The behavioural basis of prey selection by underyearling bream (Abramis brama (L.)) and roach (Rutilus rutilus (L.))

SUMMARY. A clear difference in the ability lo escape from fish predators exists between members of the Cladocera and Copepoda. The results of our laboratory studies have shown that underyearling roach and bream both found copepods more difficult to capture than cladocerans. However, bream were far more efficient than roach at catching the more elusive copepod prey. The basis for this difference was the greater strike ability of bream, most likely related to its more protrusible mouth. In their natural environment the two species of fish exhibited food resource partitioning with planktonic Cladocera predominating in roach guts and copepods and non-planktonic Cladocera composing the vast majority of the gut contents of bream. Differences in diet are partly due to their contrasting attack abilities. Additional variation may arise because of subtle differences in the timing and location of foraging.     

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.     

Food searching decisions in four cyprinid species

Synopsis Four species of cyprinids (vimba, bream, Danubian bleak and roach) which had been incubated and reared under identical conditions differed qualitatively as well as quantitatively in the use of prey search strategies during comparative experiments. While bream and vimba prefer to use sampling techniques under conditions of reduced visibility of benthic prey, roach favor almost exclusively directed search methods. Vimba and Danubian bleak, in contrast to bream and roach, rapidly increase their total search activity in response to successive presentations of novel prey. These results have several ecological implications which are confirmed by field data. It is concluded that food searching cyprinids follow decision rules which are species specific both in the amount of sampling and in the responsiveness to rapidly changing conditions.     

Foraging capacities and effects of competitive release on ontogenetic diet shift in bream, Abramis brama

Bream (Abramis brama) undergo ontogenetic diet shift from zooplankton to benthic macroinvertebrates, but the switching size may be highly variable. To unravel under what conditions bream are pelagic versus benthic foragers, we experimentally determined size‐dependent foraging capacities on three prey types from the planktivory and benthivory niche; zooplankton, visible and buried macroinvertebrates. From these data we derived predictions of size‐dependent diet preferences from estimates of prey value and competitive ability, and tested these predictions on diet data from the field. Planktivorous foraging capacity described a hump‐shaped relationship with bream length that peaked for small bream of 67 mm total length. Benthivory capacity increased with increasing bream size, irrespective if benthic prey were visible on the sediment surface or buried in the sediment. From the experimental data and relationships of metabolic demand we calculated minimum resource requirement for maintenance (MRR) for each of the prey categories used in experiments. MRR increased with bream size for both zooplankton and visible chironomids, but decreased with bream size for buried chironomids, suggesting that intermediate sized bream (120–300 mm) may be competitively sandwiched between small and large bream that are more competitive planktivores and benthivores, respectively. Prey value estimates and competitive abilities qualitatively predicted diet shift in a bream population being released from competition. Competitive release did not change the diet of the largest size‐class feeding on an optimal diet of benthic invertebrates both before and after competitive release. However, profound diet shifts towards benthic macroinvertebrates were recorded for intermediate size‐classes that fed on a suboptimal diet prior to competitive release. Thus, laboratory estimates of size‐dependent foraging capacity of bream in planktivorous and benthivorous feeding niches provided useful information on size‐specific competitive ability, and successfully predicted diet preference in the field.     

Prey vulnerability to a gape-size limited predator: behavioural and morphological impacts on northern pike piscivory

The northern pike ( Esox lucius ) is a selective and important predator in lake ecosystems. Prey size in pike is limited by pike gape size, which is a linear function of pike body length. Here we show that the absolute gape-size limit in pike is greater than previously considered, and that maximum ingestible prey size is limited by prey body depth. Further, we experimentally show that pike prefer shallow-bodied roach before deeper-bodied common bream, and small prey sizes within each prey species. Handling time in pike increases with prey body depth, and since common bream are deeper-bodied than roach, handling time is longer for bream than for roach of the same length, but equal considering body depth. Prey handling time is suggested to be a major cost to the pike, since it increases the risk of losing the prey, as well as exposure to predation, kleptoparasitism and cannibalism. Consequently, prey vulnerability is determined by risk of predation and intraspecific interactions, and behavioural preferences in the pike, and not by pike gape-size limits. The consequences for natural populations is evaluated by analysing size structures of predator and prey fish populations in a eutrophic lake.     

