Distribution and feeding of juvenile fish on invertebrates in littoral reed (Phragmites) stands

Abstract – Complex interactions between fish predators and their prey have been found in structurally complex habitats built by submerged macrophytes. In contrast, the role of comparably structured littoral reed stands in shaping biotic interactions has not been investigated. We hypothesised that reed stands may be a valuable feeding habitat for juvenile fish, and that perch and roach may segregate along the spatial and dietary niche dimensions between reed and open water habitats. In contrast, the protection effect of reed against predators was assumed to be rather low because of the lower plant volume infested in reed when compared with submerged macrophytes. We analysed biomass and growth of juvenile (age 0 and age 1) perch and roach in littoral reed habitats and in open water habitats in front of the reed in the shallow Lake Müggelsee over 4 months in 2000. Sampling was conducted by point-abundance electrofishing over the full diel cycle (day, dusk, night, dawn). Zooplankton and benthos biomasses were determined in both habitats as well, and habitat-specific diet of fish was assessed during day and night. Roach were more frequent than perch in both habitats. Food of roach included a higher proportion of zooplankton, whereas perch fed more on macroinvertebrates. Overall, diet overlap between the fish groups was high. Diel distribution of fish did not follow the expectations of habitat segregation between perch and roach. Instead, the function of reed as refuge habitat against littoral piscivores (mainly birds) may have caused the strong daytime preference for reed in almost all fish groups, which was partly upset by roach at night. The higher behavioural plasticity of roach may explain their good performance even under the conditions of high structural complexity.     

Interactions between juvenile roach or perch and their invertebrate prey in littoral reed versus open water enclosures

Abstract – Structural complexity offered by submerged macrophytes was shown to have fundamental effects on interactions between fish and their prey. However, less information is available for littoral reed (Phragmites spp.) stands. A previous field study found juvenile roach and perch to coexist within the reed stands. It was suggested that reed serves mainly as refuge against littoral piscivores, such that coexistence of perch and roach in the reed was externally forced. Several hypotheses were raised to explain why roach nevertheless showed good growth performance. Three of the hypotheses were tested experimentally. In particular, we were interested in how the confinement of fish to one of the reed or open water habitats alters feeding and growth patterns of juvenile age‐1 perch and roach. Fish were stocked separately into littoral enclosures for a 3‐week period in densities which had been found in the surrounding lake. Development of zooplankton and macroinvertebrate biomasses was observed by sampling the enclosures three times over the experimental period. Individual consumption of prey groups by the fish was calculated with a bioenergetics model, and was compared with prey group biomass in the enclosure treatments. The confinement of fish to one littoral habitat had clear effects on diet composition and growth rates. Roach fed less zooplankton and partially switched to macroinvertebrates in the reed enclosures when compared with the open water treatments, and consequently their growth rates were lower in the reed. Perch preferred macroinvertebrates in both habitats, without any difference in growth rates between the habitats. Effects of fish predation on both zooplankton and macroinvertebrate biomass were low in open water and reed enclosures. Daily consumption rates were only in a few cases higher than 40% of the available biomass of the respective prey group, but mainly were below 10% of available biomass. Therefore, we argue that both the diel horizontal migrations of roach and the relatively low consumption rate of fish when compared with the available resource biomass allow the coexistence of juvenile roach and perch in littoral reed stands.     

Impaired littoral energy pathways cause a shift to pelagic resources by fish in recovering lake food webs

Fish communities may increase in biomass and productivity due to energy subsidies from the littoral invertebrate community. In lakes recovering from acidification and metal contamination, such as those in Sudbury, Ontario, Canada, impaired benthic invertebrate communities (i.e., low diversity with higher abundance of small‐bodied taxa) allowed a critical test of the role of these littoral pathways on fish diet. We compared fish abundance, diversity, diet and biomass in eight recovering and eight reference lakes and related availability of the main littoral and pelagic invertebrate groups to fish diet regime using stable isotope analysis. A Bayesian mixing model (MixSIR) was used to estimate diet likelihood, and convex hull analysis was used to estimate trophic niche space of fish communities. Fish biomass did not differ between impaired and reference lakes despite substantial differences in potential diet. Fish depended strongly on littoral benthos in the reference lakes but consumed more pelagic food in the impaired lakes. The trophic niche of the focal, most common fish species (i.e., yellow perch, smallmouth bass, pumpkinseed and brown bullhead) was larger in the impaired lakes. We attributed these differences to low diversity at the highest trophic levels of fish communities in the impaired lakes as well as to depauperate benthic invertebrate communities. In contrast to the food webs of most temperate lakes, fish in impaired lakes preyed less on littoral invertebrates yet still managed to maintain a reference lake level of biomass standing crop by relying more on pelagic resources – macro zooplankton such as Chaoborus.     

