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Eurasian perch (Perca fluviatilis) were sampled in April, from May to June and at the end of August to test whether the current season (i.e. feeding conditions) affects the fishes’ stomach size (i.e. volume and weight). A wide range of size data were analysed to reveal the relationship between fish size (length and weight) and stomach size. No significant differences in length-specific stomach volume or stomach weight were found in fish sampled at different times of the year. However, there were differences between seasons in the size of the stomach in relation to body weight, as length-specific body weight changes during the year because of the development of gametes and changes in nutritional status. Both stomach volume and weight grew obeying the power function up to about 20 cm in total length of perch. Yet, the growth was faster than that predicted by the cube law in relation to fish length, i.e. allometric. In larger fish, stomach growth decreased in relation to growth in length, and the relative weight of the stomach even decreased in the largest size class. These dynamics match well with the typical pattern of growth and ontogenic shift in diet from small invertebrates to fish. A non-proportional power function relationship was found between stomach weight and stomach volume. peerReviewed

The family Percidae exclusively is native to freshwaters of the Northern Hemisphere, with just two of its genera divided between Eurasia and North America. Percidae comprises 11 genera and an estimated 266–275 species, reaching tremendous species richness in the North American darters. We provide an up-to-date account relating the results of the latest DNA sequence and morphological analyses to resolve the relationships of the family Percidae, including its component genera and species. We provide newly assembled distribution maps for the taxa, and summarize their primary distinguishing morphological characters and life history. For each genus, the latest phylogenetic tree of species relationships is shown and explained. We relate these findings to historic biogeography and contemporary distributions. Just recently, tremendous inroads have been made using new molecular tools and analyses that allow us to begin to understand the tremendous evolutionary diversification of the Percidae, as well as the landscape and climate factors that have shaped these patterns. This information may provide an important indication of the future responses of percid taxa to continued anthropogenic influences.

Morphology and arrangement of various receptors in Teleostei indicate trophic and environmental preferences of different species. In the Percidae family, the sensory system begins to develop during embryogenesis and evolves over the larval and juvenile stages. The olfactory placodes develop between 26 (Gymnocephalus sp.) and 78 (walleye, Sander vitreus) hours post fertilization (hpf). However, the olfactory epithelium becomes fully developed at the age of about 1 month, as in the pikeperch (Sander lucioperca). During the ontogeny of fish, taste buds develop later than the olfactory system. In pike-perch juveniles, the first taste buds appear 13 days post hatching, primarily in the mouth and the gills, but later on they become visible in other parts of the body. During embryonic development of percids, the eye is the first sense organ to form. Gymnocephalus sp. show well developed eyes already after 26 hpf, while in walleye embryos the optic vesicles are fully formed after 70 hpf. Fish maintain body balance thanks to their inner ear (labyrinth), while the movement and vibration in the surrounding water is detected by canal neuromasts of the lateral line and superficial neuromasts of the skin. In the embryos of different percid species auditory vesicles appear after 26–70 h of development, while the lateral line – after 103 h.

Mercury biomagnifies in aquatic foodwebs in freshwater lakes, and common loons (Gavia immer) breeding in eastern Canada can be exposed to reproductively toxic concentrations of mercury in their fish prey. We assessed the bioaccumulation and biomagnification of mercury in juvenile and adult common loons, and their preferred prey: yellow perch (Perca flavescens) in Kejimkujik National Park (KNP), Nova Scotia by measuring mercury levels and stable isotope ratios in tissues. Total mercury levels and stable-carbon (δ 13C) and nitrogen isotope ratios (δ 15N) were determined in composite whole-fish samples from lakes in KNP and blood samples from juvenile and adult loons captured on lakes in KNP and southern New Brunswick. Geometric mean mercury concentrations were 0.15 and 0.38 μg/g (wet wt.) in small (9-cm fork length) and large (17-cm fork length) yellow perch, and were 0.43 and 2.7 μg/g (wet wt.) in blood of juvenile and adult common loons, respectively. Mercury concentrations in perch and loons were positively associated with body mass and δ 15N values. Juvenile loons and large yellow perch had similar mercury levels and δ 15N values, indicating similar trophic status despite their 22-fold difference in body mass. Mercury concentrations were higher in yellow perch and common loons in acidic lakes. Our findings highlight the importance of both chemical and ecological factors in understanding mercury biomagnification in lakes and associated risks to fish-eating wildlife.

