Major threats to European freshwater fish species

Comparative effects of 6PPD and 6PPD-Quinone at environmentally relevant concentrations on hepatotoxicity, glucolipid metabolism and ferroptotic response in adult zebrafish

The antioxidant 6PPD and its oxidized product 6PPD-Quinone (6PPDQ) have attracted considerable attention due to their various acute toxicities to aquatic organisms. However, the chronic toxicity of two compounds in aquatic animals is still unknown. Here, adult zebrafish were exposed to 6PPD and 6PPDQ at environmentally relevant concentrations (20 μg/L) for 28 days, and histological analysis showed that 6PPD caused more severe hepatic vacuolization than 6PPDQ. Meanwhile, 6PPD induced more serious lipid accumulation and a higher increase in triglyceride and total cholesterol levels than 6PPDQ, suggesting higher hepatotoxicity of 6PPD. Furthermore, transcriptomic analysis revealed that both compounds disturbed glucolipid metabolism to different degrees by altering the expression of different peroxisome proliferator-activated receptors (PPARs), in which 6PPD inhibited gene expressions in glucolipid metabolism possibly by PPARα, PPARβ and RXR, while 6PPDQ disrupted the expressions of partial genes in similar pathways probably via PPARγ. Additionally, 6PPD but not 6PPDQ increased Fe2+ content, decreased the protein levels of ferroportin 1, ferritin and glutathione peroxidase 4, accompanied with the increase of malondialdehyde level and the decrease of glutathione content, suggesting ferroptotic response by 6PPD. Overall, our data deepened the understanding of 6PPD- and 6PPDQ-induced hepatotoxicity association with glucolipid metabolism disorders and ferroptotic responses.

Characterisation and phylogenetic analysis of the complete mitochondrial genome of two endemic lampreys from Greece (Caspiomyzon hellenicus and Caspiomyzon graecus) using Long-Read technology

BACKGROUND

The genus Caspiomyzon is comprised of three species, two of which are found in Greece (Caspiomyzon hellenicus and Caspiomyzon graecus). Both species are endemic with very restricted distribution and are classified as Critically Endangered. Caspiomyzon hellenicus is restricted to Tenagi, Philippi and C. graecus to Louros River. No studies have characterized their mitochondrial genomes.

METHODS AND RESULTS

The complete mitochondrial genome of C. hellenicus and C. graecus was generated with Oxford Nanopore long-read technology, and it was processed using various bioinformatics approaches. The final assembled contig length was 16,763 bp and 17,123 bp, respectively, and composed of 13 protein-coding genes, two ribosomal RNA genes, 22 tRNA genes, and two control regions. Repetitive sequences were detected between and within the control regions. The overall GC composition was approximately 36% for both species. The results of phylogenetics analysis using Bayesian inference and Maximum likelihood methods revealed that the Geotria australis species was sister to northern hemisphere lampreys, whereas Mordacia species constitutes a monophyletic group. Divergence time between the Greek Caspiomyzon species took place at approximately 0.7 Mya.

CONCLUSIONS

This study enhanced our understanding of the taxonomic and phylogenetic relationships within the Caspiomyzon genus from Greece based on the characterization of the full mitochondrial genomes from long-reads technology. Such efforts can aid their conservation and management locally.

Riverine Barrier Removals Could Proliferate Biological Invasions

Multiple stressors, such as pollution, climate change, invasive species and fragmentation, threaten global ecosystems, requiring holistic management actions. Freshwater ecosystems are disproportionately biodiverse and particularly impacted by fragmentation and biological invasions. Artificial barriers, such as dams and weirs, are long-standing features of global landscapes, with a divergence of views on their benefits and disbenefits. Recognition of the negative impacts of barriers on the river continuum and native biota, particularly for migratory aquatic species, has led to a rapid rate of barrier removals in recent decades, especially in North America and Europe. However, since the rise in riverine barrier construction centuries ago, global biological invasion rates have concurrently surged. Artificial barriers can paradoxically slow the spread of invasive species through freshwaters, and barrier removal efforts thus risk proliferating invasive species that disperse rapidly through connected habitats. Despite well-intended plans for river restoration through barrier removals, the subsequent spread and colonisation of invasive species have been largely overlooked. This presents a 'connectivity conundrum': the removal of barriers intuitively addresses the issues of native species migrations and dispersals, but could perversely exacerbate the spread of invasive species. Basin-scale data collection around the short- and long-term impacts on invasive species will help to underpin future restoration projects and maximise the potential beneficial outcomes of barrier removals for native species.

