Explaining recreational angling catch rates of Eurasian perch,Perca fluviatilis: the role of natural and fishing‐related environmental factors

Angling catch records are frequently used to reveal fish population developments. It is therefore important to understand the determinants of angling catches. This study focused on angler‐related, biotic and abiotic factors influencing catchability of Eurasian perch, Perca fluviatilis L. A multi‐lake (21 lakes) study based on angling diaries collected in Mecklenburg‐Vorpommern, Germany (2006/2007), found that angler‐related factors such as fishing experience, species preference and bait/lure type had a large impact on perch catch rates. Additionally, environmental conditions (nutritional status and water transparency) affected either the size or the number of perch caught by anglers. Catch rates varied seasonally, which was confirmed by an experimental fishery on a gravel pit (2008). This portion of the study showed that altered food availabilities in the course of the year caused food limitation in perch, which in turn facilitated high catch rates and female‐biased exploitation in autumn. It is concluded that both angler‐related and abiotic factors interact affecting perch catch rates and size of perch captured in recreational angling.     

Perch production in forest lakes: the contribution of abiotic and biotic factors

Horppila J, Olin M, Vinni M, Estlander S, Nurminen L, Rask M, Ruuhijärvi J, Lehtonen H. Perch production in forest lakes: the contribution of abiotic and biotic factors.
Ecology of Freshwater Fish 2010: 19: 257–266. © 2010 John Wiley & Sons A/S Abstract – The biomass, growth and production of perch (Perca fluviatilis (L.)) in five humic forest lakes in southern Finland were estimated and the abiotic and biotic factors contributing to the between‐lake differences were explored. The average perch biomass in the study lakes varied from 13.1 to 45.6 kg·ha^?1 and annual production from 6.0 to 16.5 kg·ha^?1. The highest biomass and production were found in Lake Majajärvi with highest water colour and nutrient concentration. Variability in fish density rather than in individual growth rate seemed to be the main factor behind the between‐lake differences in perch production. No dependence of perch production on water transparency was found, because transparency had a stronger effect on individual growth than on fish density. The length increment of perch in their second year increased significantly with water transparency but at older ages no such dependence was found. At age of 4 years, the growth rate of perch decreased with perch density, indicating intraspecific competition for benthic food resources. At age of 7 years, the growth rate increased with increasing roach (Rutilus rutilus (L.)) abundance, suggesting that roach served as a resource for piscivorous perch. The effects of predatory top‐down control on perch populations were probably obscured due to the variable size and water quality of the study lakes.     

Environmental determinants of fish community structure in gravel pit lakes

Gravel pit lakes are increasingly common, and there is an urgent need to better understand the functioning of these artificial and disconnected ecosystems. However, our knowledge of the environmental determinants of fish community structure within these types of lakes remains poor. In this study, we quantified the taxonomic diversity, fish species and life‐stage composition in 17 gravel pit lakes sampled in 2012 and 2013 located in south‐west France to determine the potential role of environmental variables (i.e. lake morphology, productivity, water quality and human‐use intensity) as drivers of fish community structure and composition. Our results demonstrated that fish community structure significantly differed between gravel pit lakes, and we notably found that lakes managed for angling hosted higher levels of taxonomic diversity. We also found that young and large lakes supported higher native species biomass and were dominated by native European perch (Perca fluviatilis). Older, smaller and more productive lakes, located closer to the main urban area, supported a higher biomass of non‐native species such as largemouth bass (Micropterus salmoides). Native and non‐native sport fishing species such as northern pike (Esox lucius), pikeperch (Sander lucioperca), common carp (Cyprinus carpio) and cyprinid prey species were positively associated with fishery management effort, suggesting that management practices play also a critical role in shaping fish species composition. Overall, our study demonstrated that fish community composition followed a predictable shift along environmental gradients associated with the maturation of gravel pit lakes and the associated human practices.     

