The Effects of Zebra Mussels (Dreissena polymorpha) on the Foraging Success of Eurasian Perch (Perca fluviatilis) and Ruffe (Gymnocephalus cernuus)

Complex habitat structures can influence the foraging success of fish. Competition for food between fish species can therefore depend on the competitors' abilities to cope with structural complexity. In laboratory experiments, we comparatively assessed effects of zebra mussels (Dreissena polymorpha Pall .) on the foraging success of Eurasian perch (Perca fluviatilis L.) and ruffe (Gymnocephalus cernuus (L.)). In single‐species and mixed‐species experiments, the fish were fed caddisfly larvae (Tinodes waeneri (L.)) over complex (mussel‐covered stones) and less‐complex (bare stones) substrates. With intraspecific competition, food consumption by perch and ruffe decreased significantly when the complex substrate was used. With interspecific competition, food consumption by perch and ruffe did not change with substrate complexity, but perch clearly out‐competed ruffe on both substrates. Zebra mussel beds provide a refuge for macrozoobenthos against predation by ruffe and probably also by perch. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Predator odor recognition and antipredatory response in fish: does the prey know the predator diel rhythm?

We studied in a laboratory experiment using stream tanks if two percid prey fish, the perch (Perca fluviatilis) and the ruffe (Gymnocephalus cernuus), can recognize and respond to increased predation risk using odors of two piscivores, the pike (Esox lucius) and the burbot (Lota lota). Burbot is night-active most of the year but pike hunts predominantly visually whenever there is enough light. Perch is a common day-active prey of pike and dark-active ruffe that of burbot. We predicted that besides recognizing the predator odors, the prey species would respond more strongly to odors of the predator which share the same activity pattern. Both perch and ruffe clearly responded to both predator fish odors. They decreased movements and erected the spiny dorsal fins. Fin erection showed clearly the black warning ornamentation in the fin and thus erected fin may function besides as mechanical defense also as warning ornament for an approaching predator. No rapid escape movements were generally observed. Both perch and ruffe responded more strongly to pike odor than to burbot. There were no clear differences in response between day and night. In conclusion, we were able to verify clear predator odor recognition by both prey fish. Both perch and ruffe responded to both predator odors and it seemed that pike forms a stronger threat for both prey species. Despite of diel activity differences both perch and ruffe used the same antipredatory strategies, but the day-active perch seemed to have a more flexible antipredatory behavior by responding more strongly to burbot threat during the night when burbot is active.     

Competition between perch (Perca fluviatilis) and ruffe (Gymnocephalus cernuus): the advantage of turning night into day

1. The outcome of interspecific competition for food resources depends both on the competitors’ sensory abilities and on environmental conditions. In laboratory experiments we tested the influence of daylight and darkness on feeding behaviour and specific growth rate (SGR) of two species with different sensory abilities. 2. We used perch (Perca fluviatilis) as a visually orientated, and ruffe (Gymnocephalus cernuus) as a mechano‐sensory oriented predator and tested their growth rates and behaviour under conditions of interspecific and intraspecific competition. Three different foraging conditions were used: food supplied (i) only during the day, (ii) only during the night or (iii) during both day and night. 3. In perch neither SGR nor feeding behaviour were influenced substantially by interspecific competition during daylight. During darkness their foraging behaviour changed markedly and their access to the food source as well as their SGR were negatively affected by the presence of ruffe. 4. Ruffe's foraging behaviour did not change during either day or night with interspecific competition. During the night ruffe's SGR was higher with interspecific competition, probably because of a release from intraspecific competition and the competitive inferiority of perch during the night. 5. Because of its seonsory abilities ruffe feeds predominantly at night, thereby reducing competitive interference from perch.     

Feeding behaviour determining differential capture success of evasive prey in underyearling European perch (<Emphasis Type="Italic">Perca fluviatilis</Emphasis> L.) and roach (<Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.))

