Differences In Fish Assemblage Structure Research Articles

Fish responses to multiple scales in coastal blackwater Atlantic Forest streams in Southeast Brazil

Abstract Environmental factors act at multiple spatial scales in a hierarchical manner to shape the organization of biota. However, the relative influence of different scale-related factors is poorly known, especially in Atlantic Forest Blackwater streams. Therefore, we herein aimed to evaluate local, landscape and spatial factors that shape fish assemblages in 14 blackwater restinga coastal Atlantic Forest streams under natural conditions and verify species occurrence patterns among four sub-basins during the low-precipitation season. When we combined local, landscape and spatial factors, variance partitioning explained a high proportion of variation in species matrix. Local variables pH and Total Dissolved Solids explained most of the variability, and these were the most important factors in determining fish community structure. Significant differences in fish assemblage structure among the four sub-basins were observed, and Mimagoniates microlepis, Phalloceros harpagos, and Hollandichthys multifasciatus were the species that most contributed to this dissimilarity. The important contribution of local predictors, the high number of endemic species herein recorded, the presence of an endangered species (Spintherobolus broccae), and near pristine conditions, may be used as baseline conditions for the assessment of similar environments.

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.

Differences in fish assemblage structures between tidal marsh and bare sandy littoral habitats in a brackish water lake, eastern Japan

Fish assemblage structures and environmental properties (e.g., water quality, sediment condition and prey abundance) were compared between tidal marshes, dominated by the common reed Phragmites australis, and bare sandy areas in the brackish-water Lake Hinuma, eastern Japan, by daytime seine net sampling in October 2014, and January, April and July 2015. A total of 4,076 fish individuals from 30 species and 5,431 individuals from 23 species were collected in the tidal marshes and sandy areas, respectively. Higher species richness in the former habitat was due to the restricted occurrence of ten species, including threatened or near threatened, only to that habitat. Species composition and the abundances of several dominant species, such as the commercially important icefish Salangichthys microdon and the goby Acanthogobius lactipes, also differed between the two habitats, although no interhabitat differences in the mean species and individual numbers per haul were found. Moreover, the individual number of small benthic and epiphytic crustacean feeders, including A. lactipes, was greater in the tidal marshes than in the sandy areas, whereas zooplankton feeders, including S. microdon, showed the opposite pattern. Such interhabitat differences in fish assemblage structures may be partly related to food availability, sediment condition and/or the presence or absence of vegetative structures. Because each of the two habitats harbored a unique fish assemblage, conservation efforts for both habitats are important for enhancing overall fish species diversity and sustaining fishery resources in Lake Hinuma.

Differences in Fish Assemblage Structure Between Taking and No-Taking Protected Areas: The Case of Cayar And Joal-Fadiouth Marine Protected Areas in Senegal

Differences in Fish Assemblage Structure Between Taking and No-Taking Protected Areas: The Case of Cayar And Joal-Fadiouth Marine Protected Areas in Senegal

Differences in Fish Assemblage Structure Between Taking and No-Taking Protected Areas: The Case of Cayar And Joal-Fadiouth Marine Protected Areas in Senegal

Differences in Fish Assemblage Structure Between Taking and No-Taking Protected Areas: The Case of Cayar And Joal-Fadiouth Marine Protected Areas in Senegal

Patterns in reef fish assemblages: Insights from the Chagos Archipelago.

