Food and habitat partitioning among juveniles of three fish species in the pelagial of a mesotrophic lake

An analysis of the diet of 0⁺ perch, smelt and roach caught at night of the pelagial of a mesotrophic lake showed that their food was composed mainly of herbivorous and predatory cladocerans, copepods and Chaoborus larvae during summer, and of herbivorous cladocerans and copepods during October. An analysis of habitat use by juveniles revealed separation among the species: roach occurred in the upper, perch and smelt in the deeper water layers. Food and habitat were alternatively partitioned among the juveniles. In early summer the lowest food overlap between perch and smelt coincided with high habitat overlap. In October high food overlap between perch and smelt corresponded with low habitat overlap. Smelt and roach fry used common food resources throughout the season, but they were segregated in habitat.     

Trophic relationships and seasonal utilization of salt-marsh creeks by zooplanktivorous fishes

Synopsis In a high salinity estuary at North Inlet, South Carolina, co-occurrence and possible competition among adults of four dominant zooplanktivorous fishes were minimized by seasonal adjustments in lateral and vertical distributions as well as in dietary preferences. In winter, Atlantic silversides, Menidia menidia, occupied the entire water column while other planktivores were rare or absent from the estuary, and they consumed large prey such as mysid shrimps and fish larvae. An immigration of bay anchovies, Anchoa mitchilli, in the spring resulted in a redistribution of species with Atlantic silversides shifting to the surface waters and bay anchovies dominating the lower half of the water column. Both fishes consumed mostly copepods in the spring, but each favored a different species. There was little similarity in the large prey items consumed by the two fishes. Striped anchovies, Anchoa hepsetus, arrived in mid-summer and were most abundant at the surface while bay anchovies continued to dominate the bottom waters. Atlantic silversides were rare in all summer collections. The diets of the two anchovies were similar, but vertical separation during the period of maximum zooplankton abundance probably minimized competition. Rough silversides, Membras martinica, which were obligate surface dwellers, shared the upper water column with striped anchovies, but the two species had very different diets during their period of co-occurrence. Although seasonal changes in fish diets reflected shifts in zooplankton composition and all fishes consumed a variety of prey types, preferences for some prey taxa and total avoidance of others were indicated. Electivity indices indicated an especially strong selection for fiddler crab megalopae by all fishes in the summer and fall. All fishes, except rough silversides, which fed almost exclusively on copepods and crab zoeae, consumed large prey items when they were available. Fine scale partitioning of the food resources was apparent in the selection of different copepod and insect species by the fishes. Spatial and temporal separation in the distribution and/or dietary preferences of the zooplanktivores fishes probably reduces the potential for resource competition. Given the high abundances and selectivity of the planktivores, significant impacts on some zooplankton populations probably result.     

Feeding chronology and habits of Alosa spp. (Clupeidae) juveniles from the lower Hudson River estuary, New York

Synopsis Feeding habits of juvenile alewife, A. pseudoharengus, blueback herring, A. aestivalis, and American shad, Alosa sapidissima, were examined over a 24 h period at an inshore location on the lower Hudson River. Feeding periodicity differed by species: alewives showed no diel differences, whereas shad fed least intensively near dawn and herring least intensively at night. Alewives fed primarily on chironomids and the amphipod Corophium lacustre, shad on Formicidae and larval chironomids, and herring on chironomids and copepods. Diel variation in prey selection was evident. Dietary overlap was generally greatest between alewife and herring and least between shad and herring.     

Feeding interactions between the introduced ctenophore Mnemiopsis leidyi and juvenile herring Clupea harengus in the Wadden Sea

We analysed feeding interactions between Mnemiopsis leidyi and juvenile Clupea harengus in the Wadden Sea. Biomass, diet overlap, prey selectivity, predation impact and stable isotope composition (C, N) of both species were assessed from June to September 2010. High biomass of C. harengus was found in June and July (wet weight 3.0 ± 1.8 g m^?3) followed by a steep decline from August to September (wet weight 0.01 ± 0.01 g m^?3), coinciding with a dramatic increase in M. leidyi biomass (wet weight 18.3 ± 16.1 g m^?3 during August). These two species showed a high overlap in their respective diets (copepods, meroplankton) during the study period. Predation impact of C. harengus on calanoid copepods was highest in June and July where 84 and 41 % of the standing stock were eaten per day in June and July, respectively. Predation impact of M. leidyi on calanoid copepods was highest in September (16 %). Based on stable isotope analysis C. harengus and M. leidyi were assigned to a trophic level of 3.08 and 2.47, respectively. Furthermore, we assessed the potential of competition between M. leidyi and C. harengus in a mesocosm experiment. Results indicated that at present zooplankton densities intraspecific competition in C. harengus seemed to be greater than interspecies competition with M. leidyi. Due to the low predation impact of M. leidyi and the reduced temporal overlap, competition between M. leidyi and C. harengus during the study period was estimated as low. Nevertheless, considering the high dietary overlap and the inter-annual variation in biomass and occurrence of both species and their zooplankton prey, competition in the Wadden Sea area cannot be excluded.     