The effect of feeding behaviour on the prey capture efficiency of young-of-the-year European perch and roach was investigated in laboratory experiments using planktonic crustaceans possessing different escape abilities—Daphnia sp. and Cyclops sp. Two sets of experiments were performed. In the first set, the feeding efficiency and behaviour of 270 fish individuals were determined by stomach content analyses and video record evaluations. In the second set of experiments, analysis of attack-effort, which was evaluated as attack-distance and repeated strikes, was undertaken. Except for situations in which Daphnia was offered at high densities, the feeding efficiency of perch was significantly higher compared to roach in all other combinations of prey types and densities. Roach consumed significantly less prey compared to perch when feeding exclusively on the evasive Cyclops and when it was offered in a 1:1 ratio mixture with Daphnia. The mean swimming speed was similar in both fish species, but behavioural differences were evident during prey search and capture. Perch swam through the aquaria in short and fast movements that were interrupted by many stops. Roach exhibited rather continuous swimming that was punctuated by slowdowns instead of stops. The perch attacks were very intensive and repeated strikes occurred, particularly when feeding on evasive Cyclops. On the other hand, roach revealed strong schooling behaviour restricting the fish during inspection of the experimental aquaria. The distinct differences in feeding efficiency between perch and roach were demonstrated to be closely related to differences in their feeding behaviour. Discontinuous searching for prey, vigorous attacks, occurrence of repeated strikes and the absence of schooling increased perch prey capture efficiency, particularly when foraging on evasive copepods.     

Overwinter changes in mass and lipid content of Perca fluviatilis and Gymnocephalus cernuus

The body condition, lipid reserves and mortality of 0 and 1 year‐old perch Perca fluviatilis and ruffe Gymnocephalus cernuus , sampled during the winter in Lake Constance, Germany, were compared. Length‐frequency analyses did not provide evidence for overwinter mortality in either species. The fresh and dry mass of perch as well as their lipid contents decreased during winter, while ruffe were heavier and contained more lipid at the end of the winter. The superior performance of ruffe was mainly attributed to its sensory capabilities, which allowed it to ingest zoobenthos throughout the winter, while the zooplankton feeding of perch was constrained by low light levels. In lakes that undergo a process of re‐oligotrophication, this advantage of ruffe over perch may be even more pronounced, since lower food supply during the growth season and thus lower fish lipid content at the start of winter is probably better tolerated by ruffe than by perch.     

Feeding behaviour of major 0 + fish species in a shallow, eutrophic lake (Tjeukemeer, The Netherlands)

The forage base and the food selectivity of 0+ representatives of six abundant freshwater fish species were studied in a shallow, eutrophic Dutch lake. Most species relied on the zooplankton; the size-selective predation in early summer was directed to the smaller copepods and in late summer to larger cladocerans and copepods than concurrently present in the lake. Daphnia spp. and cyclopoid copepods were the main zooplankton taxa for smelt, perch and pikeperch. Energetically, the large cladoceran, Leptodora kindtii, was especially important for pikeperch. Bream and roach preyed upon smaller zooplankton than the other fish species. The influence of the zooplankton predation by abundant 0+ fish was clear from a small mean Daphnia size in September; this size is to be used as an indicator in fishery management. Neomysis integer, the most important macrofauna species, was consumed by perch, pikeperch and ruffe; pikeperch was most size-selective in this respect. The 0+ ruffe was à typically benthivorous fish. Only the 0+ pikeperch became piscivorous, especially in years when smelt was abundant.     

Diet niche relationships among predator and prey fish species in their early life stages in Lake Võrtsjärv (Estonia)

In Lake Võrtsjärv pikeperch was observed not to shift to piscivory in their first autumn of life, although juvenile stages of a variety of fish species were abundant in the lake. It was hypothesized that the diets of predator and prey fish fry overlap and that coarse fish species are important food competitors for juvenile piscivores and thus, pikeperch and perch fry do not shift to piscivory during their first growing season. To discover the possible linkages in this pattern, in 2009 the feeding relationships of pikeperch, perch, ruffe and roach fry were analysed. The stomach content analyses showed that in the summer period, Mesocyclops leuckarti was the most frequent prey for perch and ruffe, pikeperch consumed Leptodora kindti in large quantities, and roach ate mostly plant material. Towards autumn, M. leuckarti was the most abundant prey for all percids. However, average stomach content weight and the number of prey items eaten by ruffe were considerably higher than for other fish fry. Since the feeding opportunities of fish fry are considered poor in the examined lake, the prey has the potential to restrict the recruitment to piscivory of their predators, as prey fish seem to have better abilities to persist in this ecosystem. Furthermore, supposed competition in the juvenile stage may result in a reduced top‐down effect on coarse fish.     

