoracinae species were tested in this study. Relative swimming ability related to body length and body shape was calculated. The results indicated that the average absolute swimming speeds (Uind‐a, Ucrit‐a, and Uburst‐a) of all the experimental fish were 10.20 ± 0.01, 57.58 ± 3.28, and 69.54 ± 2.94 cm/s, respectively, and the corresponding relative Uind, Ucrit, and Uburst related to body length (Uind‐l, Ucrit‐l, Uburst‐l) were 1.15 ± 0.07, 5.04 ± 0.26, and 7.23 ± 0.28 BL/s, respectively. Moreover, relative Uind, Ucrit, and Uburst related to body shape (Uind‐s, Ucrit‐s, and Uburst‐s) were 0.80 ± 0.13, 2.49 ± 0.51, and 4.32 ± 0.57 cm−2/s, respectively. No significantly differences in relative swimming speeds existed among five species. Only Oxygymnocypris stewartii was significantly weaker in Uburst‐s than Schizothorax o'connori. The body shape showed a stronger relationship with swimming speed than the body length did. Schizothoracinae fish in the Yarlung Zangbo River basin are less sensitive to the water flow and performed weaker Ucrit and Uburst compared to those in the Yangtze River basin, indicating that Schizothoracinae fish in the Yarlung Zangbo River may be more susceptible to threats from environmental changes. The paper enriched the research on the swimming ability of Schizothoracinae fishes and provided efficient data for the fish conservation in the Yarlung Zangbo River. [ABSTRACT FROM AUTHOR]

Freshwater fishes are facing considerable threats in the Arabian Peninsula which is considered as a highly stressed region in the Middle East. It is predicted that northern Oman is likely to face decreasing rainfall and increasing temperature in coming decades. In this study, we focused on an endemic cyprinid fish Cyprinion muscatense, as a model to investigate impacts of climate change on the mountain fishes inhibiting in this arid region. This species is expected to be strongly affected by climate change because of its limited distribution range in a montane area surrounded by lowlands and sea, limiting the species in shift to other areas. We used an ensemble approach by considering two regressions‐based species distribution modeling (SDM) algorithms: generalized linear models (GLM), and generalized additive models (GAM) to model the species habitat suitability and predict the impacts of climate change on the species habitat suitability. Based on the distribution models, the montane area located in northeastern Oman was identified as the most suitable habitat for this species. Our results indicate that, even under the minimum greenhouse gas emissions scenario (RCP 2.6), climate change will produce a high reduction in its potential future habitats. According to the results of percent contribution, elevation and annual minimum temperature were the most important variables in predicting the species suitable habitats. Results also showed that only a small percentage of suitable habitats for the species within boundaries of protected areas. Therefore, the impact of climate change on the species appears particularly alarming. Although our study was restricted to a single cyprinid freshwater species, decreases in potential habitats are likely predicted for other cyprinid fish species restricted to the mountains of this region, suggesting severe consideration is needed for aquatic systems in future conservation planning, especially for endemic freshwater fishes. [ABSTRACT FROM AUTHOR]

A variety of hierarchical gene flow models have been proposed to explain the distribution of genetic variation in aquatic environments. These models, including the Stream Hierarchy (SH), Death Valley (DV), Headwater (HW), and Widespread Gene flow (WG) models, provide testable hypotheses that focus on the degree of within-basin or within-stream network connectivity and an organism's dispersal abilities. We tested these models using Tlaloc hildebrandi (Profundulidae, Cyprinodontiformes), a freshwater fish endemic to the highlands of the Grijalva and Usumacinta River basins in southern Mexico. Data from ultraconserved elements (UCEs) showed that although T. hildebrandi was recovered as monophyletic, the sub-basins were not. We generated single nucleotide polymorphisms from the UCEs to analyse the data in a population genetic framework. These results differed between analyses such that two (STRUCTURE analysis) or three (DAPC analysis) genetic groupings were recovered. Overall, the results of this study provide support for the SH model. Some individuals from the Jataté sub-basin, however, conformed to the HW model, due to historical connections among headwater streams and rivers of the Jataté and Amarillo–Chenalhó clades/clusters. The greatest degree of gene flow has occurred from the Grijlava to the Usumacinta basins, two geographically proximate basins that have been hypothesized to have had previous connections. [ABSTRACT FROM AUTHOR]

In order to study the individual biology of endemic fish in China, lay a foundation for the conservation of its germplasm resources, and consolidate the basic biological data of endemic fish in the world. According to the ethical code and fishing permit, 21 samples of Schizothorax (Racoma) biddulphi (Günther, 1876) were collected from the Muzati River in Tarim River system from 2021 to 2022, and their morphological characteristics, age identification and anatomical observation were analyzed by classical biological methods. S. biddulphi has a long body, a conical head, a pointed snout and a lower mouth. Requires 2 pairs. The scales are small and neatly arranged; Bare or scaly chest; The lateral line scale is slightly larger. The lateral line is complete. The correlation equation between body length and body weight is: W = 4.148 × 10-5L2.791. There were 5 kinds of age identification materials: 15+ for lapillus and asteriscus, 14+ for vertebra, 11+ for opercular bone, and 9+ for anal scale. The peritoneal wall of S. biddulphi is black; The tooth type is 2·3·5-5·3·2; The gill harrow was 11~13 for laymen and 15~18 for experts. Diphysocyte; Gallbladder oval; The number of vertebrae is 4+42-43+1, and the number of ribs is 23 or 24. S. biddulphi is a special species in the Tarim River system, and its evolutionary adaptation is closely related to the uplift of the Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

