Fish Richness Research Articles

Current environmental conditions are weak predictors of fish community structure compared to community structure of the previous year

Predicting fish community structure in streams is a challenge considering the strong dynamics of these environments. In this study, we tested whether using a fish dataset obtained in a previous time was relevant to predict fish community structure in a subsequent time. We also tested whether temporal beta diversity of fish communities was correlated with environmental variability, stream size and order. To test these hypotheses, we collected data on fish communities, environmental and spatial variables from 15 streams in the Rio das Mortes Basin (Mato Grosso State, Brazil) in two consecutive drought periods (in 2016 and 2017). The gradients in fish richness and abundance were correlated between years. The results of a variation partitioning analysis indicated that the fish community structure in 2016 was the main explanatory matrix of the fish community structure in 2017 (when compared to environmental and spatial variables). A variation partitioning analysis, based only on environmental and spatial variables, showed a much higher residual variation. We did not detect significant relationships between fish temporal beta diversity and our explanatory variables. Our results indicate that our predictive power may be substantially increased by using data on past communities as explanatory variables. This is a viable analytical strategy because long-term studies are becoming more frequent. Temporal autocorrelation analyses of community data can also be useful to evaluate priority effects. In addition, these analyses can help plan biomonitoring programs. The second part of the results indicates, however, that our ability to predict temporal beta diversity is still limited.

Hiding in Plain Sight: Elopomorph Larvae Are Important Contributors to Fish Biodiversity in a Low-Latitude Oceanic Ecosystem

Leptocephalus larvae of elopomorph fishes are a cryptic component of fish diversity in nearshore and oceanic habitats. However, identifying those leptocephali can be important in illuminating species richness in a region. Since the Deepwater Horizon oil spill in 2010, sampling of offshore fishes in the epi-, meso-, and upper bathypelagic depth strata of the northern Gulf of Mexico resulted in 8982 identifiable specimens of leptocephalus larvae or transforming juveniles, representing 90 recognized and established species and an additional 36 distinctive leptocephalus morphotypes not yet linked to a known described species. Leptocephali account for ~13% of the total species richness of fishes collected in the offshore region. A new morphotype of Muraenidae leptocephalus is described. DNA barcoding of selected specimens has further expanded the determination of several leptocephalus morphotypes.

Effects of mangrove encroachment on tidal wetland plant, nekton, and bird communities in the Western Gulf of Mexico

Woody encroachment is occurring in many marsh-mangrove ecotones across the globe, with multiple drivers contributing to an increase in mangrove cover. As a result, marsh plant species are often displaced, resulting in a striking regime shift from grass and forb-dominated habitats to taller, woody vegetation. Our goal was to quantify the bottom-up effects of mangrove woody encroachment into coastal wetlands on associated plant, nekton, and bird assemblages. In 2012, we established several large (>20 ha) survey areas at tidal wetland sites with or without black mangroves (Avicennia germinans) on the Texas (USA) coast in the Gulf of Mexico, an area highly susceptible to mangrove encroachment. From 2012 to 2015, we recorded vascular plant cover and diversity, sampled nekton at the water-vegetation interface using seine nets, and compared wintering shorebird and wader use among sites using the citizen science database eBird. Marsh plant species richness was 50% lower at sites with mangroves, and some species, such as Distichlis spicata, were absent from these sites entirely. The relative abundance and species richness of nektonic fish and invertebrates were similar between sites, but certain species (e.g., bay anchovies Anchoa mitchilli, grass shrimp Palaemonetes spp.) were more common at sites without mangroves. Citizen science data indicated that shorebird and wader species richness was 20% lower at sites with mangroves. Shorebird assemblages were markedly different between site types; six shorebird and three wader species were only detected in marsh sites. Our results indicate that coastal wetlands dominated by mangroves support different plant and animal assemblages than marsh-dominated areas. These results were largely consistent with the results of a previous manipulative experiment in the same area, lending considerable confidence to the conclusion that mangroves influence the associated plant and animal communities. Therefore, as woody encroachment continues and mangrove cover gradually increases, this change may lead to complex bottom-up effects on a range of ecosystem processes and services.

