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

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

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

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

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

Species-specific spatial distribution in relation to environmental characteristics underpins the species diversity of coral reef fishes. This study aimed to elucidate (1) the broad-scale spatial distribution (spatial variation of fish density at intervals of several-kilometers), influenced by topographic features (exposed reef vs. inner reef), substrate characteristics and depth, and (2) the microhabitat associations (habitat association within several centimeter scale) concerning substrate availability for seven angelfish species (family Pomacanthidae) in an Okinawan coral reef. Broad-scale analysis revealed (1) Chaetodontoplus mesoleucus was primarily found in deep inner reefs with greater coverage of branching Acropora and dead coral; (2) Centropyge bicolor and C. tibicen were primarily found at shallow inner reefs with greater coverage of branching Acropora, dead coral, and sand; (3) C. ferrugata and C. vrolikii were primarily found at shallow exposed reefs with greater coverage of rock, and (4) C. heraldi and Pygoplites diacanthus were primarily found at deep exposed reefs with greater coverage of rock. Microhabitat-scale analysis revealed that three species (C. mesoleucus, C. bicolor, and C. heraldi) showed significant positive association with acroporid corals. Centropyge tibicen showed a significant positive association with living corals. The remaining three species (C. ferrugata, C. vrolikii, and P. diacanthus) did not show a positive association with living corals. This suggests that coral loss impacts angelfish population in a species-specific manner. These two spatial scale viewpoints offer valuable insight for comprehensive understandings of angelfish spatial distribution in relation to substrate characteristics. [ABSTRACT FROM AUTHOR]

Freshwater fish diversity reaches its zenith in large tropical rivers. Although the origins of this diversity have been relatively well studied, the mechanisms that maintain high fish diversity in tropical rivers remain largely unknown. It has been hypothesized that the annual flood pulse, a perennial feature of many lowland rivers in the tropics, reduces competitive exclusion and consequently promotes species coexistence. During the high-water season, superabundant allochthonous resources and relatively low fish density may reduce intra- and interspecific competition. During the low-water season on the other hand, resource availability is low and predation pressure high, offsetting competitive differences between species and controlling fish population sizes. Here, we tested the potential role of these mechanisms for species coexistence using a food web model where fish species exhibit strong differences in competition strength and compete for finite resources. We simulated fish interactions when a regular flood pulse was either present or absent. We found that extinction rates in the simulations without an annual flood pulse were consistently higher when compared to those with a flood pulse, indicating more species could coexist when a regular annual flood pulse is present. If the flood pulse is a relevant mechanism for fish species coexistence, as our model results suggest, then flood pulse changes could result in species extinctions and lower fish diversity. Deforestation, climate change, and the construction of large hydropower dams are current drivers of hydrological change across the tropics, increasing the urgency to understand the role of natural flooding regimes for the maintenance of tropical freshwater fish diversity. [ABSTRACT FROM AUTHOR]

Many freshwater ecosystems worldwide are threatened by increasing water turbidity and extensive submerged aquatic vegetation (SAV) loss, with potential consequences on aquatic communities. Such changes in water quality and habitat features affect the relative abundance of species in the community and/or the composition of ecological guilds altering the trophic network. Here, we estimated the relationship between fish species and both SAV abundance and water quality in Lake St. Pierre (Québec, Canada), a shallow fluvial lake of the St. Lawrence River. To explain the association between the fish community and environmental variables, we performed multiple linear regressions on fish abundance, species richness, and Shannon diversity calculated at 133 stations, along a gradient of turbidity, temperature, and SAV abundance. In addition, we estimated the relationship between dominant fish species abundance and environmental variables by using canonical correspondence analysis (CCA). Species richness and abundance were positively related to SAV. Turbidity was negatively related to fish abundance, but had an unexpected positive effect on diversity (Shannon and species richness). By quantifying the association between fish species and habitat features, this study contributes to a better understanding of mechanisms structuring fish communities in changing environments. [ABSTRACT FROM AUTHOR]

We investigated the temporal dynamics of population genetics of the Chinese longsnout catfish (Leiocassis longirostris) given wild population decline due to anthropogenic disturbances such as overfishing in the upper Yangtze River. We compared genetic variation and structure between five age classes (1, 2, 3, 4 and 5 years old) using the mitochondrial DNA (mtDNA) control region and 12 microsatellite markers. The five age classes had high haplotype diversity (h = 0.8743) and nucleotide diversity (π = 0.0082) inferred from the control region, and observed heterozygosity (HO = 0.7342) and polymorphism information content (PIC = 0.6764) inferred from microsatellites. Low genetic distances based on the control region and the median-joining network representing a widespread distribution of haplotypes identified close genetic relationships between age classes. The results of AMOVA and pairwise fixation index (FST) using microsatellites demonstrated the significant genetic differentiation between age classes and FST was mostly low but significantly different between age classes (P < 0.05). Overall, L. longirostris in the upper Yangtze River has maintained considerable genetic diversity, but temporal genetic instability was detected between age classes. With the implementation of a ten-year fishing ban in the Yangtze River from 2021, it is expected that genetic differentiation between age classes will gradually decrease with the recovery of fish resources, and future genetic monitoring of L. longirostris populations is recommended. [ABSTRACT FROM AUTHOR]

The ichthyofauna of a large lake located in one of the biggest urban centers in Southern South America was studied for 15 years. Variations in ichthyofauna composition by sampling site and period, as well as the influence of abiotic parameter variations on the fish community, were tested through multivariate statistical analysis. Likewise, alterations in abundance of morphological anomalies by species, sampling site, and sampling period were verified. Fish community structure alterations demonstrated dissimilar levels of environmental quality in different areas, with sampling sites 1 and 4 considered the poorest and sampling sites 2 and 5 the highest environmental quality areas of the lake. Concerning temporal alterations of the fish fauna, species richness varied significantly, and non-native species emerged in the lake along the studied years. Statistical analysis pointed to a significant abundance of morphological anomalies occurring during four periods, as well as in all sampling sites; however, the highest abundance of anomalous specimens and anomaly types had been recorded for sampling site 1, reinforcing its low environmental quality. The use of different parameters of fish community structure and the observation of morphological alterations' occurrence in integrative analyses can be an accurate tool to diagnose spatial and temporal discrepancies in aquatic environment quality. [ABSTRACT FROM AUTHOR]