Discerning ecosystem change and food web dynamics underlying anthropogenic eutrophication and the introduction of non-native species is necessary for ensuring the long-term sustainability of fisheries and lake biodiversity. Previous studies of eutrophication in Lake Victoria, eastern Africa, have focused on the loss of endemic fish biodiversity over the past several decades, but changes in the plankton communities over this same time remain unclear. To fill this gap, we examined sediment cores from a eutrophic embayment, Mwanza Gulf, to determine the timing and magnitude of changes in the phytoplankton and zooplankton assemblages over the past century. Biogeochemical proxies indicate nutrient enrichment began around ~ 1920 CE and led to rapid increases in primary production, and our analysis of photosynthetic pigments revealed three zones: pre-eutrophication (prior to 1920 CE), onset of eutrophication with increases in all pigments (1920–1990 CE), and sustained eutrophication with cyanobacterial dominance (1990 CE–present). Cladoceran remains indicate an abrupt decline in biomass in ~ 1960 CE, in response to the cumulative effects of eutrophication and lake-level rise, preceding the collapse of haplochromine cichlids in the 1980s. Alona and Chydorus, typically benthic littoral taxa, have remained at relatively low abundances since the 1960s, whereas the abundance of Bosmina, typically a planktonic taxon, increased in the 1990s concurrently with the biomass recovery of haplochromine cichlid fishes. Overall, our results demonstrate substantial changes over the past century in the biomass structure and taxonomic composition of Mwanza Gulf phytoplankton and zooplankton communities, providing a historical food web perspective that can help understand the recent changes and inform future resource management decisions in the Lake Victoria ecosystem. [ABSTRACT FROM AUTHOR]

Members of the genus Cyprinion (Cypriniformes: Cyprinidae) are found in the Indus River basin west to the Arabian Peninsula and the Tigris‐Euphrates River drainages (Persian Gulf basin). The taxonomic status of Cyprinion including Cyprinion muscatense is poorly understood when compared to other cyprinid genera. C. muscatense has been considered as a member of the Cyprinion watsoni‐microphthalmum group and a valid species endemic to the Arabian Peninsula. Here, we redescribe C. muscatense based on an integrative morphological and molecular approach and freshly sampled material from several localities in the Oman Mountains ecoregion. The results showed that C. muscatense is distinguished from the other Cyprinion species in the Arabian Peninsula by having a short, thin, and slightly serrated last unbranched dorsal fin ray; the lower number of circumpeduncular scales; lateral line scales; and also scales between the lateral line and the dorsal‐fin origin. Subterminal mouth, presence of one pair of small barbels at the mouth corner, 3–4 unbranched and 9½–10½ dorsal‐fin branched rays, 12–14 pectoral‐fin rays, 7–8 pelvic‐fin rays, 2–3 unbranched and 6½–7½ branched anal‐fin rays, and 37–40 lateral line scales are other morphological characteristics of C. muscatense. C. muscatense is also well distinguished by molecular characters among its congeners. The first molecular phylogenetic analysis of the genus, covering all currently recognized Cyprinion species except for C. watsoni, is also presented. C. muscatense is resolved as the sister species to another endemic fish of the Arabian Peninsula Cyprinion mhalense, with a Kimura‐2‐Parameter model distance of 5.3%. [ABSTRACT FROM AUTHOR]

This study presents primary observations of the natural diet of two endemic fishes, Delminichthys ghetaldii and Telestes dabar, along with an examination of their niche overlap. The feeding habits of these species were analyzed based on a dataset comprising 115 specimens collected from five karst poljes during the year 2018. Statistical analyses, including one-way ANOVA and Tukey's HSD post-hoc testing, were employed to discern significant differences in body size and weight among the five populations of Delminichthys ghetaldii. Numeric indices such as numerical abundance, weight percentage of abundance, and frequency of occurrence, alongside a composite index (IRI - index of relative importance), were applied to elucidate the feeding strategy of these species. The diversity of diet and poljes utilization was assessed using Simpson's diversity index, while predation selectivity was analyzed through the electivity index. Considerable overlap in the diet of Delminichthys ghetaldii was observed among the five poljes, as well as in the overlap between these two species. The findings of this study indicate that Delminichthys ghetaldii exhibits a zoophagous planktivorous diet, i.e. carnivorous, while Telestes dabar demonstrates a phytofagous planktivorous diet, i.e. herbivorous. [ABSTRACT FROM AUTHOR]

Aim: This study aimed to illustrate the changing diversity patterns of native freshwater fish in the past two centuries and to identify priority locations for native fish conservation to counter future degradation. Location: Japanese archipelago. Methods: We used the published native fish fauna data in 39 lakes across Japan, analysing historical and current diversity and projecting future distribution patterns based on the Japanese Red List. We assessed fish assemblages' taxonomic, phylogenetic, and functional alpha and beta diversity across different periods. Additionally, we proposed a cumulative diversity index that incorporated taxonomic, phylogenetic and functional facets, and then examined its relationship with the latitudinal positioning of the lakes across periods. Results: We observed a significant decrease in the richness of native freshwater fish since historical periods. Accompanying this decline were significant reductions in both phylogenetic relatedness and functional redundancy. Fish beta diversity increased from the past to the present and is predicted to decline drastically, indicating an ongoing homogenization process. Using the cumulative diversity index, we identified Hokkaido and Kyushu as crucial habitats for endemic fishes. These islands, with unique biogeographical backgrounds, contributed substantially to the national dissimilarity patterns of native fish assemblages in the historical period. However, the contribution is diminishing due to the ongoing decline in fish endemism. Main Conclusions: The conservation priority of native freshwater fish in Japan should be assigned to Hokkaido and Kyushu due to the inhabited endemic species. The proposed framework for assessing the cumulative diversity of biotic communities presented the potential to aid macroecological explorations that underpin biodiversity conservation. [ABSTRACT FROM AUTHOR]

Hypoxia, a condition when dissolved oxygen (DO) drops down below 2 mg/L1, is one of the most common stressors in aquatic environment. Aquatic animals often overcome this condition with a combination of physiological, behavioural, biochemical and molecular responses. In the present study, we examined the effect of moderate hypoxia on superoxide dismutase (SOD) activity and oxygen transport mechanism in Delminichthys ghetaldii erythrocytes. Popovo minnow (Delminichthys ghetaldii) is an endemic cyprinid fish which inhabits springs and streams in fields Ljubomir, Dabar and Fatnica in B&H, and Bacina lakes in Croatia. During autumn and spring floods, Popovo minnows emerge from the underground waters to surface estavelle. Withdrawal of the water to the underground basins brings them back to their underground habitat. Fishes were collected in the flood plain of Fatnica field (43°00'53''N; 18°19'24''E). Following erythrocyte lineage parameters were measured: number of red blood cells (RBC), hemoglobin concentration, Packed cell volume (PCV), Mean Corpuscular Volume (MCV), Mean Corpuscular Hemoglobin Concentration (MCHC) and MCH (Mean Corpuscular Hemoglobin). Also, the characterization of the SOD from RBC is presented for the first time. Native PAGE resolved the presence of three CuZn SOD isoforms, while isoelectrofocusing revealed the presence of two anionic SOD isoforms with pI 3.4 and 3.5. Exposure to conditions of mild hypoxia induced changes in fish SOD activity, hemoglobin concentration and MCH. Results indicate Delminichthys ghetaldii responds to hypoxia by enhancement of the oxygen carrying capacity and triggering SOD activity. [ABSTRACT FROM AUTHOR]