Using fish assemblages to understand environmental connectivity and usage. A contribution to the conservation of the Yucatan Wetland

The Yucatan tidal wetland (YTW), located in the southeastern portion of the Gulf of Mexico is an extensive, heterogeneous, seasonally flooded area with a high diversity and richness, but urbanization is changing the ecosystem and, therefore, could change the functions it provides. Two important functions of the wetlands have been highlighted, its function as a nursery and the transfer of biomass to other ecosystems. To corroborate those functions, the percentage of juveniles and the links of the fish assemblage with other ecosystems need to be registered. In the present study, the fish assemblage of the YTW was analyzed to determine: (1) zonation; (2) assemblage and trophic structure; (3) environmental constraints on the fish assemblage, and (4) usage and connectivity of the ecosystem. Fifty-one stations were analyzed and segregated into three zones: Z1, the coastline, characterized by oxygenated and high salinity waters, and the highest fish richness and trophic diversity. Its fish assemblage is constituted by species associated with marine (31%), brackish (30%), reef (22%), and freshwater (17%) ecosystems, with 50% of the population registered as juveniles and 33% in the first-maturity size. Z2, the brackish environment, presents average fish richness and trophic diversity and physicochemical variation, its fish assemblage is constituted by species associated to freshwater (44%), brackish (34%), marine (15%), and reef (7%) ecosystems, with 43% of the population registered in first-maturity size and 33% in juveniles sizes. Z3, the freshwater environment, characterized by low oxygen levels and salinity, low fish richness and trophic diversity and the highest biomass. Its fish assemblage is constituted by species associated with freshwater (65%), brackish (34.5%), and marine (0.5%) ecosystems, with 80% of the population registered in adult sizes. The nursery, refuge, and feeding ground functions of the YTW and the transfer of biomass, via individuals, to other ecosystems were corroborated. It can be concluded that the YTW presents an intricate trophic and functional relationship among zones and ecosystems surrounding it; thus, the detrimental impacts in the YTW will produce negative effects in the near aquatic ecosystems. Therefore, it is of priority importance to ensure that the urban development plans of the YTW ensure the connection between zones, the clean input of freshwater, and the natural flow between the sea and the YTW.

Diversity, pattern and ecological drivers of freshwater fish in China and adjacent areas

China is one of the megadiverse freshwater regions in the world, but the detailed diversity inventory, distribution pattern and ecological drivers are incompletely known, which hinders large-scale freshwater diversity conservation and pattern analysis at the global scale. Aiming to fill this knowledge gap, we compiled a comprehensive richness and distribution database of freshwater fishes in China and adject areas based on our long-term survey and exhaustive data collection from 165 hydrologic units at tributary and sub-basin grain. Then, we elucidated a biogeographical pattern using a β dissimilarity matrix with species presence/absence data and taxonomic relationships. Finally, we evaluated the explanatory power of three hypotheses, i.e., ‘area’, ‘energy’, and ‘history’, in explaining the diversity patterns. A total of 2,063 species utilizing freshwater habitats were identified in the study area. Among them, 1,651 freshwater species were recorded in China, of which 1034 species are endemic to China. Four major freshwater zoogeographic regions, the Palearctic, High Central Asia, East Asia, and South Asia, were identified from a dendrogram, and each region was characterized by different taxonomic categories (i.e., from species to order). ‘Historical’ factors play the most important role (43.64–62.96% of the total variation), or at least a comparable role to that of contemporary climate, in explaining the freshwater fish diversity patterns (species richness and species endemicity). In conclusion, the uplift of the Qinghai-Tibetan Plateau, nearby orogeny, and the following formation of the East Asian monsoon climate had profound impacts on the diversification and distribution of ichthyofauna in China and adjacent areas.