Fish species richness is one of the most common descriptors of aquatic biodiversity and an important indicator of the ecological condition of stream reaches and regional biological diversity. However, inadequate sampling effort underestimates the true number of species and, consequently, might provide erroneous information about the ecological conditions of, and trends in, aquatic environments. We sampled 24 to 39 stream reaches (each 150 m long) in seven megadiverse hydrologic units in the Brazilian states of Pará (Amazonia biome) and Minas Gerais (Cerrado biome) to estimate the sampling effort needed to reach asymptotes at hydrologic unit spatial extents. We also estimated how much of the local richness would have been captured if the sampled reach was 50 or 100-m-long. Our results indicate that up to 53 reaches must be sampled per hydrologic unit for attaining an estimated 90% of the fish species richness, depending on the relative number of rare species. In most units, 100-m-long reaches suffice for collecting about 90% of the local sampled richness. We conclude that the effort frequently used in neotropical streams is adequate to capture most of the local fish fauna. However, complete inventories of hydrographic regions would only be feasible with efforts and resources far greater than those commonly employed. Before sampling programs are implemented for estimating true species richness, adequate levels of sampling effort should be assessed wherever that richness is expected to be high. [ABSTRACT FROM AUTHOR]

Coral reef fishes perform a range of vital ecosystem functions, and can serve as indicators of ecological stress and resilience. However, many species are not observed when using Underwater Visual Census (UVC) during biomonitoring, and therefore overall biodiversity is often underestimated. Environmental DNA (eDNA) is proposed as an advanced and non-invasive next-generation biomonitoring method for determining the presence of aquatic organisms such as fish. Therefore, this study aimed to assess the community structure of coral fish from three different marine protected area reef zones (utility zone, open access zone, core zone) around Lombok Island using eDNA metabarcoding. Biological community composition, richness, and diversity were evaluated based on reads from mid-column water and sediment samples. A total of 58 species were identified from the eDNA samples using the Multiplex Barcode Research And Visualization Environment (mBRAVE) pipeline. The Shannon–Wiener index (H') showed significantly higher species diversity in the core zone than the utility and open access zones. There was no significant between-zone difference in community structure (ANOSIM, R = 0.11 < 0.25). NMDS analysis using the Bray–Curtis test showed significant between-zone differences in species diversity and abundance (PERMANOVA Adonis Pr (> F) = 0.001, p < 0.05). Based on the high number of fish species detected in this study, eDNA can be recommended as an alternative tool or as a complement to visual survey methods for biological monitoring and diversity assessment of remote reefs, with less stringent requirements in terms of field conditions (e.g. visibility) and taxonomic expertise. [ABSTRACT FROM AUTHOR]

The order Characiformes is one of the most diverse and widely distributed groups of fishes in cis-Andean basins. That diversity is reflected in the São Francisco River (Brazil), where approximately 1/3 of all described species belong to that order, with many being endemic and/or considered endangered. The great morphological diversity observed in this group has been the focus of several systematic, ecomorphological, and evolutionary studies. Here, we evaluated the morphological patterns of 39 species of Characiformes from the São Francisco River using geometric morphometric and comparative phylogenetic techniques to better understand how ecological factors can modulate morphological diversity. Our data produced a highly supported topology revealing two promoters that drive the diversity of the analyzed forms, one is associated with phylogenetic inheritance, while the other is modulated by habitat, generating similarities between phylogenetically distant species. The absence of any observed relationship between body shape and trophic niche may reflect phylogenetic inertia of food preferences and morphological characteristics. Our data highlights the importance of combined analysis of all available evidences for understanding the evolutionary routes of diverse groups, as is the case of the Characiformes of the São Francisco River. [ABSTRACT FROM AUTHOR]

We studied predatory fish species in relation to the biodiversity of fish assemblages and environmental variables at 511 sites in small and mid-sized rivers at the eastern edge of the European continent. The studied region has a high geographical and environmental heterogeneity. The impact of environmental factors on species occurrence was analyzed with generalized linear models. The main influential environmental factors on the occurrence of predatory fish species were elevation and the width and depth of the river. For the first time for a large area of Eastern Europe, optimum points and niche breadths for predatory fish species along width, depth, and velocity gradients were estimated. The width of the ecological niche can vary significantly both between different species of fish and within the same species for certain factors. Our results identify the bioindicative potential of predatory fish species in river ecosystems in this, sometimes overlooked, the eastern part of the continent. We found that the probabilities of occurrence of pike, burbot, pikeperch, and asp were close to zero when the Shannon index was less than 1 and the number of fish species was less than 5. The probability of occurrences of perch was 100% if the number of fish species in the site was more than 15. [ABSTRACT FROM AUTHOR]

The Niagara River, which connects two Great Lakes (Erie and Ontario) and forms a border between Canada and the United States, has experienced decades of abiotic and biotic disturbance as well as long-term restoration efforts. Given the iconic riverscape and importance as a binational fisheries resource, a biodiversity assessment of the mainstem Niagara River fish assemblage is overdue. Here, fish assemblage and habitat data from a standardized boat electrofishing program of the Niagara River were combined with species trait data related to substrate associations, diet preferences, reproductive strategies, and body size to quantify biodiversity patterns among river sections (sites above and below Niagara Falls), seasons (spring, summer, fall), and years (2015–2017). Sixty-five species were captured representing a variety of trait combinations. Significant differences in functional dispersion and divergence (i.e., functional diversity) were observed between river sections, seasons, and (or) years. The fish community captured in the lower river in spring 2015 had both the highest average functional dispersion (2.08 ± 0.32 SD) and divergence (0.88 ± 0.04 SD) compared to the other seasonal sampling efforts, but relatively few fishes were captured (n = 686). Although non-native fishes represented a small portion of the catch over the 3 years (8.6% of catch), the seasonal presence (spring and fall) of mostly introduced large-bodied salmonids expanded functional trait space in the lower river during these periods. The importance of rare species on functional diversity metrics suggests further insight on local species detection probabilities is needed to understand if differences in functional diversity reflect ecological patterns or are driven by sampling design. [ABSTRACT FROM AUTHOR]