Cyprinus acutidorsalis (Wang, 1979) is an endemic fish in China that is sparsely distributed in the Hainan provinces and Guangxi Zhuang Autonomous Region (GZAR). In this study, the complete mitochondrial genome of C. acutidorsalis from the Hainan population from the Wanquan River was sequenced, and its phylogenetic relationship was analyzed. The circular mtDNA was 16,581 bp in length, and the overall base composition was A (32.0%), C (27.5%), T (24.8%), and G (15.70%), with a slight bias toward A + T. The complete mitogenome encoded 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes, and a control region. Phylogenetic analysis indicated that the most closely related fish to C. acutidorsalis from the Hainan population was C. acutidorsalis from the Guangxi population. These findings offer basic molecular data and a better understanding of the phylogenetic relationships among the Cyprinus species. [ABSTRACT FROM AUTHOR]

Liobagrus geumgangensis is a novel Korean fish species endemic to the Geumgang and Mangyeonggang River basins on the Korean Peninsula. During a survey of L. geumgangensis, the discovery of Liobagrus mediadiposalis as a potential threat prompted an investigation into L. geumgangensis genetic diversity and structure. Three populations of L. geumagangensis and one population of L. mediadiposalis were investigated using a 1024-bp sequence in the cytb region of mitochondrial DNA. The Mangyeonggang River of L. geumagangensis displayed the lowest haplotype diversity (Hd) within a range of 0.000–0.337, with one to two haplotypes (h). The Jecheon region of the Geumgang River for L. geumagangensis population had the highest nucleotide diversity (π) and was within the range of 0.00000–0.00066. The h of L. mediadiposalis population was 3, the range of Hd was 0.292, and π was 0.00231. Tajima's D (D) and Fu's Fs (F) were negative and non-significant in the LgGJ population. The genetic structure of L. geumgangensis had no shared haplotypes among the three populations. The discovery of L. mediadiposalis in the Geumgang River suggests the necessity of non-habitat conservation and population management of fish farms to conserve L. geumgangensis. [ABSTRACT FROM AUTHOR]

Dam construction alters the hydrodynamic conditions, consequently impacting the swimming behavior of fish. To explore the effect of flow hydrodynamics on fish swimming behavior, five endemic fish species in the upper Yangtze River basin were selected. Through high‐speed video visualization and computer analysis, these species' swimming patterns under different flow velocities (0.1–1.2 m/s) were investigated. The kinematic and morphological characteristics of the fish were presented. The principal component analysis was used to analyse the main factors influencing the swimming ability of fish and to determine the correlation coefficients among fish behavior indicators. Fish exhibited three different swimming patterns under different flow velocities. Low velocity (0.1–0.3 m/s) corresponds to free motion, middle velocity (0.4–0.7 m/s) corresponds to cruising motion, and high velocity corresponds to stress motion (0.8–1.2 m/s). The fish kinematic index curves were obtained, and four of five fish species showed two extreme points, which means the optimal and adverse swimming strategies can be determined. With the increase in flow velocity, the tail‐beat frequency showed an increasing trend, whereas the tail‐beat angle and amplitude showed a decreasing trend. Morphological and kinematic parameters were the two main indexes that affect the swimming ability of fish, which accounts for 41.9% and 26.9%, respectively. [ABSTRACT FROM AUTHOR]

Purpose: Aplocheilus dayi (Ceylon Killifish) is a freshwater fish endemic to Sri Lanka, but its conservation has not received much attention as uncontrolled fishing for ornamental purposes and many other human activities have posed significant threats to its survival. Therefore, this study aimed to provide baseline information on the development of a captive breeding system and to study the embryonic and larval development of A. dayi. Research Method: Matured A. dayi fish were acclimatised for two weeks prior to the experiments. A suitable breeding substrate to facilitate successful spawning was identified using two substrates; spawning mop, and sand while no substrate was used as the control. The subsequent breeding experiment (to find the best sex ratio) was performed using different sex combinations (Male: female 1:1, 1:2, 1:3, and 2:4). Subsequently, eggs were collected and analysed for fertility, hatchability, and embryonic development studies. Findings: Spawning mop seemed to be the most preferred spawning substrate for A. dayi. Egg parameters, including fertilisation rate and hatchability, were not significant upon the sex ratios; however, the ratio between male: and female (1:2) had the highest significance (p<0.05) in egg production (4 eggs/day). Moreover, we found that A. dayi eggs showed a lengthy incubation period (11 - 13 days at 25±1 °C), indicating their dormancy nature to bypass the hostile conditions before being hatched. Research Limitations: The breeding pattern under captivity needs to be examined over an extended period in different experimental settings, such as using other culture techniques with varying density ratios. Originality/Value: A. dayi can be successfully bred in captivity, and further this study gives the readers factual information on the embryonic development of A. dayi. [ABSTRACT FROM AUTHOR]

Yellow-cheek carp (Elopichthys bambusa) is a typical large and ferocious carnivorous fish endemic to East Asia, with high growth rate, nutritional value and economic value. In this study, a chromosome-level genome of yellow-cheek carp was generated by combining PacBio reads, Illumina reads and Hi-C data. The genome size is 827.63 Mb with a scaffold N50 size of 33.65 Mb, and 99.51% (823.61 Mb) of the assembled sequences were anchored to 24 pseudo-chromosomes. The genome is predicted to contain 24,153 protein-coding genes, with 95.54% having functional annotations. Repeat elements account for approximately 55.17% of the genomic landscape. The completeness of yellow-cheek carp genome assembly is highlighted by a BUSCO score of 98.4%. This genome will help us understand the genetic diversity of yellow-cheek carp and facilitate its conservation planning. [ABSTRACT FROM AUTHOR]