Prey selection and growth in 0+ Eurasian perch Perca fluviatilis L. in littoral zones of seven temperate lakes

We studied the relationships between the planktonic food base and feeding patterns of juvenile mid-summer/early autumn Eurasian perch Perca fluviatilis L., a common predatory freshwater fish in large parts of Europe and Asia. The feeding of 0+ perch was studied during summer and autumn in littoral habitats of seven lakes with different environmental conditions – four Latvian (Auciema, Riebinu, Vārzgūnes, Laukezers) and three Estonian (Kaiavere, Prossa and Akste) lakes. Simultaneously, the abundance, biomass and structure of zooplankton communities were examined. We focused on the littoral areas because many studies in lakes suggest that littoral habitats are particularly important for 0+ fish growth and survival. We were interested in the question: can the diet and growth of 0+ perch be explained by zooplankton community structure? We also presumed that if the amount of zooplankton is low, more benthic invertebrates will be consumed by 0+ perch. Opposite to expectations, we found that zooplankton always counted for over 90% of diet biomass in perch. There were also clear correlations between the zooplankton biomass in a given lake, the zooplankton biomass in 0+ perch stomachs, and the fish growth rate. The study also suggested that nutrient enrichment can positively impact the 0+ perch feeding conditions in lakes.     

Response of walleye and yellow perch to water‐level fluctuations in glacial lakes

The influence of water levels on population characteristics of yellow perch, Perca flavescens (Mitchill), and walleye, Sander vitreus (Mitchill), was evaluated across a range of glacial lakes in north‐eastern South Dakota, USA. Results showed that natural variation in water levels had an important influence on frequently measured fish population characteristics. Yellow perch abundance was significantly (P < 0.10) greater during elevated water levels. Yellow perch size structure, as indexed by the proportional size distribution of quality‐ and preferred‐length fish (PSD and PSD‐P), was significantly greater during low‐water years, as was walleye PSD. Mean relative weight of walleye increased significantly during high‐water periods. The dynamic and unpredictable nature of water‐level fluctuations in glacial lakes ultimately adds complexity to management of these systems.     

Environmental influences on largemouth bass Micropterus salmoides populations in shallow Nebraska lakes

The influence of environmental variables on largemouth bass Micropterus salmoides (Lacépède) populations in 22 shallow (mean depth 1.0–2.9 m) Nebraska lakes was evaluated. Largemouth bass exhibited density‐dependent size structure and growth, but not condition. Total annual mortality averaged only 30%. Deeper lakes contained low density largemouth bass populations with a high proportion of fish >380 mm, whereas larger lakes with little submerged vegetation had faster growth. The proportion of largemouth bass >380 mm and relative abundance tended to increase with emergent vegetation coverage. More stable recruitment was evident in shallower lakes with increased emergent vegetation coverage. Strong year classes were associated with cooler September air temperatures. Largemouth bass populations exhibited density‐dependent effects in lakes up to 332 ha. Lake depth, emergent vegetation and autumn air temperatures may influence largemouth bass populations more than previously suggested.     

Habitat distribution of fish in late summer: changes along a nutrient gradient in Danish lakes

Abstract – The horizontal distribution of fish in lakes varies with species, age, predation risk, vegetation coverage and water clarity. Although sporadic data are available for specific lakes, little is known about how habitat distribution generally changes along a gradient in nutrients and clarity. Here we analyse littoral and pelagic fish catch data for 34 Danish lakes (covering 94 lake years) with contrasting total phosphorus (TP) concentrations and mean depth levels (but mainly eutrophic and shallow). Electrofishing was conducted during day along the shore or along the edge of the reed belt if such existed. Gill nets were set overnight for 18 h in open water. We calculated a littoral proportion as: LITPRO = (100 × number caught by electrofishing in the near‐shore area)/(number caught by electrofishing in the near‐shore area and nets in the open water). At all summer TP concentrations LITPRO was high for several ‘littoral’ species such as gudgeon (Gobio gobio), rudd (Scardinius erythrophtalmus) and pike (Esox lucius) and low for more typical pelagic species like pikeperch (Sander lucioperca), ruffe (Gymnocephalus cernuus) and smelt (Osmerus eperlanus). However, for many of these species including the dominant roach (Rutilus rutilus) and perch (Perca fluviatilis) LITPRO increased with TP or lake water chlorophyll a (CHLA) for fish >10 cm, suggesting a more littoral distribution with increasing turbidity. Exceptions are pikeperch and bream (Abramis brama). For bream, LITPRO increased significantly with mean lake depth only. For fish ≤10 cm LITPRO showed only a weak relationship to TP, CHLA or depth. In accordance with the TP‐dependent distribution, major changes occurred in the fish community structure during the monitoring period following nutrient loading reduction. A comparison of LITPRO from the first part of the monitoring period (1989–1993) with a subsequent period (1997–2003) for four abundant species showed a significant decline in LITPRO over time for large‐ and small‐sized roach and perch and large rudd. This suggests a fast response in fish distribution to improved water quality. It further demonstrates that fish monitoring in lakes should cover both littoral and pelagic habitats to describe the recovery process.     

