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.     

Time constraint on food choice in provisioning blue tits, Parus caeruleus: the relationship between feeding rate and prey size

Previous work on food-provisioning behaviour in blue tits suggested that the parents could gather larger prey items only by making longer foraging excursions, for example, by being more selective or by reaching more distant (and less exploited) feeding sites. Here, I show that within-nest, within-day variation in size of prey delivered by the parent could be explained by the time since its last visit. In unmanipulated conditions, size of larvae tended to increase with the time spent away from the nest. A significant positive relationship was more likely at high provisioning rates, suggesting that periods of intense feeding limited the size of prey delivered to the brood. To assess the effect of less intense feeding on prey size, I experimentally increased food availability to the tits. The parents could decide whether to eat the extra food or feed it to the nestlings. In both cases, food supplementation could result in longer time lags between natural feedings. Food-supplemented parents consumed the extra food and fed it to their nestlings, made longer foraging trips and delivered larger natural larvae than controls. In this group, size of larvae was more constant during the observation period and was independent of the time since the parent's last visit. This suggests that, below some value of visit rate, prey size is no longer limited by the duration of the foraging trip. The results support the view that tits continually vary visit rate and prey size. There is some evidence that these adjustments are made by changing food selectivity in response to changes in the state of the brood and of the parents.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Predation of perch on vendace larvae: diet composition in an oligotrophic lake and digestion time of the larvae

The diet of perch Perca fluviatilis was studied to reveal possible predation on vendace Coregonus albula larvae in an oligotrophic lake. Perch diet changed with the size of the fish: small perch ate mainly zooplankton and the diet shifted more to benthic invertebrates and fishes in larger perch. There were also annual and spatial differences in the diet, probably reflecting differences in the availability of prey animals. Perch predation on vendace larvae was only observed in the area with high availability of the larvae. The result suggested strengthened predation when the density of the larvae increases. According to bioenergetics modelling, the perch population increased natural mortality of vendace larvae only marginally. Food intake of spawning female perch was slightly reduced, whereas spawning males fed similarly to non-spawning males. Hence, the spawning period of perch was only a minor refuge for vendace larvae. Laboratory experiments of perch digestion rate demonstrated that, due to rapid digestion of the small fish larvae, diet sampling interval should not be >2 h in the field.     

Spatial and seasonal patterns in the feeding habits of juvenile Lates niloticus (L.), in the Mwanza Gulf of Lake Victoria

Flexibility in the feeding habits of juvenile Nile perch (1–30 cm total length) was studied from September 1988 to September 1989 at four sites (depth range: 1–25 m) in the Mwanza Gulf of Lake Victoria. During this period haplochromine cichlids were virtually absent in the area. We looked at the combined effects of predator size, season and habitat. Stomach content analysis showed that with increase in size, the diet of Nile perch shifted from zooplankton and midge larvae, to macro-invertebrates (shrimps and dragonfly nymphs) and fish. At a size of 3–4 cm Nile perch shifted from size-selective predation on the largest cyclopoids to predation on the largest, less abundant, calanoids. Zooplanktivory ended at a size of ca. 5 cm. Although an ontogenetic shift in the diet of juvenile Nile perch was obvious at all sampling stations, the contribution of prey types appeared to be habitat related. With increasing water depth the frequency of occurrence in the diet of most prey types decreased, but that of shrimps increased. At the entrance of the gulf (20–25 m deep) shrimps were the main food source throughout the year. Halfway the gulf (12–16 m), Nile perch showed seasonality in their feeding behaviour. Shrimps were taken there especially during the rainy season (January to May) when their densities at this station were high, whereas cannibalism prevailed during the rest of the year. In an environment with Nile perch and dagaa as alternative prey, shrimps were taken almost exclusively. They could be regarded as a key prey for Nile perch between 5 and 30 cm.     

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.     