Nursery areas of perch, Perca fluviatilis L., in the shallow coastal areas of the Baltic Sea are affected by increased water turbidity due to the ongoing eutrophication and other physical disturbances. Visually feeding fish, such as perch, which depend on clear water and good light conditions for effective foraging are often negatively affected by turbidity. We tested the following hypothesis: in laboratory experiments increased turbidity combined with decreased light intensity impairs the foraging efficiency of juvenile perch. Consumption of the mysid shrimp, Neomysis integer Leach, by 0+ perch (4–5.2 cm) and 1+ perch (6.1-7.7 cm) was tested at four levels of turbidity (1, 10, 20 and 30 NTU = Nephelometric Turbidity Units) combined with three light intensities imitating daylight (64–71 μmol m−2 s−1), twilight (1.0–1.2 μmol m−2 s−1) and night (complete darkness). There were no significant reductions in the consumption of mysids by 0+ and 1+ perch with increased turbidity and decreased light intensity in 3 h trials. The consumption of mysids by 0+ perch decreased slightly, although not significantly, with increasing turbidity in 1.5 h trial. This indicates that there are compensatory factors (e.g. increased activity of perch, increased prey encounter, reduced anti-predator behaviour of prey, altered contrast of prey) acting on reduced visual ability of juvenile perch due to increased turbidity and low illumination.

The horizontal movement patterns of perch (Perca fluviatilis L.) were studied by means of an automatic positioning system in a small Mediterranean temperate lake in northeastern Spain. Seven perch (247–265 mm in fork length, 243–271 g in weight) were implanted surgically with ultrasonic transmitters (38 mm long, 3.5 g in water) and their positions monitored approximately every 180 s using a radio-linked acoustic positioning (VRAP) system. Fish positions were integrated into a geographic information system database with information on date, time, slope and bottom depth. As a measure of the intensity of movement, the swimming speed was calculated. The Minimum Convex Polygon area was obtained as a measure of the area of activity. The data dispersion was calculated as r 2 (the mean squared distance from the center of activity). The tagged perch showed individual variations in activity levels, but all had a circadian pattern, being less active at night (average speed 6.0 cm s−1) than during the day (average speed 10.4 cm s−1). They exhibited two peaks of activity, at sunrise and sunset. Two patterns of movement emerged, the first characterised by movement between the limnetic and the littoral zones, the second restricted to the shoreline. Fish appeared to follow the same path, reducing the area of activity to a limited part of the lake. Also, fish returned to the same place after movements, showing site fidelity but only for a few days. Overall, although perch could be very abundant in open waters (limnetic zone), they demonstrated a high dependence on the littoral zone.

The behaviour of radio-tagged adult pikeperch (Stizostedion lucioperca (L.)) from two areas in the Danish River Gudenaa were recorded prior to, and during the spawning period. Eight of 13 tagged fish in the lower reaches of the river were located throughout the whole study. Five of these fish moved upstream to various sites in the river prior to spawning, which occurred from late April to June. The three remaining fish moved to the fjord. These movements were interpreted as a spawning migration, and it is suggested that the lower reaches of the River Gudenaa constitute an over-wintering area for pikeperch, which use different spawning areas. Ten pikeperch caught just downstream of an impassable hydropower plant were radio-tagged and translocated upstream of the dam to a reservoir. Within a week, half of the fish moved to a lake situated more than 30 km upstream the reservoir. This behaviour is hypothesised to be a homing response. The study reveals that the pikeperch is a highly mobile species with a complicated migration pattern, even in relatively small river systems.