Reduced fish diversity despite increased fish biomass in a Gulf of California Marine Protected Area.

Multi-use marine protected areas (MUMPAs) are a commonly applied tool for marine conservation in developing countries, particularly where large no-take reserves are not socially or politically feasible. Although MUMPAs have produced benefits around the world, the persistence of moderate fishing pressure reduces the likelihood of achieving the primary objective of these areas, which is the conservation of ecosystems. In this study we used traditional and functional metrics to evaluate how fish assemblages changed through time in a MUMPA, including shifts in species responses and in ecological processes. We conducted visual censuses of fishes at Espíritu Santo Island, México (MUMPA; N = 320; 24°N, 110°W) from 2005 to 2017 to assess fish richness, size-distribution and density. Three functional indices were calculated using six traits (size, mobility, period of activity, aggregation, position in water column and diet): functional richness (volume occupied by species), dispersion (complementarity between species) and originality (inverse of functional redundancy). We compared fish diversity among three management zone types (sustainable fishing, traditional fishing and no-take zones), through a 13-year period, assessing which species increased or decreased in occurrence, density, and biomass, and how indices respond over time. Despite a general increase in biomass and stability in density and originality, we detected a reduction in fish biodiversity in the form of declines in species and functional richness, which could imply the risk of local extinction and decrease in certain ecosystem processes. In addition, changes in functional dispersion showed that some functions are losing representation through time. Although no single cause is apparent, such factors as competitive interactions, habitat loss and persistence of fishing pressure potentially explain these decreases. The rise in biomass was associated with a general increase in the average size, rather than increased biomass of commercial species, as the latter remained stable during the study period. Expansion of no-take areas, enforcement of fishing regulations, and surveillance in core zones, should be implemented to reverse the decline in particular species and to promote conservation of fish functional diversity in this MUMPA.

Influences of climate and nutrient enrichment on the multiple trophic levels of Turkish shallow lakes

ABSTRACT Climate warming threatens the structure and function of shallow lakes, not least those in the Mediterranean climate. We used a space-for-time substitution approach to assess the response of trophic and community structures as well as the richness and evenness of multiple trophic levels to temperature, hydrological, and nutrient constraints. We selected 41 lakes covering wide climatic, hydrological, and nutrient gradients within a short distance for reducing the effect of biogeographical factors in the western Anatolian plateau of Turkey. Generalized linear model analyses revealed that temperature was overall the most important driving variable, followed by total nitrogen (TN) and salinity. The chlorophyll a:total phosphorus ratio, the cyanobacteria:total phytoplankton biovolume ratio, the fish:zooplankton biomass ratio, the proportion of small fish, and fish richness increased with increasing temperature, whereas macrophyte plant volume inhabited (PVI, %), richness, and evenness decreased. Grazing pressure, macrophyte coverage, piscivore biomass, phytoplankton richness, and evenness decreased significantly with both increasing TN and temperature. Temperature and nutrients also separated the northern highland lakes from other lakes in a non-metric multidimensional scaling analysis. Additionally, salinity reduced richness and evenness of phytoplankton and zooplankton. Our results indicate major changes in lake structure and functioning with warming and eutrophication, and highlight the need for strict control of nutrients and water use.

Evaluation of River Fragmentation and Implications for the Conservation of Migratory Fish in Southeastern Brazil.

In freshwater systems, the abundance and diversity of long-distance migratory fish are limited by the maintenance of longitudinal connectivity and natural flow regimes of rivers. Using a graph-based view of each riverscape, we analyzed the river fragmentation process and overlapped with the probable number of migratory species in each remaining stretch. Applying this methodology in basins, we assess historical and potential scenarios quantifying segment extensions free from dams determining the fish richness based on the available habitat for each species. The highest number of migratory species was observed in fragments longer than 100 km. In the future scenario, there was an increase in the number of fragments, with an increase in the number of stretches shorter than 50 km, inadequate to maintain most of the migratory species. Segments of the highest classification order and located in the longest lotic fragments were considered the most important for the species habitat conservation. Dam construction in these segments could seriously affect the ecological processes at a regional level. The proposed analyses enable to approach basins with high diversity of species and nonsalmonid species, supporting the lack of base data concerning those areas, and determine priorities for studies and conservation.