Comparison of response distance to prey via the lateral line in the ruffe and yellow perch

The ruffe Gymnocephalus cernuus and the yellow perch Perca flavescens (both Percidae), have very different cephalic lateral line systems. The ruffe, which is nocturnal and frequents turbid water, has a cephalic lateral line with very wide canals, large neuromasts, and membranes covering the canal openings. This anatomy is convergent with that of many deep-sea fishes. The yellow perch has a lateral line composed of neuromasts enclosed in narrow canals freely open to the water. This anatomy is typical of active, diurnal, shallow-water fishes. Laboratory experiments in the dark using infra-red video equipment revealed that the ruffe detects Daphnia magna (Crustacea: Daphnidae) and the mayfly Hexagenia limbata (Insecta: Ephemeridae) at a greater distance than the yellow perch and that it also swims faster whilst searching for prey. The swimming of the ruffe consists of a thrust by the pectoral and caudal fins, followed by a glide, the prey being detected during the glide. It is suggested that the membranes over the openings in the ruffe's lateral line function to eliminate self-generated laminar flow 'noise' from reaching the neuromasts.     

Optimal foraging: the difficulty of exploiting different feeding strategies simultaneously

Summary The foraging efficiency of a visually feeding fish, perch (Perca fluviatilis) was studied on two prey species (Daphnia magna and Chaoborus obscuripus) presented either separately or combined. It is shown that when both prey species are present, the foraging efficiency of the predator is reduced. This is due to the predator's inability to simultaneously cope with prey species with different anti-predatory behaviour. In the mixed-meal experiment the predator captured both prey species in equal proportions in disagreement with optimal foraging models assuming that handling time and encounter rate for a prey species are independent of other prey species. The results are, however, in agreement with optimal foraging models assuming that handling time and encounter rate are influenced by short time learning.     

Interactions between invading benthivorous fish and native whitefish in subarctic lakes

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Correlations between type‐indicator fish species and lake productivity in German lowland lakes

Morphotypes for 67 lakes in the German lowlands were derived, based on maximum depth and mixis type. A threshold of 11 m maximum depth was identified to be the best level to discriminate shallow from deep lake morphotypes. The fish communities in these two morphotypes were significantly different. Indicator species analyses based on fish biomasses found vendace Coregonus albula in deep lakes and ruffe Gymnocephalus cernuus , bream Abramis brama , white bream Abramis bjoerkna , roach Rutilus rutilus , pikeperch Sander lucioperca and small perch Perca fluviatilis in shallow lakes to be the most representative species of their communities. Lake productivity was closely related to biomass and in part abundance of the type‐indicator species, with vendace declining with increasing chlorophyll a concentration in the deep lakes, whereas biomass of pikeperch, bream, white bream and ruffe increased and biomass of small perch decreased with increasing chlorophyll a . These results indicate that assessment of ecological integrity of lakes by their fish fauna is generally possible, if lakes are initially separated according to a depth‐related morphotype before the assessment, and if eutrophication is considered to be the main anthropogenic degradation.     

Effect of temperature and roach Rutilus rutilus group size on swimming speed and prey capture rate of perch Perca fluviatilis and R. rutilus

Effects of temperature and group size of roach Rutilus rutilus on foraging behaviour of perch Perca fluviatilis and R. rutilus were tested in two laboratory experiments. A temperature experiment with P. fluviatilis and R. rutilus in aquaria (with either one P. fluviatilis or two R. rutilus) was tested at five temperatures: 4, 8, 12, 16 and 20° C, and showed that P. fluviatilis had a lower swimming speed and capture rate than R. rutilus, especially at 4 and 8° C. The effect of group size was tested at four R. rutilus abundances: 0, 2, 4 and 6, all at 16° C, and revealed that swimming speed and capture rate of P. fluviatilis were lowest at the highest R. rutilus abundance, whereas R. rutilus was relatively unaffected. Perca fluviatilis occupied positions closer to the bottom than R. rutilus, especially when feeding, and this tendency was reinforced at the highest roach abundance.     