Comparison of losses of planktivorous fish by predation and seine-fishing in a lake undergoing long-term biomanipulation

SUMMARY 1. Piscivore stocking at artificially high densities and fishing are the two common approaches to reduce the amount of planktivorous and benthivorous fish in lake biomanipulation programmes. Both measures have advantages and disadvantages, but their relative efficacy has not previously been directly compared.
2. We calculated the average annual catch of roach and bream in a lake undergoing long-term biomanipulation (Feldberger Haussee, Germany) by seining each year between 1992 and 1998. We compared this value with a bioenergetics estimate of annual consumption rates of the dominant cohorts of piscivores, pikeperch and pike, in 1997 and 1998. We also determined species composition and length distribution of prey fish in stomachs of the piscivores.
3. Roach was the dominant prey species of both pikeperch and pike, whereas bream was rarely taken by either piscivorous species. Seining removed on average larger specimens of roach than were found in the stomachs of the piscivores.
4. Based on stocking densities of the piscivores, published mortality rates, and individual consumption rates, feeding of pikeperch and pike on roach exceeded the manual removal of roach by seining by a factor of 4–15 (biomass) in 1997 and 1998.
5. Based on these results, a combination of fishing and piscivore enhancement is recommended. Whereas the stocks of adult roach and bream have to be reduced mainly by fishing, the predation of piscivores should be directed predominantly towards the juvenile zooplanktivorous fish. Therefore, small size-classes of piscivorous fish should be promoted by fisheries management, including stocking and harvest regulations.     

Interference competition in a planktivorous fish (Rutilus rutilus) at different prey densities and temperatures

The effect of interference competition can be assessed by comparing the capture rate of a predator foraging alone with that of the predator within a group. Since such an effect could be prey density dependent, a constant density of prey must be maintained while assessing this effect, irrespective of the elimination of prey by predation. However, when studying a predator-harvester, such as a planktivorous fish, which collects zooplankton at a rate of up to 1 prey s^?1, instantaneous replacement of each consumed prey item is not feasible. This problem was solved in short-lasting mesocosm experiments by minute-by-minute supplementation to replace eliminated Daphnia and maintain a constant average prey density. Such experiments were performed with different numbers of foraging roach (Rutilus rutilus) at three prey densities and in two ranges of ambient temperature. The number of Daphnia required at the start of each experiment to establish the initial prey density and the number that it was necessary to add per minute were determined in experiments conducted without prey supplementation and in preliminary experiments with prey supplementation. The results of this study revealed that fish foraging in a group eat less, due to both exploitation and non-aggressive competition for space. Moreover, the effect of interference competition was stronger at higher temperatures, irrespective of the prey density, indicating that natural populations of roach foraging in shoals may suffer more from competitive interactions in warmer waters.     

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.     

Prey selection by the larvae of three species of littoral fishes on natural zooplankton assemblages

The prey selection of larvae of three common littoral fish species (pike, Esox lucius; roach,Rutilus rutilus; and three-spined stickleback, Gasterosteus aculeatus) was studied experimentally in the laboratory by using natural zooplankton assemblages. Zooplankton prey was offered at four different concentrations to study the functional responses of the planktivores. The diets of pike and sticklebacks were formed mainly of copepod juveniles and adults, which dominated the prey communities, although sticklebacks ate also cladocerans. The diet of roach larvae consisted of rotifers, cladocerans and copepods, without prey selection, in equal proportions indicating a more omnivorous diet. All fish larvae were able to feed selectively although in sticklebacks prey selection was less pronounced. Pike and roach larvae preferred large prey to smaller prey types. Patterns of prey selection are discussed in the context of size-selection theory and apparent vs. true selection.     