Influence of habitat structures on fish abundances and diversity: comparing mainstream and tributary communities in the urban uMsunduze Catchment, KwaZulu-Natal, South Africa

Various factors drive the decline of freshwater vertebrate biodiversity. These include changing landscape and urbanisation, introduced invasive species, altered habitat, water quality deterioration, instream barriers, and climate change. In the present study, we evaluated the impact of different habitat features on the fish assemblages in an urban river using catch per unit effort (CPUE) as a proxy for fish assemblage per site and season. We sampled 17 main sites and 21 ad-hoc sites in the uMsunduze Catchment in Pietermaritzburg, uMgungundlovu District, KwaZulu-Natal, South Africa, during 2022-2023. We collected data using an electro-shocker, fyke nets, and gill nets, and we also recorded and calculated habitat features such as substrate types, hydraulic biotopes, in-situ water quality, ecohydraulics, average depth, and velocity. We used Generalised Linear Models to determine the habitat features driving fish communities. We calculated the Shannon-Weiner and Pielou diversity indices to compare between rivers. We used the Fish Response Assessment Index (FRAI) tool to understand each site's ecological integrity per season. Our results indicated that various features, including substrate (mud, sand, gravel), fast intermediate and fast deep ecohydraulics, electrical conductivity, habitat (glide, pool), and average velocity significantly impacted the CPUE of fish. There was no variation in diversity indices between tributaries, but there was a significant difference in fish diversity between the uMsunduze mainstream and its tributaries. The FRAI scores showed great deterioration in the system's ecological health, and most sites, especially the mainstream sites, were critically or extremely modified. We suggest that the relevant authorities take action to mitigate the pressures compromising the uMsunduze Catchment's ecological integrity. There is an urgent need for conservation measures for the two "near threatened" species, Enteromius gurneyi and Amphilius natalensis, the former now extirpated as per our study.

The role of river connectivity in the distribution of fish in an anthropized watershed

The ongoing biodiversity crisis is especially severe in freshwater habitats. Anthropized watersheds, such as the Seine-Normandie basin in France, are particularly affected by human interference. The study of fish species distribution in watersheds often relies on environmental drivers such as land use or climate. Yet, fish are also exposed to river connectivity constraints, such as dams, that are understudied despite their potential impact on fish dispersal. For this study, we investigated the role of local and whole-basin longitudinal connectivity in fish distribution. We designed connectivity indices based on river network characteristics and specific mobility for 33 species and included these indices in species distribution models, taking into account habitat suitability, to quantify their role in species distribution. Keeping the best index for each species, an average of 29 % - and up to 57 % - of explained fish distribution, depending on species, was tied to connectivity. We found that high connectivity often had a significant and positive linear effect on species presence probability. Using a scoring system across multiple indices, we found connectivity indices that took local context into account (e.g. the ecological zonation of the river) performed consistently better than others. Indices that took only dispersal limitation into account scored higher for 12 species, while barriers, alone, were the most important constraint for 10 species, the remaining 11 being associated with both. This work points to fragmentation as a cause for lower likelihood of presence for many non-diadromous river fish species. It highlights the importance of considering both physical and functional connectivity constraints in fish distribution and provides additional insights for river management and restoration.

Acoustic playback is better than food to trap one of the worst invasive fishes

With the number of invasive alien species increasing globally, the management of invaded areas is constantly seeking innovative and effective solutions. Thanks to recent technological advances, acoustic signals are increasingly used in species management, either as an indicator of the presence of species or as a stimulus to repel species from risky areas or attract species for monitoring or eradication purposes. However, acoustic-based solutions are still rarely used by freshwater managers. In the present study, we explored the potential of acoustic playback to trap the round goby Neogobius melanostomus, a highly invasive aquatic species. We equipped traps with specifically-designed cost-effective, easy-to-deploy underwater speakers to broadcast resynthesized reproductive calls and tested four conditions by crossing the presence or absence of acoustic and food. The traps were deployed in Lake Sainte-Croix and Lake Brunet: two French lakes where round goby invasion is ongoing. Consistent with a previous test of acoustic trapping conducted on round gobies from the Great Lakes, broadcasting reproductive calls overall improved trapping success. Acoustic alone was the best trap configuration with a tendency to have more round gobies in the traps. By contrast, food increased the proportion of bycatch and was particularly attractive to crayfish, which reduced the probability of finding round gobies in the traps. Contrary to our expectation, the proportion of reproductive gobies in the traps was not increased by acoustic signals. Our results provide support for the inclusion of acoustic approaches in the toolbox of freshwater managers.