Collapse of the native ruffe (<Emphasis Type="Italic">Gymnocephalus cernua</Emphasis>) population in the Biesbosch lakes (the Netherlands) owing to round goby (<Emphasis Type="Italic">Neogobius melanostomus</Emphasis>) invasion

We investigated the change in benthic fish communities in three artificial lakes of the Biesbosch area in the Netherlands between two time periods: before and after the invasion of round goby (Neogobius melanostomus). Native ruffe (Gymnocephalus cernua), the dominant species in benthic gillnet and littoral beach seining catches before the invasion, almost completely disappeared in all lakes only 2 years after the invasion. We found a significant increase in 0 + perch (Perca fluviatilis) and, in some lakes, pikeperch (Sander lucioperca) abundance in gillnet catches after invasion. In the post-invasion period, the 0 + fish community was dominated by perch, and the older fish community was dominated by round goby. The species richness of 0 + fish increased in the post-invasion period owing to the invasion of gobiids. However, it did not change for older fish between periods. Our results clearly show that, owing to a similar benthic lifestyle and high niche overlap, ruffe was the only species negatively influenced by the round goby invasion. The competitive superiority of round goby over ruffe is so strong that the once-dominant species of the overall benthic fish community collapsed after only a few years of coexistence.     

Resource limitation during early ontogeny: constraints induced by growth capacity in larval and juvenile fish

The presence of and mechanisms behind density-dependent growth and resource limitation in larval and juvenile stages of organisms with high mortality such as fish are much debated. We compare observed consumption and growth rates with maximum consumption and growth rates to study the extent of resource limitation in young-of-the-year (YOY) roach (Rutilus rutilus) and perch (Perca fluviatilis). Diet, habitat use, consumption rate and growth rate were measured under varying YOY fish densities over 2 years in four lakes. In the first year, YOY roach and perch were studied under allopatric conditions. Experimental addition of perch roe in the second year also allowed study of YOY of the two species under sympatric conditions in two of the lakes. The diet of YOY roach was dominated by cladoceran zooplankton and YOY roach habitat use was restricted to the shore region in both years. This restricted habitat use did not involve any cost in foraging gain in the first year as consumption and growth rates were very close to maximum rates. During the second year, when the two species coexisted, resources were limited in late season, more so in the littoral than in the pelagic habitat in one lake while the reverse was the case in the other lake. The diet of YOY perch was also dominated by zooplankton, and with increasing perch size the proportion of macroinvertebrate prey in the diet increased. After hatching, YOY perch first utilized the pelagic habitat restricting their habitat use to the shore after 1 to several weeks in the pelagic zone. During the larval period, perch were not resource limited whereas juvenile perch were resource limited in both years. The fact that YOY perch were more resource limited than YOY roach was related to the higher handling capacity and lower attack rate of perch relative to roach, rendering perch more prone to resource limitation. Estimates of resource limitation based on consumption rates and growth rates yielded similar results. This supports the adequacy of our approach to measure resource limitation and suggests that this method is useful for studying resource limitation in organisms with indeterminate growth. Our results support the view that density-dependent growth is rare in larval stages. We suggest that density-dependent growth was absent because larval perch and roach were feeding at maximum levels over a wide range of larvae densities. Received: 14 June 1999 / Accepted: 29 October 1999     

Ontogeny of critical and prolonged swimming performance for the larvae of six Australian freshwater fish species

Critical (<30 min) and prolonged (>60 min) swimming speeds in laboratory chambers were determined for larvae of six species of Australian freshwater fishes: trout cod Maccullochella macquariensis, Murray cod Maccullochella peelii, golden perch Macquaria ambigua, silver perch Bidyanus bidyanus, carp gudgeon Hypseleotris spp. and Murray River rainbowfish Melanotaenia fluviatilis. Developmental stage (preflexion, flexion, postflexion and metalarva) better explained swimming ability than did length, size or age (days after hatch). Critical speed increased with larval development, and metalarvae were the fastest swimmers for all species. Maccullochella macquariensis larvae had the highest critical [maximum absolute 46·4 cm s^?1 and 44·6 relative body lengths (L_B) s^?1] and prolonged (maximum 15·4 cm s^?1, 15·6 L_B s^?1) swimming speeds and B. bidyanus larvae the lowest critical (minimum 0·1 cm s^?1, 0·3 L_B s^?1) and prolonged swimming speeds (minimum 1·1 cm s^?1, 1·0 L_B s^?1). Prolonged swimming trials determined that the larvae of some species could not swim for 60 min at any speed, whereas the larvae of the best swimming species, M. macquariensis, could swim for 60 min at 44% of the critical speed. The swimming performance of species with precocial life‐history strategies, with well‐developed larvae at hatch, was comparatively better and potentially had greater ability to influence their dispersal by actively swimming than species with altricial life‐history strategies, with poorly developed larvae at hatch.     