Artificial flow regime promotes abiotic and biotic gradients: Testing the concept of longitudinal zonation in an off-river reservoir

Fragmentation and interconnection of water bodies cause severe changes in the natural flow regime of continental water systems. However, assessments of these impacts on the freshwater fish distribution are still scarce. We investigated whether an artificial flow regime generated by discharges from an aqueduct would promote a longitudinal environmental gradient in an off-river reservoir. We tested the hypothesis that the incoming water from aqueduct discharges promotes environmental gradient between lotic and lentic conditions. We expect that environmental changes and the artificial flow regime promote the structuring of fish assemblage and that the lotic-lentic transition areas present the highest fish species richness. A longitudinal gradient in environmental characteristics with differing fish assemblage structure was found. Temporal changes in the fish assemblages occurred only in areas near the discharge of the aqueduct. The highest fish richness and diversity were recorded in the transition zone during the wet season, associated with the greater environmental heterogeneity of this ecotone, whereas the lowest was found in the lotic zone, probably associated with the altered flow regime. The greatest abundance was recorded in the upper lentic zone in the wet season, whereas the lowest was found in the lower lentic zone in both seasons. Our results corroborate the hypothesis that the artificial flow regime, modulated by the seasonality of discharges and the influence of environmental variables, promotes longitudinal gradients in reservoirs when rivers are not present. The findings are relevant in a scenario where ever more interconnections of aquatic bodies have been diffused around the world.

Freshwater fish richness baseline from the São Francisco Interbasin Water Transfer Project in the Brazilian Semiarid

Abstract Among Neotropical freshwater ecoregions, the Mid-Northeastern Caatinga (MNCE) is a fish knowledge gap. Its temporary drainages are receptors of the São Francisco interbasin water transfer project (SFR-IWT) in the Brazilian semiarid. We provide a comprehensive baseline of fish richness of the five SFR-IWT basins. Species richness, shared, endemic, threatened and non-native species were obtained using sampling, ichthyologic collections, literature and online repositories (306 localities). In total 121, species were recorded, 111 of them native, and 16 (14.41%) listed for all basins. Higher richness of native species (78, 70.27%) was recorded in the São Francisco lower-middle stretch (SFRE), including 23 endemic, 61 (54.95%) in MNCE basins (13 endemic), and 28 (25.23%) shared between both ecoregions. In the MNCE, 50 species were recorded in Jaguaribe (JAG), 39 in Piranhas-Açu, 36 in Paraíba do Norte, and 32 in Apodi-Mossoró (APO). The number of species shared between the SFRE and each receptor basin varied from 24 (23.08%, JAG) to 20 (22.22%, APO). JAG contains 81.97% of the receptor basins’ species. Its higher richness and endemism deserve special attention regarding the ongoing hydrological changes. This study will help detect possible modifications in the ichthyofauna of the main MNCE drainages.

Mesophotic ecosystems at Fernando de Noronha Archipelago, Brazil (South-western Atlantic), reveal unique ichthyofauna and need for conservation

Abstract Although several studies on the ichthyofauna of the Fernando de Noronha Archipelago have been carried out, its mesophotic fish diversity has never been surveyed before. Here we used SCUBA and technical rebreather diving, baited remote underwater videos and remotely operated vehicle to record shallow (≤ 30 m depth) and mesophotic (31 to 150 m depth) fishes. Nineteen fish species belonging to 14 families are reported here as new records, representing an increase of 8.2% in marine fish richness for the region, which now has a total of 250 species and 77 families. These new records include four potential new species and highlight the importance of surveying mesophotic ecosystems, even in well studied sites. Our results also emphasize the need for protection and attention to the unique ichthyofauna found at mesophotic depths.