Species conservation requires a clear understanding of habitat availability and subsequent use of those habitats. In cases where species declines have occurred and gone undetected by conservation managers, habitat alteration, fragmentation, and loss are often the largest contributors. River fragmentation often results in altered flow regimes, subsequently impacting the availability of riverine habitats. Blue sucker (Cycleptus elongatus) is associated with riffle and run habitat, which is especially impacted when river flows are altered. The goal of this research was to identify the extent of blue sucker habitat and mobility of the species in the Colorado River, Texas. To understand habitat selection and use, blue suckers (N = 49) were surgically implanted with telemetry tags. During 2015–2017, thirty-eight attempts were completed to relocate individuals. Optimized hotspot analysis identified three river reaches critical for blue suckers that accounted for 20% of the study area. Blue suckers used these locations year-round including during spawning. Habitats used by blue sucker were composed of gravel, cobble, boulder, and bedrock typically in riffle and run habitat. Mobility, as measured by home range size, increased as riffle density decreased. Larger home ranges were presumably necessary to find habitat to complete aspects of their life history. Results of this study suggest suitable habitats are limited throughout the fragmented riverscape. Conservation action in the form of habitat construction or increased stream connectivity through barrier mitigation could have positive impacts on the future of blue suckers in the lower Colorado River, Texas. [ABSTRACT FROM AUTHOR]

Large dams disrupt river ecosystems, causing negative effects on fish assemblages. Few studies, however, have investigated how Neotropical fish diversity responds to river regulation in longer temporal scales. In this study, we used a multi-metric approach to investigated temporal changes in taxonomic and functional fish diversity over 15 years-period following the construction of a large dam in the Upper Tocantins River, Amazon. We analyzed biological and environmental data collected in the impounded area before (2000–2002) and after (2003–2014) river regulation. Diversity metrics responded differently to the impoundment. Some metrics were not affected, as they showed little variation over years, such as fish abundance, species, and trait richness. Other metrics changed significantly between periods, such as taxonomic composition, temporal beta diversity, and trait abundance. Species with traits that are sensitive to hydrological alterations declined in the impoundment, while sedentary species were favored. Assemblage trajectories were variable, but community structure developed into a different state in the impoundment. Landscape variables explained changes in fish dissimilarity over time. In general, our study supports the notion that fish diversity in Amazonian rivers is vulnerable to river damming, but also indicates that different metrics show particular responses to this disturbance. [ABSTRACT FROM AUTHOR]

A comparison of fish diversity was carried out among 45 sites within four localities in the Mexican Tropical Western Atlantic (TWA) and Tropical Eastern Pacific (TEP) regions. Several taxonomical and functional diversity indices were considered, and their relationships with the coral cover were investigated in each locality. We found that despite a lower number of species, the localities within the Mexican TEP region had equal or even higher functional diversity than the localities in the Mexican TWA region where sites within the Caribbean Sea appeared particularly poorly diversified. Divergent relationships between fish diversity and coral cover were observed between the two oceanic regions. On the one hand, it tended to be positive in the TWA, and on the other hand, it was negative in the two TEP localities. This contrast may be explained by the low coral species richness and the homogeneous habitat (low structural complexity) provided by a high cover of coral in the TEP. This study highlighted how the fish assemblages can be functionally diversified within the TEP, a region generally considered poorly diversified, and how the relationship between fish diversity and coral cover may vary between oceanic regions. [ABSTRACT FROM AUTHOR]

Fish and benthic invertebrates are important groups that inhabit shallow coastal areas. Many studies use these two groups separately to answer questions related to environmental relationships, but few assess the correlation between these two groups. This study aimed to assess correlation between richness and composition of fish and benthic invertebrate assemblages and to evaluate their responses to environmental variables in sandy beaches in a tropical coastal area in south-eastern Brazil. We tested for a correlation between fish and benthic invertebrates and evaluated which environmental variables influenced each group. Fish and invertebrate taxonomic richness were not correlated across sites. In addition, the two groups were not significantly correlated, even after controlling the effects of the environmental variables. The taxonomic richness of the two groups were influenced by different set of environmental drivers: fish were influenced mainly by the physicochemical variables, being positively correlated with salinity and dissolved oxygen, and negatively with temperature, whereas invertebrates richness were related mainly to granulometric variables, decreasing in fine and very fine sediment. Fish and invertebrate showed similar patterns with more influence of environmental variables than biotic variables that had comparatively more effects on the invertebrate than on the fish assemblage. Spatial segregation in species distribution along the beaches were found with the Gerreid fish predominating in semi-exposed beaches whereas the sparid Diplodus argenteus, the haemulid Orthopristis ruber and the clupeids Harengula clupeola and Sardinella brasiliensis predominated in the exposed beaches. The Polychaetae families Syllidae and Dorvilleidae, and isopod of the family Cirolanidae predominated in semi-protect beaches, whereas polychaetas of the families Glyceridae and Saccocirridae predominated in the exposed beaches. In this study, we showed that fish and benthic invertebrates are influenced by different environmental variables in tropical sandy beaches and no significant correlation was found between these two taxonomic groups. Our findings are a step to a better understanding of the fish-benthic invertebrate relationship and a contribution to management policies aiming the conservation of tropical coastal areas. [ABSTRACT FROM AUTHOR]