Alewife planktivory controls the abundance of two invasive predatory cladocerans in Lake Michigan

1. We sampled along a nearshore transect (10-m bathymetric contour) in Lake Michigan to determine diet, 24-h feeding periodicity, daily ration and food requirements of an invasive fish, the alewife, Alosa pseudoharengus , relative to zooplankton abundance and production. Our objective was to determine whether the alewife controls the abundance of two invasive, predatory cladocerans, Bythotrephes longimanus and Cercopagis pengoi .
2. Bosminidae was the most abundant prey taxon and Chydoridae, Leptodora , Chironomidae and Bythotrephes were the least abundant. Neither Bythotrephes nor Cercopagis were important prey for small alewives (≤100 mm). Bythotrephes was eaten by over 50% of large alewives (>100 mm) and accounted for 10–27% of the diet weight. Cercopagis was eaten by about 30% of the large alewives but only accounted 1% of the diet weight.
3. Food weight in stomachs was highest early in the night for small alewives and lowest at night for large alewives. Chironomidae and large Chydoridae were the preferred prey of small alewives. Bythotrephes and large Chydoridae were the preferred prey for large alewives.
4. Food requirements of alewife were much less than production for most prey taxa, although the consumption of Bythotrephes greatly exceeded production on both dates. Alewives consumed only 3% of Cercopagis production. High selectivity and food requirements of alewife for Bythotrephes , and low selectivity and food requirements for Cercopagis , probably explain the difference in abundance between these two invasive cladocerans at our nearshore site in Lake Michigan.     

Planktivory in the changing Lake Huron zooplankton community: Bythotrephes consumption exceeds that of Mysis and fish

1. Oligotrophic lakes are generally dominated by calanoid copepods because of their competitive advantage over cladocerans at low prey densities. Planktivory also can alter zooplankton community structure. We sought to understand the role of planktivory in driving recent changes to the zooplankton community of Lake Huron, a large oligotrophic lake on the border of Canada and the United States. We tested the hypothesis that excessive predation by fish (rainbow smelt Osmerus mordax, bloater Coregonus hoyi) and invertebrates (Mysis relicta, Bythotrephes longimanus) had driven observed declines in cladoceran and cyclopoid copepod biomass between 2002 and 2007. 2. We used a field sampling and bioenergetics modelling approach to generate estimates of daily consumption by planktivores at two 91‐m depth sites in northern Lake Huron, U.S.A., for each month, May–October 2007. Daily consumption was compared to daily zooplankton production. 3. Bythotrephes was the dominant planktivore and estimated to have eaten 78% of all zooplankton consumed. Bythotrephes consumption exceeded total zooplankton production between July and October. Mysis consumed 19% of all the zooplankton consumed and exceeded zooplankton production in October. Consumption by fish was relatively unimportant – eating only 3% of all zooplankton consumed. 4. Because Bythotrephes was so important, we explored other consumption estimation methods that predict lower Bythotrephes consumption. Under this scenario, Mysis was the most important planktivore, and Bythotrephes consumption exceeded zooplankton production only in August. 5. Our results provide no support for the hypothesis that excessive fish consumption directly contributed to the decline of cladocerans and cyclopoid copepods in Lake Huron. Rather, they highlight the importance of invertebrate planktivores in structuring zooplankton communities, especially for those foods webs that have both Bythotrephes and Mysis. Together, these species occupy the epi‐, meta‐ and hypolimnion, leaving limited refuge for zooplankton prey.     