Mensurative approach to examine potential interactions between age-0 yellow perch (Perca flavescens) and bluegill (Lepomis macrochirus)

Bluegill (Lepomis macrochirus) and yellow perch (Perca flavescens) populations are often sympatric in the Great Plains region of the U.S.A. and portions of Canada; however, very little attention has been given to potential interactions between these species for available resources, especially during the early life stages. Relationships between age-0 bluegill and yellow perch growth and relative abundance were explored across multiple lakes and years within the Nebraska Sandhill region, USA. In addition, four habitat patch types (open water, Phragmites spp., Typha spp., Scirpus spp.) were sampled for age-0 bluegill and yellow perch, and food habits were examined for each species during August, September, and October of 2009 in one of these lakes. Age-0 yellow perch growth was negatively related to age-0 bluegill relative abundance across a spatiotemporal scale. Age-0 bluegill and yellow perch exhibited similar habitat use (moderate–high overlap), but generally consumed different important and dominant prey taxa (bluegill consumed both macroinvertebrates—56?% and zooplankton—44?%, while yellow perch consumed more zooplankton—66?%), which resulted in low overall diet overlap between species. Previous research indicates that age-0 yellow perch diet ontogeny often results in feeding predominately on macroinvertebrates and positively selecting them (and avoiding zooplankton prey) at sizes observed in our study. Therefore, yellow perch growth rates may be compromised by the presence of bluegill because of the need to consume less energetically profitable prey items such as zooplankton.     

The feeding ecology of the pit-making ant lion larva,Myrmeleon bore: Feeding rate and species composition of prey in a habitat

The prey species composition and feeding rate of the pit-making ant lion larva,Myrmeleon bore Tjeder, which inhabits open sandy areas, were examined. Not less than 30 prey species, most of which were ants, were collected during a research period of 1.5 years. First instar larvae most often (81.1%) captured ants. Although 3rd instar larvae captured larger-sized prey than individuals of any other instar, they also captured small prey. The feeding rate of 3rd instar larvae was estimated by using the frequency of observed predation (FOP; (no. of ant lions handling a prey)/(total no. of pits observed)), the prey-handling time and the rhythm of daily foraging activity. FOP ofM. bore larvae was constant on the whole from spring to autumn. It was estimated that each captured 1.25 prey per day on average during this period. This estimate, however, was the feeding rate for days on which there was no rain. Assuming that the larvae cannot capture prey due to pit destruction when there is more than 10 mm of rainfall per day, the figure was reduced to 1.03 prey/day. The estimated feeding rate was evaluated with reference to larval foraging behavior.     

Effects of prey density on nocturnal zooplankton predation throughout the ontogeny of juvenile <Emphasis Type="Italic">Platax orbicularis</Emphasis> (Teleostei: Ephippidae)

Juvenile Platax orbicularis switches foraging tactics from diurnal herbivory to nocturnal zooplanktivory within a day. To examine how juvenile fish actively feed on zooplankton prey during nighttime, a field-recorded video analysis was conducted in the reefs off Kuchierabu-jima Island, southern Japan. Juveniles consistently showed fast and sudden attacks that were accurately directed at individual zooplankton prey, and changed feeding frequencies with different prey densities. A negative relationship was observed between feeding frequency and prey density, with higher feeding frequencies occurring at lower prey concentrations, implying a disturbance effect of clouded zooplankton prey on the juvenile fish. A clear transition from a ram-based to a suction-based feeding mode was observed with fish size, suggesting that changes in the feeding behaviors occur even in juveniles fishes, without drastic morphological changes.     

A new look at optimal foraging behaviour; rule of thumb in the rainbow trout

A realistic model of foraging behaviour in stream-living rainbow trout was developed to address some shortcomings of previous tests of optimal foraging theory. The model predicts prey selection based upon both energy-maximization and number-maximization strategies. Trout diet selection on the basis of prey size and prey calorific content was examined under laboratory conditions.
Diet composition was strongly influenced by relative abundance of prey types under all feeding regimes, as predicted by the model. Additional important factors include fish stomach capacity and daily digestive capacity. Experimental results strongly suggest that prey selection in rainbow trout is not based on calorific content. Examination of energy (kJ) obtained from observed diets showed no energy penalties associated with 'suboptimal' food choices, since all fish (regardless of their choices) consumed far more energy than required for their basic metabolic needs.     