The Tocantins-Araguaia River basin hosts an elevated number of fish species, and new species have been continuously described. In this basin, we investigated patterns of endemic fish species descriptions examining their association with species distribution range, altitudinal gradient, fluvial hierarchy of watercourses, and sampling effort. For each species, we collected its year of taxonomic description, geographical coordinates of its holotype, body size (a proxy for species range), fluvial hierarchy of watercourses, and both altitude and sampling effort related to the locality of the holotype. The number of taxonomic descriptions was positively correlated to sampling effort, and better-sampled regions accumulated more descriptions over time. Moreover, altitude was positively correlated to the year of species description, whereas body size was negatively correlated to it. While species with recent descriptions were more associated to first to third order streams, species with recent and older descriptions were associated to high-order rivers. Therefore, fish species with broader distributions tend to have older descriptions in regions of lower altitude, whereas species with restricted distributions recent descriptions at higher altitudes. Increasing efforts in the upper regions of the Tocantins-Araguaia basin seems to be a good and fruitful strategy for reducing the Linnean shortfall. [ABSTRACT FROM AUTHOR]

Intrinsic postzygotic hybrid incompatibilities are usually due to negative epistatic interactions between alleles from different parental genomes. While such incompatibilities are thought to be uncommon in speciation with gene flow, they may be important if such speciation results from a hybrid population. Here we aimed to test this idea in the endemic cichlid fishes of Lake Victoria. Hundreds of species have evolved within the lake in <15k years from hybrid progenitors. While the importance of prezygotic barriers to gene flow is well established in this system, the possible relevance of postzygotic genetic incompatibilities is unknown. We inferred the presence of negative epistatic interactions from systematic patterns of genotype ratio distortions in experimental crosses and wild samples. We then compared the positions of putative incompatibility loci to regions of high genetic differentiation between sympatric sister species and between members of clades that may have arisen in the early history of this radiation, and further determined if the loci showed fixed differences between the closest living relatives of the lineages ancestral to the hybrid progenitors. Overall, we find little evidence for a major role of intrinsic postzygotic incompatibilities in the Lake Victoria radiation. However, we find putative incompatibility loci significantly more often coinciding with islands of genetic differentiation between species that separated early in the radiation than between the younger sister species, consistent with the hypothesis that such variants segregated in the hybrid swarm and were sorted between species in the early speciation events. [ABSTRACT FROM AUTHOR]

Candidia barbata is a primary freshwater fish distributed in the western portion of Taiwan Island, but this species has also been found in southern and eastern Taiwan. Previous studies have documented that human-intervention populations of freshwater fishes exist not only in eastern Taiwan but also widely. To investigate the native population genetic diversity and structure and evaluate the sources of human-intervention populations of C. barbata, the sequences from the mitochondrial DNA cytochrome b gene and d-loop region were analyzed. These results indicated that (1) the native populations were distributed in northern, northwestern, western and southwestern Taiwan; (2) the human-intervention populations originated from multiple sources, including native populations and aquarium stocks; (3) most aquarium stocks originated from the northwestern and western populations; (4) the geological history of Taiwan Island shaped the native distribution range and population genetic structure; (5) the effective size of the populations declined greatly; and (6) the native populations could be assorted into three distinct management significant units (α − γ). Finally, the human-mediated dispersal of freshwater species in Taiwan was more severe than expected and should be evaluated and monitored carefully. [ABSTRACT FROM AUTHOR]

The 2010 Gulf of Mexico Deepwater Horizon was the largest oil spill in human history that occurred during a 12-week period in a region less than 100 km from the coast of Louisiana; however, after more than a decade of post-spill research, few definitives can be said to be known about the long-term impacts on the development and distribution of fishes in and around the region of the disaster. Here, we examine endemic Gulf of Mexico fish species that may have been most impacted by noting their past distributions in the region of the spill and examining data of known collecting events and observations over the last twenty years (ten years prior to the spill, ten years post-spill). Five years post-spill, it was reported that 48 of the Gulf's endemic fish species had not been collected and, with expanded methods, we now report that 29 (of the 78 endemic species) have not been reported in collections since 2010 (five of these are only known from observations post-spill). Although the good news that some previously 'missing' species have been found may be cause to celebrate, the lack of information for many species remains a cause for concern given focused sampling efforts post-spill. [ABSTRACT FROM AUTHOR]

The large number of cryptic species and extensive intraspecific phenotypic plasticity among freshwater fishes pose a challenge to the correct assessment of diversity within these taxa, which is crucial for their conservation. Recently, three different genetic lineages have been identified within the Italian endemic South European roach Sarmarutilus rubilio , a threatened species with a broad ecological niche. Using geometric morphometrics, we tested the existence of morphological differences associated with genetic common ancestry (i.e. between lineages) and/or environmental parameters. We observed streamlined body shapes in sites scarcely altered by human intervention and with fast water flow; on the contrary, we observed deeper body shapes in canals and in one reservoir with slow/still water flow. Our results suggest that morphological diversity in the South European roach is mainly a result of phenotypic plasticity in response to different environmental drivers (i.e. lotic vs. lentic hydrodynamic patterns) rather than different genetic backgrounds. [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]

Geological events can strongly affect the genetic structures and differentiation of fish populations. Especially, as an endemic fish of the genus Sinocyclocheilus in the Yunnan‐Guizhou Plateau, the effects of key geological events on the distributions and genetic structures remain poorly understood. Examining the phylogeographic patterns of Sinocyclocheilus fishes can be useful for elucidating the spatio‐temporal dynamics of their population size, dispersal history and extent of geographical isolation, thereby providing a theoretical basis for their protection. Here, we used single nucleotide polymorphisms (SNP) method to investigate the phylogeographic patterns of Sinocyclocheilus fishes. Our analysis supports the endemicity of Sinocyclocheilus, but the samples of different regions of Sinocyclocheilus contain multiple ancestral components, which displayed more admixed and diversified genetic components, this may be due to the polymorphism of the ancestors themselves, or gene infiltration caused by hybridization between adjacent species of Sinocyclocheilus. We estimate that the most recent common ancestor (MRCA) of Sinocyclocheilus fish in the Central Yunnan Basin at approximately 3.75~3.11 Ma, and infer that the evolution of Sinocyclocheilus in the central Yunnan Basin is closely related to the formation of plateau lakes (around 4.0~0.02 Ma), and identifies the formation of Dianchi Lake and Fuxian Lake as key geological events shaping Sinocyclocheilus population structure. It is also the first time to prove that the altitude change has a great influence on the genetic variation among the populations of Sinocyclocheilus. [ABSTRACT FROM AUTHOR]

