Diel variation in diet composition of a riverine fish community

Although diel food habit studies have been undertaken on a number of individual species, few studies have examined diel variation in the diets of fish communities. We examined the diel diet variation and feeding periodicity of a fish community in the Juniata River, Pennsylvania. Nine species, totalling 1,098 fish, were collected at 4-h intervals over a 24-h period in October 1989, in numbers sufficient to describe their diel variation in diet composition. Diel variation in diet composition was evident in all species, as no single prey taxon was dominant in the diet of any species during any 4-h interval. Ephemeropterans were the most important prey taxa for four species of centrarchids, whereas chironomids were the main prey of banded killifish, mimic shiners, and spotfin shiners. Algae was the major component in the diet of spottail shiners, whereas bluntnose minnows contained mostly detritus. Feeding activities of rock bass, redbreast sunfish, and pumpkinseed occurred at low levels throughout the day; peak feeding occurred from 2000 to 0400 hours. Food consumption of smallmouth bass increased throughout the day with peak consumption occurring at 2000 hours. Non-centrarchids fed little during daylight hours and showed peak activity at 2000–2400 h. Construction of a 24-hour diet from six 4-h interval estimates and feeding periodicity data provided a comprehensive representation of the diel feeding ecology of all species collected.     

Diel variation in the vertical distribution of fish and plankton in Lake Kinneret: a 24-h study of ecological overlap

Diel vertical migration (DVM) behaviour is a predator avoidance mechanism observed within many zooplankton species in the presence of zooplanktivorous fish. A 24-h survey was carried out in June 1998 to investigate diel variation in the vertical distribution of fish, zooplankton and phytoplankton (chlorophyll) in Lake Kinneret, Israel. Fish revealed diel variation in vertical distribution but had no spatial overlap with zooplankton, and consequently no apparent influence on zooplankton dispersal. Zooplankton revealed some diel variation in distribution being affected by thermocline and oxycline position and movement of the internal the internal seiche wave. Cyclopoid species closely follow the movement of the seiche wave implying that, due to their greater motility, they are following conditions that are suitable to them. The Cladocera species and small rotifers only partly, which may be part of their phototaxic behaviour. Physical forces like convection, horizontal and vertical forcing probably have a role in contributing to a homogeneous distribution of the plankton by preventing stratification or interfering with the more motile zooplankton which may be attempting to migrate.     

Temporal and spatial variation in the species composition of trawl samples from a demersal fish community

The temporal variation in species and size structure of the demersal fish community of a 70–150m deep open coastal locality of SW Norway was studied by multivariate analysis of bottom trawl data both from surveys and from fixed locations sampled repeatedly through 48-h periods. The trawl data were related to echo recordings from individual tows made during the 48-h experiments, Between-site variation was greater than short-term variation at single sites. Short-term variation was largely cyclical, diel variation, involving several species. Catches of the numerically dominating species, Sebastes viviparus and Trisopterus esmarki , did not follow any diel patterns. Acoustical recordings suggested that these species undertook diel vertical migrations largely within the lower 5 m of the water column. This corresponds to the vertical opening of the trawl.     

Diel pattern of pelagic distribution and feeding in planktivorous fish

Summary The spatial distribution of juvenile roach (Rutilus rutilus), rudd (Scardinius erythrophtalamus), bream (Abramis brama) and bleak (Alburnus alburnus) was registered by echosounding during two years in small Bavarian lakes. The gut contents of the fish were analysed in order to reconstruct their rhythmicity of food intake. Fish were found in the pelagic zone only during the night, feeding before midnight with maximal rate. The vertical position of the fish was dependent on the water transparency following a light intensity in the order of 10^-3 Lux. The diel migration between littoral and pelagic zones was a mainly horizontal one with a vertical component. Both the speed of increase of fish density in the open water and of the vertical movement was correlated to the speed of change of light intensity. Shoals broke up into single fish during the offshore migration. The span of presence in the pelagic zone was identical with the duration of the dark period. During winter no diel migration nor periodical feeding took place.     

枸杞岛岩礁生境主要鱼类的食物组成及食物竞争

基于2009年3月-2010年2月枸杞岛沿岸岩礁生境渔业资源调查数据,对岩礁生境中的3种定居性鱼类（褐菖鲉、大泷六线鱼和斑头六线鱼）和3种非定居性鱼类（花鲈、黄姑鱼和小黄鱼）的食物组成及食物关系进行了研究.结果表明： 麦秆虫、钩虾、褐菖鲉幼鱼、鳀鱼和中国毛虾等是6种鱼类的主要饵料生物,且饵料组成随季节而变化.3种定居性鱼类中,大泷六线鱼和斑头六线鱼在秋季食物竞争激烈;3种非定居性鱼类中,黄姑鱼和小黄鱼在夏季食物竞争激烈;非定居性鱼类和定居性鱼类之间,黄姑鱼分别与褐菖鲉（秋季）和大泷六线鱼（冬季）食物竞争激烈.黄姑鱼是引起岩礁生境中6种主要鱼类食物竞争的关键鱼种.枸杞岛岩礁生境中6种主要鱼类的摄食活动对褐菖鲉幼鱼的资源量有一定影响.     

