Fish Richness Research Articles

Cleansing our waters: how riffle fish communities in the Spring River of Kansas responded to pollution legislation, mining remediation, and improved water quality.

Metal pollution from mining is a threat to lotic fishes, although legislation that requires improved water quality and provides funding for remediation has been enacted to combat this stressor. The Spring River in southeastern Kansas historically received inputs of cadmium, copper, lead, and zinc that reduced the prevalence of several sensitive and imperiled fishes. Long-term reductions in these toxic metals have occurred since the 1990's because of management activities, but presently it is unknown how riffle fish communities responded to improved water quality. As such, the objective of our research was to quantify changes in riffle fish community structure between 1993-1995 and 2019-2021 using a before-after-control-impact (BACI) study design. Responses were quantified with univariate analyses to examine the interactive effects of time period (i.e., historical versus contemporary), pollution tolerance classification (i.e., intolerant, moderately-intolerant, moderately-tolerant, and tolerant), and site position (i.e., above versus below the most severe historical metal pollution inputs) on relative abundance, occupancy, and species richness of riffle fishes. We used multivariate analyses to examine temporal changes in community structure above and below pollution inputs. Our findings indicated that intolerant fish species relative abundance increased between the historical and contemporary time periods throughout the Spring River. Occupancy of all fishes increased over time in the formerly metal contaminated portion of the Spring River, becoming similar to values in the reference reach. Changes in species richness depended on site position and pollution tolerance, as temporal increases of intolerant and moderately intolerant species richness were most pronounced in the lower Spring River below historical metal pollution inputs. Multivariate analyses revealed a significant interaction between time period and site position, as there was a shift in community structure over time in the lower reach that was less pronounced in the upper reach. Most of the intolerant species that increased in prevalence are of high conservation priority, thus our research suggested that legislation enacted to improve water quality produced a ripple effect that stimulated the recovery of imperiled fish species.

Detrimental effects of urbanisation on animal assemblages and a key ecological function persist across ecosystems

Abstract Context Urbanisation is pervasive across landscapes and seascapes and leads to the loss, degradation and fragmentation of many natural ecosystems and this has widespread consequences for animals and the ecological functions they support. While the impacts of urbanisation are understood for many individual coastal ecosystems in isolation, it is unclear how these impacts influence animal assemblages and ecological functions across different coastal ecosystems within the same landscape. Objectives We aimed to determine how urbanisation modifies fish and crustacean assemblages and the function of carrion consumption across multiple coastal ecosystems set within the same landscape in eastern Australia. Methods We sampled fish and crustacean assemblages in three distinct coastal ecosystems (estuaries, rocky headlands and surf zones) with baited remote underwater video systems and quantified rates of carrion consumption using scavenging assays. Results Urbanisation had negative effects on the richness and abundance of coastal fish and crustaceans and the ecological function of carrion consumption, and these impacts were almost always consistent across estuaries, rocky headlands and surf zones. Species richness and abundance were lowest at the most urbanised sites, whereas rates of carrion consumption were lowest at sites closest to urbanised areas, across all ecosystems. Conclusions We highlight the negative effects of urbanisation on coastal fish and crustacean assemblages, and a vital ecological function, and the consistency of these effects on distinct coastal ecosystems located within the same landscape. Managing the pervasive impacts of urbanisation on animal assemblages and ecological functions will, therefore, require targeted approaches that address the underlying impacts of urbanisation across multiple coastal ecosystems.

Long-term contamination by non-native fish assemblages in a Neotropical floodplain.

Biological invasions are a major threat to biodiversity in species-rich regions. Therefore, it is important to understand mechanisms behind the long-term establishment of non-native fish species in aquatic environments in the Neotropical region. Here, we associated fish biomass, species richness, and the proportion of non-native species (contamination and Kempton's indices) to quantify the non-native pressure over fish biodiversity in lakes and rivers of the Parana River floodplain, seasonally, from 2000 to 2017. We divided species into native and non-native assemblages sampled in spatio-temporal gradients. Temporal trends were examined using linear regressions and generalised additive models. Fish biomass in gillnets increased for both native and non-native fish species, but their Kempton indices were inversely correlated. Extinction of native species occurred locally with biotic differentiation of non-native species in lakes, rivers, and ecosystem contamination. A constant increase in fish biomass resulted in overwhelming biodiversity of non-natives at the end of the time series evaluated. Native biotic resistance to introductions was not detected in deterministic trends. The observed patterns were consistent with previous studies showing native biotic homogenisation and extinction of species in response to biological invasions, landscape fragmentation, and riverine impoundments. Increases in abundance and species richness of non-native fish were the biodiversity drivers that resulted in non-native species outweighing native species in the Parana floodplain.