Differences in feeding selectivity and efficiency between young-of-the-year European perch (Perca fluviatilis) and roach (Rutilus rutilus) — field observations and laboratory experiments on the importance of prey movement apparency vs. evasiveness

Feeding selectivity and efficiency of young-of-the-year European perch and roach were compared under field and laboratory conditions. In laboratory experiments, the importance of prey evasiveness versus prey movement conspicuousness for fish selectivity was evaluated with respect to changing Cladocera/Copepoda prey ratio. Feeding efficiency was additionally investigated in relation to feeding time (5, 10, 20 min) and prey density (approx. 50, 200, 700 ind. L⁻¹). In Říov Reservoir, the diet of both fish species was nearly exclusively composed of crustacean zooplankton. In roach, diet shifted from rotifers and bosminids in May, towards Daphnia sp. and Leptodora kindtii in June and July. Daphnia contributed almost exclusively to the roach diet since June, composing on average more than 94% of total prey. Cyclopoid copepods, occurred in the roach’s diet only on the first sampling date; later on both cyclopoid and calanoid copepods were completely absent. On the other hand, copepods played an important role in the diet of perch. In early and mid-June when their share in the zooplankton was particularly high, copepods contributed by more than 50% to the diet of perch. Although their contribution dropped with their decline in zooplankton in June/July, by the end of July they again comprised about one third of perch’s diet. In both fish species, the increase in numbers of cladocerans in their diet was related to increase in SL. In roach, the numbers of consumed prey were doubled every twenty days during the investigated period. In perch the increase was not so consistent, but significantly higher efficiency of perch was reported on three out of six sampling dates. In laboratory experiments, roach showed a distinct avoidance for copepods and a preference for cladocerans. Both prey categories were only fed non-selectively when they dominated the prey mixture. Perch selectivity was more diversified. Contrary to roach, perch were fed copepods non-selectively on a balanced prey ratio. Further, with an increasing share of Cladocera, a situation resembling that of roach and Copepoda was avoided. However, when the share of copepods in the prey mixture dropped below ten percent, they were consumed non-selectively and with their ongoing decline in the prey mixture their preference even increased. Feeding efficiency differed significantly between perch and roach when foraging on copepods exclusively or on a prey mixture where copepods predominated. In the short time feeding experiment (5 min) with copepods, perch consumed on average 5.9 times more prey than roach. Although roach increased their success with increasing time it was still 1.7 times greater than for perch in the long time feeding experiment (20 min). Total numbers of prey consumed were positively affected by prey density and feeding time. With increasing feeding time, the consumption rate generally declined. With a fourfold increase in feeding time, the numbers of consumed prey increased on average only two times. Only in roach feeding on copepods did the numbers of prey consumed per minute of feeding increase with increasing feeding time. However, the overall numbers were low. Differences in feeding selectivity and efficiency between perch and roach juveniles were found to be significant both in the field and laboratory experiments. In roach, selectivity was determined solely by prey evasiveness. By contrast, perch’s selectivity was influenced by prey movement conspicuousness; prey escape abilities did not play an important role. Perch were more efficient foragers on evasive prey, but its feeding efficiency for non-evasive prey was not lower than that of roach. According to our observations, we suggest feeding behaviour to be responsible for the roach’s inefficiency in capturing evasive copepods.     