Extinction debt of fishes in Great Lakes coastal wetlands

Declines in North American freshwater biodiversity can be largely attributed to anthropogenic disturbances that reduce habitat quantity, quality, and connectivity. In the Laurentian Great Lakes, wetlands have been significantly lost as a result of agricultural land-use practice, yet high species richness and several at-risk fishes persist. These patterns lead to the hypothesis that Great Lakes wetland fishes are in extinction debt, meaning there is a time lag between habitat loss and local extinction. To test this hypothesis, we sampled current species richness of wetland-specialist fishes in protected and unprotected wetlands in the Lake Erie basin. We predicted species richness in unprotected wetlands using parameter estimates (slope and intercept) from protected wetlands. Extinction debt was measured as a positive difference between predicted and observed species richness. We determined how much area would be required to support current species richness and compared this to minimum-area requirements for eight at-risk fishes. Species richness was significantly higher than predicted in unprotected wetlands, indicating that fishes in them are in extinction debt. This result indicates that there is time available to restore disturbed wetlands and prevent local extinction. We identified 17 wetlands of high priority for restoration (>10 species bound for extinction) and determined that the restoration of 178 km2 of wetland habitat would reduce the risk of future biodiversity loss. This is the first direct study of extinction debt in freshwater fishes. Additional extinction-debt assessments in aquatic systems are needed to extend the ecological theory and fundamental application of extinction debt beyond terrestrial systems.

Optimizing hydropower dam location and removal in the São Francisco river basin, Brazil to balance hydropower and river biodiversity tradeoffs

To support eco-friendly hydropower planning in developing regions, we propose a spatial optimization model for locating dams to balance tradeoffs between hydropower generation and migratory fish species richness. Our model incorporates two special features. First, it is tailored to the dispersal of tropical migratory fishes, which typically require long, unimpeded river stretches to complete their life-cycle. To model fish with this type of dispersal pattern, we introduce the concept of a river pathway, which represents a novel way to describe river connectivity. Second, it combines decisions about dam placement and removal, thus facilitating opportunities for hydropower offsetting. We apply our model to the São Francisco River basin, Brazil, an area of hydropower-freshwater biodiversity conflict. We find that dams have reduced weighted migratory fish richness 51% compared to a pre-dam baseline. We also find that even limited dam removal has the potential to significantly enhance fish biodiversity. Offsetting the removal of a single dam by the optimal siting of new dams could increase fish richness by 25% above the current average. Moving forward, optimizing new dam sites to increase hydropower by 20%, rather than selecting the fewest number of dams, could reduce fish species losses by 89%. If decisions about locating new dams are combined with dam removal, then a win-win can even be achieved with 20% greater hydropower and 19% higher species richness. Regardless of hydropower targets and dam removal options, a key observation is that optimal sites for dams are mostly located in the upper reaches of the basin rather than along the main stem of the São Francisco River or its main tributaries.

Identifying candidate reference reaches to assess the physical and biological integrity of wadeable streams in different ecoregions and among stream sizes

