Fish Community Structure Research Articles

Komposisi Jenis dan Struktur Komunitas Ikan di Ekosistem Lamun Pantai Sindhu, Sanur, Bali

Sindhu Beach is one of the beaches which located in Sanur. The coastal areas of Sindhu Beach has long been used for various economic activities, such as recreation areas or marine tourism. So that these activities can adversely affect the sustainability of the seagrass ecosystem as a habitat for various types of aquatic biota, especially fish. This study aims to determine the composition of fish community species and structures, to know the types of seagrass, and also to know the condition of water quality in the seagrass ecosystem of Sindhu Beach, Sanur, Bali. This study has been conducted from January to February 2018 by direct observation method. The results of the composition of fish species as a whole found 537 of fish that consisting of 22 species and it came from 11 families. The overall value of community structure is obtain by the value of the diversity index (H') of 2.68, uniformity index (E) 0.87, and the dominance index (C) 0.09. The types of seagrasses which found in the study location was consist of 8 species of seagrass covering Enhalus acoroides, Syringodium isoetifolium, Halodule pinifolia, Halodule uninervis, Thalassia hemprichii, Cymodocea rotundata, Halophila ovalis, and Halophila spinulosa. The result of measurement of water quality parameters from all stations were obtain the average measurement of dissolved oxygen 7,1 mg / l, salinity 30o/oo, pH 8,24, and temperature 29,80C. The result of measurement of water quality parameter shows that the condition of seagrass ecosystem of Sindhu Beach was still considered optimal for marine life.

Conservation implications of fish-habitat relationships in channelized agricultural headwater streams.

Channelized agricultural headwater streams are common throughout agricultural watersheds in the midwestern United States. Understanding fish-habitat relationships within these streams will provide information that can assist with developing conservation and restoration strategies for these degraded streams. From spring 2006 to fall 2010, we collected fishes and measured riparian habitat, instream habitat, and water chemistry variables from seven sites in Cedar Creek, Indiana, and 14 sites in Upper Big Walnut Creek, Ohio. We found that fish community structure was more strongly correlated with instream habitat than riparian habitat or water chemistry in both watersheds. We also observed interrelationships among instream habitat, watershed size, and fish communities within both watersheds that suggest that the hydrological changes that occur with increasing watershed size are the underlying factor for fish community changes that occur with increasing watershed size. Our results suggest that conservation and restoration efforts within channelized agricultural headwater streams in the midwestern United States, where nutrients and herbicide concentrations are low, need to address physical habitat degradation to positively influence fish community structure.

Patterns of Seasonal Stability of Lake Phytoplankton Mediated by Resource and Grazer Control During Two Decades of Re-oligotrophication

Human-induced changes in external nutrient loading affect the phytoplankton community and abundance directly by changing the amount of nutrients available, but also indirectly through changes in the zooplankton (that is, grazer) community structure, mediated in part by changes in the fish community structure and biomass. Such shifts affect the species dynamics and community succession of lake phytoplankton communities, and they may ultimately influence community stability. However, the relative importance of different biotic mechanisms influencing the community stability of phytoplankton along nutrient and associated zooplankton grazing pressure gradients remains unclear. Here, we evaluated the importance of four potential stabilizing biotic metrics—taxon richness, synchrony, community dominance and biomass of phytoplankton to the seasonal stability over two decades of re-oligotrophication in 20 Danish lakes. We found no clear temporal patterns in seasonal stability across lakes but considerable variations in the individual lakes. Total phosphorus (TP) affected the seasonal stability of the phytoplankton communities either directly or indirectly through changes in community dominance. Total nitrogen (TN) influenced the seasonal stability indirectly via changes in phytoplankton taxon richness, synchrony, and community dominance. Grazer richness (that is, zooplankton taxa richness) impacted the seasonal stability indirectly through changes in phytoplankton taxon richness and synchrony. Grazing pressure, using the biomass ratio of zooplankton:phytoplankton as a proxy, had an indirect effect on seasonal stability via changes in synchrony and community dominance. Compensatory dynamics (as indicated by the synchrony of phytoplankton) exerted dominant control of phytoplankton seasonal stability at high TN and high grazer richness and pressure, while the portfolio effect (as indicated by taxon richness) contributed to phytoplankton seasonal stability at low TN and high grazer richness. However, a strongly negative selection effect (as indicated by community dominance of phytoplankton) was observed at high nutrient levels and low grazer richness. Grazer richness and grazing pressure had stronger stabilizing effects on the seasonal succession of the phytoplankton communities than did TP and TN. Our results highlight how various biotic mechanisms (for example, compensatory dynamics and portfolio effect) can change in their importance in maintaining the seasonal stability of phytoplankton communities subjected to nutrient and grazer control.

