Fish Assemblage Structure Research Articles

Fish community structure along altitudinal gradients with relation to environmental variables in Ratuwa River of Eastern, Nepal

Studies on fish community structure along altitudinal gradients of rivers are lacking in Nepal. This study was carried out to gauge the fish diversity and composition along elevational gradient in Ratuwa River. The altitudinal gradient varies between 70 m to 1300 m. Fish samples were collected based on habitat representativeness from April (spring) 10-18, July (summer) 10-18, October (autumn) 10-18, 2020 and January (winter) 10-18, 2021. A total of 3447 specimens representing 4 orders, 14 families and 36 species were identified. Both fish diversity and abundance of studied ichthyofauna vary with altitudinal gradient. The present study affirmed that fish species of Opsarius bendelisis, Schistura multifasciatus, Garra annandalei, Brachydanio rerio, Aspidoparia morar, and Schistura scaturigina are the major contributory species (>1%) for both space and time spectrums. Fish community structure testing for both to space and time showed significant difference in spatial spectrum (R=0.72, P<0.01) but no significant difference in temporal variation (R=-0.034, P>0.05). The present results hinted that fish assemblage structure varied significantly from low to high elevations, altitude, water temperature, water velocity, dissolved oxygen and pH was found as major influential factors (P<0.05) for species distribution.

The Combined Impact of Hydropower Plants and Climate Change on River Runoff and Fish Habitats in Lowland Watersheds

Aquatic ecosystems are particularly vulnerable to anthropogenic activity and climate change. The changes in flow regimes in Lithuanian lowland rivers due to the operation of hydropower plants (HPPs) and the impact of altered flow on some fish species have already been studied. The impact of climate change on future natural river runoff and the structure of fish assemblages was also investigated. However, it is still unknown how the combined effect of climate change and flow regulation related to hydropower generation may affect fish assemblages in the downstream river reaches below the Lithuanian HPPs. In this study, the physical habitat modelling system MesoHABSIM was used to simulate spatial and temporal changes in aquatic habitats availability for different fish species under the influence of HPP at different climate change scenarios. Changes in the available habitat were assessed for common fish species in four HPP-affected rivers representing different hydrological regions of Lithuania. The modelling results showed that the operation of HPP under climate change conditions in most rivers could be beneficial for small benthic fish species such as gudgeon Gobio gobio and stone loach Barbatula barbatula. Meanwhile, for larger fish species (e.g., chub Squalius cephalus and vimba Vimba vimba) the alteration in the temporal availability of suitable habitat was relatively higher.

Impacts of land use and hydrological alterations on water quality and fish assemblage structure in headwater Pampean streams (Argentina)

Impacts of land use and hydrological alterations on water quality and fish assemblage structure in headwater Pampean streams (Argentina)

Assemblage Structure of Larval Fishes in Epipelagic and Mesopelagic Waters of the Northern Gulf of Mexico

The early life stages of fishes play a critical role in pelagic food webs and oceanic carbon cycling, yet little is known about the taxonomic composition and distribution of larval fishes in the northern Gulf of Mexico (GOM) below the epipelagic (<200 m). Here, we provide the first large-scale characterization of larval fish assemblages in the GOM across epipelagic, mesopelagic, and bathypelagic regions (0–1,500 m), using samples collected during the Natural Resource Damage Assessment conducted following the Deepwater Horizon oil spill (DWHOS). These data contain > 130,000 ichthyoplankton specimens from depth-discrete plankton samples collected across 48 stations in the GOM during six cruises conducted in 2010 and 2011. We examined indices of abundance and diversity, and used a multivariate regression tree approach to model the relationship between larval fish assemblages and environmental conditions. The total abundance of larval fish followed a generally decreasing trend with increasing depth, and family-level richness and diversity were significantly higher in the epipelagic than mesopelagic and bathypelagic regions. Fourteen distinct assemblage groups were identified within the epipelagic, with depth, surface salinity, and season contributing to the major branches separating groups. Within the mesopelagic, seven distinct assemblage groups were identified and were largely explained by variation in depth, season, and surface temperature. Bathypelagic assemblages were poorly described by environmental conditions. The most common epipelagic assemblage groups were widely distributed across the GOM, as were all mesopelagic assemblage groups, suggesting limited horizontal structuring of GOM larval fishes. Of the mesopelagic-associated fish taxa, four dominant families (Myctophidae, Gonostomatidae, Sternoptychidae, Phosichthyidae) comprised the majority of the catch in both the epipelagic (63%) and combined mesopelagic and bathypelagic (97%) regions. Dufrêne-Legendre indicator analysis confirmed that these dominant families were characteristic of epipelagic and mesopelagic assemblages; the larvae of less common mesopelagic-associated families largely identified with epipelagic assemblage groups. A lack of baseline data about the distribution patterns of early life stages of mesopelagic fishes in the GOM was apparent following the DWHOS, and these findings provide a valuable reference point in the face of future ecosystem stressors.