Feeding habits of sand smelt (Atherina boyeri, Risso 1810) in Trichonis Lake (Western Greece)

The feeding habits of sand smelt (Atherina boyeri, Risso, 1810) from Trichonis Lake (Western Greece) were investigated. Stomach contents were analyzed from 240 specimens with total lengths ranging from 35 to 112 mm. Samples were taken at monthly intervals (January–December 1997). Of the total number of stomachs examined, 53 were empty (22.1%). However, values varied greatly with season (maximum in January: 50%; minimum in August: 7.6%). Prey analyses of stomach contents identified 15 important items (%Rn > 0.05) belonging to six major groups: crustacean (copepods, cladocera), mollusca (bivalve: larvae), insects (larvae), cestode worms and finfish (fry and eggs). Dominant prey were larvae of the bivalve Dreissena polymorpha (%Rn = 33.8), the copepods Eudiadomus drieschi (%Rn = 26.4) and the cladocera Diaphanosoma brachyurum (%Rn = 24.2). The importance of cladocera and copepods decreased with increasing size of the sand smelt, while the importance of bivalve larvae, fish eggs and finfish fry increased with increasing sand smelt size. Seasonal changes in diet composition and prey abundance in sand smelt stomachs were recorded as coinciding with the seasonal composition and abundance of the zooplankton community in the surface layers of Trichonis Lake. Bivalve larvae were the dominant prey of A. boyeri during January to May, while copepods and cladocera dominated from June to December.     

Temperature sensitivity of vertical distributions of zooplankton and planktivorous fish in a stratified lake

Recent studies have indicated that temporal mismatches between interacting populations may be caused by consequences of global warming, for example rising spring temperatures. However, little is known about the impact of spatial temperature gradients, their vulnerability to global warming, and their importance for interacting populations. Here, we studied the vertical distribution of two planktivorous fish species (Coregonus spp.) and their zooplankton prey in the deep, oligotrophic Lake Stechlin (Germany). The night-time vertical centre of gravity both of the fish populations and of two of their prey groups, daphnids and copepods, were significantly correlated to the seasonally varying water temperature between March and December 2005. During the warmer months, fish and zooplankton occurred closer to the surface of the lake and experienced higher temperatures. The Coregonus populations differed significantly in their centre of gravity; hence, also, the temperature experienced by the populations was different. Likewise, daphnids and copepods occurred in different water depths and hence experienced different temperatures at least during the summer months. We conclude that any changes in the vertical temperature gradient of the lake as a result of potential future global warming may impact the two fish populations differently, and may shape interaction strength and timing between fish and their zooplankton prey. Priority programme of the German Research Foundation—contribution 9.     

Ontogenetic changes in habitat use by whitefish,Coregonus lavaretus

Synopsis The whitefish, Coregonus lavaretus, in the lake Mj?sa exhibited two niche changes during their life cycle. Juveniles (< 25 cm body length) were confined to the shallow (0–30 m) epibenthic zone. Medium sized whitefish (25–35 cm body length) expanded their habitat use to include the deep (30–90 m) epibenthic zone as well as the pelagic zone. From a body length of 35 cm, habitat use was restricted to the deep epibenthic zone. Small fish in the shallow epibenthic zone ate small and medium-sized prey (zooplankton, insect larvae and surface insects). Medium-sized fish in this zone were in addition feeding on the larger amphipod, Pallasea quadrispinosa. In the pelagic zone, the diet of medium-sized whitefish was dominated by zooplankton, although some larger prey like surface insects and age-0 smelt, Osmerus eperlanus, were also eaten. In the deep epibenthic zone, the diet of both medium-sized and large (< 35 cm) whitefish consisted mainly of the large prey P. quadrispinosa.     

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.     

Foraging behaviors and the interaction of alewife,Alosa pseudoharengus,and bloater,Coregonus hoyi

Synopsis Alewife, Alosa pseudoharengus, and bloater, Coregonus hoyi, are common planktivores in Lake Michigan. Both alewife and bloater use a variety of feeding modes. Alewives can filter, gulp and particulate feed; bloaters can only gulp and particulate feed. We examined handling time per prey and probability of capture for alewife and bloater particulate feeding on Mysis relicta. Using these estimates and available data for filtering alewives, cost curves were derived for alewife and bloater particulate feeding and for alewife using all three modes of feeding. Alewives filter small prey relative to their own body size and particulate feed on larger prey. Feeding mode appears to be dependent on prey size and density and shifts in feeding mode are apparently based on maximizing biomass eaten per time. The ability to filter confers a competitive advantage on alewife when small prey are abundant as they were in the mid 1960s in Lake Michigan. If the zooplankton are large, bloater young-of-year do not suffer this relative disadvantage. In fact, large bloaters can consume prey on the bottom not available to alewife. This shifting competitive balance may explain, in part, the observed dynamics of alewife and bloater.     