Understanding the drivers of variability in the composition of fish assemblages across the Indo-Pacific region is crucial to support coral reef ecosystem resilience. Whilst numerous relationships and feedback mechanisms between the functional roles of coral reef fishes and reef benthic composition have been investigated, certain key groups, such as the herbivores, are widely suggested to maintain reefs in a coral-dominated state. Examining links between fishes and reef benthos is complicated by the interactions between natural processes, disturbance events and anthropogenic impacts, particularly fishing pressure. This study examined fish assemblages and associated benthic variables across five atolls within the Chagos Archipelago, where fishing pressure is largely absent, to better understand these relationships. We found high variability in fish assemblages among atolls and sites across the archipelago, especially for key groups such as a suite of grazer-detritivore surgeonfish, and the parrotfishes which varied in density over 40-fold between sites. Differences in fish assemblages were significantly associated with variable levels of both live and recently dead coral cover and rugosity. We suggest these results reflect differing coral recovery trajectories following coral bleaching events and a strong influence of ‘bottom-up’ control mechanisms on fish assemblages. Species level analyses revealed that Scarus niger, Acanthurus nigrofuscus and Chlorurus strongylocephalos were key species driving differences in fish assemblage structure. Clarifying the trophic roles of herbivorous and detritivorous reef fishes will require species-level studies, which also examine feeding behaviour, to fully understand their contribution in maintaining reef resilience to climate change and fishing impacts.

Marinas as habitats for nearshore fish assemblages: comparative analysis of underwater visual census, baited cameras and fish traps

Understanding the ecological role that artificial structures might play on nearshore fish assemblages requires the collection of accurate and reliable data through efficient sampling techniques. In this work, differences in the composition and structure of fish assemblages between the inner and outer sides of three marinas located in the temperate northern-eastern Atlantic Ocean were tested using three complementary sampling techniques: underwater visual censuses (UVC), baited cameras (BCs) and fish traps (FTs). UVCs and BCs recorded a comparable number and relative abundance of species, which in turn were much greater than those recorded by FTs. This finding supports the use of UVCs and BCs over FTs for broad ecologically studies, especially when dealing with structurally complex habitats such as artificial structures. We found differences in fish assemblage structure between the inner and outer sides of marinas, independently of the sampling method. Four small-sized species (Similiparma lurida, Thalassoma pavo, Sarpa salpa and Symphodus roissali) associated with structurally complex vegetated habitats dominated, in terms of abundance, the outer sides of marinas; Diplodus vulgaris, Diplodus sargus and Gobius niger, species with high ecological plasticity in habitat requirements, dominated the inner sides of marinas. The information provided in this study is of great interest for developing sound monitoring programmes to ascertain the effects of artificial structures on fish communities.

Seasonal and spatial differences in fish assemblage structures in dyke foot waterways connected to Lake Kitaura, Ibaraki Prefecture, Japan

Seasonal and spatial differences in fish assemblage structures in dyke foot waterways connected to Lake Kitaura, Ibaraki Prefecture, Japan

Assessment of fish floodplain use during an extreme flood event in a large, regulated river

Anthropogenic alterations to large, North American rivers have caused widespread changes in river function, and are likely responsible for freshwater biodiversity declines. The fish assemblage of the Missouri River has been affected by decades of homogenized flow and channelization, and these changes have contributed to declines in several native species. Little is known about fish use of altered floodplain habitats in large rivers that have been regulated to no longer inundate their floodplain. We collected fish and habitat data at five locations on the Missouri River, Nebraska floodplain during the largest and longest-lasting flood in over 50 years to understand how fish would distribute themselves across a suite of novel floodplain habitats. We found differences in fish assemblage structure between all but two sampling locations. Differences in the fish assemblage between Tieville Bend and three other sites were largely caused by the high abundance of black bullhead at Tieville Bend. Attempts to relate species abundance to habitat measurements suggest that factors influencing floodplain habitat use are complex, and possibly driven by habitat components not measured in this study. Future work is needed to investigate relations between the fish assemblage and its use of floodplain resources.

Influence of a large dam on the longitudinal patterns of fish assemblages in Qingyi Stream.