The Lower Mekong River and its three major tributaries, the Sekong, Sesan, and Srepok rivers, are systems with high aquatic biodiversity that now face impacts from new hydroelectric dams. Despite the ecological, economic, and cultural importance of the freshwater biota, knowledge about aquatic ecology in this region remains poor. We used morphological and stable isotope data to explore how fish functional and trophic diversity vary between the four rivers that comprise the Mekong-3S river system. During our field surveys, the Sesan had experienced greatest flow alteration from dams and had lowest taxonomic and functional diversity, with species less packed and less evenly dispersed within morphological space compared to the other rivers. The Sekong had greatest functional diversity, with species less packed in morphological space. Species in the Mekong and Srepok were more evenly distributed in morphological space and had intermediate levels of functional diversity. Isotopic niche diversity in the Sesan did not appear to be significantly different from the Srepok and Sekong rivers. Conversely, the more species-rich Mekong fish assemblage encompassed a greater isotopic space with species less packed and evenly distributed. Greater trophic redundancy was observed amongst fishes of the 3S rivers than the Mekong. Species functional redundancy could buffer river food webs against species loss caused by dams; however, additional traits and niche dimensions should be evaluated to test this hypothesis. Overall, morphological and isotopic evidence from the Mekong and 3S rivers indicate that river impoundment and flow regulation function as an environmental filter that reduces fish functional diversity. [ABSTRACT FROM AUTHOR]

Habitat characteristics play an important role in determining the structure of fish communities. The decline in fish diversity and abundance with the decline in coral diversity and cover may be explained by habitat specialisation and partitioning among reef fishes and/or preferences for particular corals that are susceptible to disturbance. These preferences may develop at different life history stages. Here, we investigated patterns of habitat specialisation and ontogenetic shifts in habitat preference among 14 co-existing damselfish species at Lizard Island lagoon on the Great Barrier Reef. Although live coral cover contributed only 26% of the substratum, 28% of adults and 57% of new settlers were mostly found on live coral, indicating a strong preference for live coral habitat by new settlers. Only a few species exhibited a high degree of habitat specialisation and low overlap in habitat use with other species. Specialisation differed among species and life stages. New settlers were more commonly associated with finely branched corymbose corals and using those habitats with higher frequency than expected based on habitat availability alone. Adults were more commonly linked to more open branching morphologies or non-coral substrata. Our results suggest that habitat loss may not uniformly impact on all life stages. While adult individuals may not be as reliant as juveniles on corals, detrimental effects of habitat loss on juvenile survival may have longer-term impacts on adult populations. As juveniles show preferential associations with particular coral species, such as corymbose corals, the loss of these growth forms is likely to have the most significant negative impacts on this critical life history stage. [ABSTRACT FROM AUTHOR]

The Amazon basin has a freshwater fish diversity comparable to a tropical sea. Although many Amazonian fish species are popular ornamental fish across the world, the ecology of most species in their natural habitat remains poorly known (van der Sleen and Albert 2017). We report on shoaling behavior in Platydoras hancockii in a floodplain forest of the middle Rio Negro, Brazil. As the shoal consisted of only adult males, whereas gravid females were caught individually in nearby areas, we hypothesize that this aggregation may relate to spawning. Moreover, considering that Platydoras hancockii is capable of producing sounds, it is possible that these aggregations entail the formation of a chorus-like call with the function of attracting females from a larger area. [ABSTRACT FROM AUTHOR]

Assessment of headwater biodiversity is essential for maintaining upstream downstream ecosystem services of rivers. Fish biodiversity assessment was conducted in the headwater tributaries of the glacial-fed Tamor River and rain-fed Kamala River in eastern Nepal. A total of eight sites were sampled. pH, dissolved oxygen, conductivity and temperature were estimated using multi-meter field probe. Standard electrofishing was conducted for fish sampling with two rounds of fishing for 20 min each at site. Catch per Unit Effort (CPUE) was calculated for each sample and the samples were identified in the field itself following standard literature. Unidentified samples were brought to the laboratory for further identification. Descriptive statistics was performed; Species richness, Shannon Weiner Diversity and Simpson’s Diversity Index were estimated. One way ANOVA and an independent t test were performed respectively to look at the variation in fish abundance between seasons and between the tributaries of the Tamor River and the Kamala River. Threat status categories of the fish species was compared with those of IUCN. pH was neutral to alkaline in both the types of streams. Significant variation (p = 0.01) in seasons as well as between two types of headwater tributaries were observed in pH, temperature and conductivity. Temperature and conductivity were significantly higher in the rain-fed tributaries. These parameters were significantly higher during the pre-monsoon and lowest during the winter in both types of streams. A total of 8940 fishes belonging to four orders, 10 families, 26 genera and 34 species were enumerated. Significant variation in Shannon-Weiner Diversity Index (p = 0.015) and Species Richness (p = 0.005) between the glacial fed and rain fed streams with higher values of these indices in the rain fed tributaries. Fish abundance also varied significantly (p = 0.02) between seasons in the Tamor’s tributaries with higher abundance in the pre-monsoon and lowest during the winter. Cypriniformes was the most dominant taxa with Schistura beavani (26.14), Barilius vagra (8.46) and Garra gotyla gotyla (7.63). Schizothorax richardsonii (10.31) and Schistura beavani (47.19) were the most dominant species in the Kamala’s and the Tamor’s tributaries. These findings indicate that fish assemblages reflect the different ecological regimes of the glacial-fed and rain-fed headwaters. The findings of this study contribute to the knowledge of fish diversity and also compliment the threat status of the IUCN fish data. Replication of similar studies encompassing temporal and spatial scales is necessary for the development pf effective conservation strategies. [ABSTRACT FROM AUTHOR]

The trophic structure of the fish community ecosystem in the Terminos Lagoon (southern Gulf of Mexico) has shown a range of functional changes. The description of the heterogeneity of functional traits in a biological community allows the identification of the relevant functions in an ecosystem. An analysis was conducted of the functional traits (trophic level, reproductive and trophic guild, habitat, estuary use, essential habitat, salinity tolerance, body shape, mouth type, caudal fin type, and maximum length) of the fish community of the lagoon for three different years (1980, 1998 and 2011). We developed a new index to analyze the variation of functional diversity called the functional traits diversity index ( FADI). This index takes into account the abundance of traits and emphasizes less common traits (i.e., those that are less redundant). The functional redundancy was different in the three periods studied. The FADI value for 1998 was the highest and was outside of the expected probability distribution, indicating a greater abundance of species with unique functional traits. A principal components analysis was performed to assess the relative contribution of functional traits to the overall variance of functional diversity over the three periods. We found that the trophic level, body shape, and mouth type were the most influential traits in the functional diversity changes. The environmental changes were correlated with the variability of the functional structure. Depth was the most influential environmental variable in the principal component analysis. The results indicate a reorganization of the functional structure of the fish community in the Terminos Lagoon. The FADI was helpful in explaining these changes observed throughout the three periods studied. [ABSTRACT FROM AUTHOR]