Prey selection by age-0 walleye pollock, Theragra chalcogramma, in nearshore waters of the Gulf of Alaska

Juvenile walleye pollock, Theragra chalcogramma, is the dominant forage fish on the continental shelf of the Gulf of Alaska, yet little is known about the feeding habits of this important interval of pollock life history. The taxonomic composition and size of prey found in the stomachs of age-0 juveniles collected at three nearshore locations in the Gulf of Alaska in September 1990 were compared to the composition and size of zooplankton collected in concurrent plankton tows. The maximum length of prey consumed increased dramatically over the length range of pollock examined (58–110 mm) from approximately 7 mm to 30 mm, due mainly to the consumption of large euphausiids and chaetognaths by the bigger individuals. The maximum width of prey changed little over this size range although there was a general increase in prey width with increasing predator size. The minimum prey length and width did not change with increasing fish size. Juvenile pollock generally selected the larger prey sizes relative to what was available. Juvenile pollock showed a marked preference for adult euphausiids and decapod larvae and an avoidance of copepods and chaetognaths relative to the numbers collected in net tows. These results are discussed relative to the feeding ecology of these juvenile fishes. This revised version was published online in July 2006 with corrections to the Cover Date.     

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 feeding in two native and one alien fish species from the Murray-Darling Basin, Australia

Investigations into the feeding of the early stages of fishes can provide insights into processes influencing recruitment. In this study, we examined ontogenetic changes in morphology and feeding behaviour of two native Australian freshwater species, Murray cod, Maccullochella peelii peelii, and golden perch, Macquaria ambigua, and the alien species, common carp, Cyprinus carpio. Murray cod free embryos are large and well developed at the onset of feeding, whereas the other two species begin exogenous feeding much younger and are smaller and less-developed. Carp commence exogenous feeding 3 days earlier than golden perch, and show more advanced development of the eyes and ingestive apparatus. We conducted feeding experiments, presenting larvae of the three species with a standardised prey mix (comprising equal numbers of small calanoid copepods, large calanoid copepods, small Daphnia, and large Daphnia). Larvae of most tested ages and species showed a preference for mid-sized prey (300–500 μm wide). This was true even when their gapes substantially exceeded the largest prey offered. Daphnia were consumed more than similar-sized copepods. The results of this study suggest that survival through their larval period will be threatened in all three species if catchable prey <500 μm in width are not available throughout such time. They also suggest that interspecific competition for prey may occur, especially when larvae are very young. The precocious development of structures involved in feeding and the extended transition from endogenous to exogenous feeding of early carp larvae are likely to have contributed to the success of this species since its introduction to Australia.     

Temporal variation in feeding morphology and size-structured population dynamics in fishes

Considerable variation in morphology associated with resource use is a classic example of local adaptation to the environment. We demonstrate that a temporal change in feeding morphology might occur within a population. In a 5-year natural field experiment, we estimated gill raker morphology, resource density and population dynamics of the roach and its competitor, the perch. Despite a variation in density of zooplankton resources and perch across years, no change in roach density was observed. However, gill raker morphology in roach covaried with size structure of the zooplankton resource across years. A laboratory experiment confirmed that gill raker morphology has a great effect on roach foraging efficiency on zooplankton and that there is a functional trade-off with regard to zooplankton foraging. We suggest that the response in gill raker structure is an adaptation to deal with the rapid population dynamics of zooplankton, which are in turn mediated by changes in the size structure of the competing perch.     