Abstract Efforts to quantify disturbances to aquatic systems often use landscape-level metrics, presumably linked to ecological integrity, but fewer studies have directly linked ecological integrity to instream habitat, and applied these results to unsampled stream reaches throughout a landscape. We developed a flexible, quantitative approach that characterizes stream impairment across a landscape and identifies least-disturbed stream reaches to serve as benchmarks for high quality physical habitat and ecological integrity. Fish and macroinvertebrate community characteristics, reach-level physical habitat and water quality metrics were summarized in 891 wadeable stream reaches across two ecoregions in Missouri, USA. The influence of reach and water-quality characteristics as well as landscape-level variables on 7 fish and 3 macroinvertebrate community biological indicator metrics was then modeled using boosted regression trees (BRTs). On average, reach-level models explained more variance (25 and 27% in the two ecoregions examined) in biotic metrics than landscape-level models (18% and 20%). Abiotic and biotic associations differed among ecoregions and stream sizes, however, reach-level habitat (e.g., bankfull width/depth ratio, channel incision height) and water quality (e.g., dissolved oxygen, total chlorophyll) were consistently top predictors. At the landscape scale, fish richness in the agriculturally dominated ecoregion increased with decreased fragmentation/flow modification. Invertebrate metrics in the forested ecoregion showed community degradation apparent with crop coverage as low as 8–10% of the riparian zone, while urban impairment, most notably in the agricultural ecoregion, was best detected using invertebrate indicators of biotic integrity and measures of fish trophic ecology. Relationships among landscape-scale variables and reach characteristics identified as top predictors in BRTs also highlighted potential mechanistic relationships among landscape, habitat, and measures of ecological integrity. Using the results of the landscape-level models, estimates for overall ecological integrity were predicted for over 28,000 stream reaches throughout Missouri, and a total of 1423 candidate reference reaches were identified. The objective approach to characterizing stream impairment developed in this study offers specific advantages, including a reach and landscape-level evaluation of human disturbance as well as an inductive, multi-metric determination of ecological integrity.

A tale of two habitats: preliminary comparison of fish abundance and diversity between saltmarsh- and mangrove-dominated creeks in the Nahoon Estuary, South Africa

A preliminary assessment of abundance and richness of fishes utilising saltmarsh and mangrove habitats in the Nahoon Estuary, situated on the eastern coast of South Africa, was undertaken during July 2017. The structural composition and complexity of the two habitats were assessed and underwater cameras were used to provide preliminary insight into the use of the different habitats by fish taxa. The saltmarsh habitat had a higher fractal dimension and density of stems than the mangrove habitat. The species richness of fishes was slightly higher in the mangroves than in the saltmarsh, with nine and seven taxa recorded in the two habitats, respectively. The mean relative abundance of fishes was higher in the saltmarsh than in the mangroves and this was mainly due to the dominance of shoaling estuarine zooplanktivores in the saltmarsh. The mean relative abundance of estuary- associated marine fish species was, however, higher in the mangroves, which may be indicative of greater nursery use of this habitat by marine fishes. Although this is the first study to simultaneously assess the role of both saltmarsh and mangroves as fish habitat in estuaries of temperate South Africa, the findings are preliminary, and further study on seasonal differences in species assemblages is recommended.

The distribution and richness of the Italian riverine fish provided by the BioFresh database

Freshwater fish are recognized to be endangered worldwide, but wide gaps in species distribution knowledge limit the implementation of effective conservation plans. The BioFresh project aims to produce the widest synthesis at the national level. The aim of this research is assessing the comprehensiveness and representativeness of information included in the Italian synthesis, composed of 10000 sampling sites and 50000 fish presence records. The assessment was produced at the secondary river basin (SRB) level in two distinct periods, past (1984-1999) and recent (2000-2014), comparing different statistical models of frequency counts of species detected within each SRB. The results highlighted a poor overall knowledge of the Italian fish distribution for both periods. In the all-species dataset, only 11.8 % and 11.1 % of the SRBs were found to have been sufficiently explored in the past and recent periods, respectively. In the native species dataset, these percentages increased to 16 % and 24.7 % respectively, which suggests the presence of background noise in the richness estimates produced by exotic species. Although the information available is far from exhaustive, the BioFresh project, in which data collected over a wide time span are georeferenced and freely available, represents the first synthesis for future research aimed at the management and conservation of the Italian fish fauna.