Fish Assemblages in Seagrass (Zostera marina L.) Meadows and Mussel Reefs (Mytilus edulis): Implications for Coastal Fisheries, Restoration and Marine Spatial Planning

Seagrass meadows and mussel reefs provide favorable habitats for many fish species, but few studies have compared the associated fish assemblages directly and examined the influence of environmental variables. Knowledge of fish assemblages associated with disparate habitats is needed for the conservation of coastal fisheries and marine spatial planning. Catch per unit effort data derived from fyke nets showed similar species richness and diversity in seagrass meadows and mussel reefs, suggesting that both habitats support elevated marine biodiversity of mobile fauna. However, it was shown that fish assemblage structure differed between those habitats, and also fish abundance in seagrass meadows was significantly higher than in mussel reefs by comparing the data with a multivariate extension of Generalized Linear Models (GLM). Furthermore, employing underwater video recordings to compare fish abundances in high and low water current speed mussel reefs with a Generalized Linear Mixed Model with negative binomial distribution, data revealed similar fish abundances (in terms of the MaxN metric) despite the variation in current speed, probably because the mussel formations provide sufficient shelter, even from high water currents. The commercially important species Atlantic cod (G. morhua), however, was significantly more abundant in the low water current mussel reef. Therefore, restoration efforts targeting G. morhua could benefit from restoring low current mussel reefs. Our study provides input for the conservation of coastal recreational and commercial fisheries, habitat restoration and marine spatial planning where certain habitats may be prioritized.

Biodiversity exploration in autumn using environmental DNA in the South China sea

The South China Sea (SCS) is an important part of the Indo-Pacific convergence zone, with high biodiversity and abundant marine resources. Traditional methods are primarily used to monitor biodiversity. However, a few studies have used environmental DNA (eDNA) metabarcoding to research the assemblage structure of the SCS. This study used eDNA metabarcoding to survey the SCS assemblage and its relationship with environmental factors over a month-long time-series (August 30th to September 30th, 2020) of seawater samples from the central part of the SCS (9°–20°86′ N, 113°–118°47′ E). 32 stations were divided into six groups (A, B, C, D, E, F) according to longitude. We collected water samples, extracted eDNA, and amplified 18S rRNA gene V4 region (18S V4), 18S rRNA gene V9 region (18S V9), and 12S rRNA gene (12S). Krona diagrams were used to show species composition. We identified 192 phytoplankton, 104 invertebrate, and 61 fish species from 18S V4, 18S V9, and 12S, respectively. Generally, the three assemblage structures exhibited an increase in species diversity with increasing longitude. Group E had the highest fish diversity. Groups F and C had the highest phytoplankton and invertebrate diversity, respectively. Canonical correspondence analysis showed that four factors (chlorophyll a, depth, salinity, and temperature) were correlated with assemblage structure. Chlorophyll a was the main environmental factor that affected fish, phytoplankton, and invertebrate assemblage structures; salinity was strongly correlated with fish and invertebrate assemblage structures; temperature was a key factor that impacted fish and invertebrate assemblage structures; and depth was strongly correlated with invertebrate assemblage structure. Our results revealed that eDNA metabarcoding is a powerful tool for improving detection rate and using multiple markers is an effective approach for monitoring biodiversity. This study provided information that can be used to enhance biodiversity protection efforts in the SCS.