Using seasonally collected data (2009-2010) from 15 sampling sites that represent first- to fifth-order streams within the Qingyi watershed, we examined the spatio-temporal patterns of fish assemblages along two longitudinal gradients to explore the effects of a large dam on fish assemblages at the watershed scale. No significant variation was observed in either species richness or assemblage structure across seasons. Species richness significantly varied according to stream order and gradient. Dam construction appeared to decrease species richness upstream substantially, while a significant decrease between gradients only occurred within fourth-order streams. Along the gradient without the large dam, fish assemblage structures presented distinct separation between two neighboring stream orders, with the exception of fourth-order versus fifth-order streams. However, the gradient disrupted by a large dam displayed the opposite pattern in the spatial variation of fish assemblages related with stream orders. Significant between-gradient differences in fish assemblage structures were only observed within fourth-order streams. Species distributions were determined by local habitat environmental factors, including elevation, substrate, water depth, current discharge, wetted width, and conductivity. Our results suggested that dam construction might alter the longitudinal pattern in fish species richness and assemblage structure in Qingyi Stream, despite the localized nature of the ecological effect of dams.

Geographical patterns in the body‐size structure of European lake fish assemblages along abiotic and biotic gradients

AbstractAimOur aim was to document geographical patterns of variation in the body‐size structure of European lake fish assemblages along abiotic gradients, and any differences in fish assemblage structure. We hypothesized that patterns in the body‐size structure of entire lake fish assemblages are primarily temperature driven and consistent with the dominant pattern of the temperature–size rule, which suggests a decrease in adult body size with increasing developmental temperature for many ectothermic species.Location356 European lakes.MethodsVariation in the body‐size structure of fish assemblages was explored on a continental scale along gradients of temperature, morphometry, productivity and fish assemblage structure for 356 European lakes. The mean fish assemblage body‐size and individual body‐size distributions were selected as size metrics. Separate analyses were conducted for lakes located within five ecoregion subsets (Borealic Uplands/Tundra, FennoScandian Shield, Central Plains, Western Plains and Western Highlands) and for lakes with different functional fish classifications (cold‐, cool‐ and warmwater fish assemblages).ResultsGeographical patterns of variation in the body‐size structure of European lake fish assemblages could be clearly discerned along a temperature gradient for both the continental dataset (356 lakes) and the smaller geographical (ecoregion) subsets. We found systematic changes in fish assemblage body‐size structure across temperature gradients in correspondence with the dominant thermal fish guild. The majority of the lakes, mainly located in the warmer European lowlands, were dominated by eurythermic cool‐ and warmwater fish assemblages, with smaller sized individuals characterized by linear individual body‐size distributions. Lakes located in colder regions and dominated by stenothermic coldwater salmonids with larger sized individuals were characterized by unimodal or bimodal size distributions. The mean body size of cold‐, cool‐ and warmwater fish assemblages changed uniformly along the temperature gradient.Main conclusionsPatterns of variation in the body‐size structure of European lake fish assemblages are consistent with the temperature–size rule. Temperature modifies fish assemblage size structure uniformly within the thermal fish guilds and in different ecoregions. Furthermore, our results indicate an increasing predictive power of temperature to explain variability in body‐size structure when moving from warmer to colder geographical regions.

Complementarity of Rotating Video and Underwater Visual Census for Assessing Species Richness, Frequency and Density of Reef Fish on Coral Reef Slopes

Estimating diversity and abundance of fish species is fundamental for understanding community structure and dynamics of coral reefs. When designing a sampling protocol, one crucial step is the choice of the most suitable sampling technique which is a compromise between the questions addressed, the available means and the precision required. The objective of this study is to compare the ability to sample reef fish communities at the same locations using two techniques based on the same stationary point count method: one using Underwater Visual Census (UVC) and the other rotating video (STAVIRO). UVC and STAVIRO observations were carried out on the exact same 26 points on the reef slope of an intermediate reef and the associated inner barrier reefs. STAVIRO systems were always deployed 30 min to 1 hour after UVC and set exactly at the same place. Our study shows that; (i) fish community observations by UVC and STAVIRO differed significantly; (ii) species richness and density of large species were not significantly different between techniques; (iii) species richness and density of small species were higher for UVC; (iv) density of fished species was higher for STAVIRO and (v) only UVC detected significant differences in fish assemblage structure across reef type at the spatial scale studied. We recommend that the two techniques should be used in a complementary way to survey a large area within a short period of time. UVC may census reef fish within complex habitats or in very shallow areas such as reef flat whereas STAVIRO would enable carrying out a large number of stations focused on large and diver-averse species, particularly in the areas not covered by UVC due to time and depth constraints. This methodology would considerably increase the spatial coverage and replication level of fish monitoring surveys.