Feeding,development, and growth of juvenile perch <Emphasis Type="Italic">perca fluviatilis</Emphasis> in mesocosms in the presence of filter-feeding zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> pallas

Quantitative and qualitative changes in the feeding spectra and growth patterns are studied in the larvae and juveniles of perch in artificial water ecosystems (mesocosms) in the presence of a filter-feeding zebra mussel. At a stocking density of 0.75 kg/m², the presence of a zebra mussel leads to a change in the feeding conditions of zooplankton, to a decrease in its abundance in regards to critical values for fish feeding, to an increase in the abundance of organisms of macrobenthos in the food, and to the rapid transition of the fish to feeding on chironomids. As a result of these changes, the growth rate of perch larvae decreases, their development at step D ₁ is delayed, the differentiation of the juveniles by size is accelerated, their size and weight variability increases, and individual predators (cannibals) appear.     

Does browning-induced light limitation reduce fish body growth through shifts in prey composition or reduced foraging rates?

1. Browning of waters, coupled to climate change and land use changes, can strongly affect aquatic ecosystems. Browning-induced light limitation may have negative effects on aquatic consumers via shifts in resource composition and availability and by negatively affecting foraging of consumers relying on vision. However, the extent to which light limitation caused by browning affects fish via either of these two pathways is largely unknown.
2. Here we specifically test if fish growth responses to browning in a pelagic food web are best explained by changes in resource availability and composition due to light limitation, or by reduced foraging rates due to decreased visual conditions.
3. To address this question, we set up a mesocosm experiment to study growth responses of two different fish species to browning and conducted an aquaria experiment to study species-specific fish foraging responses to browning. Furthermore, we used a space-for-time approach to analyse fish body length-at-age across >40 lakes with a large gradient in lake water colour to validate experimental findings on species-specific fish growth responses.
4. With browning, we found an increase in chlorophyll a concentrations, shifts in zooplankton community composition, and a decrease in perch (Perca fluviatilis) but not roach (Rutilus rutilus) body growth. We conclude that fish growth responses are most likely to be linked to the observed shift in prey (zooplankton) composition. In contrast, we found limited evidence for reduced perch, but not roach, foraging rates in response to browning. This suggests that light limitation led to lower body growth of perch in brown waters mainly through shifts in resource composition and availability, perhaps in combination with decreased visibility. Finally, with the lake study we confirmed that perch but not roach body growth and length-at-age are negatively affected by brown waters in the wild.
5. In conclusion, using a combination of experimental and observational data, we show that browning of lakes is likely to (continue to) result in reductions in fish body growth of perch, but not roach, as a consequence of shifts in prey availability and composition, and perhaps reduced foraging.

     

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man‐made floodplain waterbody

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man‐made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.     

Morphology dependent foraging efficiency in perch: a trade‐off for ecological specialization?

Trade-offs in foraging efficiency leading to divergent natural selection between and within populations exploiting different resources are thought to be a primary cause of trophic polymorphism. In this study we focused on the trade-offs in foraging efficiency and growth in a polymorphic perch population. Specifically, we related habitat-specific growth and diet of perch to perch morphology. In a subsequent laboratory study we experimentally tested the trade-off by testing the efficiency of perch with different morphology feeding on pelagic ( Daphnia sp., Chaoborus sp.) and littoral (mayfly larvae) food resources. The feeding performance was tested in different physical environments to see if we could predict growth patterns in the field based on foraging rate and behavior of perch.
In the field study, we found that the perch from the littoral and the pelagic zones differed in both morphology and diet. Within the littoral zone the deeper-bodied individuals grew faster compared to the more streamlined individuals, whereas the opposite pattern was found in the pelagic zone. In the aquarium experiments, perch from the littoral zone had higher capture rates on the pelagic prey types in vegetation trials and on mayfly larvae in both open water and vegetation trials. The pelagic perch had higher capture rates on the pelagic prey types in open water trials. The littoral perch had lower search velocity than the pelagic perch in open water trials whereas the opposite pattern was found in vegetation trials. The attack velocity of the pelagic perch was also higher than that of the littoral perch independent of vegetation structure. Our results suggest that there is a functional trade-off between performance in alternate habitats and general body form in perch. Such trade-offs may promote divergent natural selection and could be the mechanism that give rise to and upholds the pattern in the field.     