Linking flow alteration with fish assemblage structure in a river regulated by a small hydropower project in the Western Ghats of Karnataka, India

AbstractSmall hydropower projects (SHPs) are promoted as low‐impact alternatives for large hydropower. SHPs are generally commissioned on small‐ to medium‐sized mountainous rivers, often in biodiverse regions, with backing in the form of subsidies, facultative policies and exemption from impact assessments as they are considered ‘green’. However, the ecological impacts of SHPs are understudied especially in highly seasonal tropical streams of Western Ghats of India, a global biodiversity hotspot and a distinct freshwater fish eco‐region. We compared SHP‐affected segments of a dammed and an undammed river in the Western Ghats of Karnataka, to assess how altered flow regime affects seasonal variability in habitat and water quality, and influences fish assemblage structure. We found that flow alteration by the SHP varied between different segments of the dammed river and with season. Furthermore, the nature of flow alteration influenced habitat variability, water quality and fish assemblage response in the dammed river. We observed that the dewatered segment of the dammed river experienced a lotic to lentic shift in habitat and water quality, which favoured fish species with eurytopic affinities. Fluctuating flows in the downstream segment subdued natural variability in flow regime and created novel habitats and water‐quality conditions, affecting fish assemblages. The upstream segment of the dammed river retained natural variability in habitat and water quality, but did not mimic the undammed river in terms of fish composition. We also observed potential constraints on recruitment for migratory species of fish in the dammed river. Based on our results, we suggest how the placement of dewatered segment, and timing the closure of SHP operation in dry season based on ecological thresholds are potential solutions to mitigate the impacts of the SHPs. Furthermore, we recommend effective impact assessments, and adaptive management with active interventions to maintain genetic and ecological connectivity, as key to enhance the sustainability of the SHPs.

Variation in processes structuring fish assemblages as inferred from metacommunity analyses: Differences between headwater and adventitious streams within a river network

Community assembly is generally affected by the spatial position of local patches. Examining metacommunity processes and structures in small streams with different river network positions (e.g., headwater streams in the periphery of river networks vs adventitious streams in relatively central positions) may help us better understand how spatial position influences metacommunity structuring. In this study, based on data collected from sampling 24 headwater and 15 adventitious stream sites in the Xin’an Basin, China, we examined whether and how fish metacommunity processes and structures differed between the 2 stream types. We used distanced-based redundancy analysis coupled with forward selection to assess the relative roles of environmental and spatial factors in metacommunity processes, and we applied the elements of metacommunity structure analysis, extended by using different ordinations, to identify metacommunity structures. We found that the 2 types of streams were similar in environmental heterogeneity, but fish assemblages in adventitious streams were more dissimilar to one another than were assemblages in headwater streams and had more riverine immigrants. The amount of among-stream variation in species composition was low in both stream types. In headwater streams, assemblage–environment relationships were stronger than assemblage–space relationships, but we found the opposite pattern in adventitious streams. Species turnover was strong in both headwater and adventitious streams. However, assemblages in headwater streams showed both nested and quasi-nested structures, whereas the assemblages in adventitious streams were more consistent with Clementsian structure. Our results suggest that different metacommunity processes may occur in small streams with distinct river network positions and that extended elements of metacommunity structure analysis can help identify the underlying mechanisms that produce metacommunity structure. The effect of spatial position within river networks on stream fish metacommunity structuring appears to be weak, but our analyses do imply that river immigrants can influence species composition in adventitious streams to some extent.

Influence of cage farming and environmental parameters on spatio-temporal variability of fish assemblage structure in a tropical reservoir of Peninsular India

