Feeding of an Iberian stream cyprinid assemblage: seasonality of resource use in a highly variable environment

Food resource use by seven cyprinids from an Iberian stream was analysed over 9 months. Differences in food resource use were found both between species and within species between seasons. Plant material was a more important food for carp, nase, goldfish and barbel than for gudgeon, roach and chub, irrespective of the season. Chironomid larvae were the staple animal food for the former five species throughout the year. Roach and chub, especially the latter, displayed large seasonal variations in prey use, with chironomid larvae only being important during autumn. Ephemerellid nymphs and ephemeropteran imagos dominated the animal diet of chub during spring and summer, respectively. Dipteran adults and Formicidae were the most important prey for roach during spring and summer, with other common prey being ephemerellid nymphs and hydropsychid larvae. Food resource overlap among the three dominant species (roach, barbel and chub) displayed a large seasonal variation. High overlaps were observed during autumn when these species used the same resources. During summer overlaps were much lower with each species specialising on different prey. The remaining less abundant species had large diet overlaps amongst themselves and with barbel, over all seasons. It is suggested that morphological constraints, habitat partitioning and temporal changes in food resource limitation may be involved in producing these patterns of food resource use.     

Comparative study of reproductive biology in single- and multiple-spawner cyprinid fish. I. Morphological and histological features

To clarify the dynamics and regulation of oogenesis in single- and multiple-spawning cyprinid fish with group-synchronous oocyte development, a multidisciplinary approach to their reproduction was undertaken using three species from the River Meuse (Belgium): the roach Rutilus rutilus as a single spawner, and the bleak Alburnus alburnus and the white bream Blicca bjoerkna as multiple spawners. The gonadosomatic index (GSI) and histomorphometric changes (distribution of oocyte size, relative proportion of the various oocyte stages) in the ovary are compared. Different patterns of GSI and oocyte growth were observed both between the single- and multiple-spawner fish and between the two multiple spawners. Maximum GSIs were higher in roach (21%) than in bleak and white bream (17.7 and 14.5%, respectively), and compared to the rapid decline of GSI in the roach population, the GSI of multiple spawners decreased progressively during the spawning season. In roach, a short gonadal quiescent period and an early onset of vitellogenesis was recorded from late summer onwards whereas, in bleak and white bream, exogenous vitellogenesis was not systematically observed before winter. A protracted spawning season and/or a low water temperature in autumn are hypothesized to explain this long period of gonadal quiescence. In bleak, during the spawning season, the oocytes recruited arose from the stock of endogenous vitellogenesis and attained the final maturation stage very rapidly. This recruitment occurred during the whole spawning season. In white bream, the differentiation of vitellogenic oocytes from smaller oocytes was completed before the onset of the spawning season. During the spawning period, the proportion of vitellogenic oocytes decreased progressively whereas the percentage of oocytes in the final maturation stage remained approximately constant.     

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.     

Feeding of fish in Lake Glubokoe

Lake Glubokoe is inhabited by 13 species of fish. The commonest are roach, bream, perch and ruff. Comparison of seine catches for 1950 and 1984 revealed a considerable decrease in the share of perch (from 31% to 2%) and ruff (from 18.5 to less than 0.1%) in 1984. The richest food resource in the lake is crustacean plankton. In summer, it is mostly consumed by roach. Estimation of the electivity shows that, unlike perch, roach selectively consumes small crustaceans (Bosmina and Polyphemus). Poor growth rate of all common species of fish points to their food limitation. In summer the diets of common species of fish are differentiated to a considerable extent. Of 36 pairs of combinations a high food overlap was found only in 2 cases: 1) O + perch and Leucaspius delineatus, 2) yearlings and adult roach. Low diet overlap in fish during intensive feeding in summer probably reflects a feedback between the volume and intensity of food competition. The populations of bream and ruff probably compete for chironomid larvae which inhabit the sublittoral, as perch, roach and Leucaspius delineatus probably do for large littoral insects. However, intraspecific competition appears to be more important than interspecific for the roach and bream populations (the two most numerous species in the lake).     