Diel periodicity of Subantarctic copepods: relationships between vertical migration, gut fullness and gut evacuation rate

A zooplankton community in the Polar Frontal Zone north of SouthGeorgia was sampled for 5 days in February 1994. Feeding ofvarious copepodite stages of six copepod species was assessedby a series of gut fluorescence/gut evacuation experiments.Feeding periodicity was compared to vertical distribution andmigration patterns, as revealed by Longhurst Hardy PlanktonRecorder (LHPR) and ring net catches. Despite chlorophyll alevels reaching only 0.8 mg m^–3 and daily carbon rationsbased on phytoplankton intake being low, feeding of all thecopepods was restricted mainly to the 8 h night-time perid.During the daytime, the epipelagic community was verticallydispersed within the top 100 m. At night, upward migration bymost species led to a convergence of almost all zooplanktersin the upper half of the surface mixed layer. However, large-amplitudevertical migrations which crossed the thermocline were performedonly by Metridia lucens and Pleuromamma robusta. Although feedingby both migrants and non-migrants was mainly at night, therewas no diel signal in gut evacuation rate. The gut evacuationrates of the nine copepod species and stages differed significantly(5-fold) and were negatively related to the extent of theirdiel vertical migration. The long gut-passage times of the migratoryspecies, M.lucens and P.robusta, would have allowed them timeto defaecate some of the food eaten near the surface at depth,contributing to an active carbon transfer out of the mixed layer.However, their scarcity at this site meant that their grazingcomprised only -<1.4% of total copepod ingestion, so theircombined gut flux is likely to have been negligible (-0.4 mgcarbon day^–1).     

Night,day, sunrise,sunset: do fish under snow and ice recognize the difference?

1. Although boreal lakes are ice‐covered for several months annually, little is known about the behaviour of fish under ice. To consider the reasons for diel vertical migrations (DVM) it is important to compare periods under ice as opposed to under open water. Echosounding provides a tool for non‐intrusive continuous monitoring of fish, even in winter. 2. Changes in the vertical distribution of fish through six 48‐h periods were monitored using a stationary, mounted echosounder that beamed vertically either from the bottom up or from the surface down from February to April, 2003. The up‐beaming and down‐beaming transducers were run alternately for 24 h each over the 48‐h period. Standard echo analysis software was used to detect fish traces and estimate the vertical and temporal distribution of fish abundance. Fish were sampled with a winter seine. 3. Prominent diel vertical migration in response to changing light level was detected throughout the study period (late winter to spring). Fish were highest in the water column at sunset and sunrise. In daylight, most detected fish were well below 10‐m depth. The number of fish detected was greatest during the night when they occurred throughout almost the whole water column, sometimes with a considerable number very close to the ice. Fish were mostly vendace and whitefish. 4. It became evident from data from the up‐beaming transducer that at night fish may occupy the layer closest to the surface. These fish would not have been detected if we had only used the down‐beaming transducer. The overall pattern of DVM in winter was very similar to that in summer. The results support the suggestion that DVM is a genetically fixed behavioural trait responding to the contemporary level of illumination.     

In situ diel variation in gut pigment contents of Ceriodaphnia sp. in stratification and destratification periods

The short-term, in situ diel grazing of Ceriodaphnia sp. duringperiods of stratification and mixing was investigated usingthe technique of fluorimetric analysis of the gut pigments.There were considerable seasonal differences in feeding behaviourIn mixing, when the concentration of chlorophyll a in the watercolumn was high and Ceriodaphnia abundance was low, gut pigmentcontents showed clear diel variation patterns, probably dueto diel variations of the high values of feeding activity observedin the 24 hour cycle The maximum values were found at dawn.On the other hand, no diel variations in gut pigment were observedduring periods of stratification and while the amounts of pigmentsin the water and in the gut were very low, species abundancewas high. Taking into account the ambient conditions, the authorsdiscuss the possibility that the change of feeding of the Ceriodaphniasp. observed when the environment changed from a mixing periodto one of stratification represents a change from herbivorousto detritivorous behavior.     