Does morphological variation between young‐of‐the‐year perch from two Swedish lakes depend on genetic differences?

Heynen M, Hellström G, Magnhagen C, Borcherding J. Does morphological variation between young‐of‐the‐year perch from two Swedish lakes depend on genetic differences?
Ecology of Freshwater Fish 2010: 19: 163–169. © 2009 John Wiley & Sons A/S Abstract – Different local environmental conditions have often been found to generate phenotypic diversity. In the present study we examined morphological differences between young‐of‐the‐year perch from two lake populations with differences in size‐specific predation risk. A common garden setup was used to examine the genetic and environmental components of the morphological variation. We found differences in head and jaw length and slight differences in body depth between the wild young‐of‐the‐year perch from Lake Ängersjön and Lake Fisksjön. The differences found between the wild fish from the two lakes were not maintained under common garden rearing. The observed morphological divergence between the wild young‐of‐the‐year perch from Lake Ängersjön and Lake Fisksjön seems to stem mainly from a plastic response to different environmental conditions in the two lakes. It is clear that the morphological traits are not influenced by direct reaction to the size‐specific risk of cannibalism, but probably stem from a combination of different environment characteristics, including resource and habitat use, and the density of other piscivores, such as pike.     

Ice fishing reveals size structure but not abundance of Eurasian perch in small boreal lakes

Management of inland recreational fisheries would benefit from stock abundance and size structure data. Feasibly standardised angling methods such as ice fishing could produce representative catch-per-unit-effort (CPUE) information on the abundance of different-sized fish in small lakes. Here, we first used standard Nordic multimesh gillnets to obtain number-per-unit-effort (NPUE), biomass-per-unit-effort (BPUE) and size structure data on Eurasian perch (Perca fluviatilis) stocks in 11 small boreal lakes in summer. Second, the same lakes were ice-fished by voluntary anglers using a pre-defined, loosely standardised protocol to obtain angling-based NPUE, BPUE, and length frequency distributions. Effects of environmental variables such as water oxygen concentration and light penetration on angling catch rates were controlled statistically. Neither perch Nordic gillnet NPUE nor BPUE corresponded to ice-fishing CPUEs. However, the length distribution of the catch did not differ between methods. Our results imply that traditional ice fishing applying natural baits is relatively unselective for fish size and could produce valid length-based indicators for management purposes while angling CPUE was poorly related to Nordic gillnet CPUE.     

Impact of environmental and innate factors on the food habit of Chinese perch Siniperca chuatsi (Basilewsky) (Percichthyidae)

Laboratory and field investigations were conducted to study the food habit of Chinese perch Siniperca chuatsi (Basilewsky) from first feeding through adult stage. Only fish larvae were consumed by Chinese perch larvae (2–21 days from hatching), and the presence of zooplankton did not have any significant effect on their survival rate. The ability of Chinese perch to feed on zooplankton is clearly limited by some innate factor. Instead of gill rakers, Chinese perch larvae have well‐developed sharp teeth at the first feeding stage, and are well adapted to the piscivorous feeding habit unique to the larvae of Chinese perch, e.g. they bite and ingest the tails of other fish larvae. At the first feeding stage (2 days from hatching), daily rations were both very low, either in light or complete darkness. Although early‐staged Chinese perch larvae (7–17 days from hatching) could feed in complete darkness, their daily rations were always significantly higher in light than in complete darkness. Late‐staged Chinese perch larvae (21 days from hatching) were able to feed in complete darkness as well as in light, similar to the case of Chinese perch yearlings. Chinese perch yearlings (total length, 14–16 cm) consumed prey fish only and refused shrimp when visual cues were available (in light), but they consumed both prey when visual cues were not available (in complete darkness), suggesting that prey consumption by Chinese perch yearlings is affected by their sensory modality in predation. Both prey were found in the stomachs of similar‐sized Chinese perch (total length, 14–32 cm) from their natural habitat, suggesting that shrimp are consumed by Chinese perch at night. Prey selection of Chinese perch with a length >38 cm, which consumed only fish in the field, appears to be based upon prey size instead of prey type. These results suggest that although environmental factors (e.g. light intensity) affect prey detection by Chinese perch, this fish is anatomically and behaviourally predisposed to prey on live fish from first feeding. This makes it a difficult fish to cultivate using conventional feeds.     