Piscivore-Prey Fish Interactions: Mechanisms behind Diurnal Patterns in Prey Selectivity in Brown and Clear Water

Environmental change may affect predator-prey interactions in lakes through deterioration of visual conditions affecting foraging success of visually oriented predators. Environmental change in lakes includes an increase in humic matter causing browner water and reduced visibility, affecting the behavioural performance of both piscivores and prey. We studied diurnal patterns of prey selection in piscivorous pikeperch (Sander lucioperca) in both field and laboratory investigations. In the field we estimated prey selectivity and prey availability during day and night in a clear and a brown water lake. Further, prey selectivity during day and night conditions was studied in the laboratory where we manipulated optical conditions (humic matter content) of the water. Here, we also studied the behaviours of piscivores and prey, focusing on foraging-cycle stages such as number of interests and attacks by the pikeperch as well as the escape distance of the prey fish species. Analyses of gut contents from the field study showed that pikeperch selected perch (Perca fluviatilis) over roach (Rutilus rutilus) prey in both lakes during the day, but changed selectivity towards roach in both lakes at night. These results were corroborated in the selectivity experiments along a brown-water gradient in day and night light conditions. However, a change in selectivity from perch to roach was observed when the optical condition was heavily degraded, from either brown-stained water or light intensity. At longer visual ranges, roach initiated escape at distances greater than pikeperch attack distances, whereas perch stayed inactive making pikeperch approach and attack at the closest range possible. Roach anti-predatory behaviour decreased in deteriorated visual conditions, altering selectivity patterns. Our results highlight the importance of investigating both predator and prey responses to visibility conditions in order to understand the effects of degrading optical conditions on piscivore-prey interaction strength and thereby ecosystem responses to brownification of waters.     

Structure,development and function of the branchial sieve of the common bream,Abramis brama,white bream,Blicca bjoerkna and roach,Rutilus rutilus

Synopsis The filter feeding organ of cyprinid fishes is the branchial sieve, which consists of a mesh formed by gill rakers and tiny channels on the gill arches. In order to establish its possible role during growth we measured the following morphological gill raker parameters over a range of sizes in three cyprinid fishes, bream, white bream and roach: inter raker distance, bony raker length, raker width, cushion length and channel width. At any given standard length common bream has the largest inter raker distance, roach the lowest and white bream is intermediate. In the comb model of filter feeding the inter raker distance is considered to be a direct measure of the mesh size and retention ability (= minimal size of prey that can be retained) of a filter. For the three species under study there is a conflict between the comb model and experimental data on particle retention. Lammens et al. (1987) found that common bream has a large retention ability whereas roach and white bream have a much smaller one. A new model, the channel model (Hoogenboezem et al. 1991) has been developed for common bream; in this model the lateral gill rakers can regulate the mesh size of the medial channels on the other side of the gill slit. The present data indicate that this model is not appropriate for white bream and roach. At any given standard length white bream and roach only reach 70% of the raker length of common bream, which means that in this model the gill slits should to be very narrow during filter feeding. The gill rakers consist of a bony raker and a fleshy cushion. The bony rakers have a rather long needle-like part outside the cushion in bream, but not in white bream and roach which have blunt gill rakers. Blunt gill rakers are not suited to reduce the diameter of the medial channels. The comb model seems more appropriate for white bream and roach, but doubts about the validity of this simple model remain. The sum of the areas of the medial channels is an approximation of the area through which water flows in the filter. This channel area therefore gives an impression of the capacity or flow rate of the filter. With this capacity estimation and an estimation of energy consumption we calculated an energy ratio of filter feeding. The energy ratio decreases with increasing standard length with an exponent close to the expected exponent of -0.40. The energy ratio is highest in bream, intermediate in white bream and lowest in roach.     

Ecological consequences of food partitioning for the fish population structure in a eutrophic lake