Space-time dynamics in monitoring neotropical fish communities using eDNA metabarcoding

The biodiverse Neotropical ecoregion remains insufficiently assessed, poorly managed, and threatened by unregulated human activities. Novel, rapid and cost-effective DNA-based approaches are valuable to improve understanding of the biological communities and for biomonitoring in remote areas. Here, we evaluate the potential of environmental DNA (eDNA) metabarcoding for assessing the structure and distribution of fish communities by analysing water and sediment from 11 locations along the Jequitinhonha River catchment (Brazil). Each site was sampled twice, before and after a major rain event in a five-week period and fish diversity was estimated using high-throughput sequencing of 12S rRNA amplicons. In total, 252 Molecular Operational Taxonomic Units (MOTUs) and 34 fish species were recovered, including endemic, introduced, and previously unrecorded species for this basin. Spatio-temporal variation of eDNA from fish assemblages was observed and species richness was nearly twice as high before the major rain event compared to afterwards. Yet, peaks of diversity were primarily associated with only four of the locations. No correlation between β-diversity and longitudinal distance or presence of dams was detected, but low species richness observed at sites located near dams might that these anthropogenic barriers may have an impact on local fish diversity. Unexpectedly high α-diversity levels recorded at the river mouth suggest that these sections should be further evaluated as putative “eDNA reservoirs” for rapid monitoring. By uncovering spatio-temporal changes, unrecorded biodiversity components, and putative anthropogenic impacts on fish assemblages, we further strengthen the potential of eDNA metabarcoding as a biomonitoring tool, especially in regions often neglected or difficult to access.

Degrees of honesty: cleaning by the redlip cleaner wrasse Labroides rubrolabiatus

Cleaning symbioses among coral reef fishes are highly variable. Cleanerfishes vary in how much they cooperate with (i.e. remove only ectoparasites) or cheat (i.e. bite healthy tissue, scales or mucus) on their fish clients. As a result, clients use various strategies to enforce cooperation by cleaners (e.g. punishment or partner choice), and cleaners use tactile stimulation to manipulate cheated client behaviour. We provide the first detailed observations of cleaning behaviour of the redlip cleaner wrasse Labroides rubrolabiatus and ask where interactions with this cleanerfish lie on the continuum of cleanerfish honesty, client control, and cleanerfish manipulation. Ninety per cent of redlip cleaner wrasses took jolt-inducing cheating bites from their clients, but they did so at a very low rate (~ 2 jolts per 100 s inspection). Retaliatory chases by clients were uncommon. Three-quarters (30 of 40) of cleaner wrasses used tactile stimulation on their clients, but rarely did so to reconcile with cheated clients. Instead, the majority (70%) of tactile stimulation events targeted a passing client that then stopped for inspection. The relationship between redlip cleaner wrasses and their clients appears to be less conflictual than those documented in other Labroides cleanerfishes. Future studies should test whether this low level of conflict is consistent across space and time and is underpinned by a preference for ectoparasites over other client-gleaned items. As an active cleaner that appears to take few cheating bites from their clients, L. rubrolabiatus has the potential to be as important a driver of fish health and community structure on coral reefs as its better-known relatives.

Trophic structure of ichthyofauna in streams of the Contas River basin, Brazil

ABSTRACT Understand how environmental factors correlate with the trophic structure of fish communities is a fundamental step to allow designing models for the functioning of stream ecosystems and planning conservation actions. Thus, this study aims to characterize the trophic structure of fish communities of streams of the Contas River basin and evaluate the relationships between local environmental factors (stream structure and limnological variables) and trophic structure. We sample nine streams of the Upper Contas sub-basin and nine of the Gongogi sub-basin using electric fishing. We analyzed the diet of 24 species, arranged in six trophic guilds, according to stomach contents: detritivores, omnivores, insectivores, invertivores, piscivores, and algivores. The results show high proportions of detritivores (46.62%), omnivores (28.55%), and insectivores (11.8%). Invertivores were correlated to colder streams, and with little proportion of sand in the substrate. Algivores were positively related to temperature and proportion of sand in the substrate. The relationship between other guilds and the environmental factors was not significant, probably due to limitations in the number of streams in the analysis. The sub-basins did not differ regarding the trophic structure, corroborating the perception that the trophic structure is more influenced by local factors than by broader scale factors.