The Effects of Hybridization and Parasite Infection on the Survival and Behaviour of Endangered Landlocked Salmon Subject to Predation-Implications for Genetic Rescue

A prerequisite of genetic rescue in endangered and genetically depauperate populations is to pre-evaluate between possible pros and cons of hybridization for the life history and survival of the target population. We hybridized the critically endangered Saimaa landlocked salmon (Salmo salar m. sebago) with one of its geographically closest relatives, anadromous Baltic salmon from River Kymijoki. In two similar experiments, conducted in semi-natural streams during overwintering (at age 1.5) and in early summer (age 2+), we studied how hybridization and eye parasite infection (Diplostomum pseudospathaceum) affected survival from predation by Northern pike (Esox lucius). Additionally, we recorded movements of the juvenile salmon using passive integrated telemetry to gain insights into the effect of hybridization and infection on antipredatory behaviour (movement activity and habitat use). Among the uninfected groups, we found significantly lower mortality of hybrid salmon (mortality ± S.E. 14.5% ± 5.4%) compared to purebred landlocked salmon (37.2% ± 9.4%), supporting a positive effect of hybridization under predation risk. This benefit, however, was cancelled out by the parasite infection, which impaired vision and increased the susceptibility to predation. The negative effects of infection were particularly pronounced in the anadromous salmon due to lower infection resistance, compared to the landlocked salmon. Hybridization per se did not affect the activity levels of salmon, but overwintering activity correlated positively with eye cataract coverage, and summer activity was highest in anadromous salmon. These results demonstrate that controlled supplementation of a small animal population with genetically more diverse hybrids could entail both positive and negative implications, at least in the first crossbred generation.

Deconstructing the geography of human impacts on species' natural distribution

It remains unknown how species' populations across their geographic range are constrained by multiple coincident natural and anthropogenic environmental gradients. Conservation actions are likely undermined without this knowledge because the relative importance of the multiple anthropogenic threats is not set within the context of the natural determinants of species' distributions. We introduce the concept of a species 'shadow distribution' to address this knowledge gap, using explainable artificial intelligence to deconstruct the environmental building blocks of current species distributions. We assess shadow distributions for multiple threatened freshwater fishes in Switzerland which indicated how and where species respond negatively to threats - with negative threat impacts covering 88% of locations inside species' environmental niches leading to a 25% reduction in environmental suitability. Our findings highlight that conservation of species' geographic distributions is likely insufficient when biodiversity mapping is based on species distribution models, or threat mapping, without also quantifying species' expected or shadow distributions. Overall, we show how priority actions for nature's recovery can be identified and contextualised within the multiple natural constraints on biodiversity to better meet national and international biodiversity targets.

High spatial variability in a species-rich assemblage of diadromous fishes in Hong Kong, southern China