Microhabitat use and diet of 0+ cyprinid fishes in a lentic, regulated reach of the River Great Ouse, England

In the River Great Ouse, 0+ roach, bream, chub, bleak and gudgeon were each divided into three' ecospecies' on the basis of their morphology: young larvae, old larvae and juveniles. Ecologically similar species were positively associated and dissimilar species were negatively associated. All ecospecies, except juvenile bleak preferred water < 1 m deep, within 6 m of the bank with some plant cover. Habitat use was similar for all species. It is suggested that this habitat offers increased growth rate, reduced predation risk and increased food abundance to all species, and that species overlap is due to complementary habitat use rather than aggregation. During the early larval period all species fed predominantly upon rotifers and diatoms. During the late larval period there was a switch to Cladocera, primarily Chydoridae and Ceriodaphnia sp., and chironomid larvae. Species-specific dietary selection was evident during the juvenile period, with roach feeding primarily upon aufwuchs, bream upon Cladocera, chub upon Diptera, and gudgeon upon Copepoda.     

Feeding biology of bleak, Alburnus alburnus, in Lake Koronia, northern Greece

The feeding of bleak, Alburnus alburnus (L.), was studied in a natural eutrophic lake of northern Greece by an analysis of gut contents. Feeding was more intense during the first half of the day. Monthly analyses showed temperature-dependent feeding intensities, which were high during summer and the beginning of autumn and showed a decline in winter. The low feeding intensity in April coincided with the maximal value of the GSI. Bleak is a zooplankton feeder mainly, consuming Copepoda and Bosmina all the year round. During the hot period the diversity of its food increased. Other Cladocera, mainly Diaphanosoma , but also Moina, Daphnia and other less abundant genera, were found also. Meanwhile, Hydracarina and insect nymphs were found frequently, but in very low quantities. The size of bleak did not play an important role in its food composition. The stenophagic nature of its feeding could be explained in terms of the abundance of zooplankton in the environment. The influence of feeding intensity on the condition factor of the species is discussed.     

The occurrence of Sphaerostoma bramae (Digenea: Allocreadiidae) in the roach from the Worcester-Birmingham canal

Two hundred roach (Rutilus rutilus) were examined over a twelve-month period to provide information concerning the occurrence of Sphaerostoma bramae. Infection levels were high during the autumn and winter and at this time of year the parasite population was composed almost exclusively of immature parasites. Maturation was rapid in the spring but was accompanied by a decrease in the infection level. In late summer, after egg-laying, losses due to the death of spent parasites began to be replaced by the recruitment of immature parasites and this recruitment reached its peak in the autumn and winter. The annual cycle of occurrence and maturation is discussed in relation to fluctuating environmental variables and the feeding behavior of the roach.     

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

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

Seasonal Variation in the Diets of Bluefish, Pomatomus saltatrix (Pomatomidae) and Striped Weakfish, Cynoscion guatucupa (Sciaenidae) in Southern Brazil: Implications of Food Partitioning

The stomach contents of 516 Pomatomus saltatrix and 506 Cynoscion guatucupa from southern Brazil were examined. Both species preyed primarily upon teleosts and crustaceans and occasionally squid. Seasonal variation in the diet was related to prey availability in the area, confirming the opportunistic feeding behaviour of both species. During the summer, P. saltatrix preyed upon four prey species (Loligo sanpaulensis, Artemesia longinaris, Mullus argentinae and Paralonchurus brasiliensis), whereas in the autumn and winter Engraulis anchoita was the predominant prey. C. guatucupa similarly preyed upon A. longinaris and P. brasiliensis during the summer, with juvenile C. guatucupa and E. anchoita also consumed. The latter species was an important dietary constituent during other seasons, as were A. longinaris (autumn), Umbrina canosai (winter), Trachurus latami and euphausids (spring). Although P. saltatrix had a broader diet than C. guatucupa during the summer, the latter species had a broader diet overall. Diet breadths were lower from autumn to spring, due to the predominance of E. anchoita in the diet of both species. This restricted diet resulted in significant intra- and inter-specific diet overlap during the winter but, because of the seasonal abundance of E. anchoita, the high levels of diet overlap do not necessarily indicate competition.     

Seasonal changes in the diets and relative abundances of perch and roach in the littoral and pelagic zones of a large lake

In the Enonselkä and Laitialanselkä basins of Lake Vesijärvi, perch Perca fluviatilis and roach Rutilus rutilus were abundant in the littoral and in the pelagic zones throughout the summer. In the littoral zone, roach was always more numerous than perch, while perch dominated in the open water. Intraspecific diet overlap values were higher than interspecific values. In the pelagic zone, perch <155 mm fed mainly on the cladoceran Leptodora kindtii , while small bosminids were most important food items for roach. Large perch were piscivorous, feeding mainly on smelt Osmerus eperlanus . In the littoral zone small perch foraged on zooplankton and chironomid larvae and large perch on chironomids and fish (small perch). Small roach fed mainly on bosminids and detritus, while for roach <185 mm macrophytes ( Elodea Canadensis, Lemna trisulca ) were also of importance. Detritus was more common in the food of roach in Laitialanselkä than in Enonselkä. The slower growth rate of roach in Laitialanselkä compared with Enonselkä was probably connected with this. However, considering the latitude of the lake, the growth rate of both roach and perch was relatively fast in both basins. The results indicated that in a large lake both perch and roach are able to utilize effectively the different habitats and diverse food resources. By segregation in food resource utilization they are able to co-exist in large quantities, at the same time maintaining a relatively fast growth rate.     