In the highly eutrophic lake, Frederiksborg Slotssø, the diet composition of the bream (Abramis brama L.) and roach (Rutilus rutilus L.) populations was examined during three periods with different food availability. The length range of bream and roach was 9–34 cm (TL) and 5–18 cm (TL), respectively. The relative food composition was examined for 2 cm and 1 cm length intervals of bream and roach, respectively. During all three periods, bream shifted from benthic cladocerans (Alona sp.) to zooplankton and chironomids within a transitional length of 15.0–20.0 cm. These foodshifts were coupled with a change in feeding behaviour from particulate to filter feeding. The biomass of chironomids was too low to sustain the consumption of larger bream (>20.0 cm) which initiated feeding in the pelagic zone even in periods when the mean length and biomass of the preferred zooplankton, Daphnia cucullata, were low. In contrast to bream, roach fed mainly on zooplankton. With increasing size, roach progressively shifted to larger zooplankton species due to the increasing mesh size of their branchial system. The importance of benthic animals in the diet of roach was minor due to low feeding efficiency on prey buried in the sediment. Detritus appeared in the diet of bream and roach in periods of low availability of animal food items. Feeding on detritus may provide an energetic advantage to bream and roach and increase the carrying capacity for these species in lakes, where detritus is highly abundant. Especially for the larger fish due to the decrease in their relative metabolic demands. However, the ability of bream to filter feed and with increasing size to retain food items smaller than those retained by roach may be the main mechanism for the dominance of bream over roach in highly eutrophic lakes.     

A comparison of the effects of prey and non-prey neighbours on foraging rates of Epischura nevadensis (Copepoda: Calanoida)

SUMMARY. 1. Adults of the calanoid copepod, Epischura nevadensis , aggregate in situ near the thermocline in Lake Tahoe, California-Nevada. together with adults of another species of calanoid copepod, Diaptomus tyrelli and juveniles of both species. With a series of laboratory predation and algal clearance trials, we show that foraging rates of adult E. nevadensis are determined not only by the density of co-occurring potential prey (small copepods), but also by the presence of co-occurring non-prey neighbours (large, adult copepods). These effects occur at densities and in zooplankton assemblages found naturally, emphasizing the ecological importance of neighbours other than prey on zooplankton feeding.
2. Neighbours are distinguished primarily by size. Although predation rates increase linearly with the densities of small copepods. both algal clearance and predation rates decrease in the presence of large copepods. We also show, with a field predation experiment using small enclosures, that adults are size selective within species and that Diaptomus are selected over conspecifics of the same size.
3. We hypothesize that by reducing foraging rates in the presence of large zooplankton. E. nevadensis avoids predators and reduces predation risk at the cost of reduced energy consumption.     

Strategies of zooplanktivory shape the dynamics and diversity of littoral plankton communities: a mesocosm approach

Planktivorous fish can exert strong top‐down control on zooplankton communities. By incorporating different feeding strategies, from selective particulate feeding to cruising filter feeding, fish species target distinct prey. In this study, we investigated the effects of two species with different feeding strategies, the three‐spined stickleback (Gasterosteus aculeatus (L.)) and roach (Rutilus rutilus (L.)), on a low‐diversity brackish water zooplankton community using a 16‐day mesocosm experiment. The experiment was conducted on a small‐bodied spring zooplankton community in high‐nutrient conditions, as well as a large‐bodied summer community in low‐nutrient conditions. Effects were highly dependent on the initial zooplankton community structure and hence seasonal variation. In a small‐bodied community with high predation pressure and no dispersal or migration, the selective particulate‐feeding stickleback depleted the zooplankton community and decreased its diversity more radically than the cruising filter‐feeding roach. Cladocerans rather than copepods were efficiently removed by predation, and their removal caused altered patterns in rotifer abundance. In a large‐bodied summer community with initial high taxonomic and functional diversity, predation pressure was lower and resource availability was high for omnivorous crustaceans preying on other zooplankton. In this community, predation maintained diversity, regardless of predator species. During both experimental periods, predation influenced the competitive relationship between the dominant calanoid copepods, and altered species composition and size structure of the zooplankton community. Changes also occurred to an extent at the level of nontarget prey, such as microzooplankton and rotifers, emphasizing the importance of subtle predation effects. We discuss our results in the context of the adaptive foraging mechanism and relate them to the natural littoral community.     

Effects of brown and turbid water on piscivore–prey fish interactions along a visibility gradient

1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predator–prey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25–200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predator–prey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free‐swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free‐swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator–prey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher‐order interactions.     