Fish assemblage structure in Palair reservoir, a medium tropical reservoir along the river Paleru, a tributary of river Krishna in Southern India, was studied along the spatial gradient of the impoundment. The abundance and assemblage structure of wild fish aggregated around the fish cage units installed in the reservoir were assessed and compared with other sites. Seasonal sampling was carried out and fish community structure in terms of species composition and abundance, trophic guild, niche, tolerance, resilience and conservation status were analyzed. A total of 38 fish species were recorded wherein the family Cyprinidae dominated in the number of species (15) followed by Cichlidae and Channidae (3 each). Margalef richness index (d), Pielou’s evenness index (J’), Simpson’s index (1-λ) and Shannon index (H’) revealed significant variation across different zones. Species richness was maximum in the Site1 (d = 4.44–5.12), whereas the abundance of individuals was maximum at Site4 (H’ = 2.65–2.86) i.e. near cage in the lacustrine zone. The important species contributing to the dissimilarities among the zones were identified and percentage of their contribution was estimated using SIMPER analysis. Trophic guild of fishes indicated the dominance of omnivorous species followed by carnivores, indicating the heterotrophic phase of the reservoir. The spatial and seasonal variations in the fish assemblage structure were tested applying statistical analyses such as PERMANOVA and nMDS. The results indicated a positive impact of cage farming in supporting the wild fish fauna, influencing the large aggregations of fishes around the cages. The temporal variability in the cage-associated fish assemblage was related to recruitment periods of juveniles (e.g. E. maculates and E. suratensis in summer, and S. seenghala in monsoon seasons). The links between fish assemblages and environmental parameters were explored through DISTILM and the deterministic factors for fish abundance in the reservoir were phosphate, pH, dissolved Oxygen, total hardness and depth. The study also indicated the impacts of cage culture with record of accidental escapes of farmed fish to the reservoir system. The baseline information generated and recommendations formulated in the study are crucial for the conservation of fish diversity, fisheries enhancement and management planning of tropical peninsular reservoirs.

Assemblage structure and spatial diversity patterns of kelp forest-associated fishes in Southern Patagonia.

Knowledge of the ecology of the fish fauna associated with kelp (primarily Macrocystis pyrifera) forests in Southern Patagonia is scarce, especially in how abiotic and biotic variables influence their structure, diversity, and distribution. This information is important for the management and conservation of this unique ecosystem, which has minimal anthropogenic impacts at present. We analyzed data from 122 quantitative underwater transects conducted within kelp forests at 61 stations from Chile’s southern Patagonian fjords to the Cape Horn and Diego Ramirez archipelagos and the southern tip of Argentina, including the Mitre Peninsula and Isla de los Estados. In total, 25 fish species belonging to 13 families were observed. Multivariate analysis indicated that there are significant differences in fish assemblage structure among locations and wave exposures, which was driven primarily by Patagonotothen sima and Paranotothenia magellanica, which occurred on exposed and semi-exposed stations. P. cornucola was mainly distributed across sheltered stations of the Kawésqar National Park. Temperature, salinity, depth, and kelp density influenced fish assemblage structure, with the highest diversity in areas with the lowest temperature and greater depth at Isla de los Estados. In contrast, species richness, diversity, abundance, and biomass were all lower in areas with high density of the understory kelp Lessonia spp., which might be driven by the absence of P. tessellata, P. squamiceps and P. cornucola, the most important species in terms of occurrence, abundance, and biomass. Our study provides the first broad-scale description of the fish assemblages associated with kelp forests along the southern cone of South America based on non-invasive visual transects, improving our knowledge of the distribution of fish assemblages across several environmental conditions in this vast and little-studied area.

FISHMORPH: A global database on morphological traits of freshwater fishes

AbstractMotivationGlobal freshwater fish biodiversity and the responses of fishes to global changes have been explored intensively using taxonomic data, whereas functional aspects remain understudied owing to the lack of knowledge for most species. To fill this gap, we compiled morphological traits related to locomotion and feeding for the world freshwater fish fauna based on pictures and scientific drawings available from the literature.Main types of variables containedThe database includes 10 morphological traits measured on 8,342 freshwater fish species, covering 48.69% of the world freshwater fish fauna.Spatial location and grainGlobal.Major taxa and level of measurementThe database considers ray‐finned fishes (class Actinopterygii). Measurements were made at the species level.Software format.csv.Main conclusionThe FISHMORPH database provides the most comprehensive database on fish morphological traits to date. It represents an essential source of information for ecologists and environmental managers seeking to consider morphological patterns of fish faunas throughout the globe, and for those interested in current and future impacts of human activities on the morphological structure of fish assemblages. Given the high threat status of freshwater environments and the biodiversity they host, we believe this database will be of great interest for future studies on freshwater ecology research and conservation.