Relating groundfish diversity and biomass to deepsea corals and sponges using trawl survey catch data

Deep-sea corals and sponges (DSCS) inhabit the world’s oceans and are often associated with high fish abundance. However, the precise nature and extent of any association is difficult to quantify and remains poorly understood. We investigated associations between DSCS and demersal fish using data from the Northwest Fisheries Science Center’s bottom trawl survey (2003-2015). General linear mixed models showed that average species density of groundfish was slightly higher and groundfish biomass slightly lower in tows with DSCS. Multivariate analyses were used to examine relationships among fish community structure, DSCS biomass, and environmental parameters (depth, latitude, bottom temperature). No strong correlations occurred between the community structure of groundfish and DSCS biomass; instead, bottom temperature and depth were the primary drivers of community composition. However, indicator species analysis also showed various species-specific associations with DSCS. Specifically, some flatfish species exhibited relationships with coral and sea pen biomass, whereas some rockfishes were associated with high sponge biomass. Our results provide information on the broad-scale associations among DSCS and demersal fishes that may be useful for developing studies focused on the functional value of DSCS as essential fish habitat and the role they play in groundfish life history and ecology.

Long-term variations in fish community structure under multiple stressors in a semi-closed marine ecosystem in the South China Sea

Daya Bay is an ecologically and economically crucial semi-closed bay along the southern coast of China. It is proven to be a stressed ecosystem and therefore obviously vulnerable to further extrinsic disturbance. This study used fish data from bottom-trawl surveys, conducted from 1985 to 2018, to analyze variations in the fish community structure over the past 30 years. The results showed that warm-water fish species were overwhelmingly dominant during all years, suggesting the bay's tropical to subtropical characteristic. By 2015, the number of fish species had decreased by 29.44% of that caught in 1987, moreover, values of the Shannon–Wiener diversity index and the Margalef richness index were lower in 2015 compared to 2004. There were evident shifts in the fish community composition from pelagic to demersal species, as suggested by the dominant species found in springtime, the dominant families, and percentages denoting the numbers of species in the main orders. Average fish body weight in landings declined from 13.4 g to 7.58 g, the body sizes of four typical commercial fish species decreased by varying degrees over the last 30 years. Abundance–biomass comparison curves suggested that the Daya Bay fish community was more stressed in 2015 than in 2004 during all seasons, except winter. In general, the fish community structure in Daya Bay is consequently in an unsteady state. Multiple anthropogenic disturbances, such as fishing (including overfishing and changes in the main fishing gears), the destruction of natural habitats, pollutants, and anthropogenically induced temperature changes, are likely to have caused obvious shifts in the bay's fish community structure. Therefore, we emphasize the need for integrating management of multiple anthropogenic stressors to achieve ecosystem-based management.

Forecasting the legacy of offshore oil and gas platforms on fish community structure and productivity.

There are currently thousands of offshore platforms in place for oil and gas extraction worldwide, and decommissioning efforts over the next three decades are estimated to cost more than US$200 billion. As platforms reach the end of their useful lifetime, operators and regulatory agencies will assess the environmental impact of potential decommissioning strategies. Among the many factors that will be weighed in preparation for these major economic and engineering challenges is the fate of the fish and invertebrate communities that inhabit the structures underwater. Offshore platforms act as inadvertent artificial reefs, and some are recognized among the most productive fish habitats in the global oceans. We present a model for forecasting changes to fish communities surrounding offshore installations following a series of decommissioning alternatives. Using 24 platforms off southern California, we estimate fish biomass and somatic production under three possible decommissioning scenarios: leave in place, partial removal at 26-m depth, and complete removal of the platform and underlying shell mound. We used fish density and size data from scuba and submersible surveys of the platforms from 1995-2013 to estimate biomass and annual somatic production. Bottom trawl surveys were used to characterize future fish assemblages at platform sites under the complete-removal decommissioning scenario. Based on a conservatively modeled extrapolation of the survey data, we found that complete removal of a platform resulted in 95% or more reduction in the average fish biomass and annual somatic production at the site, while partial removal resulted in far smaller losses, averaging 10% or less. In the event that all surveyed platforms are completely removed, we estimated a total loss of more than 28,000kg of fish biomass in the Southern California Bight. Platform habitats, which attract reef-dwelling fish species, had minimal overlap in community composition with the surrounding soft-bottom habitat. To best serve the wide range of stakeholder interests, the site-specific biomass, productivity and species composition information provided in this study should be incorporated into strategic decommissioning planning. This approach could be used as a model for informing "rigs to reefs" discussions occurring worldwide.