Mediterranean Islands as Refugia for Elasmobranch and Threatened Fishes

ABSTRACTAimThe Mediterranean Sea is one of the most anthropized seas in the world but also a marine biodiversity hotspot with many fish species under threat. The main goal of the study is to test whether on the heavily fished and anthropized Mediterranean coast, the less impacted Corsica and Balearic Islands, can be considered as refugia for threatened and elasmobranch fishes independently of protection by marine reserves.LocationThe French Mediterranean coast and three north‐western Mediterranean islands: Corsica and also Mallorca and Minorca from the Balearic archipelago.MethodsWe performed 187 fish surveys using environmental DNA metabarcoding on three islands and 109 along the continental coast. Of the 78 surveys on islands 22 correspond to no‐take marine reserves and of the 109 continental surveys 26 were carried out within reserves. After eDNA filtration, extraction, amplification, and sequencing we estimated the number of fish species but also the number commercial, threatened and elasmobranch fish species on each sample. We then performed an ANOVA by permutation to test the effect of insularity and protection on these four biodiversity metrics. We also modelled these four biodiversity metrics as a function of protection and human pressure but also environmental, habitat and sampling conditions. We also built species accumulation curves to obtain asymptotes representing the potential regional pools for each species category on both island and continental coasts.ResultsWe obtained a total of 175,982,610 reads over the 187 eDNA samples that were assigned to 153 fish species including 17 elasmobranch species among which 7 were only detected on islands. We observed a higher total fish richness on continental than island surveys regardless of protection but a higher threatened and elasmobranch fish richness on the island than on continental surveys. We obtained a significant, negative and predominant human gravity impact on the diversity of elasmobranch species. The modelled asymptote reached 148 teleostean fish species on islands and 196 on the continental coastline with a very similar rate of diversity increase with sampling effort but the shape of the species accumulation curves differed markedly for elasmobranchs with a stronger increase in diversity with sampling effort on islands.Main ConclusionsOur findings highlight that Mediterranean islands can be refugia for sharks and rays but also threatened fishes in this overexploited region. Our results also suggest that reducing or banning trawling activities may play a key role for conserving vulnerable fishes, beyond the benefits of no‐take marine reserves, which appear limited on these large home‐range species.

Habitat Diversity Mitigates the Impacts of Human Pressure on Stream Biodiversity.

Recent decades have witnessed substantial changes in freshwater biodiversity worldwide. Although research has shown that freshwater biodiversity can be shaped by changes in habitat diversity and human-induced pressure, the potentials for interaction between these drivers and freshwater biodiversity at large spatial extents remain unclear. To address these issues, we employed a spatially extensive multitrophic fish and insect database from 3323 stream sites across the United States, to investigate the ability of habitat diversity to modulate the effect of human pressure on the richness and abundance of fish and insects. We found evidence that high levels of habitat diversity were associated with increased richness and abundance of fish and insects (including whole-assemblage and individual trophic guilds). We also show that the effects of human pressure on the richness and abundance of fish and insects tend to become positive at high levels of habitat diversity. Where habitat diversity is low, human pressure strongly reduces insect richness and abundance, whereas these reductions are attenuated at high levels of habitat diversity. Structural equation modeling revealed that human pressure reduced habitat diversity, indirectly negatively affecting the richness and abundance of fish and insects. These findings illustrate that, in addition to promoting greater fish and insect biodiversity, habitat diversity may mitigate the deleterious effects of human pressures on these two stream assemblages. Overall, our study suggests that maintaining high levels of habitat diversity is a useful way to protect freshwater biodiversity from ongoing increases in human pressure. However, if human pressures continue to increase, this will reduce habitat diversity, further threatening stream assemblages.