Caridean shrimps (Caridea) are the dominant macroinvertebrates in most anchialine ecosystems. Hawaiian anchialine ecosystems, primarily composed of shallow surface pools connected to the ocean via hypogeal networks of cracks, tubes, and other voids, support 10 caridean shrimp species, including two federally listed as endangered. Little is known about most of these species. The objective of this study was to identify factors that affect the abundance and distribution of Metabetaeus lohena (Alpheidae), an uncommon species found across the Hawaiian Archipelago, at Kaloko-Honokōhau National Historical Park, Island of Hawai'i. This park supports the highest concentration of anchialine pools in the State of Hawai'i and is critical to protecting this threatened ecosystem. During 2017, we measured the density of M. lohena during nighttime surveys, as well as a variety of other biological, physical, and chemical parameters, in 130 pools. Metabetaeus lohena occupied 71.5% of the pools surveyed, with a mean density of 7.32 individuals/m2 (95% CI = 5.14–9.49). Invasive fish and the endemic shrimp Halocaridina rubra (Atyidae) had the strongest effects on M. lohena density, with negative and positive relations, respectively. In the first estimate of M. lohena density at this scale, our data indicate that Kaloko-Honokōhau supports about 11,480 shrimp (95% CI = 8,054–14,906) in the pools surveyed. Furthermore, our models predict that this park could support an additional 1,695 individuals (95% CI = 955–3,008) for a population of about 13,175 shrimp if fish were removed from 19 pools in which M. lohena are absent. [ABSTRACT FROM AUTHOR]

Inle Lake is an ancient lake in Myanmar, which is an important area with unique and diverse fauna. Its ichthyofauna is believed to have formed non‐radiatively, but the historical processes are poorly understood. To elucidate the mechanisms that shape species diversity in this moderately isolated biogeographical 'island', this study focused on a typical endemic fish of Inle Lake, Channa harcourtbutleri (Channidae, Anabantiformes), with its widely distributed sister species, C. limbata, and estimated the historical distribution and diversification processes of the endemic fish based on genome‐wide polymorphism (MIG‐seq) and mitochondrial DNA data. Channa harcourtbutleri contained two genetically and morphologically distinct groups inhabiting Inle Lake and the surrounding rivers respectively. These two groups were genetically the closest to each other; however, the riverine group showed some similarity to the closely related species, C. limbata from Southeast Asia. The mtDNA haplotypes of the endemic species were not monophyletic; most of the riverine group had haplotypes identical or close to those of C. limbata from the upper Irrawaddy and Salween rivers. The time tree suggested that C. harcourtbutleri diverged from C. limbata in the early Pleistocene and then experienced secondary contact with C. limbata in the late Pleistocene. Genetic and morphological differentiation within C. harcourtbutleri suggests that local adaptation to different environments has played an important role for the coexistence of its two forms with some reproductive isolation. Further, the results highlight the importance of multiple colonization and allopatric speciation in shaping biodiversity in the long‐term, moderately isolated environments. [ABSTRACT FROM AUTHOR]

Australia has a highly endemic freshwater fish fauna, but basic biological knowledge for most is lacking. This includes an understanding, and description, of their parasite fauna. Additionally, the impacts of introduced fish species, and their parasites which have transferred across to native species, are also mostly unknown. This review provides the current level of knowledge of parasitic infection of the freshwater fish in Australia, both introduced and native. Only about a third of the native freshwater fish, but almost two‐thirds of introduced fish, have been reported as a host for a parasite. The majority of records occur along the eastern coastline of Australia and throughout the Murray Darling Basin; two drainage regions were yet to record any parasite infections. Of the 124 fish species, across 43 families, found as hosts in Australia, only 11 species had more than 10 reports of infection, with 31% of fish species only having single reports. A total of 13 different types of parasites were reported, with digeneans, protozoans, nematodes and monogeneans the most commonly reported. Significant gaps in the knowledge of parasites, and their potential impacts, of Australian freshwater fish still exist, and the need for fish biologists and fish parasitologists to work together is highlighted to ensure that as much information about each group can be obtained. [ABSTRACT FROM AUTHOR]

Microphysogobio longidorsalis is endemic to South Korea and inhabits small areas of the Namhangang, Bukhangang, and Imjingang Rivers in the Hangang River water system. Endemic species usually are more vulnerable than species with a wide distribution. Notably, there is a lack of basic conservation data for M. longidorsalis. We analyzed 19 microsatellite loci in six populations of M. longidorsalis in South Korea to characterize their population structure and genetic diversity. The genetic diversity of the microsatellites was 0.741–0.779, which is lower than that of other freshwater fishes. The pairwise genetic differentiation of microsatellite (FST) values ranged from 0.007 to 0.041, suggesting low genetic differentiation between the populations. The Jojongicheon stream population (CP) had an effective population size of <100. Therefore, conservation efforts are required to prevent inbreeding depression in M. longidorsalis. Discriminant analysis of principal components showed that the Hangang River water system would be a single management unit (MU). Our findings provide fundamental genetic insights for the formulation of conservation strategies for M. longidorsalis. [ABSTRACT FROM AUTHOR]

The Río San Pedro and Río La Pasión lie within the Usumacinta River Basin, a globally significant center of freshwater fish diversity. Both rivers are listed among Central America's top 50 regions for conserving freshwater biodiversity. This study presents an updated checklist of 70 fish species, of which six are non-native to the Usumacinta River Basin. From these species, 69 are reported from the Río La Pasión and 56 reported from the Río San Pedro, representing higher species richness than previously reported. The checklist derives from a systematic survey of fishes conducted in 2019 and records available in public databases and published literature. Seventy-eight percent of the species were reported in both rivers, and Cichlidae and Poeciliidae had the most species. Secondary species represent 59% of the species reported, followed by peripheral species with 22% of the species. The species with highest fidelity in Río La Pasión were the armored catfish Pterygopichthys spp. and the livebearer Gambusia sexradiata; and the cichlids Thorichthys meeki and Oscura heterospila had highest fidelity in the Río San Pedro. Thorichthys helleri was widely distributed in both rivers. According to the IUCN Red List of Threatened Species, there are four species classified as Vulnerable in Río La Pasión. However, 62% of the species are of Least Concern, 25% of the species are Data Deficient, and 6% are listed as Not Evaluated. More research is needed to document the status of the fish fauna, and improved habitat protection is required to conserve stocks. [ABSTRACT FROM AUTHOR]