China has experienced substantial coastal reclamation and damming of rivers. These changes have the potential to impact migrations of diadromous fishes between the sea and fresh waters, but the composition of these fishes and the impacts of barriers to their movement in China have received little attention. We inventoried the species composition and distribution of diadromous fishes, and the impacts of barriers on them, in the Hong Kong Special Administrative Region (HKSAR), southern China. Fish assemblages were surveyed using hand-nets, supplemented by cast-netting and single-pass snorkel surveys, in 24 small coastal streams across three regions. Surveys were undertaken on multiple occasions during the wet and dry seasons to account for the monsoonal tropical climate. Twenty-eight diadromous fishes were collected, mostly gobies, amounting to over half (53%) of the total richness of primary freshwater fishes; four additional species are known from literature records. Diadromous richness was 48% greater during the wet season, when all species were encountered. Richness varied substantially among streams, from a maximum of 17 (2 streams that were diversity hot spots) to none (3 streams). The most widespread diadromous fish was Glossogobius giuris (71% frequency of occurrence), followed by Mugil cephalus (58% occurrence) and Eleotris oxycephala (50% occurrence). The remaining 25 diadromous fishes occurred in fewer than half of the streams; 12 species were confined to a single stream and may be locally threatened. There were conspicuous spatial differences in diadromous assemblages across HKSAR, despite its limited extent (1114 km2), the proximity of the surveyed streams, and the broad geographic distribution of most species. Regional species assemblages were influenced by localized habitat characteristics, with a noticeable distinction between areas with and without large, fast-flowing, and highly oxygenated streams. The presence of in-stream barriers (weirs: 0.3-8.7 m high) did not affect spatial patterns in species assemblages, although, on average, diadromous richness was lower in weir-obstructed streams (4.0 vs. 6.9 species in unobstructed streams). In total, 18 species were confined to unobstructed streams or sections below weirs, whereas the remaining 10 species were recorded both above and below weirs. Only the mottled eel (Anguilla marmorata) and a goby (Stiphodon multisquamus) were able to ascend weirs over 2 m. Although at least 400 m of the lower course of each stream was sampled, diadromous fishes were confined to the first 300 m in 12 of the 13 weir-obstructed streams. Remarkably, the tally of 32 diadromous species in HKSAR exceeds the 19 known from mainland China, highlighting the need for further research on composition and conservation status of diadromous fishes.

A climate vulnerability assessment of the fish community in the Western Baltic Sea

Marine fisheries are increasingly impacted by climate change, affecting species distribution and productivity, and necessitating urgent adaptation efforts. Climate vulnerability assessments (CVA), integrating expert knowledge, are vital for identifying species that could thrive or suffer under changing environmental conditions. This study presents a first CVA for the Western Baltic Sea's fish community, a crucial fishing area for Denmark and Germany. Characterized by a unique mix of marine, brackish, and freshwater species, this coastal ecosystem faces significant changes due to the combined effects of overfishing, eutrophication and climate change. Our CVA involved a qualitative expert scoring of 22 fish species, assessing their sensitivity and exposure to climate change. Our study revealed a dichotomy in climate change vulnerability within the fish community of the Western Baltic Sea because traditional fishing targets cod and herring as well as other species with complex life histories are considered to face increased risks, whereas invasive or better adaptable species might thrive under changing conditions. Our findings hence demonstrate the complex interplay between life-history traits and climate change vulnerability in marine fish communities. Eventually, our study provides critical knowledge for the urgent development of tailored adaptation efforts addressing existing but especially future effects of climate change on fish and fisheries in the Western Baltic Sea, to navigate this endangered fisheries systems into a sustainable future.

The Importance of Baseline Health Surveillance Efforts in Freshwater Fish Conservation Using the Threatened Iberian Leuciscids as an Example

Freshwater fish species are experiencing the highest decline among vertebrates in this century. Although a great effort has been made to identify and tackle threats to the conservation of this taxa, several knowledge gaps still exist particularly for noncommercial endangered species, including considerations regarding fish health status. These species face deteriorating environmental conditions in their natural habitats that may lead to stress and increased risk for infectious disease outbreaks. Establishing health surveillance is crucial to identify and predict physiologic disruption in fish populations. Additionally, information retrieved may be used to direct targeted efforts to contribute to improving the conservation status of these species. We used threatened Iberian leuciscids as a case study to discuss the current knowledge regarding their health surveillance and to suggest recommendations for the establishment of practical health assessments that can benefit conservation plans for these species and be implemented in threatened or endangered freshwater fish species plans globally.

A multi-tissue de novo transcriptome assembly and relative gene expression of the vulnerable freshwater salmonid Thymallus ligericus