Associations of fish with various types of littoral habitats in reservoirs

Fish associations with different types of littoral habitats were studied in four canyon‐shaped reservoirs in the Czech Republic in years 2010 and 2011 by gillnets. Two to three habitats per reservoir–beaches (former meadows), stump fields (former forest) and rubble slopes–were defined and sampled along the longitudinal axis of reservoirs. Effects of reservoir, habitat and locality (position along longitudinal axis) on fish biomass, abundance and species structure were tested for juvenile and adult fish separately. Hierarchical analysis of variance revealed that habitats differed significantly in fish biomass and abundance. Redundancy analysis showed that analysed environmental variables had significant influence on fish community structure. Most variability in community structure was explained by reservoir and then by combination of habitat and slope steepness. Locality position had the smallest influence on community structure. For both adult and juvenile fish total abundance and biomass, the most inhabited habitat was beaches; rubble slopes were the least inhabited. Habitat associations differed among species. Among adults, bream Abramis brama, white bream Blicca bjoerkna and roach Rutilus rutilus were associated with beaches and stump fields, whereas perch Perca fluviatilis, ruffe Gymnocephalus cernuus, asp Aspius aspius and pike Esox lucius were associated with rubble slopes. Bream, white bream, bleak Alburnus alburnus, roach, ruffe and pikeperch Sander lucioperca were associated with beaches among juveniles, whereas the only juvenile associated with rubble slopes was perch. We showed that most common species are associated with distinct habitats and also that utilisation of various littoral habitats differs in general.     

Spatio‐temporal,ontogenetic and interindividual variation of age‐0 diets in a population of yellow perch

Dietary niches of fishes have traditionally been evaluated at the population level, with diet pattern central tendencies compared spatio‐temporally among habitats and populations. More recently, however, studies have emphasised the importance of within‐population diet variation and niche partitioning. Several studies have examined diets of young yellow perch (Perca flavescens) at the population level and have described an ontogenetic transition from zooplankton to benthic prey during the first year of life. However, independent of ontogenetic diet shifts, intrapopulation variation of young yellow perch diets remains largely unexplored. We quantified patterns of diet composition in age‐0 yellow perch collected from Saginaw Bay, Lake Huron, USA during July–October, 2009 and 2010. We observed substantial variation in diet composition among individuals across and within sites, but found relatively weak evidence indicating an ontogenetic diet shift. Zooplankton were the dominant prey for age‐0 yellow perch on most occasions, and individual diets were composed primarily of either zooplankton (e.g. Daphnia spp., Calanoida) or benthic (i.e. Chironomidae larvae, Chydoridae) prey. These patterns were not simply attributable to differences in prey availability and ontogenetic diet shifts, because a) not only diet composition, but also prey selectivity (Chesson's α) varied among sites and b) individual and spatial diet differences were evident independent of ontogeny. Within‐cohort differences in diet composition may be an important, but often overlooked, phenomenon with implications for cumulative trophic interactions and intracohort growth and survival among young fish.     

The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), on insect emergence and benthic invertebrate abundance in experimental ponds

Abstract The effects of perch, Perca fluviatilis L., and bronze bream, Abramis brama (L.), predation on the production of insects emerging at the water surface and the autumn biomass of benthic macro-invertebrates were assessed in a series of experimental ponds. The study attempted to discover whether fish affect food availability for diving and dabbling ducks in freshwater habitats. Ten ponds (bisected by fine netting) were used for the study: one was left totally fish-free, whilst one half of each of three groups of three ponds was stocked with either perch, bream or perch plus bream. The relative abundance of emerging insects (mainly Chironomidae) was significantly reduced in two perch ponds, two perch + bream ponds and two bream ponds. The autumn standing crops of benthic macroinvertebrates were significantly reduced in one perch pond, three bream ponds and one perch plus bream pond. These results support findings of a contemporaneous large bio-manipulation experiment carried out in two adjacent lakes. During the biomanipulation studies, aquatic invertebrate standing stocks greatly increased after the removal of fish and decreased following restocking.     

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.     