Observing changes of fish community in a semi-arid subtropical coastal lagoon subject to ecological conservation

El Soldado is a semi-arid subtropical coastal lagoon subject to ecological conservation in the Gulf of California, where we reviewed the changes in the fish community structure before (1972; 1978–79; 1990–92) and after (cycle 1, 2018–2019; cycle 2, 2019–2020) the decree as a protected area, and we determined spatio-temporal changes between two consecutive annual cycles. We conducted monthly fish sampling cycles 1 and 2 with a small trawl net at three sites, where water and sediment variables were recorded, and drift macroalgae biomass was estimated. Results showed 99 fish species have been recorded in previous studies, and our study added 11 species. The fish assemblage (2018–2020) comprised 34 marine species and nine of them were dominant in both cycles. In general, higher fish abundance, richness, and diversity were observed in the cycle 1. Spatial changes, in both cycles, showed higher fish abundance, richness, and diversity in the innermost area of the lagoon, characterized by silty sediment and higher drift macroalgae biomass. Temporal changes showed higher fish abundance, richness, and diversity in summer-autumn during cycle 1, while during cycle 2, the higher values were in winter-autumn, mainly associated with seasonal variations in water temperature and the biogeographic affinity of fish species, but were also attributed to changes in the density of species classified as dominant. There was notable a drastic decrease of fish richness, diversity, and density during summer in cycle 2, which was attributed to be a warmer year. El Soldado fish community showed changes before and after the decree as a protected area, but also in the contiguous cycles. These changes include the addition of species, the prevalence of common species over 48 years, and the current dominant species that belong to indicator groups, which exhibit effectiveness in the conservation of this ecosystem.

An Empirical Assessment of Diversity in Fish Species: Case Study of Madhubani District, India

Sarisab Pahi Chaur is a wetland sites in the Madhubani district, Bihar has rich fish diversity. The present investigation was undertaken the status of fish diversity and seasonal impacts on them in Sarisab Pahi Chaur of Madhubani, Bihar. A total number of 29 species representing 17 families of 9 orders of class Actinopterygii were identified from Sarisab Pahi Chaur wetland, the various species of order Cypriniformes 49% and Clupeiformes 16% dominated in the wetland followed by order Siluriformes 15%, Perciformes 12%, Channiformes 6%, Symbrachiformes, Beloniformes, Anguilliformes and Mugiliformes respectively. In present investigation species diversity of fishes of Sarisab Pahi Chaur, ranged between the lowest 0.943 June, 2021 and the highest 1.346 May, 2022. Species evenness (J) of fishes of Sarisab Pahi Chaur, varied from the lowest 0.787 July, 2021 and the highest 0.933 March, 2022 during the investigation period. Species richness (d) of fishes of Sarisab Pahi Chaur, varied from the lowest 6.603 June, 2021 and the highest 12.411 May, 2022. The value of Shannon-Wiener diversity, Species richness and the Evenness in different months are the different value which is depends upon the fish density and physico-chemical parameters of water of wetland. The paper takes into account to explore the importance of wild variety in fish seed production and its support in sustainable livelihood development.

A framework for integrating stream ecosystem theories into spatial modeling of fish richness and assemblage structure

A framework for integrating stream ecosystem theories into spatial modeling of fish richness and assemblage structure

Environmental DNA Reveals the Impact of Submarine Groundwater Discharge on the Spatial Variability of Coastal Fish Diversity.

Submarine groundwater discharge (SGD) has recently been recognized as an influential factor in coastal ecosystems; however, little research has been conducted on its effects on coastal fish diversity. To investigate the relationship between SGD and fish diversity, we conducted a survey at the coastal island scale using the environmental DNA (eDNA) method. Our findings indicate that fish species richness and functional richness peak at stations with high SGD. Environmental variables, such as salinity, dissolved inorganic nitrogen (DIN) concentration, and SGD, significantly influence fish diversity. Carnivore fish richness was negatively correlated with salinity, while planktivore fish richness was positively correlated. Additionally, SGD and DIN concentrations were found to be crucial in shaping omnivorous and pelagic communities, respectively. This study highlights the role of SGD in enhancing nutrient conditions favorable for diverse fish communities and demonstrates the effectiveness of eDNA metabarcoding for rapid marine biodiversity assessment. These findings provide valuable insights for coastal ecosystem monitoring and management.