Headwater fishes in the southeastern United States make up much of the fish biodiversity of the region yet many are imperiled. Despite this, the specific habitat requirements of imperiled headwater fishes in lowland Coastal Plain streams have rarely been quantified. Using data collected over three years of seasonal sampling we provide estimates of the microhabitat requirements of the imperiled Yazoo darter ( Etheostoma raneyi Suttkus and Bart), a small benthic insectivore. Our results indicate that the species is a microhabitat specialist and that optimum microhabitat within degraded contemporary streams consists of a narrow range of water depths (about 20-30 cm), current velocity ≥ 0.25 m·s, complex stable debris piles, rooted macrophytes, and likely coarse substrate. No pronounced or generalized seasonal shifts in microhabitat use occurs, and no evidence exists for intraspecific partitioning of microhabitat. Though stable and complex instream cover is one of the most important variables explaining variation in microhabitat use by Yazoo darters, such cover is rare in the degraded streams within the range of the species. Current conservation classifications of the Yazoo darter by governmental agencies and nongovernmental organizations as well as associated management plans that are based on the assumption that Yazoo darters are habitat generalists should be reviewed in recognition of the increased risk of decline because Yazoo darters are microhabitat specialists. These considerations should also be extended to other closely related imperiled species of snubnose darters. [ABSTRACT FROM AUTHOR]

Tidepools are considered ecosystems of high interchangeable fish biota. However, natural and anthropogenic actions that alter negatively marine ecosystems functioning (e.g., algal exploitation) are causing homogenization of fish biodiversity. Here, we describe the functional and taxonomic assembling of fishes in beach rocks of northeastern Brazil. Traits of fish species were retrieved from Fishbase and beta diversity was assessed by the dispersion of abundance, presence-absence and functional diversity in the multivariate space. We explained spatial-temporal variation in: alpha diversity, taxonomic and functional community composition; as well as temporal variation in functional, beta and gamma diversities. We found an annual stability in fish diversity and composition, and that fish biota was assembled mainly per tidepools' depths. Substrate heterogeneity was correlated to depth, highlighting the role of local features as filters to organize the fish fauna vertically in tidepools, especially a cultivation of algae that influences the local assembling. We also highlight the uniqueness status of beach rocks in the Brazilian tropical region. [ABSTRACT FROM AUTHOR]

Studies on morphological differences among populations from different ecological regions help towards understanding diversification of traits and is a fundamental step in adaptive radiation and ultimately, speciation. This study investigates the occurrence of variations in morphological traits among wild populations of zebrafish ( Danio rerio) from India that inhabit a variety of habitat and ecological regimes. Geometric morphometric methods and traditional morphometric analysis were used to quantify the extent of differences in morphological traits between four populations of wild D. rerio from still-water (stagnant) (Kalibazaar, in West Bengal) and slow -medium flowing (Asan, Kaushalya and Seripetkalwa in Uttarakhand, Haryana and Andhra Pradesh respectively) habitats within India. Multivariate analyses showed significant effect of populations on morphology, post-hoc paired comparisons between populations show differences in body size as well as shape across these populations. Relative warps analyses on the landmarks selected for body shape showed higher loadings for caudal peduncle, head and eye regions. Population-wise scatterplots along relative warp1 (RW1)- relative warp4 (RW4) axes revealed Asan population cluster expands beyond the other population clusters along the RW1- RW2 axes, while the Kalibazaar cluster spreads out from the others along the RW3-RW4 axes. Multiple regression models to predict relation between shape and ecological attributes indicate the strongest role of dissolved oxygen, stream velocity and abundance of predators in explaining variations in morphology across these populations. This is significant as a first study utilising the tools of morphometric analyses in Danio rerio and indicating the role of multiple (biotic and abiotic) selective forces in shaping phenotypic variations in morphology. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effects of physical characteristics on fish assemblages. To this end, we studied 42 lakes distributed in two river basins of the Brazilian Pantanal: the Negro River basins in the South Pantanal and the Cuiabá River basins in the North Pantanal. We hypothesized that fish diversity and composition change significantly between these basins in response to physical differences and landscape structure (the geographical position of the basins). The alternative hypothesis was that local assemblages are distributed randomly between the two basins because of a regional homogenizing factor in the system. Our analysis suggests that the physical characteristics (lake area, depth and distance from the river margin) and the effect of geographical position of the basin were the main factors determining the organization of fish assemblages in these basins. This would indicate that regional fish diversity is not uniform over large areas of these Pantanal floodplains, but that communities close to each other are more similar than those that are further apart. Although there was a small variation between the lakes, this was not sufficient to affect the communities of both basins, either in composition or in diversity. Our study also supports the hypothesis that fish assemblages in the littoral zone of the Cuiabá River are richer and more diverse than assemblages in the corresponding area of the Negro River and that these differences are related to landscape characteristics. Hence, our results strongly suggest that area lake, depth, position of the basin, and smaller contribution of distance from the river margin are the key factor determining fish assemblage structure in floodplain lakes in the Cuiabá River and Negro River basins. [ABSTRACT FROM AUTHOR]

Release of captive bred individuals into the wild is now a conservation management approach to increase the depleted natural wildlife populations. Such method has been initiated for conservation of wild fish population on Qinghai Tibetan Plateau (QTP), a region of high level of species endemism. Platypharodon extremus is an endemic schizothoracine fish species and a dominated species in the plateau water ecosystem of the QTP in the past, it is now enlisted as an endangered species. However, phylogenetic and genetic information have not been previously considered in the ongoing stock enhancement program. In this study, genetic and demographic processes of the populations across the distribution of this species were assessed, using the mitochondrial DNA control region and Cyt-b. We found that all populations displayed low nucleotide diversity suggesting severe historical bottleneck events and high haplotype diversity indicating recent population expansion. Both the phylogenetic tree and the minimum spanning tree showed no significant genealogical structures corresponding to sampling locations. Population histories including bottleneck, exponential expansion and the absence of population structure indicate that demographic processes highly influenced genetic variation within and among populations of P. extreums. The data presented is consistent with a historical bottleneck and recent population expansion for all four populations based on several complementary analyses of the genetic data and inferred from demographic history (0.26 to 0.36 Mya). This genetic variation and demographic processes should become the baseline information for evaluating genetic effects of stock enhancement program and ongoing conservation decision making. [ABSTRACT FROM AUTHOR]