Competition,predation, cannibalism: the development of young‐of‐the‐year perch populations in ponds with bream or roach

Piscivory of perch can occur within a few weeks after perch hatch, leading to the development of two size‐cohorts, with the larger perch becoming cannibals. However, the possibility of early piscivory is assumed to depend on the hatch timing of the prey and predator. Two species, bream (2006) and roach (2007), were tested as the prey fish. The bream (hatching 12 days after perch) were preyed upon by the perch, leading to the predicted development of two sizes of cohorts as well as to cannibalism. With roach (hatching simultaneously with perch), however, no piscivory or cannibalism occurred and the perch population was unimodally distributed. The results of this experimental pond study underpin recent theoretical findings that size differences between predator and prey, determined through differences in the timing of hatching as well as differences in juvenile growth rates, foster the occurrence of early piscivory in YOY perch that may lead to bimodality and finally to intra‐cohort cannibalism.     

Diet composition and prey preference of tench, Tinca tinca (L.), common bream, Abramis brama (L.), perch, Perca fluviatilis L. and roach, Rutilus rutilus (L.), in two contrasting gravel pit lakes: potential trophic overlap with wildfowl

The abundance of benthic macroinvertebrate taxa and the relative abundance of zooplankton taxa were compared with the diet of bream, tench. perch and roach from two gravel pit lakes during May-July 1986 and 1987. Significant food preferences were demonstrated between species and between lakes. Chironomid pupae dominated the macroinvertebrate diet of perch, roach, ate predominantly either Spirogyra sp. (St Peters Lake) or Daphniu hyalina (Main Lake).
The Main Lake, bream fed largely upon chironomid larvae and the bivalve Sphuerium but in St Peters Lake they positively selected a variety of less abundant benthic invertebrate taxa. Bream switched from benthos to zooplankton in the Main Lake in 1986. Tench ate large numbers of Aselhs and showed positive selection of various macroinvertebrate prey in St Peters but ate D. hjulim in Main Lake. Tropic overlap for chironomids and other macroinvertebrate prey was demonstrated between perch, bream and tench, and potentially with wildfowl which used the gravel pits for breeding and wintering.     

The food, growth and abundance of five co-existing cyprinids in lake basins of different morphometry and water quality

The food, growth and abundance of five co-existing cyprinid fish species in the eutrophic Lake Hiidenvesi were studied. The diet overlaps within the cyprinid community in shallow lake basins were compared with those in a deep basin, where littoral resources are less available. Roach, bleak and white bream inhabited both the shallow and the deep parts of the lake. Their growth rate was slow, probably due to the low availability of animal food, indicated by the increasing proportion of detritus and plant material in the diets towards the end of the summer. In the deep basin, roach and bleak, contrary to white bream, did not forage on the very abundant invertebrate Chaoborus flavicans, explained by the migration behaviour of C. flavicans. Blue bream, unlike other cyprinids, utilized copepods and had a relatively fast growth rate, but was mostly restricted to the shallow areas. The condition of the bream stock was weak both in terms of growth and abundance. The availability of zoobenthos was low and bream was not able to compete for zooplankton with the more specialized planktivores.     

Foraging tactics and prey-selection patterns of omnivorous and carnivorous calanoid copepods

The foraging tactics and prey-selection patterns of omnivorous and carnivorous calanoid copepods are reviewed. Calanoid foraging tactics are envisioned as falling along several closely coupled continua reflecting swimming behavior, feeding behavior, and dietary habit. The consequences of these foraging tactics on prey-selection patterns are explored in the context of a graphical model. It is hypothesized that the prey-selection patterns of calanoid copepods are determined, to a large extent, by calanoid foraging tactics and the size relationships of predator and prey.     

Ontogeny of prey attack behaviour in larvae and juveniles of three European cyprinids

Synopsis The ontogenetic change in time costs of prey attacks as well as the change in capture efficiency for representative cladoceran and cyclopoid prey was investigated in roach, Rutilus rutilus, bleak, Alburnus alburnus, and blue bream, Abramis ballerus. Video recordings were used for measuring the timing of attacks, whereas capture efficiencies were determined by direct observation. Decreases in the time cost of attacks reflect the decreasing importance of prey fixation during growth of the fish. No differences in capture efficiencies were found among the three cyprinid species, indicating that attack behaviour is unlikely to function as a basic mechanism leading to differences in prey selectivity among the investigated species. Increasing capture efficiency during early development may lead to increasing selectivity for cyclopoid prey in the field.