Recently reports of orange chromide (Etroplus maculatus) stocked in the tanks showed mass mortality in Mangaluru, India. E. maculatus is an ornamental fish, which is exported to different countries around the globe and these belong to the genus of Etroplus where another two species share the same genus [E. canarensis (Canara pearlspot) and E. suratensis (Pearlspot)]. These native fish were discovered in the Western Ghats which is one of the highest biodiversity spots in the world. The goal of the current investigation was to pinpoint the aetiological agent linked to mass mortality of E. maculatus. The E. maculatus had internal symptoms of an enlarged spleen and kidney, while symptoms externally included discoloration of the body and petechial hemorrhages. Infectious spleen and kidney necrosis virus (ISKNV) of the genus Megalocytivirus was identified as the aetiological agent by polymerase chain reaction (PCR) amplification of the major capsid protein (MCP) gene with an amplicon size of 563 basepair (bp). The isolated ISKNV sequence was found to be closely related to the ISKNV isolated from Malaysian Molly fish (Xiphophorus hellerii) and Australian Angel fish (Pterophyllum scalare) according to phylogenetic analysis. The sequence was subsequently added to the NCBI GenBank database with the accession number ON149089.1. Girisha et al (2020) earlier reported that the SISS cell line was utilized for the purpose of virus propagation and same was followed in the present study. Cytopathic effects (CPEs) were evident in the infected SISS cells showing the rounding, expansion and eventually cell detachment from the flasks after 10 days. The current study confirms that E. maculatus, an endemic species is susceptible to ISKNV infection, suggesting that its host range has expanded especially in India after our report from 2020. [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]

Simple Summary: The complete mitochondrial genome has been widely used in phylogenetics-related studies, as it offers valuable insights into evolutionary relationships. In this study, we reported the complete mitogenome of the elongate loach (Leptobotia elongata) and conducted a detailed analysis of its characteristics which was employed to infer phylogenetic relationships. These findings reveal that both the gene arrangement and composition of mitochondrial genes in the elongate loach are comparable to those found in other bony fishes. Our study further demonstrated that the Cobitidae species under investigation could be grouped into two distinct clades, with elongate loach showing a sister relationship with L. microphthalma. Collectively, our research enhanced the understanding of the mitochondrial genome structure and contributed to the phylogenetic analysis of the elongate loach. The elongate loach is an endemic fish in China. Previous studies have provided some insights into the mitochondrial genome composition and the phylogenetic relationships of the elongate loach inferred using protein-coding genes (PCGs), yet detailed information about it remains limited. Therefore, in this study we sequenced the complete mitochondrial genome of the elongate loach and analyzed its structural characteristics. The PCGs and mitochondrial genome were used for selective stress analysis and genomic comparative analysis. The complete mitochondrial genome of the elongate loach, together with those of 35 Cyprinidae species, was used to infer the phylogenetic relationships of the Cobitidae family through maximum likelihood (ML) reconstruction. The results showed that the genome sequence has a full length of 16,591 bp, which includes 13 PCGs, 22 transfer RNA genes (tRNA), 2 ribosomal RNA genes (rRNA), and 2 non-coding regions (CR D-loop and light chain sub-chain replication origin OL). Overall, the elongate loach shared the same gene arrangement and composition of the mitochondrial genes with other teleost fishes. The Ka/Ks ratios of all mitochondrial PCGs were less than 1, indicating that all of the PCGs were evolving under purifying selection. Genome comparison analyses showed a significant sequence homology of species of Leptobotia. A significant identity between L. elongata and the other five Leptobotia species was observed in the visualization result, except for L. mantschurica, which lacked the tRNA-Arg gene and had a shorter tRNA-Asp gene. The phylogenetic tree revealed that the Cobitidae species examined here can be grouped into two clades, with the elongate loach forming a sister relationship with L. microphthalma. This study could provide additional inferences for a better understanding of the phylogenetic relationships among Cobitidae species. [ABSTRACT FROM AUTHOR]

Background: Organisms with broad distribution ranges, such as fish, often exhibit local ecological specializations based on their utilization of food and habitat. Populations of species that live in different habitat types (lotic vs. lentic) show morphological variations. However, the phenotypic differences of endemic fish populations in a small karst river basin under anthropogenic pressure are still not fully understood. In this study, the functional traits and morphological variations of the populations of endemic Pseudophoxinus antalyae Bogutskaya, 1992, in the Düden Stream basin, which is subjected to various anthropogenic disturbances and habitat types in southwestern Anatolia of Türkiye, were examined using linear measurements and geometric morphometric analysis. Results: Differences have been identified in functional traits, particularly those related to food acquisition between populations. Results of both univariate and multivariate analyses revealed significant differences in body shape and size among populations living at sites along the stream with different habitat and environmental characteristics. Conclusions: The reason for these differences determined in the morphology and traits of the populations may depend on habitat types, ecological, or environmental, and obstruction of gene flow. More detailed studies are needed to explain the mechanisms (genetic and ecological) that cause these differences. [ABSTRACT FROM AUTHOR]

The Nujiang River is rich in aquatic biodiversity, especially endemic fish. However, long-term human interference, such as cascade hydropower construction, has significantly changed aquatic habitats and threatened populations' number and genetic diversity. This study used two mitochondrial gene markers, cyt b, and COI, combined with microsatellite molecular markers developed based on transcriptome data, which were used to study the genetic structure and genetic diversity of Placocheilus cryptonemus in Nu River. The cyt b gene showed that the haplotype mismatch distribution map of the P. cryptonemus population showed a unimodal distribution, indicating that the population expansion may occur during the evolutionary process. Microsatellite analysis showed high information content with high genetic diversity, the whole population was moderately genetically differentiated. There are certain differences in various molecular markers, and the results obtained are not completely consistent, but the overall results show that the level of genetic diversity among the populations of P. cryptonemus is moderate, and the genetic differentiation was not obviously, but the genetic differentiation of the mainstream population in different river basins was obviously. It may be related to different geographical and climatic differences, as well as the species' own habitat habits. [ABSTRACT FROM AUTHOR]