Radiotracer Studies on Waterborne Copper Uptake,Distribution, and Toxicity in Rainbow Trout and Yellow Perch: A Comparative Analysis

Rainbow trout (Oncorhynchus mykiss) are often used to estimate important biotic ligand model (BLM) parameters, such as metal-binding affinity (log K) and capacity (B_max). However, rainbow trout do not typically occupy metal-contaminated environments, whereas yellow perch (Perca flavescens) are ubiquitous throughout most of North America. This study demonstrates that dynamic processes that regulate Cu uptake at the gill differ between rainbow trout and yellow perch. Rainbow trout were more sensitive to acute aqueous Cu than yellow perch, and toxicity was exacerbated in soft water relative to similar exposures in hard water. Whole body Na loss rate could account for acute Cu toxicity in both species, as opposed to new Cu uptake rate that was not as predictive. Time course experiments using radiolabelled Cu (⁶⁴Cu) revealed that branchial Cu uptake was rather variable within the first 12 h of exposure, and appeared to be a function of Cu concentration, water hardness, and fish species. After 12 h, new branchial Cu concentrations stabilized in both species, suggesting that metal exposures used to estimate BLM parameters should be increased in duration from 3 h to 12+ h. In rainbow trout, 71% of the new Cu bound to the gill was exchangeable (i.e., able to either enter the fish or be released back to the water), as opposed to only 48% in yellow perch. This suggests that at equal exposure concentrations, proportionally more branchial Cu can be taken up by rainbow trout than yellow perch, which can then go on to confer toxicity. These qualitative differences in branchial Cu handling between the two species emphasize the need to develop BLM parameters for each species of interest, rather than the current practice of extrapolating BLM results derived from rainbow trout (or other laboratory-reared species) to other species. Data reported here indicate that a one-size-fits-all approach to predictive modeling, mostly based on rainbow trout studies, may not suffice for making predictions about metal toxicity to yellow perch—that is, a species that inhabits metal-contaminated lakes around northern Canadian industrial operations.     

Assessing the short‐term effects of capture,handling and tagging of sandgrouse

Capturing and marking free‐living birds permits the study of important aspects of their biology but may have undesirable effects. Bird welfare should be a primary concern, so it is necessary to evaluate and minimize any adverse effects of procedures used. We assess short‐term effects associated with the capture, handling and tagging with backpack‐mounted transmitters of Pin‐tailed Pterocles alchata and Black‐bellied Pterocles orientalis Sandgrouse, steppe birds of conservation concern. There was a significantly higher mortality (15%) during the first week after capture than during the following weeks (< 2.5%) in Pin‐tailed Sandgrouse, but no significant temporal mortality pattern in Black‐bellied Sandgrouse. In Pin‐tailed Sandgrouse, mortality rate during the first week increased with increasing relative transmitter and harness weight regardless of season, and with increasing handling time during the breeding season. There were no significant differences in mortality rate between study areas, type of tag, sex or age or an effect of restraint time. These results suggest the use of lighter transmitters (< 3% of the bird's weight) and a reduction of handling time (< 20 min), particularly during the breeding season, as essential improvements in procedure to reduce the mortality risk associated with the capture, handling and tagging of these vulnerable species.     

Effects of temperature,swimming speed and body mass on standard and active metabolic rate in vendace (<Emphasis Type="Italic">Coregonus albula</Emphasis>)

This study gives an integrated analysis of the effects of temperature, swimming speed and body mass on standard metabolism and aerobic swimming performance in vendace (Coregonus albula (L.)). The metabolic rate was investigated at 4, 8 and 15°C using one flow-through respirometer and two intermittent-flow swim tunnels. We found that the standard metabolic rate (SMR), which increased significantly with temperature, accounted for up to 2/3 of the total swimming costs at optimum speed (U _opt), although mean U _opt was high, ranging from 2.0 to 2.8 body lengths per second. Net swimming costs increased with swimming speed, but showed no clear trend with temperature. The influence of body mass on the metabolic rate varied with temperature and activity level resulting in scaling exponents (b) of 0.71–0.94. A multivariate regression analysis was performed to integrate the effects of temperature, speed and mass (AMR = 0.82M ^0.93 exp(0.07T) + 0.43M ^0.93 U ^2.03). The regression analysis showed that temperature affects standard but not net active metabolic costs in this species. Further, we conclude that a low speed exponent, high optimum speeds and high ratios of standard to activity costs suggest a remarkably efficient swimming performance in vendace.