Investigations of fish community dynamics in the pelagic and littoral zone of the lowland Sulejow reservoir (Central Poland) have revealed an occurrence of strong inter- and intra-cohort cannibalism in the population of the key predator: pikeperch, Stizostedion lucioperca (L.). In early summer the number of young-of-the-year, YOY, pikeperch in stomach contents of older conspecifics positively correlated with density of juveniles in the pelagic zone. In two years (1994, 1997), when high density of YOY pikeperch (0.6 and 0.8 individual per m3, respectively) was observed, more than seven juvenile pikeperch per stomach of older conspecifics were found. In years of low reproductive success of pikeperch (0.05 YOY per m3), the average number of juvenile pikeperch in stomachs of predatory conspecifics was below 1. The strong density-dependent predation resulted in a sharp decline of YOY pikeperch toward late summer. Cannibalistic pressure was also observed among YOY pikeperch. In the reservoir, juvenile cohorts displayed a bimodal size distribution in early summer. Small (zooplanktivorous) individuals served as a food for bigger (piscivorous) pikeperch. During shortages of alternative food (perch, cyprinids), cannibalism by YOY from the upper modal group may enhance their recruitment, at the cost of small juveniles (low winter survival). As an effect of this cannibalistic self-regulation, long-term stabilisation of pikeperch year-class strength has been observed.

Zooplankton, using macrophytes as refuges from predation by zooplanktivorous fish, are believed to be important in maintaining the macrophyte-dominated state in shallow lakes. Their grazing upon phytoplankton is also believed to be instrumental in preserving water transparency in the establishment phase of macrophytes which follows an attempt to restore a shallow lake from the effects of eutrophication. This paper interprets the results of fish, zooplankton and macrophyte interactions from an intensive 3-year study in the Norfolk Broads of eastern England. In the presence of even a low density of 0+ fish (0.2 m−2), Daphnia spp. which typically dominate the cladoceran community in spring, and through grazing are responsible for producing clear water, are typically reduced to very low levels. This decline may become protracted, but not eliminated, by the presence of macrophytes, implying a refuge effect. The efficacy of any refuge effect appears to increase with an increasing proportion of the water column occupied by macrophytes (PVI). As macrophytes develop, the grazing role is taken over by Ceriodaphnia spp. and Simocephalus spp., and may be at a sufficient rate to maintain clear water at least within macrophyte stands and possibly in intervening open water areas through diel migration of the zooplankton. A macrophyte PVI of 30–40% may provide an adequate refuge for these species through the mechanism of predation-free space, although this depends on fish density and community structure. At high densities (1 m−2) of a suite of fish species, including efficient foragers in open water (roach, Rutilus rutilus) and within macrophytes (perch, Perca fluviatilis), any refuge effect is nullified. In stable macrophyte-dominated lakes, the shift in fish community structure towards a higher proportion of piscivorous compared to zooplanktivorous fish may have a role in promoting the refuge effect through changing the distribution of zooplanktivorous fish. Predation upon zooplankton may also be reduced through the provision of alternative prey in the form of macrophyte-associated macroinvertebrates for an alternative fish stock dominated by perch, rudd ( Scardinius erythrophthalmus) and tench (Tinca tinca).

Predation by perch (Perca fluviatilis L.) and zander (Stizostedion lucioperca L.) on their new-hatched fish was studied in the littoral and pelagic zone in the biomanipulated Bautzen reservoir (Germany). Sampling was conducted from the middle of May to the middle of August in 1997. To investigate predation, we compared the littoral and pelagic zone, because the littoral zone could provide a refuge area for age-0 fish. This study focused on: 1. timing of predation, 2. selectivity of predation and 3. feeding pressures. In the littoral zone, age-1 perch fed first on age-0 percids at the beginning of June, when age-0 percids reached a mean length of 20 mm. Age-2 and older perch and zander started feeding on age-0 percids in the middle of June in both habitats. At this time, age-0 percids reached a mean length of 30 mm. In both habitats, species selective feeding on age-0 perch and age-0 zander was found. Most of the sampling time zander fed selectively on their own descendants. In general, mean lengths of age-0 fish found in the predator stomachs were smaller than those in situ. The strongest decrease of age-0 fish abundance started in both areas before percids began to feed on age-0 fish. In the middle of June, predation pressure on age-0 fish was higher in the pelagic zone, whereas in July and August it was higher in the littoral zone. After a strong initial decline due to unknown factors, age-0 fish abundance was controlled by piscivores. Predation started at the time when age-0 fish gape sizes were big enough to feed on large daphnids. As age-1 perch started first feeding on age-0 fish, at high densities they could be an important source of early mortality on age-0 zooplanktivores. This would be advantageous for the daphnid population in two ways, because the efficiency of two different predators would be reduced. Age-0 fish are consumed by age-1 perch, and age-1 perch feed on age-0 fish and not on daphnids. Consequently, the feeding behaviour of age-1 perch could be a key to achieve a stable long-term biomanipulation.