Differences in fish assemblage structure between vegetated and unvegetated microhabitats in relation to food abundance patterns in a mangrove creek

In order to clarify the mechanisms determining fish distribution patterns in a mangrove system on Iriomote Island, in southern Japan, fish assemblage structures were determined by visual observation, along with food abundance and environmental factors, in an area of mangrove roots on the banks, and a bare sand area at the center, within downstream, midstream and upstream portions of a branch creek from the Urauchi River. The fish assemblage structures differed significantly between the area types, with the mangrove-root area supporting a more diverse and abundant fish fauna. A canonical correspondence analysis revealed that the relationships between fish distribution and their food abundance differed among trophic groups. Benthic crustacean or plant feeders were positively associated with their prey i.e. crabs and macroalgae—in other words, these trophic groups were abundant in downstream and/or midstream mangrove-root areas in which their prey were also particularly abundant. However, zooplankton feeders did not show such relationships, their abundance being positively associated with fine sediment particles (characteristic of areas with weak water movement). These results suggested that food availability is a major factor determining the distribution patterns of benthic crustacean feeders and plant feeders, whereas for zooplankton feeders other factors, such as sheltering effects against water current and/or predators, may be more significant.

A Checklist to the Common Cyprinid and Centrarchid Fishes of the Bull and Upatoi Creeks Watershed of Georgia with a Brief Glimpse of Correlative Urban Influences and Land use

Abstract We sampled fishes from eight creeks within the Bull and Upatoi creeks watershed in the summer months of June 2001 and August 2002 to provide a checklist of common fishes. This sample and its data support a more comprehensive study by the authors documenting an urbanization gradient among creeks and their associated differences in fish assemblage structure within this aquatic system. However, here we provide a simple, but useful, checklist of common Cyprinid and Centrarchid fishes to enhance future species-monitoring efforts within this watershed. We collected a total 2407 individuals representing 34 species from Lindsey, Cooper, Flatrock, Bull, Dozier, Randall, Kendall, and Baker Creeks by seining. Lepomis macrochirus (Bluegill), Cyprinella venusta (Blacktail Shiner), and Notropis buccatus (Silverjaw Minnow) were the most abundant species within the Bull and Upatoi creeks watershed. Conversely, Pimephales promelas (Fathead Minnow) and Pimephales vigilax (Bullhead Minnow) were the rarest. We calcu...

Responses of fish assemblage structures to sandy beach types in Kyushu Island, southern Japan

To determine differences in fish assemblage structures between beach morphodynamic types on an exposed sandy shore, three beach types (reflective, intermediate, and dissipative) were sampled at Fukiagehama Beach, Kyushu Island, southern Japan, in May, August, and November 2006 and 2007. Distinct differences in physical conditions and the amount of major prey invertebrates, such as copepods, mysids, and amphipods, were recognized between the three beach types. The reflective beach was characterized mainly by turbulent swashes, coarse sediment, and a low abundance of major prey invertebrates. In contrast, the dissipative beach was characterized mostly by benign swashes, fine sediment, and a high abundance of prey invertebrates. The intermediate beach tended toward an intermediate condition between the reflective and dissipative beaches. The fish assemblage structures also differed clearly between the three beach types, with species and individual numbers being greatest on the dissipative beach and lowest on the reflective beach. A similarity index indicated differences in species composition of the assemblages between the beach types. Such differences arose primarily from the differential distributions of two dominant trophic groups, zooplankton (mostly copepods) and epibenthic crustacean (mainly mysids and amphipods) feeders, between the beach types, both groups tending to increase in species and individual numbers from the reflective beach to the dissipative beach. In addition, the mean standard length of all fish collected in each month tended to decrease toward the dissipative beach. These results suggested that beach types strongly influence sandy beach fish assemblage structures.