Environmental factors associated with the decline of dwarf inanga Galaxias gracilis McDowall in New Zealand dune lakes

1. The dwarf inanga Galaxias gracilis is restricted to 13 dune lakes along an 80 km length of coastline on the west coast of the North Island, New Zealand, and its abundance has declined in at least eight of these lakes. It is therefore a rare and endangered endemic species. 2. A range of environmental variables were compared between lakes where it is still common and lakes where it is now rare to identify variables associated with its low abundance. 3. Lakes where dwarf inanga were rare all had a lower pH, lower concentrations of calcium, magnesium and silica, and higher concentrations of chloride than lakes where dwarf inanga were common. In addition, they contained different charophyte plant species, as well as stocked populations of eels and/or introduced exotic fish species capable of preying on one or more of the life stages of dwarf inanga. 4. Factors not associated with the low abundance of dwarf inanga included lake size and depth, land use in the catchment, lake level fluctuations, the extent of emergent vegetation, littoral zone substrate composition, and water quality parameters including maximum water temperature, water transparency, and minimum oxygen levels in the hypolimnion. 5. The identification of factors associated with the low abundance of dwarf inanga has allowed testable hypotheses to be developed to account for its decline in certain lakes. However, biological data, particularly on the location of spawning grounds and on the feeding requirements of larvae, are required before all these hypotheses can be tested. 6. The results have formed the basis for a management plan for the conservation of this species, in which whole-lake experiments are being carried out to identify the effects of introduced plants and fish on its population size. ©1997 John Wiley & Sons, Ltd.     

Resource-use,body condition and parasite load metrics indicate contrasting health of stocked and native game fishes in Canadian prairie lakes

This study evaluated the status of native and stocked fish species in 13 prairie lakes in central Canada over eight years (2007–14) using three metrics: resource-use (benthic versus pelagic carbon via stable isotopes); body condition (relative weight index W_r); and parasite load (cestode gut enumerations). Analyses included game and non-game fishes, like naturally occurring northern pike, Esox lucius L., and yellow perch, Perca flavescens Mitchill, but focused on stocked walleye, Sander vitreus (Mitchill) because it supports a robust recreational fishery. Walleye and northern pike were significantly more reliant on benthic carbon than yellow perch or forage fishes (p < 0.05), but this reliance was not associated with any measured environmental variables for any species. In lakes with game fishes, forage fishes exhibited higher reliance on benthic energy, possibly due to predator avoidance strategy, particularly yellow perch. Walleye body condition index was consistently lower (<95–105) than values exhibited by the other two game fishes (81–139), and parasites were only common in walleye and associated with lake-water salinity (r² = 0.93, p < 0.05) and sex (p < 0.05). Based on the results, the most desirable game fish, walleye, appears less resilient to environmental variability than northern pike and yellow perch, making this species more susceptible to impacts of future climate change.     

Effects of environmental factors on size-related growth efficiency of perch, Perca fluviatilis

Abstract – Two aspects of size-dependent growth were addressed using perch, Perca fluviatilis L, from 22 Swedish lakes. Firstly, maximum annual growth decreased linearly with length after the previous year. Secondly, median or realized growth showed a non-linear pattern, with minimum growth efficiency at intermediate length, probably related to the shift from invertebrate to fish diet. Between-lake variation in size-related growth efficiency was better explained by fish community characteristics than by abiotic factors. The growth of most size classes was negatively related to fish biomass, especially to biomass of 100 to 199-mm perch. Growth efficiency of perch >200 mm was positively related to the proportion of large perch in the community. These size- and density-dependent growth responses suggest that effects of competitive and predatory interactions will often mask the controlling or limiting effects of abiotic factors, such that realized growth of individuals and populations are poorly described by deterministic asymptotic growth models.     