The genetic structure and demographic history of nine mudskipper Boleophthalmus pectinirostris populations on the Northwestern Pacific coast were investigated using the complete mitochondrial cytochrome b sequences. Among the 248 individuals examined, 118 haplotypes were detected. As a whole, high haplotype diversity and moderate nucleotide diversity were observed within the populations. The topology of the neighbor-joining tree of B. pectinirostris haplotypes was assigned into two closely related lineages (A and B) that appeared to have strong geographic genetic structure. Lineage A included the populations from Jiangsu, Zhejiang, Fujian, Taiwan, Guangdong, Guangxi and Vietnam while Lineage B included populations from Japan and Korea. The pairwise comparisons of F were all statistically significant ( P <0.05) between populations while the analysis of molecular variance showed that most of the variances were found between the two lineages. Neutrality tests and mismatch distribution analyses revealed that B. pectinirostris had undergone population expansion during the late Pleistocene. Population expansion occurred approximately 170,000 years ago for Lineage A, and 80,000 years ago for Lineage B. Sea level changes during the late Pleistocene might have been responsible for this population expansion and lineage isolation. [ABSTRACT FROM AUTHOR]

Accurate determination of abundance and richness of fish early stages in estuarine zones is critical to support management and protection plans; it is therefore necessary to consider all influential factors. Habitat diversity, seasonality, moon phase and diel variations, and their interactions are factors that can affect richness and abundance estimations. Appropriate spatial and temporal scales in sampling design are important to understand the assemblage dynamics of fish early stages. The objective of this research is to test how temporal and spatial scales influence the determination of abundance and richness of fish early stages based on a hierarchical sampling design considering season (dry and rainy), moon phase (new, crescent, full, and waning), day period (sunrise, midday, sunset, and night), habitat (coastal, riverine, mangrove, and Vallisneria americana beds), and their interactions. Samples were collected using a conical zooplankton net and towed horizontally for 5 min at a depth of 50 cm. A variance component analyses model showed that day period, season, and their interactions were the main factors determining variations in fish early stage abundances and richness (26.68, 10.78, and 12.82 %, respectively). The highest abundance and richness occurred at night, with significant seasonal variations related to the runoff from the Grijalva-Usumacinta basin. Abundance and richness were higher in the dry season, which were related to higher dissolved oxygen and water transparency. Presented findings can be generalized to tropical and subtropical estuaries with shallow waters. [ABSTRACT FROM AUTHOR]

Lake sturgeon Acipenser fulvescens populations have experienced declines throughout much of the Great Lakes. Understanding key demographic characteristics about lake sturgeon populations can help identify potential limiting factors to their recovery. Within a single spawning season, there may be multiple spawning events, which could affect genetic diversity of the resulting cohort. Our objective was to determine whether multiple discrete spawning events resulted in a larger effective number of breeders and higher genetic diversity. Larval samples were collected following the spawning periods in 2005 ( n = 479) and 2006 ( n = 279). In 2005, there were two discrete spawning events and a longer spawning season; in 2006, the spawning events were less discrete and the spawning season was shorter. Genetic samples from larval sturgeon were analyzed at 12 microsatellite loci. The effective number of breeders (N), genetic diversity (observed heterozygosity, expected heterozygosity, allelic richness, inbreeding coefficient), and relatedness were measured for each cohort. The effective population size (N) and genetic diversity were also measured in the adult population ( n = 85). The larval cohorts had a high N (2005: 54; 2006: 73) relative to the N of the adult population (N = 28). Multiple spawning events did not result in more breeders, but did result in lower relatedness among the resulting offspring. Therefore, environmental factors should be maintained that encourage an extended spawning season, increasing the likelihood of multiple spawning events and decreasing the relatedness among individuals in the cohort. [ABSTRACT FROM AUTHOR]

Biodiversity continues to decline at a range of spatial scales and there is an urgent requirement to understand how multiple drivers interact in causing such declines. Further, we require methodologies that can facilitate predictions of the effects of such drivers in the future. Habitat degradation and biological invasions are two of the most important threats to biodiversity and here we investigate their combined effects, both in terms of understanding and predicting impacts on native species. The predatory largemouth bass Micropterus salmoides is one of the World's Worst Invaders, causing declines in native prey species, and its introduction often coincides with habitat simplification. We investigated the predatory functional response, as a measure of ecological impact, of juvenile largemouth bass in artificial vegetation over a range of habitat complexities (high, intermediate, low and zero). Prey, the female guppy Poecilia reticulata, were representative of native fish. As habitats became less complex, significantly more prey were consumed, since, even although attack rates declined, reduced handling times resulted in higher maximum feeding rates by bass. At all levels of habitat complexity, bass exhibited potentially population de-stabilising Type II functional responses, with no emergence of more stabilising Type III functional responses as often occurs in predator-prey relationships in complex habitats. Thus, habitat degradation and simplification potentially exacerbate the impact of this invasive species, but even highly complex habitats may ultimately not protect native species. The utilisation of functional responses under varying environmental contexts provides a method for the understanding and prediction of invasive species impacts. [ABSTRACT FROM AUTHOR]