Spatial and seasonal patterns in fish assemblage in Corrego Rico, upper Parana River basin

The upper Paraná River basin drains areas of intensive industry and agriculture, suffering negative impacts. The Córrego Rico flows through sugar cane fields and receives urban wastewater. The aim of this work is to describe and to compare the fish assemblage structure in Córrego Rico. Six standardized bimonthly samples were collected between August 2008 and June 2009 in seven different stretches of Córrego Rico. Fishes were collected with an experimental seine and sieves, euthanized, fixed in formalin and preserved in ethanol for counting and identification. Data were recorded for water parameters, instream habitat and riparian features within each stretch. Non-metric multidimensional scaling, species richness and diversity analysis were performed to examine spatial and seasonal variation in assemblage structure. Fish assemblage structure was correlated with instream habitat and water parameters. The fish assemblage was divided in three groups: upper, middle and lower reaches. High values of richness and diversity were observed in the upper and lower stretches due to connectivity with a small lake and Mogi Guaçu River, respectively. Middle stretches showed low values of richness and diversity suggesting that a small dam in the middle stretch negatively impacts the fish assemblage. Seasonal differences in fish assemblage structure were observed only in the lower stretches.

Seasonal response of fish assemblages to habitat fragmentation caused by an impoundment in a Neotropical river

Changes in fish assemblages between the zones above and below Funil dam in Southeastern Brazil were investigated to evaluate the possible impacts of this impoundment in two contrasting seasons: summer/wet and winter/dry. We expect differences in fish assemblage structure and in environmental conditions between seasons and between the reservoir and the zone downriver of the dam. A total of 3,579 individuals comprising 38 species, including six non-natives, were collected. As expected, the comparatively high habitat complexity and water flow regime of the downriver zone favored a richer and more abundant fish assemblage compared with the reservoir, especially in the wet season. In this period, water covers part of the riparian vegetation, increasing habitat availability and nutrient input. Additionally, the dam prevents upriver migration of rheophilics fish species such as the Characiformes Prochilodus lineatus and Leporinus copelandii, and the Siluriformes Pimelodus fur and Pimelodus maculatus, thus increasing shoals below the dam. Although the reservoir represents a simplified ecosystem highly influenced by non-native top predator species (e.g. the Perciformes Cichla kelberi and Plagioscion squamosissimus), seasonal processes (e.g. water level fluctuations and flood pulses) seem to play a role in structuring of the fish assemblage. Environmental variables, mainly turbidity, temperature, and conductivity were significantly associated to spatial-temporal patterns of fish assemblage. In this freshwater tropical reservoir, the spatial scale, rather than the seasonal changes in environmental variables, was the dominant factor structuring fish assemblage in the reservoir and in the zone downriver of the dam.

Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 446:259-273 (2012) - DOI: https://doi.org/10.3354/meps09455 Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season Joaquim Ribeiro*, Gonçalo M. Carvalho, Jorge M. S. Gonçalves, Karim Erzini Centro de Ciências do Mar (CCMAR), Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal *Email: jmnribeiro@sapo.pt ABSTRACT: Fish assemblages in seagrass and unvegetated habitats located in shallow intertidal creeks within the saltmarsh area of the Ria Formosa coastal lagoon were sampled with a Riley push net at 3 sites on a monthly basis over a 1 yr period. The objective was to test if both habitats support similar fish assemblages in terms of abundance, diversity, assemblage structure, and size distribution, and to investigate how site and season affect the assemblages. Fish assemblages associated with these habitats were significantly different in terms of diversity, abundance, and assemblage structure. Seagrass supported a larger number of species and greater diversity, while unvegetated habitat supported greater fish numbers but only of a few species. The habitats were dominated by different groups of resident species that were responsible for major differences in fish assemblage structure between habitats. Pomatoschistus microps and young-of-the-year (YOY) Atherina presbyter dominated the unvegetated habitat, while seagrass was dominated by a diverse group of species, in particular syngnathids and small labrids, revealing different habitat preferences. Site and season were determinant factors conditioning the role of habitat in structuring fish assemblages. Distance between habitats, site elevation, and the amount of marsh drained affected fish assemblages in both habitats. Seasonal fluctuations in the presence and abundance of YOY from marine migrant and resident species were responsible for comparable changes in fish assemblage structure in both habitats. Both habitats provide a distinctive nursery area for different species, while common species reveal ontogenic distributional changes between habitats, where smaller fish appear first in unvegetated creeks. KEY WORDS: Fish fauna · Coastal lagoon · Saltmarsh · Intertidal habitats · Seasonal variations · Habitat association · Ria Formosa · South Portugal Full text in pdf format PreviousNextCite this article as: Ribeiro J, Carvalho GM, Gonçalves JMS, Erzini K (2012) Fish assemblages of shallow intertidal habitats of the Ria Formosa lagoon (South Portugal): influence of habitat and season. Mar Ecol Prog Ser 446:259-273. https://doi.org/10.3354/meps09455 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 446. Online publication date: February 02, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Variabilidad espacial en la estructura de la ictiofauna asociada a praderas de Cymodocea nodosa en las Islas Canarias, Atlántico nororiental subtropical