Rapid winter warming could disrupt coastal marine fish community structure

Marine ecosystems are under increasing threat from warming waters. Winter warming is occurring at a faster rate than summer warming for ecosystems around the world, but most studies focus on the summer. Here, we show that winter warming could affect coastal fish community compositions in the Mediterranean Sea using a model that captures how biotic associations change with sea surface temperature to influence species’ distributions for 215 fish species. Species’ associations control how communities are formed, but the effect of winter warming on associations will be on average four times greater than that of summer warming. Projections using future climate scenarios show that 60% of coastal Mediterranean grid cells are expected to lose fish species by 2040. Heavily fished areas in the west will experience diversity losses that exacerbate regime shifts linked to overexploitation. Incorporating seasonal differences will therefore be critical for developing effective coastal fishery and marine ecosystem management. The rate of warming in many marine ecosystems is faster in winter than in summer. Winter warming will impact fish species’ associations in the Mediterranean more than summer warming, and this has implications for how communities form and for future biodiversity, particularly in heavily fished areas.

Struktur Komunitas dan Preferensi Habitat Ikan Karang pada Terumbu Buatan di Teluk Awang dan Teluk Bumbang, Pulau Lombok

<strong>Community Structure and Habitat of Coral Fish on Artificial Reef in Awang and Bumbang Bay, Lombok Island</strong>. Artificial reefs which were placed in Teluk Awang and Teluk Bumbang intended to restore habitat fish resources. This paper aims to evaluate the development of artificial reefs in both locations. The activities was conducted in June and December 2015. Data collection included fish and benthic communities, biological parameters (phytoplankton, zooplankton, meroplanton), physical parameters (temperature, salinity, conductivity, pH, turbidity, dissolved oxygen), and chemical parameters waters (nitrates and phosphates). Observation of fish community using SCUBA diving equipment, underwater sheets, stationery and GPS, then visual observations using a modified stationary visual census technique. Visual recorded also used for benthic communities. Water sampling taken on the surface and bottom at depths of 9 m and 11 m using water quality checker. Biological parameters were taken using 60 µ, 300 µ and plankton net sizes 700 µ. Nutrients were observed in the laboratory by taking water samples in situ. Laboratory tests were carried out for nutrients as well as plankton and meroplankton. Benthic communities were categorized into four life forms, namely live coral covered, dead coral, biota (algae and other biota) as well as the abiotic component. Habitat preferences identified through analysis of factors related to fish abundance by principal component analysis method. The results showed that on those artificial reefs in Awang and Bumbang Bay found as many as 8 - 16 species of coral fish belongs to 15 families, dominated by Apogonidae (Archamia fucata), Pomacentridae (Neopomacentrus cyanomos) and Phempherididae (Phempheris oulensis), ranges of the abundance 268 to1088 individual. The ecological index showed low to moderate type of diversity, the dominance index does not indicate the dominance of certain species and the evenness index indicated that the fish dispersal characteristic is quite flat. Fish habitat preference in Awang Bay supported by the presence of algae and other biota, nutrients, and salinity. While in Teluk Bumbang supported by the abundance of fito-zooplankton, dissolved oxygen, and turbidity

Fish community structure as an indicator of the ecological significance: A study from Ulhas River Estuary, Western coast of India

Fish community structure as an indicator of the ecological significance: A study from Ulhas River Estuary, Western coast of India