Diet overlap among ruminants in Fennoscandia

Information on overlap in resource use is central to understanding of interspecific exploitation competition and resource partitioning. Despite this, measures of diet overlap among northern ruminants in Fennoscandia is limited to one earlier study (reindeer and sheep). Diet overlap between sympatric moose and roe deer calculated with Schoener’s index was 20.7% and 33.6% during summer (data from one area) and winter (data from two areas), respectively, whereas average diet overlap between moose and red deer was 32.0% during winter (data from four areas). Diet overlap between a coastal island population of red deer and sheep was 59.3% during summer and 63.9% during winter. Summer diet overlap between a sheep and a goat population and a sheep and a reindeer population calculated with data on main types of forage plants was 77.0% and 55.1%, respectively. However, overlap calculated with main plant groups was sometimes considerably higher than when calculated for individual forage species. Neither difference in feeding type nor body mass successfully predicted diet overlap between species pairs (n=9), although there tended to be negative correlation (r _p =–0.586, P=0.098) between diet overlap of main plant groups (calculated across studies) and difference in feeding type. Received: 19 October 1999 / Accepted: 31 January 2000     

Patterns of diet overlap between populations of non-indigenous and native fishes in shallow ponds

No significant differences in the diet composition were detected for any of the populations of four non-indigenous fish species (brown bullhead Ameiurus nebulosus , pumpkinseed Lepomis gibbosus , topmouth gudgeon Pseudorasbora parva and eastern mudminnow Umbra pygmaea ) and two native fish species (gudgeon Gobio gobio and roach Rutilus rutilus ), between two small shallow ponds and between habitats within the ponds, during late summer. Based on diet composition, groups of size classes within species ('functional groups') were distinguished. For most functional group combinations of exotic fishes, diet overlap values were low. Although chironomid larvae formed the most important food source, differential consumption of chironomid size classes allowed an important degree of niche differentiation between non-indigenous fishes. In contrast, high diet overlap was found between the functional groups of indigenous gudgeon and of several non-indigenous fishes, indicating a high potential for interspecific exploitative competition. The diet of roach consisted almost entirely of non-animal remains (detritus and plant material). The high proportion of such low-energy food in the diet of this species may be indicative for a competition induced niche shift to suboptimal food sources.     

Trophic ecology of red roach (Rutilus arcasii) in a seasonal stream; an example of detritivory as a feeding tactic

1. Diel feeding activity and diet of red roach (Rutilus arcasii) were determined on five occasions (February, April, June, August and November 1985) in a seasonal, fluctuating stream subject to severe summer droughts and cold winter floods. 2. Except in June, the two age groups of the population (1 + and >1+) fed mainly on detritus and showed no significant differences either in their feeding intensity or in the relative contribution of the main diet components (detritus, plants and invertebrates). 3. The size, abundance and availability of drifting invertebrates influenced red roach feeding. When drift was scarce or inaccessible, both age groups fed on detritus, plants, or a combination of the two. These niche shifts were a trophic tactic aimed at maintaining feeding when other, more nutritional and energetically valuable foods were scarce. 4. A comparison with other populations suggested that a detritus-based diet had no major cost in the life history of the red roach. We hypothesize that the highly opportunistic trophic strategy of this Iberian endemic cyprinid is an adaptative response to seasonal Mediterranean streams.     