We analysed population dynamics of Daphnia galeata in littoral and pelagic areas of the long-term biomanipulated Bautzen reservoir during spring and early summer of two consecutive years. Simultaneously, consumption of the age-0 fish community was estimated by means of a bioenergetics model. As a consequence of biomanipulation, the abundance of adult planktivorous fish in Bautzen reservoir is low and the interactions between underyearling percids and Daphnia are a key process in the food web of this water. In both years, density and mean size of D. galeata were markedly lower in littoral than in pelagic areas, whereas no differences were found in the size at maturity and clutch size. However, the lower proportion of adults in the littoral zone resulted in drastically reduced birth rates, which could not explain the strong fluctuations in Daphnia abundance. These findings were consistent during the whole investigation period. Daphnia consumption by age-0 fish was markedly higher in the littoral than in the pelagic zone and accounted for up to 50% and even 100% of Daphnia mortality in this habitat. However, due to gape-size limitation, age-0 fish did not feed on daphnids before June. We conclude that besides underyearling percids older planktivorous fish contribute to the suppression of D. galeata in the littoral zone of Bautzen reservoir and that recruitment of daphnids in this habitat mainly takes place via (active or passive) immigration.

This radio telemetry study is part of a large interdisciplinary research program on the colonisation and development of the Marchfeldkanal(MFK)-system, a man made channel. The immigration of fishes into the MFK is dependent on the effectiveness of fish bypass channels at several weirs. To investigate the efficiency of the lower most fishway we estimated the population densities along the MFK-system and below the weirs using electrofishing. In addition, the movements of 15 radio-tagged pike-perch at the fishway were observed. Although more than 57000 fishes of 35 species passed the bypass channel, pike-perch (Stizostedion lucioperca) were under-represented in the fishway traps compared to their occurrence in the channel. The average daily movement of radio-tagged pike-perch was 108 m (range 6–333 m) and the maximum observed daily movement was 1050 m. The entrance to the bypass channel (280 m below the weir, and 100 m above the release site) was approached a number of times by 6 tagged fish, though none of them entered the bypass channel during the period of tracking. We conclude that although pike-perch migrate actively they do not utilise the bypass channel as much as most fish species of the MFK. Therefore the weir still represents a bottleneck for the immigration of pike-perch into the MFK.

From 1990–1993 juvenile pike (Esox lucius)were stocked each spring in the eutrophic Lake Lyng (9.9 ha, max. depth 7.6 m, mean depth 2.4 m) in densities between 515 and 3616 pike ha–1. In 1989-90 the fish population consisted mainly of roach (Rutilus rutilus),rudd (Scardinius erythrophthalmus),perch (Perca fluviatilis)and ruffe (Gymnocephalus cernuus),and total fish biomass was estimated at 477 kg ha–1. Prior to stocking pike was not present in the lake. Following the first year of stocking, the density of roach, rudd and ruffe fry expressed as catch per unit effort decreased significantly by 64 to 97%. In 1991 ruffe disappeared completely. The pike stocking did not affect the density of perch significantly. The growth of pike was high and also the growth of perch increased significantly from 1990 to 1991 (p 0.4). Pike survival was low in late August/early September. We suggest that growth of the piscivorous perch increased due to increased Secchi depth and a continuous high density of 0+ planktivores in the pelagic zone of the lake during the years of pike stocking, possibly caused by behaviourial changes and the forcing of the 0+ planktivores into the pelagic zone.