Simple Summary: The aquaculture industry is constantly growing and contributes to the food demand of the world's population, which is already more than 8 billion people. In aquaculture, antibiotics are commonly used to mitigate the appearance of bacterial diseases that cause considerable damage to production. However, this activity induces antibiotic resistance, which risks the health of cultured organisms and consumers. Therefore, alternative supplements such as prebiotics have been emphasized, with their management and due to their multiple beneficial effects, as viable to improve the conditions of production and health of aquatic animals. In developed countries, these supplements are widespread in culture-producing commercial fish, representing a rich protein source worldwide. However, in developing countries such as Mexico, this technology is rare in commercial fish and practically non-existent in endemic fish species. The importance of such supplements for use in the small- and large-scale aquaculture of fish in developing countries should be underscored as relevant for their application in both commercial and endemic fish cultivated in developing countries. Continued human population growth has resulted in increased demand for products, including those derived from aquaculture. The main challenge in aquaculture is producing more every year. In recent years, environmentally friendly supplements that provide the necessary pathways for optimal production have been emphasized. One of them is prebiotics, selectively utilized substrates by host microorganisms conferring a health benefit. Interest in applying prebiotics in global fish farming has increased in recent years as it has been shown to improve growth, boost the immune system, resist stress conditions, and cause the modulation of digestive enzymes. These effects reflect reduced production and disease costs. However, in Latin American countries such as Mexico, large-scale use of these food supplements is needed as a sustainable alternative to improve fish production. This paper gives a review of the current advances obtained with the application of prebiotics in commercially farmed fish worldwide, mentions the prebiotics to use in the aquaculture industry, and updates the status of studies about the used prebiotics in global commercial fish cultivated in Mexico, as well as freshwater and marine endemic fish in this country. Also, the limitations of prebiotics application in terms of their use and legislation are analyzed. [ABSTRACT FROM AUTHOR]

Least chub (Iotichthys phlegethontis) and June sucker (Chasmistes liorus) are 2 species of conservation concern that are endemic to Utah, USA. Both species have experienced severe population decline, and conservation actions to bolster populations include habitat restoration and improvement. Critical to these habitat restoration projects is an understanding of swimming performance and capabilities for both species. We quantified swim speed performance (i.e., burst speed and prolonged speed) of least chub and June suckers. Least chub are small-bodied fish that occupy still or slow-moving water habitats with few predators. Accordingly, both burst speed and prolonged swim speed in least chub are comparatively low, although they do increase somewhat with increasing body size. June suckers are comparatively large-bodied lake suckers that inhabit Utah Lake, but as adults they ascend the Provo River and other tributaries to spawn. June suckers exhibit relatively low prolonged speed, but substantially higher burst speed, and both swim speeds increase with body size. Because of the difference in size, June suckers have a much broader range of swim speed capacity than least chub and are overall more similar to other species of fish native to the intermountain western United States (i.e., Rhinichthys osculus, Richardsonius balteatus, and Oncoryhnchus clarkii). Our results can inform habitat restoration plans, which should be designed to match swimming performance of these 2 species. [ABSTRACT FROM AUTHOR]

Ethiopia's largest freshwater lake, Lake Tana, is home to 21 endemic fish species, the majority of which are cyprinids in the genus Labeobarbus. The lake is undergoing numerous ecological changes, including an invasion of water hyacinth (Eichhornia crassipes (Mart.) Solms (WH). The aim of this study was to predict the future fish productivity in Lake Tana by considering the increasing water hyacinth infestation. This was accomplished by analyzing a 12-year fishery-independent time-series data set of Labeobarbus, collected from sites infested and not infested by water hyacinth. The stationarity of the data was investigated using the Augmented Dickey-Fuller (ADF) unit root test. First-order data differencing was applied to solve the non-stationarity data to stationarity. With the same standardized fishing gillnet and the same sites, the CPUE during the dry season decreased from 3,502 grams (3.5 kg/day) in 2010 to 360 grams (0.36 kg) in 2020 at the water hyacinth-infested sites, demonstrating a 90% decrease in the daily catch. A reduction in catch per unit effort (CPUE) is evident at the WH sites in all seasons, and the rate of fall in there was faster than at the non-infested site. Box Jenkin's auto-regressive integrated moving average models (ARIMA) modelling predicted that Labeobarbus CPUE will decline by a threefold % by 2032 compared to the current catch. Based on these results, the most suitable model for all the seasons and areas was confirmed to be ARIMA (0, 1, 0) using the lowest value of Akaike Information Criteria (AIC's). The fish production declines with expanding WH infestation will necessitate integrated water hyacinth reduction strategies, closed area and closed spawning seasons, and mesh size regulations to conserve and utilize the resource sustainably. As Labeobarbus is the only examined species in this study, forecasts should be made for other commercially significant fish species in the Lake, such as Oreochromis niloticus and Clarias gariepinus. [ABSTRACT FROM AUTHOR]

Physical cage aquaculture structure can attract native fish species in marine and freshwater ecosystems. Most studies on the effects of cage farms on native fish distribution have been undertaken in marine environments and outside of Asia as the main freshwater cage aquaculture producing region. Many studies have emphasised connections between native fish distribution and feeding time. Previous research also has shown the necessity to use modelling to monitor this effect to reduce data collection costs. Here we analyse the distribution of an endemic fish species, Rasbora maninjau, and a native fish, Gobiopterus sp., associated with tilapia cage aquaculture occurrence using a Maximum Entropy Model (MaxEnt). We find that the application of the MaxEnt model can produce reliable and accurate information on the impacts of cage aquaculture on the native fish species distribution aligning with the more expensive count data method. Our results also suggest that the species-specific interaction between the native fish and cage farms is mainly arising from an interaction between the ecological behaviour of the native fish with dimensions of the environmental condition such as turbidity. Our study therefore highlights the importance for improved appraisal of the ecology of native fish in the cage aquaculture risk assessment. [ABSTRACT FROM AUTHOR]