Nutritional quality of different starches in feed fed to juvenile yellow perch,Perca flavescens

This study determined whether accumulated liver and visceral lipid in yellow perch can be alleviated by feeding an appropriate starch source. We compared the growth performance, nutritional composition and health of yellow perch fed a control diet (no added starch) and three diets with corn, potato or wheat starch (200 g/kg diet) to replace an equal proportion of fishmeal in the control diet. Dietary starch led to increased bulk density, hardness and gelatinization levels of feed pellets compared with the control diet. At the end of an 8‐week feeding, all fish fed the test diets had similar growth rates (p > .05). However, the wheat starch diet resulted in significantly enlarged livers and increased accumulation of lipid in the liver, viscera and whole body (p < .05). This diet also caused significantly higher levels of fasting glucose, aspartate aminotransferase and alkaline phosphatase activities in serum than the control diet. Liver cell diameters were larger, and Kupffer cell numbers were lower in the fish fed the wheat starch than those fed the control diet. Potato or corn starch had less impact on fish health and is considered to be an appropriate carbohydrate sources for yellow perch under the current testing conditions.     

A synthesis of the life history and ecology of juvenile Pacific herring in Prince William Sound,Alaska

Physical and biological variables affecting juvenile Pacific herring (Clupea pallasi) in Prince William Sound (PWS) from 1995 to 1998 were investigated as part of a multifaceted study of recruitment, the Sound Ecosystem Assessment (SEA) program. Though more herring larvae were retained in eastern PWS bays, ages‐0 and ‐1 herring used bays throughout PWS as nursery areas. Water transported into PWS from the Gulf of Alaska (GOA) contributed oceanic prey species to neritic habitats. Consequently, variations in local food availability resulted in different diets and growth rates of herring among bays. Summer food availability and possible interspecific competition for food in nursery areas affected the autumn nutritional status and juvenile whole body energy content (WBEC), which differed among bays. The WBEC of age‐0 herring in autumn was related to over‐winter survival. The limited amount of food consumption in winter was not sufficient to meet metabolic needs. The smallest age‐0 fish were most at risk of starvation in winter. Autumn WBEC of herring and winter water temperature were used to model over‐winter mortality of age‐0 herring. Differences in feeding and energetics among nursery areas indicated that habitat quality and age‐0 survival were varied among areas and years. These conditions were measured by temperature, zooplankton abundance, size of juvenile herring, diet energy, energy source (GOA vs. neritic zooplankton), WBEC, and within‐bay competition.     

Diet overlap of non‐native alewife with native yellow perch and spottail shiner in nearshore waters of southwestern Lake Michigan, 2000–2007

Abstract – Lake Michigan has experienced many ecological changes as a result of introductions of non‐native species. Arguably the most significant was that of alewife (Alosa pseudoharengus), yet studies on diet overlap with native species are lacking. We analysed diet trends of alewife, spottail shiner (Notropis hudsonius) and yellow perch (Perca flavescens) collected in summer and fall 2000–2007 near Waukegan, IL, in 3–10 m depths. Mean percentage composition by dry weight for 23 prey taxa was used in multivariate analysis to test whether diet differed across species and size classes. We also tested whether zooplankton and benthic invertebrate community composition changed over time. Fish diets were similar over all years but differed seasonally. In summer, diets of large alewife were similar to both small alewife and small yellow perch, with Bosminidae, chironomid larvae and copepods as primary common prey. During fall, alewife and yellow perch size classes exhibited strong intraspecific diet overlap, while there was low diet overlap between species. Primary distinctions between species’ diets in fall were higher consumption of amphipods by yellow perch and dreissenids by spottail shiners compared to alewife, which consumed higher proportions of zooplankton. Overall, high yellow perch diet overlap with alewife during summer and with their larger conspecifics during fall could lead to negative implications for yellow perch growth before the critical overwintering period. Detailed insights into diet overlap and prey availability are critical first steps in understanding competitive interactions between native and non‐native fish that dominate the nearshore community in southwestern Lake Michigan.     

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.     

Growth performance and body composition of pike perch (Sander lucioperca) fed varying formulated and natural diets