Fish community structure before reservoir inundation in Cipanas, West Java

The reservoir is an artificial lake created by blocking the flow of the river using transverse construction of the river or dam made of rock, soil or walls. The purpose of the research was to determine and map the structure of fish community before reservoir inundation in the Cipanas River. The study used survey methods with sampling data collection techniques. The research station was determine using a purposive sampling method. The study was conducted at three stations representing inundation plan areas (6° 41’51 “S and 108° 01’32” E) and after inundation plans (6° 38’53 “S - 108° 02’06” E and 6° 37’51 “S - 108° 02’53” E) of Cipanas Reservoir. The parameters measured included relative abundance, diversity index (H’), dominance (C), uniformity (E), and water quality. Fifteen fish species of seven families were collected from Cipanas River. The diversity index was moderate which ranged of 1.20 ≤ H ≤ 2.08, the dominance index was low to moderate which ranged of 0.16 ≤ C ≤ 0.51, and the uniformity index was low to moderate which ranged of 0.27 ≤ E ≤ 0.47. The structure of the fish community at the station I was relatively unstable, while at stations II and III were classified as depressed. Water quality in the Cipanas River was in a good condition and support the life of fish based on the water quality standards class II and III according to the Government Regulation no. 82 of 2001.

Fish community structure and distribution at Lake Siawan, West Kalimantan, Indonesia

Freshwater fish in Kalimantan is the highest among Indonesian islands, with many endemic species. Therefore, a fish population study was conducted in Lake Siawan, West Kalimantan, for the purpose of determining fish diversity, abundance, local distribution, species status, and its habitat. Five sampling stations were designated and the catch per unit of efforts (CPUE) approach was adopted to get the samples. The fish caught were counted to get the species diversity and abundance. There were 57 species from 13 families that were recorded, with Cyprinidae as the dominant family with 34 species, followed by Bagridae with 4 species. Station 1 and station 5 were recorded as the highest and the lowest fish diversity, respectively. The most abundant species were Brevibora dorsiocellata and Rasbora tornieri. Four species has wide distribution and almost all of the fish found was native species. Three endemic species recorded were Hampala bimaculata, Leptobarbus hosii and Puntigrus anchisporus.

From drought to flood: Sudden carbon inflow causes whole-lake anoxia and massive fish kill in a large shallow lake

Fish kills are a recurring phenomenon in hypereutrophic lakes. The effects of a sudden injection of anoxic bottom water into surface waters are well known, as well as the degradation of phytoplankton blooms and the release of phytoplankton toxins. However, in this study we report on a new, climate-related cause of fish kills in a shallow lake. We observed that a long period of drought in a hot summer followed by heavy rain resulted in a large input of labile organic matter. This was followed by a condition of whole-lake anoxia and fish kill in the lake basin receiving the input, while the second basin, immediately downstream, was left unaffected. To test the causal relationship between these events, an oxygen model calculated that respiration had increased by 230% following the organic input and caused whole-lake nocturnal anoxia for four days despite unaltered daytime photosynthesis. One year after the fish kill, roach and bream had migrated from the downstream lake basin and re-established dense populations, while large predatory perch and pike remained very few. This imbalance in the fish food webs may last for several years and in turn increase predation on zooplankton and release phytoplankton from grazing control. The prolonged effects of fish kills on fish and lake community structure demand further research, as weather-induced anoxia can be expected to become more common.

Influences of small hydroelectric power plants on homogenization of the ichthyofauna in a tropical river

The native fishes of the Neotropical region have been heavily impacted by the construction of reservoirs that block the rivers in different degrees. Small Hydroelectric Power Plants (SHPP) have been an alternative way to take advantage of small electricity production potential, with low cost. However, there is no basis in the belief that SHPP have less deleterious effects on river habitat than large hydropower plants. The aim of this study was to evaluate eventual changes in the ichthyofauna because of the influences of SHPP in the middle reaches of a tropical river in south-eastern Brazil. The raised hypothesis is that SHPP change the ichthyofauna composition and increase the taxonomic and functional similarities (homogenization). Fish collections were carried out quarterly at six locations along a 20 km stretch of the Paraiba do Sul River, before and after the construction of the SHPP. The fish community structure changed between the two periods, with a decrease in the fish numerical abundance, whereas the species richness did not change. Sensitive species with specialized feeding habits (namely, Hartia loricariformis, Steindachineridium parahybae, Hypomasticus mormirops, Characidium alipioi, Chyphocharax gilbert, Corydoras nattereri and Pogonopoma parahybae) occurred only before the SHPP, being replaced by several species of Characiformes, among them four of genus Astyanax (namely, A. giton, A. hastatus, A. taeniatus, and A. intemedium) that are tolerant and omnivores; however, most of functional traits were maintained. The taxonomic dissimilarity increased significantly, whereas the functional dissimilarity did not differ between the two periods. The hypothesis of ichthyofauna homogenization was not confirmed in this study, probably because of the short time period since the SHPP construction.