食蚊鱼昼夜摄食节律观察

以分时段采样法研究入侵物种食蚊鱼的夏季昼夜摄食节律。食蚊鱼夏季种群内有雌鱼、雄鱼和幼鱼三个不同的摄食类群,这三个类群的摄食节律差异明显。雌鱼摄食节律成双峰型,第一高峰在10:00,而最高峰在22:00,此时肠道食物团平均重量11.70±11.60mg,饱满指数为190.22±155.61。幼鱼也成双峰型,分别在6:00和18:00有两个摄食高峰,以清晨6:00为最高,肠道食物团平均重1.08±1.09mg,饱满指数为128.44±105.49。雄鱼则成单峰型,摄食高峰出现午后14:00左右,肠道食物团平均重0.71±0.96mg,饱满指数为71.80±107.65。食蚊鱼不同摄食类群间的摄食高峰交错出现,是其协调种内关系,降低种内竞争的一种有效行为机制。     

Vertical zonation and functional diversity of fish assemblages revealed by ROV videos at oil platforms in The Gulf

An assessment of vertical distribution, diel migration, taxonomic and functional diversity of fishes was carried out at offshore platforms in The (Arabian–Iranian–Persian) Gulf. Video footage was recorded at the Al Shaheen oil field between 2007 and 2014 using a remotely operated vehicle (ROV). A total of 12 822 individual fishes, from 83 taxonomic groups were recorded around the platforms. All the species identified are considered native to The Gulf, although Cyclichthys orbicularis and Lutjanus indicus were recorded for the first time in Qatari waters. Several trends were uncovered in the vertical distribution of the fish community; most species were observed between 20 and 50 m depth and fish abundance decreased towards the bottom, with the highest abundances recorded in the upper layers, i.e. down to 40 m depth. Vertical variation in fish diversity, however, was generally not accompanied by differences in vertical movements. Carnivores and invertivores were the dominant trophic groups, being found at each depth range from surface to seabed. The functional indices showed no significant differences between water depths or diel cycles. The study demonstrates that oil platforms represent a hotspot of fish diversity and interesting sites for studying fish communities, abundance and behaviour.     

Effects of environmental variables on fish feeding ecology: implications for the performance of baited fishing gear and stock assessment

The effectiveness of baited fishing gear ultimately depends upon behaviour of the target species – activity rhythms, feeding motivation, and sensory and locomotory abilities. While any environmental parameter that mediates feeding or locomotion can have an important influence on the active space presented by the bait and fish catchability, few biologists have considered how such variation in behaviour might affect catch per unit effort (CPUE) and the resultant stock abundance estimates or population parameters. This review reveals that environment‐related variation in feeding behaviour can act through four different mechanisms: metabolic processes, sensory limitations, social interactions and direct impacts. Water temperature, light level, current velocity and ambient prey density are likely to have largest effects on fish catchability, potentially affecting variation in CPUE by a factor of ten. Feeding behaviour is also density‐dependent, with both positive and negative effects. Over time and geographic space a target species can occupy wide ranges of environmental conditions, and in certain cases, spatial and temporal variation in feeding biology could have a larger impact on CPUE than patterns of abundance. Temperature, light and current can be measured with relative facility and corrections to stock assessment models are feasible. Making corrections for biological variables such as prey density and bait competitors will be more difficult because the measurements are often not practical and relationships to feeding catchability are more complex and poorly understood. There is a critical need for greater understanding of how environmental variables affect feeding‐related performance of baited fishing gear. A combination of field observations and laboratory experiments will be necessary to parameterize stock assessment models that are improved to accommodate variation in fish behaviour. Otherwise, survey data could reveal more about variation in behaviour than abundance trends.     

Temporal plasticity in thermal‐habitat selection of burbot Lota lota a diel‐migrating winter‐specialist

In this study, animal‐borne telemetry with temperature sensors was coupled with extensive habitat temperature monitoring in a dimictic reservoir, to test the following hypotheses: behavioural thermoregulation occurs throughout the year and temperature selection varies on a diel and seasonal basis, in a winter‐specialist diel‐migrating fish. Burbot Lota lota demonstrated nightly behavioural thermoregulation throughout the year, with a large seasonal shift between selection for very cold temperatures (<2° C) optimal for reproduction during the spawning period and selection for warmer temperatures (12–14° C) optimal for hunting and feeding during non‐reproductive periods. During daylight hours, while L. lota avoided habitats warmer than optimal for reproduction and feeding during the spawning and non‐reproductive periods, respectively, active selection was limited to selection for 4–6° C habitat during the prespawning period. Although behavioural thermoregulation explained the night‐time migration, behavioural thermoregulation only partially explained daytime behaviour, indicating that diel migration is best explained by a combination of factors. Thus, thermal‐habitat selection was a good predictor of night‐time habitat occupancy in a diel‐migrating species. Together, these results show that thermal‐habitat selection by fishes may be important throughout the year and a more seasonally plastic behaviour than previously recognized.     