To assess the effect of dietary composition on growth performance and body composition of pike perch (Sander lucioperca), fingerlings with an initial body weight of 1.36 g (just trained to accept formulated feed) were fed three experimental diets in triplicate for 90 days. Two feeding groups were fed with formulated diets (CD, CD+7) containing varying levels of crude lipid (CL) of 14.65% and 21.94% dry matter (d.m.) with crude protein (CP) levels of 59.73% and 56.56%, and one feeding group was fed a natural diet (chironomids, CP = 65.93% d.m.; CL = 7.20% d.m.). Furthermore, pike perch of the same age caught in different natural habitats were analysed to determine their naturally fluctuations in body composition. Specific growth rate (SGR; CD = 3.36, CD+7 = 3.47) and feed conversion ratio (FCR; CD = 1.02, CD+7 = 0.93) of fish fed formulated diets did not differ significantly with rising dietary lipid content, due to high variability within the individuals of each feeding groups. In contrast, pike perch fed with chironomids showed a significantly lower SGR of 2.49 and higher FCR of 2.37 (on a dry matter basis). Body composition of pike perch fed formulated diets was affected by dietary composition and showed increased lipid contents [CD=6.25% original matter (o.m.), CD+7 = 9.00% o.m.] with rising dietary lipid levels. Pike perch of CD and CD+7 feeding groups showed significant increased hepatosomatic indices (HSIs) of 1.99 and 2.05 in contrast to fish fed chironomids with HSI of 1.11. Fish caught in the different natural habitats were characterised by low body lipid and dry matter contents of 0.64–1.88% o.m. and 21.08–23.75% o.m. Higher lipid incorporation of fish fed with formulated diets accompanied with poor benefit on growth performance at higher dietary lipid content indicated that pike perch ability to utilise lipids is low when dietary crude protein content is higher than 56.56%.     

Feeding ecology of fishes associated with Egeria spp. patches in a tropical reservoir, Brazil

Abstract –  This research characterised feeding ecology of fishes associated with patches of Egeria najas and Egeria densa , two submerged macrophytes, in Rosana Reservoir, Upper Paraná River basin, Brazil. Fishes were sampled using a 1 m² throw trap in patches of different macrophyte biomass and in three diel periods during a wet season. Fish diet (10 species) was primarily composed of autochthonous items (zooplankton, algae and aquatic insect larvae). Almost all intra-specific diet patterns had moderate to low levels of diet similarity, indicating a high variability in diet. Some species showed no diel patterns in feeding activity, whereas others were primarily diurnal or nocturnal. No differences in feeding activity were observed among habitats of medium and high macrophyte biomasses, and species tended to feed on the same items among these habitats. The most abundant fish species demonstrated low inter-specific diet overlap and appear not to compete for food resources. We suggest that Egeria patches are feeding grounds and shelter for small-sized fish species.     

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.     

Habitat partitioning among three predatory fish in a temperate reservoir

The diversity of predatory species plays a key role in ecosystem functioning but our understanding of the mechanisms underlying their coexistence is limited, particularly in freshwater ecosystems. Northern pike Esox lucius, European perch Perca fluviatilis and pikeperch Sander lucioperca are three widespread predatory species in European lakes, where they often coexist. As potential competitors, we hypothesised that partitioning habitat is a determinant of species coexistence. This was tested by quantifying the variability of their habitat use in tracking adult individuals in the Bariousses reservoir (France, 86.6 ha, mean depth 7.1 m). Specifically, we investigated their distribution along the littoral–pelagic and depth axes along the daily cycle and across seasons. From littoral to pelagic waters were first found pike, then perch and finally pikeperch. Pike was the closest to the surface while pikeperch was the deepest. This general pattern was, however, variable across seasons with the three species located in the upper layer in summer during reservoir stratification. Individuals were more evenly distributed along the littoral–pelagic axis and closer to the bottom when water was mixing (autumn, winter). In summer, perch used more intensively in the pelagic zone during the daytime. Other species did not show any diel change of habitats. Our results highlighted that species coexistence is associated with habitat partitioning among these three predators, with perch showing a more variable behaviour regarding habitat characteristics. Now more than ever, in the context of global change which modifies habitats, it is of crucial importance to understand the coexistence mechanisms of species that shape ecosystems.     

Evaluation of juvenile silver perch Bidyanus bidyanus (Mitchell) nutritional needs using high- and low-protein diets at two feeding levels

Juvenile silver perch Bidyanus bidyanus (Mitchell) of 3.2 g average weight were reared under controlled conditions on diets containing 23.4% and 40.6% protein. Diets were administered at 3% or 6% of the fish biomass per day. Both the protein concentrations and the feeding level of the diet influenced growth and proximate composition of the fish at the end of the 100-day growth trial. The energy requirement for these fish for maintenance was found to be 81.9 kcal × BW^–0.8 and, for each unit of energy retained per metabolic body weight, 7.05 needed to be supplied, whereas for each gram of protein retained per metabolic body weight, 5.79 g were required. The results indicate that it is possible to obtain the same weight increment when feeding a 23.4% protein diet at a level of 6% body mass day^–1 compared with only 3% body mass day^–1 of a 40.6% protein diet. This study provides the first estimation of nutrient requirements for juvenile silver perch, and these estimations require further refinement.     