The Role of Aquatic Refuge Habitats for Fish, and Threats in the Context of Climate Change and Human Impact, during Seasonal Hydrological Drought in the Saxon Villages Area (Transylvania, Romania)

In spite of the obvious climate changes effects on the Carpathian Basin hydrographic nets fish fauna, studies on their potential refuge habitats in drought periods are scarce. Multiannual (2016–2021) research of fish in some streams located in the Saxon Villages area during hydrological drought periods identified, mapped, and revealed the refuge aquatic habitats presence, management needs, and importance for fish diversity and abundance for small rivers. The impact of increasing global temperature and other human activities induced hydrologic net and habitats alteration, decreased the refuge habitats needed by freshwater fish, diminished the fish abundance, and influenced the spatial and temporal variation in fish assemblage structure in the studied area. The sites more than one meter in depth in the studied lotic system were inventoried and all 500 m of these lotic systems were also checked to see what species and how many individuals were present, and if there is was difference in their abundance between refuge and non-refuge 500 m sectors. The scarce number of these refuges due to relatively high soil erosion and clogging in those basins and the cumulative effects of other human types of impact induced a high degree of pressure on the fish fauna. Overall, it reduced the role of these lotic systems as a refuge and for reproduction for the fish of downstream Târnava Mare River, into which all of them flow. Management elements were proposed to maintain and improve these refuges’ ecological support capacity.

Spatial and temporal variation of fish assemblage structure in a neotropical Mexican river

The introduction of non-native fish into the Teuchitlán River, in west-central Mexico, was suggested as a key factor behind the change in the fish assemblage, and even in the extinction of endemic species. The characterization of the fish assemblage and the relationship between fish abundance and the anthropogenic conditions were evaluatedover 2-year period. Fish assemblage structure, species replacement, and dominance were examined along a longitudinal environmental gradient. Physical and chemical parameters of the water were recorded. The relationship between fish abundance and abiotic factors was inferred from multivariate analysis. The results showed that the non-native poecilid Pseudoxiphophorus bimaculatus was dominant, and the abundance and biomass of non-native species exceeded 50%in all sites and seasons. Species diversity and native fish abundance were greater in upstream sites, which presented higher dissolved oxygen and lower nitrates. The native ichthyofauna of the Teuchitlán River has been replaced by non-native species. This decline of the native fish species seems to be due not only to the interaction with non-native species but also to the multiple human impacts on the lotic system.

Performance of a baited underwater video system vs. the underwater visual census technique in assessing the structure of fish assemblages in a Mediterranean marine protected area

Accurate, rapid and cost-effective fish assemblage monitoring is fundamental for marine protected area (MPA) management as a pivotal tool to verify whether and to what extent MPA conservation objectives have been achieved and to redefine these objectives in the framework of an adaptive management. Recently, there has been a sharp increase in the number of video-based methods to study fish fauna, such as baited remote underwater video (BRUV) systems, that, depending on the objectives of the monitoring, can provide complementary or additional data to the more commonly used underwater visual census (UVC). Even though BRUV systems have been widely used in a wide range of geographic contexts and habitats, their use in the Mediterranean basin is still sporadic and the evaluation of the efficiency of BRUV systems and whether they can be used to complement other techniques needs investigation. Thus, the objective of this study was to assess the performance of a BRUV system in a Mediterranean MPA and to evaluate its effectiveness in assessing the structure of fish assemblages (abundance and species richness) by comparing estimates with those obtained by the UVC technique. The fish fauna were monitored by BRUV and UVC in the Capo Caccia – Isola Piana Marine Protected Area (Sardinia, Italy), in July and October-November 2020, at four sampling sites and two areas, hundreds of meters apart, for each site. Overall, 46 taxa and a total of 3620 individuals were observed by BRUV, while 36 taxa and a total of 2995 individuals were observed by UVC. The species first observed in front of the camera’s field of view and able to reach the maximum abundance were the planktivores (Chromis chromis and Oblada melanura) followed by several carnivorous species belonging to the families Labridae, Serranidae and Sparidae, and lastly two carnivores (Mullus surmuletus and Mugilidae spp.) and some high-level predators (Dentex dentex, Seriola dumerili, Sphyraena viridensis, Dicentrarchus labrax). The maximum species richness and abundance were reached between 39 and 50 min. The cumulative species richness increased until around 30 min. Species richness was higher during the BRUV compared to the UVC monitoring. The consistency in findings between BRUV and UVC and a better performance of BRUV in detecting some species (mainly high-level predators), supports BRUV as an additional technique for describing and quantifying species richness and abundance also in the Mediterranean Sea. Based on the results of this study, the advantages/disadvantages, shortcomings, suggestions and resources needed for the two techniques are outlined.