Freshwater ecosystems are among the most endangered ecosystems worldwide. While numerous taxa are on the verge of extinction as a result of global changes and direct or indirect anthropogenic activity, genomic and transcriptomic resources represent a key tool for comprehending species' adaptability and serve as the foundation for conservation initiatives. The Loire grayling, Thymallus ligericus, is a freshwater European salmonid endemic to the upper Loire River basin. The species is comprised of fragmented populations that are dispersed over a small area and it has been identified as a vulnerable species. Here, we provide a multi-tissue de novo transcriptome assembly of T. ligericus. The completeness and integrity of the transcriptome were assessed before and after redundancy removal with lineage-specific libraries from Eukaryota, Metazoa, Vertebrata, and Actinopterygii. Relative gene expression was assessed for each of the analyzed tissues, using the de novo assembled transcriptome and a genome-based analysis using the available T. thymallus genome as a reference. The final assembly, with a contig N50 of 1221 and Benchmarking Universal Single-Copy Orthologs (BUSCO) scores above 94%, is made accessible along with structural and functional annotations and relative gene expression of the five tissues (NCBI SRA and FigShare databases). This is the first transcriptomic resource for this species, which provides a foundation for future research on this and other salmonid species that are increasingly exposed to environmental stressors.

A review of conservation status of freshwater fish diversity in China

China harbors a high species diversity of freshwater fishes not shared with any of its neighboring nations. Freshwater fish diversity in the country has been under severe threat from human activities over the past decades, thus conservation freshwater fishes and ecosystems is urgently needed. To accumulate baseline data for guiding protection actions, the third red list assessment of Chinese freshwater fishes was carried out. Among Chinese freshwater fishes assessed, there are 355 at-risk species (22.3% of the total), including 69 ranked as Critically Endangered, 97 as Endangered, and 189 as Vulnerable. Two species are classified as Extinct and one as Regionally Extinct. China's threat level seems to be lower than the known average level found in the IUCN's global assessment of freshwater fishes, but this is an artifact of a high rate of species classified as Data Deficient. Conservation of freshwater fishes is presently facing a grim situation in China. Imperilment of Chinese freshwater fishes is primarily attributed to habitat loss and degradation arising from human perturbations, particularly river damming. Despite the adoption of protected areas setting up, captive breeding and release, and a fishing moratorium, conservation efforts for freshwater fishes are compromised by disproportional attention in China's biodiversity conservation, baseline data deficiency, insufficiently designed protection networks, and inefficient or inadequate implementation of conservation strategies. To achieve the objectives of Chinese freshwater fish conservation, it is proposed to conduct a national-scale survey of fish diversity and reassess their at-risk status, develop systematic conservation planning of freshwater fish diversity and ecosystems, prioritize strategies for protected areas development, perform genetic-based captive breeding for releasing in concert with other protection actions, and implement flexible fishing moratorium strategies in different water bodies.

Vertical Slot Fishways: Incremental Knowledge to Define the Best Solution

River artificial fragmentation is arguably the most imperilling threat for freshwater-dependent fish species. Fish need to be able to freely move along river networks as not only spawning grounds but also refuge and feeding areas may be spatially and temporally separated. This incapacity of free displacement may result in genetic depletion of some populations, density reduction and even community changes, which may in turn affect how meta-community balances are regulated, potentially resulting in functional resilience reduction and ecosystem processes' malfunction. Fishways are the most common and widely used method to improve connectivity for fish species. These structures allow fish to negotiate full barriers, thus reducing their connectivity impairment. Among all technical fishway types, vertical slot fishways (VSF) are considered to be the best solution, as they remain operational even with fluctuating water discharges and allow fish to negotiate each cross-wall at their desired depth. In the present study, we collected both published and original data on fish experiments within VSF, to address two questions, (1) What variables affect fish passage during experimental fishway studies? and (2) What is the best VSF configuration? We used Bayesian Generalized Mixed Models accounting for random effects of non-controlled factors, limiting inherent data dependencies, that may influence the model outcome. Results highlight that fish size, regardless of the species, is a good predictor of fishway negotiation success. Generally, multiple slot fishways with one orifice proved to be the best solution. Future work should be focused on small-sized fish to further improve the design of holistic fishways.

Using environmental DNA metabarcoding to monitor fish communities in small rivers and large brooks: Insights on the spatial scale of information