The alteration of aquatic ecosystems and increasing aquarium fish trade with exotic species is promoting the presence and invasion of these species in large river systems, with the consequent loss of native biodiversity and the homogenization of aquatic systems. The Chontalcuatlan-Amacuzac hydrological system belonging to the biogeographical province of the Balsas River is one of the main regions in Mexico devoted to the breeding and rearing of aquarium fish, where the improper handling of these organisms has caused their escape to adjacent hydrological systems and, together with urban and industrial pollution, are changing schemas and levels of regional biodiversity. As a first approximation to determine these effects, we evaluate a segment of 140 km of this hydrological system through surveys in 12 sites during the time of major climatic and flow stability, and relating environmental variables with the distribution and abundance of fish. Also, the structure of fish assemblages was assessed by means of similarity and multivariate statistical methods (correspondence and principal components analysis), and these assemblages were found to be segregated by a thermal gradient. Exotic fish were dominant in conditions of low environmental quality, while native species were restricted to areas with better quality of water and geographic isolation. Exotic taxa such as Amatitlania nigrofasciata, Pterigloplictys disjunctivus, Pterigloplictys pardalis, Poeciliopsis gracilis and Heterandria bimaculata, have achieved the degree of invasive due to the fact that they are distributed of abundant manner in the entire hydrological system. [ABSTRACT FROM AUTHOR]

Predictive models have been used to determine fish species that occur less frequently than expected (decreasers) and those that occur more frequently than expected (increasers) in streams in the eastern U.S. Coupling life history traits with 51 decreaser and 38 increaser fish species provided the opportunity to examine potential mechanisms associated with predicted changes in fish species distributions in eastern streams. We assigned six life history traits - fecundity, longevity, maturation age, maximum total length, parental care, and spawning season duration - to each fish species. Decreaser species were significantly smaller in size and shorter-lived with reduced fecundity and shorter spawning seasons compared to increaser species. Cluster analysis of traits revealed correspondence with a life history model defining equilibrium (low fecundity, high parental care), opportunistic (early maturation, low parental care), and periodic (late maturation, high fecundity, low parental care) end-point strategies. Nearly 50 % of decreaser species were associated with an intermediate opportunistic-periodic strategy, suggesting that abiotic factors such as habitat specialization and streamflow alteration may serve as important influences on life history traits and strategies of decreaser species. In contrast, the percent of increaser species among life history strategy groups ranged from 21 to 32 %, suggesting that life history strategies of increaser species were more diverse than those of decreaser species. This study highlights the utility of linking life history theory to biodiversity to better understand mechanisms that contribute to fish species distributions in the eastern U.S. [ABSTRACT FROM AUTHOR]

Associations between the morphology of animals and their ecology have contributed to our understanding of phenotypic diversity by helping to relate form and function. Most early studies on fishes used traditional measurements of linear distances on the body or fins to quantify morphological variation among taxa. More recently, geometric morphometric analyses have gained popularity for assessing phenotypic shape variation. Along with new methodologies for quantifying morphological variation, researchers have become increasingly aware of the influence of phylogeny on morphological and ecological traits. Our study, which spanned seven cyprinid genera, assessed the abilities of traditional and geometric morphometric approaches to characterize ecologically relevant morphological variation. Furthermore, we compared morphometric approaches employing two analyses (partial Mantel test and Phylogenetic Canonical Correlation Analysis (PCCA)) that test for correlations among data sets while explicitly accounting for phylogenetic relationships. Traditional morphology and body shape showed similar correlations with habitat use in all analyses. In contrast, only traditional morphology was correlated with diet; however, this was only revealed by the PCCA. Our findings indicated the taxonomic span of species under study and the statistical treatment of data are important factors to consider when choosing between traditional or geometric morphometric approaches. In addition, a better understanding of phylogenetic relationships will improve our ability to establish associations between morphology and ecology. [ABSTRACT FROM AUTHOR]

Studies for location of breeding sites and early development areas of freshwater fish in subtropical basins are still incipient. Most of the existing knowledge is based on sampling in environments impacted by dams of hydroelectric power plants and studies in areas with characteristics similar to the original are lacking. In this way, this study evaluated the spatial distribution of the ichthyoplankton in a Conservation Unit (Turvo State Park, Rio Grande do Sul State, Brazil) on the subtropical basin of the Uruguay River, in a stretch with no hydroelectric power plants and at best preservation condition. The density distribution of fish eggs and larvae was evaluated quantitatively through plankton nets samples, while the analysis of the species composition of larvae was assessed qualitatively through plankton nets and light traps sampling. There were significant differences in two stretches situated inside the park separated by a waterfall, both in the distribution of eggs and larvae and in species composition of the larval assemblage. Our results indicate that periods without the total flood of Yucumã Falls influences the composition of the ichthyoplankton and the existence of two distinct reproductive environments over an approximate length of 50 km. This result supports the hypothesis that in subtropical basins the alternation of flood and dry periods can influence the structure of fish community and evidences the importance of maintenance of hydrological conditions to fish reproduction in this river section, because showed the importance of the habitat diversity in the river channel to fish recruitment. [ABSTRACT FROM AUTHOR]

Marine fishes reach their highest diversity in coral reef ecosystems, which they utilize as territory, place of refuge and reproduction, and source of food. One type of predation among reef fishes is feeding on coral polyps, and a single, easily identifiable family of fishes, Chaetodontidae, contains the majority of obligate corallivore species. Multiple studies have examined the behaviour and ecology of Chaetodontidae and their relationship with the benthic habitat. However, many questions remain about their feeding ecology and food specifity at the species level. The present study is the first attempt to systematically decipher the feeding behavior of the obligate corallivore, Chaetodon octofasciatus. Field data were collected from four sites in the Thousand Islands, Indonesia, during two sampling campaigns in 2006, covering two seasons and two different depths. A high abundance of C. octofasciatus was positively related to hard coral cover. Out of a total of 57 scleractinian coral genera observed during the study period, 24 were utilized by C. octofasciatus. All fish collected during the study ( n = 36) had >86 % nematocysts in their guts, supporting their classification as obligate corallivores. Based on the Strauss electivity index, C. octofasciatus displayed a preference for the coral genus Acropora at all depths, while preference for Fungia became more marked at greater depth. Both Acropora and Fungia were observed at high density at all sites, with Acropora density decreasing markedly with depth and Fungia density increasing. Bite rates showed an asymptotic relationship to Acropora density, levelling off between 15 and 20 bites/5 min. The existence of a strong relationship with live coral cover and the preference for specific genera such as Acropora designate C. octofasciatus as a potential bioindicator in the Thousand Islands reefs, while making it particular susceptible to the ongoing degradation of reefs in the region. [ABSTRACT FROM AUTHOR]