Timing and site selection of spawning in a landlocked population of rainbow smelt in Wisconsin

To study the site selection and timing of spawning by rainbow smelt, Osmerus modax, in a freshwater system, smelt were sampled with fyke nets during the spawning run in spring 2002 and 2003. The sex ratio of smelt favored males in the early and late segments of the run, with over 90% of smelt caught being male. At the peak in the catch, females comprised 57% of the smelt collected. The gonadosomatic index of males and females declined significantly on the day of peak catch, signaling the peak in spawning activity. Higher catches of smelt occurred on cobble-dominated substrates during the peak of the run, but no site selection was apparent earlier or later. Groundwater outflow did not appear to affect catches. Our study suggests that smelt come inshore but do not select specific spawning substrates prior to or after the peak in spawning. Smelt do select cobble sites during the highest rates of spawning. The relation between the peak in spawning and site selection could have application in planning removal strategies for the species.     

Influence of benthic and interstitial processes on nutrient changes along a regulated reach of a large river (Rhône River,France)

An enclosure study was conducted in Ranger Lake in south-central Ontario, Canada from 4 July to 5 August 1997 to determine predation effects of the larvae of the phantom midge fly Chaoboruson the zooplankton community. Zooplankton assemblages were established in 12 enclosures (2 m in diameter, 7.5 m deep). Three densities of fourth-instar Chaoborus trivittatus (0 l^–1, 0.1 l^–1 and 0.5 l^–1) were introduced as predator treatments to the enclosures. Temperature, dissolved oxygen and zooplankton community composition were monitored for six weeks. To determine if the zooplankton community composition changed, a repeated measures multivariate analysis was performed on percent biomass of Bosmina and calanoid copepods. There were no significant differences in mean taxon percent biomass among predator treatments. There were significant differences in mean taxon percent biomass between water layers (epilimnion and metalimnion). There were also significant differences in lengths of Bosmina and calanoid copepods among predator treatments at the end of the experiment. Crop content analysis of C. trivittatusshowed that Bosmina constituted 88–98% of the prey items found in the crops. These results demonstrate that the use of deep enclosures, a Chaoborus species which vertically migrates, and lower natural densities of Chaoborus may provide prey with an important natural refuge from predation and so allow a more accurate determination of the predation impact of Chaoborus trivittatusin temperate lakes where fish control Chaoborus densities.     

Variability of kokanee and rainbow trout food habits,distribution, and population dynamics,in an ultraoligotrophic lake with no manipulative management

Crater Lake is a unique environment to evaluate the ecology of introduced kokanee and rainbow trout because of its otherwise pristine state, low productivity, absence of manipulative management, and lack of lotic systems for fish spawning. Between 1986 and 2004, kokanee displayed a great deal of variation in population demographics with a pattern that reoccurred in about 10 years. We believe that the reoccurring pattern resulted from density dependent growth, and associated changes in reproduction and abundance, driven by prey resource limitation that resulted from low lake productivity exacerbated by prey consumption when kokanee were abundant. Kokanee fed primarily on small-bodied prey from the mid-water column; whereas rainbow trout fed on large-bodied prey from the benthos and lake surface. Cladoceran zooplankton abundance may be regulated by kokanee. And kokanee growth and reproductive success may be influenced by the availability of Daphnia pulicaria, which was absent in zooplankton samples collected annually from 1990 to 1995, and after 1999. Distribution and diel migration of kokanee varied over the duration of the study and appeared to be most closely associated with prey availability, maximization of bioenergetic efficiency, and fish density. Rainbow trout were less abundant than were kokanee and exhibited less variation in population demographics, distribution, and food habits. There is some evidence that the population dynamics of rainbow trout were in-part related to the availability of kokanee as prey.     