Monitoring fish communities is central to the evaluation of ecological health of rivers. Both presence/absence of fish species and their relative quantity in local fish assemblages are crucial parameters to measure. Fish communities in lotic systems are traditionally monitored via electrofishing, characterized by a known limited efficiency and high survey costs. Analysis of environmental DNA could serve as a non-destructive alternative for detection and quantification of lotic fish communities, but this approach still requires further insights in practical sampling schemes incorporating transport and dilution of the eDNA particles; optimization of predictive power and quality assurance of the molecular detection method. Via a controlled cage experiment, we aim to extend the knowledge on streamreach of eDNA in small rivers and large brooks, as laid out in the European Water Framework Directive's water typology. Using a high and low source biomass in two river transects of a species-poor river characterized by contrasting river discharge rates, we found strong and significant correlations between the eDNA relative species abundances and the relative biomass per species in the cage community. Despite a decreasing correlation over distance, the underlying community composition remained stable from 25 to 300 m, or up to 1 km downstream of the eDNA source, depending on the river discharge rate. Such decrease in similarity between relative source biomass and the corresponding eDNA-based community profile with increasing distance downstream from the source, might be attributed to variation in species-specific eDNA persistence. Our findings offer crucial insights on eDNA behaviour and characterization of riverine fish communities. We conclude that water sampled from a relatively small river offers an adequate eDNA snapshot of the total fish community in the 300-1000 m upstream transect. The potential application for other river systems is further discussed.

Distribution and diversity of fishes and lampreys in Transylvania (Romania): a complete survey and suggestions for new protected areas

Freshwater fishes are in a serious state of decline across the world, making them one of the most threatened groups of vertebrates. The Danube River catchment area in Europe holds the richest freshwater fish community, but our knowledge of the current distribution of these species is limited. Transylvania, the largest region of Romania, is one of the important tributaries of the Danube, from where 77 fish and two lamprey species were recorded until now. Despite this large diversity of freshwater fishes, there is a lack of systematic survey of the fish fauna in this region for the past 50 years. In this study, we present data on the occurrence and distribution of fishes and lampreys collected in Transylvania from 2007 to 2022. This data covers 43% of Romania's surface and includes all major rivers from Transylvania. 65 species of fish and three species of lampreys are recorded, and an additional nine fish species are also reported based on information from competent people. Of the 77 fish and lamprey species recorded 19 (24.7%) are non-native, although their relative abundance was low (5.1%) compared to other similar regions in Europe. The first records of Eudontomyzonmariae, Neogobiusmelanostomus, Piaractusbrachypomus, Pygocentrusnattereri, and Salvelinusalpinus in Transylvanian rivers are presented, as well as the first record of Cobitiselongata outside the Nera River basin (from the Caraș River) and the detection of three new populations of the vulnerable Umbrakrameri. Data on changes in distribution that have occurred since the last comprehensive survey 50 years ago are also provided and the importance of our results in conservation planning are discussed, including the designation of new protected areas for freshwater bodies and the compilation of the Romanian Red List of fishes.

Streams in the Mediterranean Region are not for mussels: Predicting extinctions and range contractions under future climate change

Climate change is becoming the leading driver of biodiversity loss. The Mediterranean region, particularly southwestern Europe, is already confronting the consequences of ongoing global warming. Unprecedented biodiversity declines have been recorded, particularly within freshwater ecosystems. Freshwater mussels contribute to essential ecosystem services but are among the most threatened faunal groups on Earth. Their poor conservation status is related to the dependence on fish hosts to complete the life cycle, which also makes them particularly vulnerable to climate change. Species Distribution Models (SDMs) are commonly used to predict species distributions, but often disregard the potential effect of biotic interactions. This study investigated the potential impact of future climate on the distribution of freshwater mussel species while considering their obligatory interaction with fish hosts. Specifically, ensemble models were used to forecast the current and future distribution of six mussel species in the Iberian Peninsula, including environmental conditions and the distribution of fish hosts as predictors. We found that climate change is expected to severely impact the future distribution of Iberian mussels. Species with narrow ranges, namely Margaritifera margaritifera and Unio tumidiformis, were predicted to have their suitable habitats nearly lost and could potentially be facing regional and global extinctions, respectively. Anodonta anatina, Potomida littoralis, and particularly Unio delphinus and Unio mancus, are expected to suffer distributional losses but may gain new suitable habitats. A shift in their distribution to new suitable areas is only possible if fish hosts are able to disperse while carrying larvae. We also found that including the distribution of fish hosts in the mussels' models avoided the underprediction of habitat loss under climate change. This study warns of the imminent loss of mussel species and populations and the urgent need of management actions to reverse current trends and mitigate irreversible damage to species and ecosystems in Mediterranean regions.