A description of the patterns in spatial variability of fish assemblages is particularly relevant to guarantee an adequate management of these marine resources. Thirty six trawls were considered on six seagrass meadows (10 km apart) in three islands (100 km apart) of the Canary Islands to (i) analyze the spatial variability in the structure (richness, abundance and diversity) of fish assemblages associated with Cymodocea nodosa seagrass meadows, and to (ii) assess how the structural complexity of this habitat affects fish assemblage structure. A total of 3,616 fishes were captured, belonging to 30 species and 15 families. The total length of ca. 95% of individuals was < 10 cm, and ca. 90% of individuals were juveniles. Spatial variability in fish assemblage structure was larger when considering the scale of meadows than the scale of islands (27.28% vs. 6.64% respectively, in the amount of explained total variability); the smallest spatial scale (i.e., the variability among replicated trawls within each seagrass meadow) accumulated the largest amount of variability (66.07%). Differences in fish assemblage structure were largely driven by changes in the abundance of a few species, including Diplodus annularis, Spondyliosoma cantharus, Mullus surmuletus and Symphodus trutta. These species recruited into seagrass meadows, and confirmed the nursery role of this habitat in the canarian coastal waters. Mean shoot density and variation of the seagrass canopy height were the descriptors that accounted for the most variability when explaining patterns in fish assemblage structure.

Spatial and temporal variation of fish assemblages and their associations to habitat variables in a mountain stream of north Tiaoxi River, China

The spatial and temporal variations of the fish assemblages in mountain streams of China are poorly understood. The relationships between the fish assemblage and selected habitat features were examined in the North Tiaoxi River, one of headwaters of Taihu Lake. A total of 3,348 individuals belonging to 5 orders, 11 families, 25 genera and 34 species were collected including 33 native species and one invasive species. Among those, about 20 species were endemic to China. Non-metric Multidimensional Scaling (NMDS) was applied to compare fish assemblage structures from upstream to downstream during four seasons. Species assemblages differed along the stream continuum, but there was little apparent change associated with the seasons. Species richness and Shannon-Weaver index (H′) tended to increase along the stream continuum from the upstream to downstream and the proportion of invertivorous fish tended to significantly decrease along the continuum with a parallel significant increase in the percentage of omnivores. Fish assemblages were significantly related to both water quality and habitat structure variables. Canonical Correspondence Analysis ordinations (CCA) revealed that 6 of the 14 selected environmental variables had significant relationships with the fish assemblage such as distance to source, stream width, altitude, pH, water depth, and water velocity and different sampling sites were associated with different environmental variables in different seasons. The main differences in fish assemblage structure and diversity within the whole watercourse are probably related to large-scale factors such distance to source, altitude and stream width. Differences of instream characteristics are likely to be caused by natural variability of the ecosystems but also, in some case, by anthropogenic influence like human settlements, agriculture and river embankment and pollution from small factory.