Feeding habits and diet overlap of marine fish larvae from the peri-Antarctic Magellan region

The Magellan region is a unique peri-Antarctic ecosystem due to its geographical position. However, the knowledge about the distribution and feeding ecology of fish larvae is scarce. Since this area is characterized by low phytoplankton biomass, we hypothesize that marine fish larvae display different foraging tactics in order to reduce diet overlap. During austral spring 2009–2010, two oceanographic cruises were carried out along southern Patagonia (50–56°S). Larval fish distribution and feeding of the two most widely distributed species were studied, the smelt Bathylagichthys parini (Bathylagidae) and black southern cod Patagonotothen tessellata (Nototheniidae). Larvae of B. parini showed a lower increase in the mouth gape at size, primarily feeding during daytime (higher feeding incidence during the day) mostly on nonmotile prey (invertebrate and copepod eggs, appendicularian fecal pellets, diatoms). They showed no increase in feeding success (number, total volume of prey per gut and prey width) with increasing larval size, and the niche breadth was independent of larval size. Larvae of P. tessellata showed a large mouth gape at size, which may partially explain the predation on motile prey like large calanoid copepods (C. simillimus) and copepodites. They are nocturnal feeders (higher feeding incidence during night) and are exclusively carnivorous, feeding on larger prey as the larvae grow. Nonetheless, niche breadth was independent of larval size. Diet overlap was important only in individuals with smaller mouth gape (<890 μm) and diminished as larvae (and correspondingly their jaw) grow. In conclusion, in the peri-Antarctic Magellan region, fish larvae of two species display different foraging tactics, reducing their trophic overlap throughout their development.     

Diel variation in use of cover and feeding activity of a benthic freshwater fish in response to olfactory cues of a diurnal predator

Some fish recognize the threat of predatory fish through chemical cues, which may result in variation in diel activity. However, there is little experimental evidence of diel shifts in activity of prey fish in response to the diel activity of a predator. We compared the total prey consumed and the use of cover by common bullies (Gobiomorphus cotidianus), a native benthic feeding eleotrid, when exposed to the odour of an exotic predator, European perch (Perca fluviatilis), over a 12-h period. Our results showed no significant effect of perch odour on feeding activity, but a significant increase in the use of cover at night and a decrease in the use of cover by day. While common bullies may recognize the presence of a predator through chemical cues, dark conditions may inhibit this and other sensory mechanisms, affecting their ability to recognize the proximity of a predator. For example, during the daytime they may rely on visual cues to initiate cover-seeking behavior, but in the dark, vision is impaired giving them less warning of predators, thus potentially making them more vulnerable.     

Effect of spatial heterogeneity on the role of Coccinella septempunctata as an intra-guild predator of the aphid pathogen Pandora neoaphidis

The foraging behavior of starved and non-starved adult and larval Coccinella septempunctata on groups of plants in the presence of Pandora neoaphidis-infected Acyrthosiphon pisum, uninfected aphids or a mixture of these two prey types was compared. In general results of these studies confirmed the results of previous work comparing foraging behavior on a smaller spatial scale in Petri dishes. However, behaviors were modified in response to spatial complexity, prey quality, and the host plant. Starved C. septempunctata adults and larvae fed for longer and consumed more aphids than non-starved coccinellids. Both larvae and adults fed on infected aphids and in some cases entirely consumed them. This was thought to be due to the ease of capture of infected (dead) aphids and the feeding stimuli provided by the presence of the host plant and, where there was a choice of prey, uninfected aphids in the environment. Both larvae and adults spent the majority of the time foraging in the upper regions of plants and visited more plants when they were not starved or when they were in the presence of less suitable, infected aphid prey.