Do river basins influence the composition of functional traits of fish assemblages in Neotropical reservoirs?

In aquatic environments, dams are considered one of the main threats to fish species, acting as an environmental filter for certain functional traits. Although there is some predictability in the composition of the functional traits in reservoirs, it is hypothesized that the environmental filters imposed by evolutionary processes, linked to the characteristics of the basins, are determinant for the functional composition of the traits in reservoirs. For this we performed a PCoA using the functional traits composition matrix of the reservoirs. We used PERMANOVA to test the difference in functional composition between basins. We performed the same process for the species composition matrix to compare the patterns. In this study, there were taxonomic and functional differences among reservoirs inserted in different basins. It was observed that the basin is a determining factor for the functional structure of fish assemblage in reservoirs. When compared, functional and taxonomic structures follow the same pattern, although functionally the reservoir tends to be more similar. These results reinforce the idea that reservoirs act as filters for functional traits (e.g., related with reproduction, feeding and habitat use), although there is a great influence of evolutionary processes related to the basin's characteristics and origin of the ichthyofaunistic province.

Assessing Spatial and Temporal Trends in a Mediterranean Fish Assemblage Structure

Coastal fishes are not only valuable elements of marine biodiversity, but they also play an important ecological role in the functioning of coastal ecosystems: food resource, transfer of nutrients, predators. Therefore, data on the compositions of fish assemblages are of great importance. The objectives of the present study were to (i) define the faunistic characteristics of a typical fish community on the Mediterranean coast; (ii) investigate spatiotemporal changes in fish assemblages. Based on a set of indices (Fast protocol) and a long-term data set (6 years, 612 visual counts, 154 h of diving), changes in coastal fish communities were analyzed. Our results indicated that there was a significant shift in fish community structure, with a general decline of the calculated indices. In our study, part of the observed variability in fish assemblage structure could be due to different factors as site location and sampled year. The changes in the fish assemblages associated with inter-annual fluctuations observed in this study also provide important insights into how fish communities may change under environmental and anthropogenic influences.

Changes in fish assemblages following the implementation of a complete fishing closure in the Chishui River

The Chishui River is the first to have a complete fishing-closure in the Yangtze River basin. To explore how fish assemblages changed following the implementation of the fishing closure, field surveys were conducted biannually in three reaches (upper, middle and lower) along its longitudinal gradient during 2007 to 2019. A total of 143 species from eight orders and 24 families was collected. Diversity index for all three reaches showed no significant changes through time. However, non-metric multidimensional scaling (NMDS) ordination analysis revealed significant temporal changes in the structure of fish assemblages for all reaches (P＜0.05 in all cases). Time-lag analysis further showed that the fish assemblages in the upstream had reverted to the early study periods (P＜0.05), with the relative abundance of some large-sized species (e.g., Onychostoma simum and Spinibarbus sinensis) returning to former levels immediately after fishing closure. Fish assemblages in the midstream and downstream reaches also showed trends to returning to the early study periods, but did not reach statistical significance (P > 0.05). These discrepancies might be attributed to varying human disturbances and the type of fish species composition along the longitudinal gradient.