Flood pulse and the dynamics of fish assemblage structure from neotropical floodplain lakes

Abstract – The dynamics of fish assemblages from seven floodplain lakes of Salado River (Argentina) was monthly analysed during two contrasting hydrological seasons. Partial canonical correspondence analysis indicated that assemblage structure was predictably linked to environmental characteristics that varied along temporal and spatial scales. Species distributed differentially along an environmental gradient of temperature, hydrometric level, conductivity, macrophyte cover and transparency in relation to their sensory capabilities (following piscivory‐transparency‐morphometry model) and life history strategies. During high water season, assemblages were associated with temperature and hydrometric level, factors which varied mainly across temporal scales and exhibit a regional range of action. During low waters, assemblage structure correlated with macrophyte cover and transparency, factors that varied fundamentally on spatial scales and have local impact. These results indicate that the determinism of fish assemblages does not vary substantially between hydrometric periods, although the environmental variables affecting fish assemblages and their scale of action are clearly different.     

Potential effects of global climate change on fisheries in the Trasimeno Lake (Italy), with special reference to the goldfish Carassius auratus invasion and the endemic southern pike Esox cisalpinus decline

Global climate changes have led to a gradual warming of the planet, resulting in decreased precipitation and rising temperatures in Mediterranean inland waters. In Trasimeno Lake, the largest shallow lake in Italy, some non‐native fish species have probably benefited from these changes as they are thermophilic and characterised by wider habitat preferences. Fish data collected by gillnets and fyke nets between 1956 and 2016, and by electrofishing in 1993 and 2014, were used to analyse changes over time in the fish community in relation to environmental conditions. An explosion in goldfish Carassius auratus (L.), following its introduction in 1988, coupled with water level fluctuations and reduced transparency, contributed to the reduction in commercial fish catch in the lake, and to the decline of the endemic southern pike Esox cisalpinus Bianco & Delmastro, already threatened by reduced spawning habitat and interspecific competition with other non‐native predatory fishes.     

Identifying across-system sources of variation in a generalist freshwater fish: correlates of total and size-specific abundance of yellow perch

Abstract –  Variation in fish abundance across systems presents a challenge to our understanding of fish populations because it limits our ability to predict and transfer basic ecological principles to applied problems. Yellow perch ( Perca flavescens ) is an ideal species for exploring environmental and biotic correlates across system because it is widely distributed and physiologically tolerant. In 16 small, adjacent systems that span a wide range of environmental and biotic conditions, yellow perch were sampled with a standard suite of gear. Water quality, morphometry, vegetation, invertebrates and fish communities were concurrently measured. Multimodel inference was used to prioritise regressors for the entire yellow perch sample and three size groups (35–80, 81–180, ≥181 mm TL). Across systems, pH and fish richness were identified as the key drivers of yellow perch abundance. At very low pH (<4.0), few fish species and few yellow perch individuals were found. At ponds with moderately low pH (4.0–4.8), numbers of yellow perch increased. Ponds with high pH (>4.8) had many other species and few yellow perch. Similar patterns for pH and fish community were observed for the two largest-size classes. Negative interactions were observed between the medium- and large-sized yellow perch and between the largest and smallest yellow perch, although interspecific interactions were weaker than expected. This examination of variability for an indicator species and its component-size classes provides ecological understanding that can help frame the larger-scale sampling programs needed for the conservation of freshwater fish.     

南昌市13个湖泊的鱼类群落结构及其物种多样性特征

为了解南昌市面积1 km2以上湖泊的鱼类群落结构及其物种多样性特征,探究影响湖泊鱼类群落结构空间分布的环境因子,于2019-2020年在南昌市13个湖泊进行了鱼类资源调查。结果显示,采集到的39种鱼类隶属5目、9科、33属;优势种以鲫（Carassius auratus）、?（Hemiculter leucisclus）为主;不同湖泊的鱼类群落结构被划分为3个类群,与湖泊功能定位密切相关。鱼类Shannon-Wiener多样性指数值平均值为2.15,丰富度指数平均值为2.97,均匀度指数平均值为0.92,Shannon-Wiener多样性指数、丰富度指数与湖泊面积、水深、pH和透明度存在显著的相关性。冗余分析（RDA）表明,水深、pH、总氮和氨氮是引起鱼类群落结构在南昌市不同湖泊间差异的主要影响因子,人为活动干扰可能对调查区域内湖泊的鱼类群落结构和生物多样性特征施加影响。     

Development of a feeding strategy for silver perch, Bidyanus bidyanus (Mitchell), based on restricted rations