The non-Haplochromis fish fauna in Uganda: an update on the distribution and a review of data gaps

Freshwater fishes are the second most threatened group of vertebrates after amphibians. In most developing countries, the conservation of freshwater fishes is largely hampered by limited information and data. The Red List assessments by the International Union for Conservation of Nature (IUCN) provide a benchmark for monitoring and mitigating species extinction risk, but these assessments require, inter alia, quantitative information on the species range in the wild. This information is largely missing for many species that face extinction threats. Here, we combine species occurrence data, expert knowledge, and literature to (i) review and update the distribution of non-Haplochromis fish species native to Uganda and (ii) determine the national geographical range of these fish species relative to their global range. For the latter, we use the IUCN's standard protocol for mapping distribution of freshwater species from which we derive both the national and global extent of occurrence (EOO) and area of occupancy (AOO). We show that at least 110 non-Haplochromis species occur in Uganda, with the majority species having a wide distribution outside the national boundaries. However, substantial gaps exist in data on presence of the species in their native range, where more than 60% of the species are designated as "possibly extant." We elaborate on fish species previously believed to occur in Uganda, e.g., Amphilius kivuensis Pellegrin, 1933; Bagrus degeni Boulenger, 1906; Marcusenius macrolepidotus (Peters, 1852); Petrocephalus catostoma (Günther, 1866); and Lacustricola pumilus (Boulenger, 1906), but where recent studies suggest they lack a native distribution within the country. In addition, we highlight fishes with occurrence records that site them in areas beyond their previously known range, requiring further investigations to ascertain their present status. This work has potential to (i) trigger evidence-driven policies aimed at site-based conservation and rethinking of extent of protected areas, (ii) stimulate data collection, especially in areas where fishes are designated as "possibly extant" and "presence uncertain," and (iii) aid the IUCN Red List assessments, for which conservation status of the majority non-Haplochromis species is outdated and many others remain unevaluated due to lack of quantitative information on their range.

Appraising the Genetic Makeup of an Allochthonous Southern Pike Population: An Opportunity to Predict the Evolution of Introgressive Hybridization in Isolated Populations?

Biological invasions are a major threat to the conservation of biodiversity, as invasive species affect native biota through competition, predation, pathogen introduction, habitat alteration, and hybridisation. The present study focuses on a southern pike population, Esox cisalpinus (Teleostei: Esocidae), that has been introduced outside the species' native range. Using microsatellite markers, this study's objective was to gather baseline genetic information and assess the presence of hybrids between this species and E. lucius in the introduced population. The resulting estimates of genetic diversity and effective population size are comparable to those observed in the species' native range. Although different methods yield contrasting and uncertain evidence regarding introgressive hybridization, the presence of late-generation hybrids cannot be completely ruled out. Large numbers of breeders as well as multiple introductions of genetically divergent cohorts and introgressive hybridisation may explain the high genetic diversity of this recently introduced southern pike population. The present study issues a warning that the conservation of southern pike' introgressive hybridisation between northern and southern pike might be underestimated. The genetic information gathered herein may unravel the origin, number of introduction events, and evolutionary trajectory of the introduced population. This information may help us understand the evolution of introgressive hybridisation in the southern pike's native areas.

The Quality and Bacterial Community Changes in Freshwater Crawfish Stored at 4 °C in Vacuum Packaging

Crawfish can be easily spoiled due to their rich nutrition and high water content, which is difficult to preserve. In this study, the dominant spoilage organisms in crawfish which were stored at 4 °C in vacuum packaging were identified by high-throughput sequencing technology; after sequencing the full-length 16S rRNA gene, the changes in the bacterial community structure, diversity and quality (texture, flavor, etc.) were analyzed. Our results reflected that the specific spoilage organisms (SSOs) of crawfish were Aeromonas sobria, Shewanella putrefaciens, Trichococcus pasteurii and Enterococcus aquimarinus, since their abundances significantly increased after being stored for 12 days at 4 °C under vacuum conditions. At the same time, the abundance and diversity of the microbial community decreased with storage time, which was related to the rapid growth of the dominant spoilage organisms and the inhibition of other kinds of microorganisms at the end of the spoilage stage. Function prediction results showed that the gene which contributed to metabolism influenced the spoilage process. Moreover, the decline in texture of crawfish was negatively correlated to the richness of SSOs; this may be because SSOs can produce alkaline proteases to degrade the myofibrillar protein. On the contrary, the unpleasant flavor of crawfish, resulting from volatile flavor compounds such as S-containing compounds and APEOs, etc., is negatively correlated to the richness of SSOs, due to the metabolism of SSOs by secondary metabolites such as terpenoids, polyketides and lips, which can lead to decarboxylation, deamination and enzymatic oxidation. These results are very important to achieve the purpose of targeted inhibition of crawfish spoilage at 4 °C in vacuum packaging.