Fish assemblage structure in a Neotropical urbanised prairie stream exposed to multiple natural and anthropic factors

AbstractA myriad of factors affect stream fish assemblages, and most of them are intimately regulated by surrounding land uses. One of the most pernicious impacts on streams is the release of urban effluents. Accordingly, understanding the fish assemblage patterns as well as the environmental drivers that modulate them in the context of urban streams which also are exposed to other land uses is mandatory. We evaluated the longitudinal patterns of fish assemblages in an urbanised Neotropical prairie stream exposed to downstream patches of different surrounding land uses. Several variables of water quality, in‐stream habitat and riparian corridors were measured, and their relationships with fish metrics were explored. A fish metric selection protocol was implemented, and several multivariate analyses were used. Three main patterns of fish response were observed. Assemblage‐level attributes as diversity, richness, biomass, number of families and trophic guilds and proportion of Characiformes and intolerant species were responsive to the natural gradient in habitat (pools) and riparian (riparian width) conditions expected in non‐impacted lotic ecosystems. Conversely, a downstream continuum of recovery in water quality (dissolved oxygen, conductivity, NO3:NH4 and bacteriological loads) and habitat structure (sediment depth) would influence the distribution of fish species regarding their environmental tolerance and habitat preferences. Finally, local habitat aspects (nitrites, submerged macrophytes, bare soil cover and bank incisions by livestock) seemed relevant for the trophic structure (omnivorous species) of fish assemblages. A complex natural and anthropic longitudinal scenario together with local disruptions imposed by surrounding land uses were directive for fish.

The role of emergent physical and chemical properties of Florida spring complexes in predicting fish assemblage structure

Florida spring complexes (springs and their associated runs) represent patches of clear, cool freshwater habitat in a landscape of tannin-stained wetlands, streams, and rivers. These spring complexes differ in morphology, water quantity and quality, and biotic characteristics as well as in their connections to other water bodies. The purpose of this study was to determine whether watershed effects or emergent physical, chemical, and biologic properties of Florida spring complexes would predict fish assemblage structure. Spring complex morphology and water quality metrics were collected from water managers or from the literature, with the exception of dissolved oxygen, which was measured in situ. Fish data were collected by video surveys using GoPro® cameras on stationary tripods at 2 to 5 locations on the banks of each spring complex. Videos were analyzed for the total number of individuals of each species/video, species richness, and diversity. The environmental characteristics of spring complexes differed between watersheds, as the St Johns River spring complexes, which are near the east coast, differed from watersheds closer to the west coast of Florida. However, specific characteristics that discriminated between springs, like low dissolved oxygen concentration or abundant macrophytes, crossed watershed boundaries. Fish assemblages also differed between the St Johns River and western watersheds, but the differences were more subtle than the differences in environmental characteristics, and the characteristics of individual spring complexes also predicted fish assemblage structure. Conductivity, dissolved oxygen concentration, and macrophyte coverage best explained the variation in the fish assemblage structure among spring complexes. The overlap in spring complex fish assemblages across watersheds may be the result of the geologic youth of the freshwater fish assemblages, the high degree of hydrologic connectivity between water bodies, and possible impairment of spring complexes in Florida.

Spatial and seasonal patterns of fish assemblages in mountain streams of the Ren River, southwest China.

The spatial–temporal patterns of fish assemblages in lotic systems can provide useful information in developing effective conservation measures. This study aimed to explore the spatial and seasonal changes in fish assemblages and their association with environmental factors in mountain streams of the Ren River, southwest China. Field investigations were conducted at 18 sites during the rainy and dry seasons in 2017. A total of 1,330 individuals, belonging to three orders, eight families, 19 genera, and 21 species, were collected. Analysis of similarities (ANOSIM) showed that the structure of fish assemblages varied significantly at the spatial scale, but not at the seasonal scale. In low‐order sites, fish assemblages were mainly dominated by cold‐water and rheophilic species (e.g., Rhynchocypris oxycephalus, Scaphesthes macrolepis, Metahomaloptera omeiensis, and Gnathopogon herzensteini), while those in high‐order sites were predominated by warm‐water and eurytopic or stagnophilic species (e.g., Squalidus argentatus, Hemiculter leucisculus, and Zacco platypus). Canonical correspondence analysis (CCA) showed that the fish assemblages were structured by a combination of large‐scale landscape factors (e.g., altitude and C‐link) and small‐scale habitat features (e.g., channel width, water temperature, and depth). Among these factors, landscape had the greatest influence on fish assemblages, while local habitat variables were less important or were only significant in certain seasons.