How do spatial and environmental factors affect the fish community structure in seasonally flooded karst systems?

Spatial and temporal variation of the physical and chemical conditions of coastal karst wetland ecosystems, which annually range from flooded to completely dry, generate a very dynamic fish community structure. We assessed the relative influence of spatial dependence and environmental factors on fish community structure in a seasonally flooded tropical karst system on the north-western coast of the Yucatan Peninsula, Mexico. Sampling was carried out between November 2009 and April 2010, while the area was inundated by seasonal floodwater. Fish biomass, abundance and species richness, as well as environmental variables and geographic location, were recorded. A variation partitioning analysis was performed to assess the influence of the spatial and environmental variables on the fish community using multiple regression, and a principal coordinates analysis of neighbor matrices (PCNM). Spatial factors had a greater influence on the changes in the community structure than the environmental factors. After spatial variation, environmental effects from conductivity, oxygen saturation, temperature and depth further shaped the community. These results imply that, despite the diversity of niches and wide variation in environmental conditions, the structuring force of the community is the spatial dynamic probably linked to species dispersal mechanisms and reproductive strategies.

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

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

Diversity of Reef Fish in Tapian Nauli Bay, Central Tapanuli

Tapian Nauli Bay is along the coast of Sibolga Bay starting from the border of Sibolga City towards Barus, Tapanuli Tengah. In the Tapian Nauli Bay area there are plenty of fish biological resources and coral reef ecosystems. It is known that the reef fish community is a biotic component of the coral reef ecosystem that can be utilized as marine biological resources.This study aims to examine the diversity of reef fish. The method used in monitoring reef fish is a method Underwater Visual Census (UVC).The reef fishes observed were then grouped into 3 groups of fish, namely: target species, indicator species, and major species, then the structure of the reef fish community was calculated. The results showed that the composition of reef fish species in Sitardas Beach and Bakar island was dominated by major fish (97%), then followed by target fish (2%) and indicator fish (1%).And, overall the diversity of reef fish species in the Sitardas Beach and Bakar island waters shows a low level and shows a relatively unstable uniformity level.

Seasonal changes in fish diversity, density, biomass, and assemblage alongside environmental variables in the Yangtze River Estuary.

The present study used multivariate techniques, to analyze the fish species diversity and distribution patterns in order to determine the possible role of environmental parameters as drivers of fish community structure and composition in the Yangtze River Estuary (YRE). This analysis was conducted using data obtained in the YRE from February 2012 to December 2014. Analysis of the catch data showed that species composition, total density, and total biomass varied significantly between stations and seasons. Thirty-eight species belonging to 18 families were collected. Sciaenidae was the most dominant family accounting for 40.8% of total captured specimens. In descending order, Collichthys lucidus, Cynoglossus gracilis, Chaeturichthys stigmatias, and Lophiogobius ocellicauda dominated catches in the YRE. These four species constituted 64.2% of the total catches and showed average dissimilarities of 74.19% between stations and 81.3% between months. The highest number of fish specimens captured was recorded in August 2012 while the highest species richness was observed in December 2013. The mean fish density and biomass for the YRE was 0.35 individuals/m2 and 2.5g/m2, respectively. The mean density and biomass for the most important and dominant species changed significantly between stations and seasons. Canonical correspondence analysis indicated that salinity and chlorophyll-a were the key variables that structured the fish assemblage in the YRE. High total species density and biomass were recorded in high saline stations (North Branch) of the YRE. This study confirms that most species captured in the YRE needs estuarine conditions to complete their growth and development. Hence, the findings in this study are important to understanding and developing suitable conservation plans for the management of fish resources in the YRE.