Seasonal variation in the interactions between piscivorous fish,planktivorous fish and zooplankton in a shallow eutrophic lake

The interactions between the higher trophic levels in a shallow eutrophic lake were studied during the course of a year. Three fish species determined the main pathways of organic matter flow within the system: the predominantly planktivorous bream (Abramis brama), the obligate planktivorous smelt (Osmerus eperlanus), and the piscivorous pikeperch (Stizostedion lucioperca). Of the thirteen common zooplankton taxa Daphnia hyalina and cyclopoid copepods were utilized most by the planktivorous fish, while the large production of small cladocerans is almost left unutilized.The seasonal variations of production and consumption are large. This is mainly affected by seasonal variation of the water temperature. The production of O + smelt is efficiently utilized by the pikeperch. Being the most important zooplankton consumer, as well as the most important prey group, O + fish plays a key role in the Tjeukemeer food web.     

Zooplankton Communities in the Shallow Lake Guiers (Senegal,West Africa)

Seasonal variations of zooplankton communities and their interactions with phytoplankton and environmental parameters were studied over a twelve‐month period in Lake Guiers (Senegal, West Africa). Zooplankton was most abundant during the warm and rainy season corresponding to the flood event (July to October) with peaks for rotifers and cyclopoid copepods in July–August and September–October, respectively. Filamentous cyanobacteria were the dominant phytoplankton during the warm season (August to November), while diatoms were dominant during the cool season (December to April). Temperature increase and river flooding both played an important role in these successions, favoring intense development of cyanobacteria and cyclopoid copepods. Trophic interactions also seem to be an important factor in structuring of the plankton community. Overall, the plankton composition displayed a trend toward a eutrophication state. Our study confirms the existence of seasonality in zooplankton communities and the importance of using biological indicators such as phyto‐ and zooplankton to monitor water quality, in particular in tropical freshwater ecosystems. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of larval and juvenile perch: the importance of diet and fish density

In August, growth rate of young–of–the–year (YOY) Perch In lake enclosures could be explained by both YOY density and mean cladoceran biomass, suggesting that in a lake where YOY perch are dominant, growth may be density dependent in late summer and mediated through top–down control on daphnid biomass. In June, growth rate of YOY perch could not be fully explained by YOY density or by mean cladoceran biomass, suggesting that growth and survival during the first part of the summer is negatively affected by a diet of Bosmina and cyclopoid copepods only. The experiments also suggest why YOY perch have a slow growth and a low abundance in eutrophic lakes where small zooplankton dominate. The June experiment also indicated that growth of late larval or early juvenile perch improved when a larger cladoceran became available and was included in the diet.     

Seasonal changes in zooplankton abundance in the lower Rhine during 1987–1991

Zooplankton in the River Rhine was surveyed for five years at the Dutch sampling stations, Lobith (German/Dutch border) and Maassluis (at the point of discharge of the river into the North Sea). The zooplankton abundance showed an apparent seasonal pattern at both stations, characterized by low densities during the winter period, and higher densities during the summer period, with a spring peak. Zooplankton was dominated by rotifers at both stations, although during the winter periods the contribution of copepods was considerable. The rotifers were dominated byBrachionus angularis, B. calyciflorus, Keratella cochlearis andK. quadrata; the copepods by cyclopoid nauplii; the cladocerans by small-sized species mainly belonging toBosmina. At Maassluis the relative contribution of copepods was higher than at Lobith. Furthermore, the zooplankton at Maassluis included the speciesEurytemora affinis, characteristic for estuarine conditions. In spring, the rotifer density and water temperature and rotifer density and chlorophylla concentration were positively correlated. Furthermore, both rotifer density and chlorophylla were inversely correlated with discharge. The possible role of environmental factors (water temperature, chlorophyll content, discharge and biotic factors) controlling the river zooplankton dynamics is indicated.     

Temporal variation and feeding ecology of juvenile Sebastes in rocky intertidal tidepools of northern California, with emphasis on Sebastes melanops Girard

This study examined the seasonal use of rocky intertidal areas by young-of-the-year (YOY) Sebastes spp. at three locations in northern California, 2003 to 2005. Six species of Sebastes were noted during the study with black rockfish Sebastes melanops comprising >99% of the total number sampled. Sebastes melanops were noted in rocky intertidal areas from May to August with peak abundances occurring in May or June. Variation in recruitment and feeding was evident among years. Diet analysis, using the index of relative importance (% I _RI) and the modified index (% I _M), showed that YOY S. melanops and Sebastes mystinus consumed a variety of prey items with harpacticoid copepods and gammaridean amphipods being the dominant prey categories. The rocky intertidal appears to serve as an important habitat for YOY S. melanops in northern California.     

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.