Community structure of target reef fish at four tiny islands coral reefs in inner Kotania bay, Maluku Province, Indonesia

Study on community structure of target reef fish at four tiny islands coral reefs in inner Kotania bay was conducted from September 2017 to February 2018. Underwater Visual Census method was used to collect and examine data concerning several parameters of target reef fish community structure. At least 18 families of target reef fish which consist of 37 genera and 105 species were found during the study. Good and excellent categories of coral reefs condition had higher species richness and individual abundance of target reef fish, while lower in fair category. Seven target reef fish species have a wide distribution, while other 15 species were limited. In general, target reef fish community at four tiny islands coral reefs had high species diversity and evenness indexes with low species dominance value. It can be concluded that target reef fish community in the area in stable or in steady state condition.

Functional diversity of fishes in the Minjiang Estuary, Southeast China

Based on samples collected by bottom trawl in May, August, November and December 2016 in the Minjiang Estuary, species richness and functional diversity of fishes, as well as their spatial-temporal variations, were quantified by a trait-based approach. The functional diversity varied with the changes of species richness. The species richness averaged across all stations were (17.8±5.1) species in spring, (22.4±5.6) in summer, (17.7±6.3) in autumn, and (12.1±2.3) in winter. Functional diversity also showed seasonal variation, with the highest in summer as (33.94±28.70), followed by (9.93±8.83) in winter, (11.30±7.55) in spring and (19.05±19.32) in autumn. The key functional species varied seasonally, as Setipinna taty contributing to 26% of the total functional value in spring, Polydactylus sextarius at 26% in summer, Harpadon nehereus climbing to 69% in autumn, and Collichthys lucidus at 38% in winter. The seasonal variations of fish species function were determined by life history and its interaction with other species.

Potency of reef fishes in Tuhaha bay waters, Central Maluku Regency, Maluku Province, Indonesia

The research aimed to provide data on taxa composition, density, standing stock and potency of reef fishes at Tuhaha bay waters in 2017. There were 35 families, 105 genera and 243 species of reef fishes found in Tuhaha bay. Four areas of coral reef at good until excellent categories and various habitat had high species richness of reef fishes. Species richness, density and standing stock of major reef fishes species were higher than target and indicator species. Potency (biomass) of economically food fish (target species) ranged from 1.65 - 5.59 tons ha−1 of coral reef (total 2.93 tons ha−1). Total potency, Maximum Sustainable Yield and Allowable Total Catch of economically food fish in 389,70 ha of Tuhaha bay coral reef area were 1,141.82, 590.91 and 456.73 tons, respectively. The status of reef fishes in two coral reef areas belonged to a high category, while the other nine areas had a moderate category.

Changes in a Fish Community in a Small River Related to the Appearance of the Invasive Topmouth Gudgeon Pseudorasbora parva (Temminck & Schlegel, 1846)

In recent years, the topmouth gudgeon (Pseudorasbora parva) has been one of the most invasive fishes in Europe. Pseudorasbora parva can potentially affect ecosystems, fish communities, and particular fish species. Electrofishing was carried out over a five-year period at three study sites in the Ciemięga River (eastern Poland) before and after P. parva had been found in the river. Changes in the occurrence, abundance, and density of native fish species after the appearance of the invader were determined. Changes in the species’ richness were calculated, and correlations were estimated between the occurrence and density of P. parva and particular fish species and richness indices. The presence of P. parva has not affected the density of native species but coincides with a significant increase in estimated species richness and the total density of fish. There was a significant relationship between the presence of this invasive species and the fish community’s composition, though the PERMANOVA result was unclear with regards to site-specific effects. Moreover, tench and bleak were associated positively, whereas Eurasian perch and sunbleak were associated negatively with the occurrence of P. parva. Pseudorasbora parva density was highly correlated with Cyprinidae density (excluding P. parva), species richness, and the Margalef diversity index. Thise study has shown that the presence of predatory fish in the river (Salmo trutta L.) may reduce the numbers of invasive P. parva.