The study was performed in June–August 1993, in eighteen enclosures (1 x 2 m) built in a fertile, small (area 2.5 ha) and shallow (max. depth 1.7 m) lake, Little Mere (north-western England). Three densities of Nuphar lutea leaves were manipulated in enclosures to 10%, 50% and 90% coverage of the water surface. Perch (total length ca. 15 cm) was stocked in half of the enclosures in a density 3 fish m–2. The vertical distribution of Chironomusf.1. plumosuslarvae (classified in the size classes: 0-5, 5–10, 10–15, 15–20 and >20 mm) in the bottom sediment showed a clear pattern, with bigger larvae burrowing to the greatest depth. Densities of all larval size classes except 0-5 mm were negatively affected both by plant density and by perch in three sediment layers considered (0–2, 2-5 and 5–10 cm). The larvae formerly at the surface did not move deeper in the sediments to avoid fish predation. The size distribution of the larvae, with the prevalence of the 15–20 and 10–15 mm larvae, found in the guts of perch was the most similar to that in the upper sediments at low and medium plant densities, and to that in the intermediate, 2-5 cm, sediment layer at high plant density. The effect of the interaction between plant density and fish was significant for all the larvae except those of 10–15 and 15–20 mm. Although the results of the experiment showed size-selective feeding by perch, the direct overall effect of the fish on the size-structure of the larvae was limited by vertical distribution of the prey in the bottom sediment. In addition, it was modified by nymphaeids, which, at high density, altered food conditions and acted as a refuge for Chironomuslarvae both directly (providing shelter) and indirectly (providing fish with the additional, epiphytic prey).

The effects of piscivores upon zooplanktivore behaviour and distribution and the impact of zooplanktivores on the abundance and distribution of zooplankton are well documented. However, the potential indirect effect of piscivores reducing the predation pressure upon grazing zooplankton through behavioural changes of zooplanktivores has received little attention, even though this may be an important mechanism in enhancing the stability of submerged macrophytes in shallow lakes. Preliminary observations from an unreplicated large-scale field enclosure experiment and a replicated pond experiment suggest that this mechanism is plausible with the set of piscivores (pike Esox luciusand perch Perca fluviatilis)and the zooplanktivores (0+ roach Rutilus rutilusand perch) common in temperate Europe. The presence of piscivores typically changed the habitat use and the activity level of zooplanktivores and the presence of zooplanktivores typically changed the habitat selection of cladoceran zooplankton. In the case of piscivore/zooplanktivore interactions, the risk of predation was enough to generate clear responses even where the losses to predation were low. However, only in the enclosure experiment was an indirect impact of the presence of piscivores, enabling Daphnia spp. to utilise open water in the presence of a high density of zooplanktivorous fish observed. Whether the magnitude and direction of the effect of piscivores is sufficient to benefit zooplankton may depend on the functional group (capable of foraging within structured habitats) of the predator (both piscivore and zooplanktivore), absolute and relative densities of predator and prey and predator dietary choice.

The life history of Etheostoma caeruleum was studied from collections made between September 1976 and July 1981 in Bayou Sara, a lower Mississippi River tributary. The principal habitat of rainbow darters was shallow gravel riffles or runs over firm substrates. In Bayou Sara, the reproductive season extended from late March through April and possibly into June. Males and females were sexually mature in their first year. Counts of unovulated mature ova ranged from 17–125 (\( {\bar {\text {X}}} \) = 66). Rainbow darters reached a maximum age of 37 months and a maximum size of 50 mm. Individuals reached an average of 34 mm in the first year and 41 mm after two years. A significantly higher number of males than females was present in the 1+ and 2+ year classes. Chironomids, siphlonurids, and simuliids comprised the bulk of the diet. Simuliid and hydropsychid consumption increased with increased size.

Etheostoma swaini, the gulf darter, was collected from the Black Creek drainage in southern Mississippi (February 1978 — April 1979). The gulf darter generally inhabits small- to moderate-size creeks and occurs over a sand or sandy mud bottom, often in association with aquatic vegetation or a layer of organic debris. Larval dipterans were the most important food items, both numerically and volumetrically. Chironomids were found in 71-100% of the stomachs in all except the unusual March 16 collection. The length frequency distribution and the scale annuli analysis indicated there were three year-classes present in the population at any one time. Fifty-one percent of the specimens taken were less than 12 months old. During the mid- February to late March spawning season gulf darters were most often collected over clean gravel or gravel- sand substrates. Laboratory observations suggest that the female burrows into the gravel where the demersal, adhesive eggs are deposited. Female gulf darters significantly outnumbered males at a ratio of 59:41.