Coexistence of Fish Species in a Large Lowland River: Food Niche Partitioning between Small-Sized Percids,Cyprinids and Sticklebacks in Submersed Macrophytes

In the spring and summer of each year, large patches of submersed aquatic macrophytes overgrow the bottom of the alluvial Warta River downstream of a large dam reservoir owing to water management practices. Environmental variables, macroinvertebrates (zoobenthos and epiphytic fauna, zooplankton) and fish abundance and biomass were assessed at this biologically productive habitat to learn intraseasonal dynamics of food types, and their occurrence in the gut contents of small-sized roach, dace, perch, ruffe and three-spined stickleback. Gut fullness coefficient, niche breadth and niche overlap indicated how the fishes coexist in the macrophytes. Chironomidae dominated in the diet of the percids. However, ruffe consumed mostly benthic chironomids, while perch epiphytic chironomids and zooplankton. The diet of dace resembled that in fast flowing water although this rheophilic species occurred at unusual density there. The generalist roach displayed the lowest gut fullness coefficient values and widest niche breadth; consequently, intraspecific rather than interspecific competition decided the fate of roach. Three-spined stickleback differed from the other fishes by consuming epiphytic simuliids and fish eggs. The diet overlap between fishes reaching higher gut fullness coefficient values was rather low when the food associated with the submersed aquatic macrophytes was most abundant; this is congruent with the niche overlap hypothesis that maximal tolerable niche overlap can be higher in less intensely competitive conditions.     

Feeding habits,forage selection,and diet overlap in Alpine chamois (<Emphasis Type="Italic">Rupicapra rupicapra</Emphasis> L.) and domestic sheep

Fecal microhistological analyses have been used to assess the summer diet of chamois (Rupicapra rupicapra L., 1758) and domestic sheep and to evaluate diet overlap. The aim of our work was to investigate interspecific interactions and to assess the effects of sheep grazing on the summer feeding habits of chamois. A high dietary overlap (Pianka’s index = 0.93–0.99) was found, despite differences in the use of some plant groups. Sheep presence strongly affected chamois feeding habits: a reduction of highly digestible forbs was observed in the chamois diet during August, when both species grazed in the same range. As a consequence of sheep grazing, chamois may have been forced to reduce niche breadth and to change their food habits, increasing percentages of monocotyledons in the diet and feeding mainly on Cyperaceae. The diet overlap between sheep and chamois suggests that resource-mediated interactions as well as direct competition must be taken into account when evaluating chamois and sheep compatibility on Alpine meadows.     

Feeding Ecology of Northeast Atlantic Mackerel,Norwegian Spring-Spawning Herring and Blue Whiting in the Norwegian Sea

The Norwegian spring-spawning (NSS) herring (Clupea harengus), blue whiting (Micromesistius poutassou) and Northeast Atlantic (NEA) mackerel (Scomber scombrus) are extremely abundant pelagic planktivores that feed in the Norwegian Sea (NS) during spring and summer. This study investigated the feeding ecology and diet composition of these commercially important fish stocks on the basis of biological data, including an extensive set of stomach samples in combination with hydrographical data, zooplankton samples and acoustic abundance data from 12 stock monitoring surveys carried out in 2005–2010. Mackerel were absent during the spring, but had generally high feeding overlap with herring in the summer, with a diet mainly based on calanoid copepods, especially Calanus finmarchicus, as well as a similar diet width. Stomach fullness in herring diminished from spring to summer and feeding incidence was lower than that of mackerel in summer. However, stomach fullness did not differ between the two species, indicating that herring maintain an equally efficient pattern of feeding as mackerel in summer, but on a diet that is less dominated by copepods and is more reliant on larger prey. Blue whiting tended to have a low dietary overlap with mackerel and herring, with larger prey such as euphausiids and amphipods dominating, and stomach fullness and feeding incidence increasing with length. For all the species, feeding incidence increased with decreasing temperature, and for mackerel so did stomach fullness, indicating that feeding activity is highest in areas associated with colder water masses. Significant annual effects on diet composition and feeding-related variables suggested that the three species are able to adapt to different food and environmental conditions. These annual effects are likely to have an important impact on the predation pressure on different plankton groups and the carrying capacity of individual systems, and emphasise the importance of regular monitoring of pelagic fish diets.     

Ligula infestation of bleak Alburnus alburnus (L.) in the tidal Thames

Heavy infestations of the cestode Ligula are reported in bleak Alburnus alburnus (L.) from the tidal Thames. This parasite has not apparently been recorded previously from this host in the British Isles. The life cycle of the parasite is briefly summarized. Data on this infestation suggest an increase in the incidence of infestation up to a maximum in young bleak, followed by a decrease in older fish. There also appears to be a decrease from summer to autumn. The positive relationship between the weight of the parasite and the length of the host is discussed. Observations are made on the effect of Ligula on its host; it is suggested that many of the young bleak die during the autumn and winter, following their infestation.     