To develop a feeding strategy for the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell), a series of eight experiments was done in 1 m³ cages in an aerated, earthen pond to determine the effects of feeding rate (% body weight) and feeding frequency (no. of feeds day^?1) on the growth and feed conversion ratio (FCR) of fingerlings and larger fish under ambient water temperatures over the range 13.8–30.6°C. Fish were fed extruded pellets of a silver perch diet containing 34% digestible protein and 14 MJ kg^?1 digestible energy. Commercial silver perch farmers were consulted about feeding practices for large fish (>500 g) and at water temperatures below 12°C, and winter feeding practices for other warmwater species were used to complete the strategy. In the feeding experiments, growth and FCR increased with increasing feeding rates to a level above which only FCR increased. Optimal feeding rates and frequencies were those which resulted in maximal growth, while minimizing effort (feeding frequency) and FCR. The highest feeding frequency required for maximal growth, including that of small fingerlings was twice (2 ×) daily, and the optimal feeding rates varied with water temperature and size of fish. The optimal daily regimes were: small fingerlings (initial mean weight, 2.0 g) 7.5% 2 × at a mean temperature of 23.3°C; fingerlings (14.9–27.7 g) 7.5% 2 × at 27.1°C, 5.0% 2 × at 23.7°C and 2.0% 1 × at 16.8°C; and large silver perch (162.5–510.6 g) 0.5% 1 × daily or 1.0% on alternate days at 15.6°C, 1.0% 1 × at 17.3°C, 3.0% 2 × at 24.1°C and 2.0% 2 × at 27.9°C. It is suggested that regimes of 0.5% 1 × daily for fingerlings (<50 g) and 0.5% 1 × on alternate days for larger fish are used at temperatures of 9–12°C, and 0.5% 3 days week^?1 and 0.5% 1 day week^?1 for fingerlings and larger fish, respectively, at 6–9°C. Feed inputs should not exceed 150 kg ha^?1 day^?1 in ponds less than 0.3 ha and 100 kg ha^?1 day^?1 in larger ponds. Our research has established a feeding strategy for silver perch based on restricted rations.     

Food abundance affects both morphology and behaviour of juvenile perch

Abstract –  Behaviour and morphology were both shown to differ between 1+ perch from two lakes that in earlier studies showed differences in size-specific predation risk. As the level of nourishment is known to affect behaviour and morphology, we fed perch of the two lakes in tanks for 40 days with two food levels, to study whether observed differences remain stable with changes in food availability. The perch fed in excess grew significantly, while the perch at the low food conditions lost weight, clearly indicating undernourishment. In aquarium experiments, the starved perch from both lakes were much bolder in the trade-off between foraging and predator avoidance than their well-fed conspecifics. In addition, the shape of perch differed significantly between feeding treatments. At low food levels perch got a more slender body, while at high food levels they developed a deeper body and a relatively smaller head. Independent of feeding level, the comparison between the two lakes revealed a clearly deeper body and a larger head area for one population, a shape difference that remained stable after the feeding period. The results give evidence that the level of nourishment is an important factor that quickly alters risk-taking behaviour. In body morphology, however, more stable shape characteristics must be distinguished from more flexible ones. Consequently, the level of nourishment is a potential factor that may quickly hide other proximate cues and must be considered attentively in studies, in which shape changes and behaviour are related to environmental factors like diet, predation pressure or habitat diversity.     

Fish assemblage structure in relation to seasonal environmental variation in sub‐lakes of the Poyang Lake floodplain,China

The Yangtze River and its watershed have undergone vast changes resulting from centuries of human impacts, yet ecological knowledge of the system is limited. The seasonal variation and spatial variation of three sub‐lakes of Poyang Lake, a huge wetland in the middle Yangtze Basin, were investigated to examine how fish assemblages respond to seasonal hydrology and associated environmental conditions. In all three sub‐lakes, fish assemblage structure revealed strong variations associated with seasonal water level fluctuation. Fish species richness in all sub‐lakes was highest during the middle of the monsoon season and lowest during the dry season. Fish numerical abundance and biomass varied significantly, with several of the most common species having inconsistent patterns of seasonal variation among sub‐lakes. Fish assemblage structure was significantly associated with environmental gradients defined by water level, aquatic macrophyte coverage, conductivity and dissolved oxygen concentration. Assemblage composition in all three sub‐lakes underwent strongest shifts between December and April, the period when water levels were lowest and fishing has the greatest impact on fish stocks. Future impacts that change the hydrology of the middle Yangtze would alter the dynamics of habitat connectivity and affect environmental conditions and fish assemblages of the Poyang Lake wetland system.