How does invasion degree shape alpha and beta diversity of freshwater fish at a regional scale?

Freshwater ecosystems appear more vulnerable to biodiversity loss due to several anthropogenic disturbances and freshwater fish are particularly vulnerable to these impacts. We aimed to (1) identify the contribution of land use, spatial variables, and invasion degree in determining freshwater fish alpha (i.e., species richness) and beta (i.e., local contributions to beta diversity, LCBD) diversity, evaluating also the relationship between invasion degree and nestedness (β nes) and turnover (β sim) components of beta diversity. (2) Investigate the relationship between alpha diversity and LCBD, under the hypothesis that alpha diversity and LCBD correlate negatively and (3) investigate the relationship between species contributions to beta diversity (SCBD) and species occurrence, hypothesizing that non-native species show a lower contribution to beta diversity. The linear mixed models and the partition of R 2 retained the invasion degree as the most important variables explaining alpha and beta diversity, having a positive relationship with both diversity components. Furthermore, land use related to human impacts had a positive influence on alpha diversity, whereas it showed a negative effect on LCBD. Regression model further showed that invasion degree related positively withβ sim, but negatively withβ nes, suggesting that non-native species were involved in the replacement of native species in the fish community. Alpha diversity and LCBD showed a weak positive correlation, meaning that sites with low species richness have higher LCBD. SCBD scaled positively with species occurrence highlighting that rarer species contribute less to SCBD. Finally, native and exotic species contributed similarly to beta diversity. These results suggest that invasion degree plays a central role in shaping alpha and beta diversity in stream fish, more than land use features reflecting habitat alteration or other geospatial variables. Furthermore, it is important to evaluate separately the native and the non-native components of biotic communities to identify linkages between invasion dynamics and biodiversity loss.

Influence of climate change and extreme weather events on an estuarine fish community

Extreme weather events are becoming more frequent as a result of climate change, and the increasing frequency of these events may lead to significant changes in fish assemblages. In this sense, this work aimed to study the effects of climate change and extreme weather events on fish assemblages in the Rio Minho estuary (Portugal). Between 2010 and 2019, continuous weekly sampling with fyke nets was carried out to assess the dynamics of fish assemblages in the estuary. In addition, temperature and precipitation data were obtained from satellite information to assess the relationship between climatic variables and fish composition, structure, and diversity. Fish populations changed significantly over time, becoming less diverse and largely dominated by a few, mostly invasive species (e.g., carp, goldfish, pumpkinseed, and tench), while the abundance of most native species declined over the years (e.g., panjorca, stickleback, and shad). High temperatures and low precipitation negatively affected native species, while the invasive species benefited from increased temperatures and extreme weather events (droughts and floods).

Euryhaline Aliens Invading Italian Inland Waters: The Case of the Atlantic Blue Crab Callinectes sapidus Rathbun, 1896

Alien invasive species represent a major threat in Italian freshwaters. Despite national and European regulations aimed at the control and prevention of new invasive species, the number of allochthonous species is increasing and so is the rate of spread. One of the most widespread invasive animals in coastal areas of the Mediterranean Sea is the blue crab Callinectes sapidus, a native of the Western Atlantic from Nova Scotia to Argentina. The species is euryhaline, and besides coastal waters, it is also commonly recorded in upper estuaries and lower reaches of rivers. Considering its fast adaptability and invasiveness, the main purpose of this work is to assess whether its biological plasticity and invasive capability may represent, in addition to marine and coastal habitats, also a potential threat for inland waters. Samples were collected in seven sites distributed between Southern and Central Italy. The new records are herein presented, starting from the original introduction by ballast waters and the actual westward migration in inland waters of Latium and Tuscany. In addition, the threat to biodiversity is also discussed, considering the blue crab aggressiveness toward both vertebrates and invertebrates, which may limit the distribution of native freshwater fish and macrofauna.