A remarkable diversification of the freshwater ichthyofauna in the Peri-Mediterranean is an outstanding legacy of the complex paleogeographical and evolutionary history of southern Europe. The Dinaric karst on the Balkan Peninsula harbours endemic cyprinoid genera including Phoxinellus and Delminichthys (fam. Leuciscidae), an ancient monotypic genus Aulopyge (fam. Cyprinidae) and endemic species of the Dinaric Telestes, Squalius and Phoxinus genera (fam. Leuciscidae). In this study, evolutionary body shape changes of these endemic European cyprinoid were explored using a geometric morphometrics approach in a phylogenetic framework. By projecting phylogeny obtained from cyt b mtDNA sequences into a morphospace, a strong phylogenetic signal was found in fish body shape, but not in size. Principal component analysis on both uncorrected and size-corrected (allometry free) shape variables revealed that closely related species tend to be clustered in the same area of morphometric space implying that evolutionary allometry did not significantly influence morphological evolution. Therefore, body shape might be used as a reliable taxonomic trait and indicator of phylogenetic relationships. The observed phylogenetic signal in body shape suggests that phylogenetic constraint affects the pattern of shape variation. The phylogenetic comparative method in exploring the evolutionary trend in the body form of Dinaric cyprinoids has not yet been assessed, and our preliminary findings suggested that the body shape diversification proceeded predominantly in the head region and body depth. The diversification of the freshwater ichthyofauna supported by both molecular phylogeny and morphological evolution is mostly a consequence of the complex paleogeographical and evolutionary history of the Peri-Mediterranean area. [ABSTRACT FROM AUTHOR]

In this study, it was aimed to determine the helminth fauna of Capoeta tinca, a fish species endemic to Turkey, collected from Nilüfer Stream (Bursa) between the 2020 Spring (April) and Winter 2021 (February). 81 Capoeta tinca individuals were caught and examined for ichthyo-helminths. A total of 242 parasites of 4 species were detected in the host fish. Dactylogyrus pulcher (6.1%, 16:5 parasite/fish) and Paradiplozoon homoion (20%, 63:17 parasite/fish) were found on the gills of the host fish. Allocreadium isoporum (33%, 149: 27 parasite/fish) and Rhabdochona fortunatowi (9.8%, 14:8 parasite/fish) were recorded in the intestines of the host fish. Among these parasites, A.isoporum was the most common parasite species (33%). Infection values of the helminth parasite species found were evaluated based on season, sex, and host size, and the results were compared with other studies. P. homoion, A.isoporum, and R. fortunatowi are reported for the first time from this host fish. Additionally, Nilüfer Stream was given as a new locality record for A. isoporum and R. fortunatowi. [ABSTRACT FROM AUTHOR]

Fish exhibit complex social behaviours that can influence their stress levels and well-being. However, little is known about the link between social interactions and stress in wild fish, especially in running water environments. While many studies have explored the stress axis in fish, most have focused on specific social contexts, leaving gaps in understanding stress responses to social changes. Our study investigated collective behaviour and stress in wild Italian riffle dace (Telestes muticellus) in a controlled experimental setup simulating a natural river system. Results reveal that group-living fish have lower cortisol and oxidative stress levels in muscle tissue compared to solitary counterparts, suggesting a calming effect of conspecific presence. Additionally, we observed upregulated expression of antioxidant enzymes in group-living fish, indicating potential benefits to antioxidant defence systems. These insights shed light on the dynamic relationship between group behaviour and stress in wild fish within running water habitats and emphasise the use of multidisciplinary approaches. [ABSTRACT FROM AUTHOR]

Fish diversity plays a critical role in maintaining the balance of water ecosystems, especially in the Chongqing section of the National Nature Reserve for Rare and Endemic Fishes in the upper Yangtze River, which serves as an important habitat for rare and endemic fish, as well as an important channel for the replenishment of fishery resources in the Three Gorges Reservoir. Under a 10‐year ban on fishing in the Yangtze River basin, we investigate fish diversity and seasonal variation in the Reserve by using environmental DNA (eDNA) metabarcoding. We found fishes belonging to 85 genera, 24 families, and 8 orders in the Reserve. A comparison of eDNA metabarcoding results with the diversity of a recent fish catch revealed that eDNA metabarcoding not only enables rapid and efficient fish monitoring but also has a high sensitivity. Furthermore, the study demonstrates that eDNA metabarcoding can be used as a tool for monitoring seasonal variations of fish composition in freshwater ecosystems. The alpha and beta diversity analysis both showed compositional differences in the fish community in accordance with seasonal variations. In addition, changes in eDNA relative sequence abundance and the detection of fish species at different sampling sites may reflect shifts in habitat use and distribution. Thus, we provide detailed seasonal data on fish diversity in the Chongqing section of the Reserve. This will contribute to conservation and to the understanding of fish diversity and community dynamics in the Chongqing section of the Reserve. [ABSTRACT FROM AUTHOR]

The Neretva dwarf goby Orsinigobius croaticus (Gobiiformes, Gobionellidae) is an endemic fish native to the freshwaters of the Adriatic Basin in Croatia and Bosnia and Herzegovina, a Mediterranean Biodiversity Hotspot. Due to its limited distribution range, specific karst habitat and endangered status, laboratory studies on reproductive biology are scarce but crucial. Herein, we investigated the sound production and acoustic behaviour of the endangered O. croaticus during reproductive intersexual laboratory encounters, utilising an interdisciplinary approach. We also performed dissections and micro‐computed tomography (μCT) scanning of the pectoral girdle to explore its potential involvement in sound production. Finally, comparative acoustic analysis was conducted on sounds produced by previously recorded soniferous sand gobies to investigate whether acoustic features are species‐specific. The endemic O. croaticus is a soniferous species. Males of this species emit pulsatile sounds composed of a variable number of short (~15 ms) consecutive pulses when interacting with females, usually during the pre‐spawning phase in the nest, but also during courtship outside the nest. Pulsatile sounds were low‐frequency and short pulse trains (~140 Hz, <1000 ms). Male visual behaviour rate was higher when co‐occurring with sounds and females entered the male's nest significantly more frequently when sounds were present. Characteristic body movements accompanied male sound production, such as head thrust and fin spreading. Furthermore, μCT scans and dissections suggest that O. croaticus shares certain anatomical similarities of the pectoral girdle (i.e. osseous elements and arrangement of levator pectoralis muscles) to previously studied sand gobies that could be involved in sound production. Multivariate comparisons, using sounds produced by eight soniferous European sand gobies, effectively distinguished soniferous (and sympatric) species based on their acoustic properties. However, the discrimination success decreased when temperature‐dependent features (sound duration and pulse repetition rate) were excluded from the analysis. Therefore, we suggest both spectral and temporal features are important for the acoustic differentiation of sand gobies. [ABSTRACT FROM AUTHOR]