Optimising species detection probability and sampling effort in lake fish eDNA surveys

Environmental DNA (eDNA) metabarcoding is transforming biodiversity monitoring in aquatic environments. Such an approach has been developed and deployed for monitoring lake fish communities in Great Britain, where the method has repeatedly shown a comparable or better performance than conventional approaches. Previous analyses indicated that 20 water samples per lake are sufficient to reliably estimate fish species richness, but it is unclear how reduced eDNA sampling effort affects richness, or other biodiversity estimates and metrics. As the number of samples strongly influences the cost of monitoring programmes, it is essential that sampling effort is optimised for a specific monitoring objective. The aim of this project was to explore the effect of reduced eDNA sampling effort on biodiversity metrics (namely species richness and community composition) using algorithmic and statistical resampling techniques of a data set from 101 lakes, covering a wide spectrum of lake types and ecological quality. The results showed that reliable estimation of lake fish species richness could, in fact, usually be achieved with a much lower number of samples. For example, in almost 90% of lakes, 95% of complete fish richness could be detected with only 10 water samples, regardless of lake area. Similarly, other measures of alpha and beta-diversity were not greatly affected by a reduction in sample size from 20 to 10 samples. We also found that there is no significant difference in detected species richness between shoreline and offshore sampling transects, allowing for simplified field logistics. This could potentially allow the effective sampling of a larger number of lakes within a given monitoring budget. However, rare species were more often missed with fewer samples, with potential implications for monitoring of invasive or endangered species. These results should inform the design of eDNA sampling strategies, so that these can be optimised to achieve specific monitoring goals.

Coral reef fish density at a tourist destination responded rapidly to COVID-19 restrictions.

Throughout the world, anthropogenic pressure on natural ecosystems is intensifying, notably through urbanisation, economic development, and tourism. Coral reefs have become exposed to stressors related to tourism. To reveal the impact of human activities on fish communities, we used COVID-19-related social restrictions in 2021. In French Polynesia, from February to December 2021, there was a series of restrictions on local activities and international tourism. We assessed the response of fish populations in terms of changes in the species richness and density of fish in the lagoon of Bora-Bora (French Polynesia). We selected sites with varying human pressures-some dedicated to tourism activities, others affected by boat traffic, and control sites with little human presence. Underwater visual surveys demonstrated that fish density and richness differed spatially and temporally. They were lowest on sites affected by boat traffic regardless of pandemic-related restrictions, and when activities were authorised; they were highest during lockdowns. Adult fish density increased threefold on sites usually affected by boat traffic during lockdowns and increased 2.7-fold on eco-tourism sites during international travel bans. Human activities are major drivers of fish density and species richness spatially across the lagoon of Bora-Bora but also temporally across pandemic-related restrictions, with dynamic responses to different restrictions. These results highlight the opportunity provided by pauses in human activities to assess their impact on the environment and confirm the need for sustainable lagoon management in Bora-Bora and similar coral reef settings affected by tourism and boat traffic.

Assessing the combined effects of catchment land use and runoff on estuarine fish assemblages

Connectivity between land and sea through the movement of species, energy and nutrients means that land-based impacts can affect the structure and functioning of nearby coastal ecosystems. As the interface between land and sea, estuaries are often faced with increasing pressures from catchment modifications (e.g. the removal of terrestrial vegetation) which can alter the overall health of estuaries (e.g. the degradation of coastal water quality due to an increase in terrestrial runoff) and change the value of habitat for many marine species. These landscape-scale impacts can, however, be mediated through variations in the context and connectivity of seascapes (e.g. greater extent of vegetated ecosystems help to filter nutrients). We surveyed fish across five estuaries over four years using underwater videography and sought correlations between fish biodiversity and abundance with variables indexing catchment land use, seascape connectivity, and coastal water quality. Fish assemblages were more abundant and diverse at sites which had lower chlorophyll-a concentrations and were nearer to the estuary mouth, in conjunction with catchments containing higher percent of natural land and heterogenous seascapes. Sites with lower concentrations of chlorophyll-a supported indicator species from more diverse functional groups that had greater fisheries values, in comparison to indicator species from sites with high concentrations of chlorophyll-a. This research can help direct coastal management to better prioritise management in coastal ecosystems, thereby enhancing fish richness and abundance, functional group richness and fisheries value.