The occurrence and life history of Asymphylodora kubanicum (Platyhelminthes: Digenea: Monorchidae) in the Worcester-Birmingham canal, with special reference to the feeding habits of the definitive host, Rutilus rutilus

Two hundred roach and over 400 molluscs were examined over a one year period to investigate the occurrence and life history of Asymphylodora kubanicum in the Worcester-Birmingham canal. Larval stages, infective to the fish definitive host, were present in molluscs throughout the year but did not show a seasonal fluctuation in numbers. Parasites in the intestine of the roach showed a marked annual cycle of occurrence and maturation: low winter infection levels preceded a dramatic increase in infection during the spring and summer. Maturation of the parasite population was rapid during the spring and summer and in late summer and early autumn the parasites laid their eggs and subsequently died. The death of parasites after egg-laying resulted in the low winter infection level during which time little recruitment occurred.
Roach became infected mainly in their third year when molluscs become a dominant component of their diet. Thereafter the older fishes (<2+) are all equally susceptible to infection, but the larger (older) fishes become more heavily infected because of the greater consumption of molluscs per fish. The sex of the fish made no difference to infection with the parasite.     

Modifications in habitat use patterns and trophic interrelationships in the fish fauna of an oligotrophic artificial lake: Sainte Croix (Provence,France)

Lake Sainte-Croix is a hydro-electric reservoir on the river Verdon that came into operation about 16 years ago. The area of the lake is about 22 km² and the volume about 767 Mm³. The water level drops by as much as 16 m in winter. Sainte-Croix is a warm monomictic oligotrophic lake. The indigenous fish fauna of the Verdon originally included 8 species. Successive stocking has raised this number to 17. In catches made in 1976–1977 with 27 mm mesh nets, 80 to 90% of the fish with a body size of between 15 and 25 cm were of the four main species indigenous to the river before the dam was built: Leuciscus cephalus, Barbus fluviatilis, Chondrostoma toxostoma, Salmo trutta. Catches made at same period with 14 mm mesh nets gave only Chondrostoma toxostoma and Leuciscus cephalus.Changes in the fish fauna were apparent from catches made in 1984 and 1987 with nets of the same mesh size. There was a marked demographic increase of roach, and more recently of bleak and gudgeon, all three species introduced after the construction of the dam. At the same time, there was a decrease in catch frequency of Ch. toxostoma, L. cephalus and B. fluviatilis in the downstream area of the lake. Stomach content analysis carried out in different seasons on the six most abundant species of the lake (roach, toxostome, chub, bleak, perch and gudgeon) provided evidence on the trophic organisation of the fish fauna. We have measured niche breadth for each species by the Simpson diversity index and niche overlap by the Pianka index. Bleak is the only species to feed on zooplankton in open water. Roach is a particularly opportunistic feeder, sometimes taking plankton, but at Sainte-Croix it is exclusively herbivorous and benthophagous. Niche overlap between these two species is slight or null, depending on the season. On the other hand, there is a high degree of overlap between roach and chub and between roach and toxostome. The decrease in toxostome and chub frequency in the downstream area of the lake, where roach is most abundant, would appear to be a competitive exclusion phenomenon. There is high niche overlap between bleak and young perch, which partly explains the low abundance of the latter species; other contributory factors are the scarcity of zooplankton inshore, and the scarcity of zoobenthos resulting from the drop in the water level in winter.     

Seasonal variation in diet and trophic relationships within the fish communities of the lower Slave River, Northwest Territories, Canada

Increased industrial activities on the Peace and Athabasca River systems have raised concerns about cumulative impacts on fish and water resources downstream, in the Slave River of Alberta and the Northwest Territories, Canada. Because very little information was available on the fish communities in this system, we examined spatial and temporal patterns of diet for nine species (four piscivores and five invertebrate feeders) from three different types of habitat along the lower Slave River system and assessed trophic relationships within the communities. All actively feeding species exhibited seasonal variations in diet within and among the study areas. Dietary overlap was generally low throughout all seasons and locations. In the lower Slave River and its major tributary, the Salt River, substantial dietary overlap between piscivores (particularly walleye, Stizostedion vitreum), and invertebrate feeders occurred in the spring. In the summer no overlap occurred as walleye shifted to a more piscivorous diet, attaining a moderate degree of overlap with northern pike, Esox lucius. Compared with the Slave River, which is a large but homogeneous system upstream of its delta at Great Slave Lake, there was a greater diversity of actively feeding invertebrate feeders in the Salt River. Three of the latter were benthic feeders exhibiting moderate degrees of diet overlap during spring and summer. During the fall, few fish were feeding. Most fishes in the lower Slave River system are generalist, opportunistic feeders, consuming a number of different prey, the importance of which varies spatially and seasonally, as the abundance of these prey varies in the environment.