Resource use of crucian carp along a lake productivity gradient is related to body size,predation risk,and resource competition

Generalist fish species can feed on a wide resource spectrum and across trophic levels depending on resource availability and trophic interactions. Crucian carp (Carassius carassius) represents a good candidate species to investigate variation in the trophic ecology of generalist fish as it can be found in highly variable fish communities and its resource use is well documented. In this study, we explored the trophic ecology of crucian carp at the individual and population levels using stable isotope and gut content analysis. We tested if trophic resource use varied according to lake productivity, predation risk, intra- and interspecific competition, or individual fish size. We found that crucian carp resource preference was highly variable among and within lakes. In predator-free lakes, small crucian carp occurred in high densities, showed increased interindividual specialisation, and relied mainly on pelagic zooplankton. In presence of predators, large crucian carp occurred in low densities and included greater proportions of benthic macroinvertebrates in their diet. This shift in resource use was further favoured in productive, shallow lakes where littoral prey were probably abundant. Resource partitioning was an important factor determining crucian carp niche use, as fish had higher trophic position in absence of other cyprinids. Crucian carp showed highly dynamic resource use and food preferences in response to variable environmental conditions. Overlooking complex diet preferences of generalist fish may lead to an oversimplification of freshwater community dynamics.     

Diet and movements of pikeperch (Sander lucioperca) in a large oligotrophic lake with an exceptionally high pikeperch yield

Through the recent increases in abundance, pikeperch (Sander lucioperca) has not only become a valuable target for recreational and commercial fishing, but also the most important top predator in many lakes. Generally oligotrophic Lake Höytiäinen (283 km²) sustains one of the most economically valuable pikeperch stocks in Finland, and its annual fisheries yield (up to 5.5 kg/ha) is exceptionally high among Finnish lakes. Here, we followed seasonal movements of fish using conventional tagging, and studied short‐term and long‐term diet of pikeperch by stomach content and stable isotope analyses to examine if the movements were motivated by prey availability. A clear seasonal migration pattern was observed: in summer, 80% of the tag recoveries were obtained from the shallow and mesotrophic northern and western areas, whereas in autumn and winter, the deep and oligotrophic southern area dominated in the recaptures. The diet of pikeperch consisted of the most abundant fish species in the lake, perch (Perca fluviatilis) and roach (Rutilus rutilus), as well as insects. Stable isotope analysis indicated a shift from a dominance of pelagic food sources to littoral food sources during the growing season of pikeperch. Our results suggest that the pikeperch migrations facilitate efficient material transfer from the mesotrophic part while the deeper and oligotrophic part offers a favourable overwintering environment.     

Is scuba sampling a relevant method to study fish microhabitat in lakes? Examples and comparisons for three European species

Abstract – We compared fish microhabitat use patterns in the littoral zone of a lake using a new direct method (point abundance sampling by scuba, PASS) and the widely used point abundance sampling by electrofishing technique (PASE). We collected microhabitat data for age 0+ roach ( Rutilus rutilus L.), perch ( Perca fluviatilis L.), and pike ( Esox lucius L.). The two methods yielded different results for fish assemblage structure and microhabitat patterns. Using PASE, fish were mainly found in "shelter habitats" such as shallow waters and dense vegetation. It is likely that this behavior is caused by the disturbance of the observer stamping around. Using PASS, fish escapement behavior was rarely observed. Therefore, we concluded that this direct and nondestructive sampling technique can be used to provide an accurate microhabitat estimation of a fish community and is assumed to be more suitable than PASE for fish habitat studies.     

Sex‐dependent responses of perch to changes in water clarity and temperature

Rising temperatures and decreasing water transparency of lakes have strong wide ranging effects on fish. Fish responses to various changes in the environment are usually species‐dependent, but responses may also vary within species. In general, large individuals are considered to be more sensitive to environmental variation due to higher energy demand, than smaller individuals. Similarly, large individuals require more food to maintain bodily functions and are thus more sensitive to resource and food scarcity. These size‐specific responses to environmental gradients are also sex‐dependent in species that exhibit sexual size dimorphism (SSD). We studied in enclosures with short‐term experiments how rising temperatures and decreasing water transparency regulate the feeding rates of female and male European perch (Perca fluviatilis L.). To explore experimental results, we calculated perch SSD in nine lakes with varying environmental conditions using previously collected field data. The results of the experiments revealed that the combined effect of water transparency and temperature on the feeding rate of fish is gender‐dependent: feeding rate of females decreased more than that of males. The experimental results were also supported by field data that revealed a negative relation between water transparency and the magnitude of SSD in perch. Our results suggest that rising temperatures and decreasing water transparency may potentially decrease fish size in a sex‐dependent manner. As female size is one of the main demographic traits determining the reproductive success of a fish population, changing environments may have unexpected and far‐reaching consequences on fish population dynamics.