Fish biodiversity status and threats of Chinadi Beel in Bangladesh

This study examined the fish fauna of Chinadi Beel in Bangladesh in terms of diversity, quantity, and state of conservation. A pre-tested questionnaire and a direct catch evaluation survey were employed to conduct the study in the beel. In the examined beel, a comprehensive count of 3,360 fish specimens, encompassing 52 distinct fish species from 8 orders and 19 families, was documented. Cypriniformes was identified as the dominating order among the 8 orders examined, accounting for 51.49% of the total. Out of 52 fish species about 31 least concern (59.61%), 8 endangered (15.38%), 6 vulnerable (11.54%), 6 near threatened (11.54%) and 1 critically endangered (1.92%) species were observed according to the International Union for Conservation of Nature. The study utilized population diversity indices, specifically the Shannon-Weiner diversity index (H'), Margalef species richness (d), Pielou's evenness index (J'), and Simpson dominance index (c), to assess the species diversity, richness, and evenness of fish which value were found to be 2.50, 4.30, 0.90, and 0.30, respectively. Chinadi Beel has the capacity to function as a significant reservoir of fishing resources and a repository of genetic information for many fish species. However, the present study emphasized several anthropogenic and environmental issues, such as unregulated fishing, agricultural pollutants, illegal or harmful fishing, the construction of infrastructure for development, and climate change. Hence, it is highly recommended to implement ecosystem-based fisheries management that actively involves the local population in order to guarantee the long-term preservation of these water bodies.

Pathways linking watershed development and riparian quality to stream water quality and fish communities: Insights from 233 subbasins of the Great Lakes region

Anthropogenic stressors such as urban development, agricultural runoff, and riparian zone degradation impair stream water quality and biodiversity. However, the intricate pathways that connect these stressors at watershed and riparian scales to stream ecosystems—and their interplay with climate and hydrology—remain understudied. In this study, we used Partial Least Squares (PLS) path modeling to examine these pathways and their collective impacts on stream water quality and fish community structures across 233 watersheds in the Great Lakes region. Our study suggests that moderate levels of watershed development enhance overall fish richness, potentially due to increased water temperature and nutrient availability, but reduces both the percentages and richness of cold water and intolerant taxa. Riparian quality exerts indirect effects on water quality with climate and stream order serving as key mediators. Complementing our SEM analysis, we also used Multiple Linear Regression (MLR) models and identified a significant positive relationship between the proportion of clay and agricultural land with TN concentrations. However, TP concentrations are influenced by a more complex set of interactions involving developed areas, soil, and slope. These findings emphasize the necessity of adopting integrated management strategies to preserve the health and integrity of freshwater ecosystems in the Great Lakes region. These strategies should integrate watershed and riparian protection measures while also taking into account the effects of climate change and specific local conditions.

Seasonal dynamics and habitat preferences of juvenile fish assemblages in the Wanquan Estuary, South China: Implications for conservation and management

Tropical estuaries encompass diverse habitats, which are crucial for supporting juvenile fish by providing nurseries, refuges, and migration routes. In the present study, we investigated the seasonal and spatial dynamics of juvenile fish assemblages in the Wanquan Estuary, Hainan Island, China, examining variations during the wet and dry seasons across four types of habitats. Our research aimed to test the hypotheses: (1) the wet season supports a greater abundance and species richness of juvenile fish compared to the dry season, and (2) juvenile fish showed varying habitat preferences across seasons. We recorded a total of 3617 individuals belonging to 33 families, 50 genera, and 78 taxa. Our findings revealed significant seasonal fluctuations in the assemblage structure, with peak abundance during the wet season in August, primarily consisting of diadromous species. A notable shift towards marine species was observed in March. Spatially, juvenile fish exhibited significant habitat preferences, with a strong preference for sand substrates for most species. Contrary to common expectations, mangrove fringe habitats were not identified as the primary nursery grounds for juvenile fish. Instead, our study highlights the importance of habitat diversity and connectivity in enhancing nursery functions. Water temperature and salinity were the key drivers influencing the seasonal and temporal patterns of juvenile fish assemblages in the Wanquan River estuary The pronounced temporal dynamics of these assemblages, driven by seasonal environmental alterations affecting water variations and habitat connectivity, were more significant than spatial differences. The findings emphasize the need for focused connectivity of various habitats to support the conservation of diverse fish communities in tropical estuarine ecosystems.

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.