The diets of four species of Etheostoma (E. spectabile, E. caeruleum, E. flabellare and E. nigrum) were investigated from ten Order 3 streams in the White River drainage of southern Indiana. All species fed mainly on insect larvae, primarily chironomids, ephemeropterans and plecopterans. Dietary proportions, as frequency of occurrence, were compared using cluster analysis based on matrices of values of Spearman rank correlation, Schoener index, Jaccard association, and Pearson’s r. Certain species and, in some cases, stream pairs within species clustered closely in all analyses or in three of the four. Most clusters do not show closer intraspecific than interspecific similarity and specific streams had more influence than species in forming the logic of some clusters. It can be concluded that these fishes are opportunistic predators.

We performed a series of laboratory experiments to identify and evaluate preferences of young-of-the-year yellow perch for using six foraging sites, and to relate these preferences to the observed diet of perch in nature. The six foraging sites, the water surface, floating vegetation, open water column, submerged macrophytes, open substrate, and benthic cover, were simulated by artificial devices in 56.81 aquaria. The distribution of the number of food items removed from the six foraging sites did not differ significantly from random. The order of removals, however, revealed significant preferences. The water column site was selected before all others, while the surface and the floating vegetation sites were used last. Handling time efficiencies showed nearly opposite patterns: the midwater site required a longer handling time than all other sites while the surface and floating vegetation were among those sites with the shortest handling times. The selection of foraging sites was essentially independent of the order of encountering the feeding devices, and was not affected by experimental experience. The foraging site selection by the fish in our experiments corresponds to naturally important foraging sites for perch of the same size. Our results suggest that preference for a foraging site, whether genetic or due to early experience, can override immediate profitability.

Specimens of Percina palmaris from tributaries of the Tallapoosa River were examined for food, reproductive biology, age, and growth. Individuals were largely restricted to riffle areas with fast current and rubblegravel substrate where fish density was higher than that reported for other species of Percina. Few other species were commonly taken with P. palmaris in its preferred habitat. Both sexes matured at one year of age and males appeared ready to spawn in mid February although females did not contain mature ova until March. Spawning occurred from early May to mid June and peaked at water temperatures of 18-20° C in late May. Although mature males were significantly larger than females, the oldest specimen examined was a female in its fourth year of life (3+). Generally P. palmaris is an opportunistic sight feeder although some selectivity in food items was suggested. Twenty-six food categories were identified from stomach contents over the course of the study. Diet consisted almost exclusively of immature insects and monthly diversity ranged from a minimum of 4 to a maximum of 20 insect families. Percina palmaris possesses some specialized as well as generalized life history attributes placing it near the middle of a generalized-specialized life history continuum for Percina. This is in agreement with its systematic status in this genus.

An analysis of habitat partitioning among five species of darters (Etheostoma blennioides, E. caeruleum, E. spectabile, E. tetrazonum and E. zonale) suggests that differential use of vegetation types is of primary importance in the microhabitat separation of these species. Substrate size, depth and current appear to separate only one species consistently. A comparison of data from localities where all species were collected with localities where a one of the five species was absent suggests some degree of habitat displacement.

Darters feed on small benthic organisms, primarily insects, and evolutionarily have become increasingly small and benthic; most species are less than 80mm in standard length. Constraints on decreasing body size include living in midwater and territoriality. Lineages of darters have arisen as new habitats were invaded. Consequently, members of different lineages often vary in characteristics correlated with specific habitat variables. While competition from established taxa undoubtedly has prevented additional habitat invasions, some darters appear to have overcome these barriers through feeding site diversification. Living in various habitats has lead to a variety of reproductive strategies, termed egg-burying, -attaching, -clumping, and -clustering. Sexually selective characteristics, correlated with type of reproductive behavior and habitat, often make the male more conspicuous and therefore are constrained by predation.