To examine regional specific diversity in development and growth of Ayu ( Plecoglossus altivelis) larvae, we collected and compared collections from the Kalong estuary in Vietnam, and the Shimanto and Muko estuary, and the Niigata coast in Japan. Among the four areas, most of the morphometrics through ontogeny were similar except that the snout tended to be shorter and the anus hardly migrated in Kalong larvae. The snout length increased gradually with growth in the Vietnamese larvae, while this value increased significantly until ca. 10 mm BL, subsequently being constant up to 30 mm body length (BL) in the Japanese larvae. The water temperature when the larvae were collected was higher in the Kalong than in most of the Japan sites. Growth-rates estimated from otolith increments were from highest to lowest, Niigata (mean = 0.54 mm/day), Kalong (0.47), Shimanto (0.38) and Muko (0.34). The higher growth-rates were obtained not in Niigata of highest latitudinal region, but in Kalong of lowest latitudinal region. This indicates that Ayu could experience their early developmental stages from the cool temperate to tropical regions, implying the potential biodiversity of this fish species in the world. [ABSTRACT FROM AUTHOR]

Large predatory fish that alter the behaviour of smaller species may affect visual estimates of abundance by making organisms more or less difficult to observe and quantify. To evaluate the non-consumptive influence of large predators on rocky reef fishes observed with Baited Remote Underwater Video (BRUV), we tested the hypothesis that fish assemblages monitored when large (ca 1.5 m) piscivorous sharks, Mustelus antarcticus, were present differ from those observed when sharks were absent. We did this in two ways using recordings from rocky reefs in Batemans Marine Park, NSW, Australia. First, we examined 6 min of each 30 min tape; 3 min when sharks were present and 3 min when they were absent, in a paired sample design from 17 sites. Second, we compared fish assemblages for complete tapes (30 min) at sites with sharks present compared to sites where they were absent. The diversity and total abundance of fishes was consistently lower in the presence of sharks; we detected significant assemblage-wide change (PERMANOVA, P < 0.05). Importantly, the diversity and total abundance of fishes for complete tapes (30 min) decreased in the presence of sharks by 18 % and 36 %, respectively, underscoring the likelihood that sharks influence observed fish assemblages. Individual species responses were variable and while the abundance of many fish species decreased in response to sharks, others increased 6-fold. Overall, these results highlight the need to consider systematic differences in the abundance of large predators to avoid biases when testing hypotheses about fish assemblages using non-destructive visual methodologies. [ABSTRACT FROM AUTHOR]

Turbidity, and associated sedimentation, is increasing in aquatic ecosystems globally and is thought to be a major driver of aquatic biodiversity loss. In this study, hatching success of Spotted Gar ( Lepisosteus oculatus), a Threatened species in Canada, is reported for eggs held under clear and turbid conditions. Spotted Gar embryos were held in either clear or mildly turbid water (∼5 NTU). Fertilized eggs held in turbid water exhibited a final 24 % reduction in hatching success by the end of the hatching period. Turbidity is identified as a potential threat for this species in Canada. The decrease in hatching success found here indicates that this early life history stage is particularly vulnerable to disturbance by turbidity and sedimentation. [ABSTRACT FROM AUTHOR]

Ecomorphological changes as a result of natural perturbations in estuarine fish communities were investigated in two South African estuaries (Swartvlei and East Kleinemonde), both before and after the loss of aquatic macrophyte beds in these systems. The fish communities were analysed using an ecomorphological diversity index (EMI) and the results compared to a traditional index, the Shannon-Wiener diversity index. The EMI revealed that the major changes in fish community composition recorded in both estuaries were associated with quantitative variations at the species level. Both estuaries essentially lost their macrophyte beds and ended up with the same type of bottom habitat (bare sediment). In both cases the fish morphological variability decreased immediately after aquatic macrophyte loss and then increased to end above the initial value. The ecomorphological analysis appeared to be sensitive to major ecological disturbances that occurred during the study period and this was confirmed by the morphospace configuration. The results indicate that the ecomorphology of the fish community responds to habitat changes and that this change corresponds to alterations in the representation of the different feeding types. These findings therefore contribute to the measurement of morphological changes in estuarine fish assemblages as a result of habitat changes within the ecosystem and we propose that ecomorphological analyses add another dimension to the information provided by existing diversity indices in studying changing fish communities. [ABSTRACT FROM AUTHOR]

The Yangtze Basin is taken as a case study to investigate statistically whether the hydrologic regime affects fish diversity. Jaccard's similarity index ( I) is used to characterize the fish species similarity of any pair of sample rivers. On the basis of the IHA (Indicators of Hydrologic Alteration) method, a series of hydrologic indicators, some of which are modified according to the practical hydrologic characters of the Yangtze Basin, are used to characterize the hydrologic regime. A new index, named the degree of the hydrologic regime difference ( I) is constructed to measure the difference between hydrologic regimes of any pair of sample rivers. An exponential model is used to estimate the correlation curve of I and I. We observed a negative relationship between I and I, which suggests that hydrologic regime affects fish diversity. [ABSTRACT FROM AUTHOR]

Icthyological results of four rapid assessment surveys are presented. The surveys were completed between 1997–1999 and were conducted at the following localities: Milne Bay (Papua New Guinea), Calamianes Islands (Palawan, Philippines), Togean–Banggai Islands (Sulawesi, Indonesia), and Weh Island (Sumatra, Indonesia). Surveys were conducted over periods ranging from 9 to 22 days and consisted mainly of underwater observations while scuba diving, supplemented with small rotenone and spear gun collections. Milne Bay was characterized by a high percentage of pristine reef environments and supported the largest number of species (1040). Diversity was generally lower at the Philippine and Indonesian sites due to more habitat homogeneity and higher fishing pressure, including the widespread use of illegal fishing methods, including cyanide and explosives. [ABSTRACT FROM AUTHOR]