Anthropogenic activities decrease functional richness over time, but not other functional aspects of the fish community in a tropical bay

Functional diversity can be used to help understanding the processes shaping biological communities and the effects of human disturbances on the ecosystem's services. Untangling these biological processes is crucial to apply effective policies aiming the biodiversity conservation. Temporal changes (1983–1985, 1999–2001 and 2017–2019) in five functional indices (functional richness, divergence, evenness, specialization and originality) of the fish communities in two zones (inner and outer) of shallow areas in a tropical bay heavily human-impacted in recent decades were evaluated. The tested hypothesis was that functional indices decrease over time, because of the environmental degradation. A substantial decrease in species richness and abundance in the more recent periods (1999–2002 and 2017–2019) compared to 1983–1985 was observed. However, the functional structure remained relatively stable, with the exception of functional richness that showed a significant decrease over time. The apparent stability in the other functional indices may be due to the presence of dominant and functionally redundant species over time that compensates for the loss of species while maintaining similar functions. It was also discovered that decreases in fish richness in shallow bay areas result in losses in functional richness, with resident fish and benthivorous species being the most affected by environmental degradation. By employing a comprehensive approach that integrates the use of functional indices and taxonomic diversity to assess temporal changes in the fish community, it provides a broader understanding of ecological processes. Such insights could prove invaluable in guiding the implementation of conservation strategies.

COMPOSITION, ABUNDANCE AND DISTRIBUTION OF NON-CICHLID FISH COMMUNITY IN OGBO STREAM AND ITS FLOODPLAIN, ENHWE, DELTA STATE, NIGERIA

A preliminary survey of the composition, abundance and distribution of non-cichlid fish community was carried out at Ogbo stream and its floodplain in Enhwe, Delta StateNigeria. Water samples and fishes were sampled and analyzed using APHA methods and standard fishing gear respectively. The physicochemical parameters revealed distinct values for station 1 (Temperature: 25.63°C, Transparency: 25.09 cm, Sulphate: 7.56 mg/L) and station 2 (Temperature: 23.60 °C, Transparency: 19.90 cm, Sulphate: 6.68 mg/L). Among the parameters, only Temperature, Transparency, and Sulphate exhibited a noteworthy difference (p<0.05) between the two stations. Transparency had a negative correlation with other parameters in Station 1.A total of 725 individual fish species belonging to eight families and genera were sampled. Among the notable findings, Clariidae emerged as the most abundant family, constituting 82.90% of the total relative abundance across both stations. Clarias camerunensisexhibited the highest abundance, comprising 62.20% of the total individuals sampled. Parachanna africanaand Clarias pachynemaalso demonstrated significant presence, contributing 15.00% and 13.20% to the total relative abundance, respectively. ANOVA indicates a significant difference in the composition and abundance of fish species between the stream and floodplain (p < 0.05), emphasizing the influence of habitat-specific factors. The Margalef’s richness (1.67), dominance (0.64), diversity (1.32) and evenness (0.34) index of fishes was higher in the stream than in the floodplains. Magnesium, sulphate, temperature, and transparency were positively correlated to the distribution patterns of Pantodon bucholzi, Clarias jaensis, Phractolaemus ansorgei, and Heterotis niloticusin station 1, with the exception of P. africanaand Polypterus senegalus. There was a negative association between dissolved oxygen, nitrate, pH, and Iron, and the distribution of fishes in station 2. Ogbo stream and its floodplain have low abundance and distribution of fish species. Therefore, it demands for sampling efforts and long-term studies to unravel the checklist of species

Native fish assemblages in natural lakes across Japan: Endemism deterioration lasting centuries

AbstractAimThis 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.LocationJapanese archipelago.MethodsWe 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.ResultsWe 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 ConclusionsThe 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.

Longitudinal changes on ecological diversity of Neotropical fish along a 1700 km river gradient show declines induced by dams

In naturally flowing waters, communities are expected to increase their taxonomic and functional diversity as well as increase the complexity of food web architecture along the longitudinal gradient from headwaters to mouth. However, these theories do not necessarily apply to dammed rivers. We analysed fish communities at 12 locations along the 1700 km stretch of the transnational Uruguay River. We determined species richness, beta-diversity and its components (turnover and nestedness), trophic diversity, and isotopic niches at community level, with particular focus on areas upstream and downstream of the four existing dams. We estimated trophic diversity metrics based on diet analysis, and isotopic niche breadth based on Bayesian isotopic niche models. We detected consistent longitudinal changes, supporting predictions from the River Continuum Concept. However, taxonomic richness, trophic diversity, and isotopic niche decreased abruptly immediately downstream of dams, and the component contributing the most to beta diversity was turnover, with the highest values occurring mainly after the cascade of dams in the upper Uruguay River, fitting expectations from the Serial Discontinuity Concept. The dam-free stretches of the Uruguay River allowed the recovery of ecological diversity as fish richness and trophic and isotopic niche increased. The negative impacts of dams should urgently be considered in the Neotropics, where many large dams are projected.