The foraging ecology of larval and juvenile fishes

Knowledge of the foraging ecology of fishes is fundamental both to understanding the processes that function at the individual, population and community levels, and for the management and conservation of their populations and habitats. Furthermore, the factors that influence the acquisition and assimilation of food can have significant consequences for the condition, growth, survival and recruitment of fishes. The majority of marine and freshwater fish species are planktivorous at the onset of exogenous nutrition and have a limited ability to detect, capture, ingest and digest prey. Improvements in vision, development of fins and associated improvements in swimming performance, increases in gape size and development of the alimentary tract during ontogeny often lead to shifts in diet composition. Prey size, morphology, behaviour and abundance can all influence the prey selection of larval and juvenile fishes. Differences in feeding behaviour between fish species, individuals or during ontogeny can also be important, as can inter- and intraspecific interactions (competition, predation risk). Temporal (diel, seasonal, annual) and spatial (microhabitat, mesohabitat, macrohabitat, regional) variations in prey availability can have important implications for the prey selection, diet composition, growth, survival, condition and, ultimately, recruitment success of fishes. For fish populations to persist, habitat must be available in sufficient quality and quantity for the range of activities undertaken during all periods of development. Habitats that enhance the diversity, size ranges and abundance of zooplankton should ensure that sufficient food resources are available to larval and juvenile fishes.     

The role of size and dominance in the feeding behaviour of coexisting hummingbirds

Interspecific competition can strongly influence community structure and limit the distribution and abundance of species. One of the main factors that determine hummingbird community structure is competition for food. The temporal and spatial distribution of nectar has a strong impact on hummingbird assemblages, shaping foraging niches according to hummingbird dominance and foraging strategy. We investigated whether body size and the degree of aggressive dominance influence feeding behaviour of hummingbirds in a temperate forest in northwestern Mexico (El Palmito, Mexico) when winter migrant hummingbirds are present in the community. First, we determined the dominance status of hummingbirds and evaluated the relationship between dominance and body mass, wing disc loading and migratory status. Secondly, we determined how hummingbird species used plant species differently. Thirdly, we examined whether the most dominant hummingbird species defended floral patches with more energy and/or with a larger number of flowers. At each flower patch, hummingbird species, number of hummingbird interactions, feeding time and number of flowers present were recorded. The total number of calories available within each floral patch was also determined. Our results demonstrate that the dominance hierarchy of 13 hummingbird species (migratory and resident) was correlated with body size but not wing disc loading, and that members of the hummingbird community showed a clear separation in resource use (by plant species). Hummingbirds at the top of the dominance hierarchy defended and fed on the best flower patches, defined by the quantity of calories available. Hence, the feeding behaviour of hummingbirds at El Palmito depends on the abundance of plant species used by hummingbirds and on the amount of energy available from each flower patch. Thus, hummingbird body size, aggressive dominance and defence of quality flower patches determines niche partitioning among species.     

Diel vertical and horizontal distribution of crustacean zooplankton and young of the year fish in a sub-alpine lake: an approach based on high frequency sampling

Understanding the spatial dynamics of predators and their preyis one of the most important goals in aquatic ecology. We studiedspatial and temporal onshore–offshore distribution patternsin young of the year (YOY) Eurasian perch (Perca fluviatilis)and crustacean zooplankton (Daphnia hyalina, Cyclops prealpinus)along a transect in Lake Annecy (France). Our study representsa first attempt at coupling hydroacoustic fish survey and highfrequency zooplankton recording to assess simultaneously thelarge-scale distribution patterns of YOY fish and their zooplanktonprey over a diel cycle (day, dusk and night sampling). We hypothesizedthat the spatial distribution of zooplankton could be shapedby both anti-predator behaviour (horizontal and vertical migrations)and predation losses. Fish biomass, size structure and dietwere assessed from split-beam echosounding and net trawlingsamples, whereas crustacean abundances were estimated with asmall modified Longhurst–Hardy continuous plankton recorder.We evaluated the diel changes in the spatial distribution patternsof fish and zooplankton and determined the overlap between theirdistributions. Fish biomass was dominated by YOY perch in upperwarmer layers and salmonids (Coregonus lavaretus and Salvelinusalpinus) in the colder and oxygenated deep layers. YOY perchwere aggregated in dense schools in the epilimnion during theday and dispersed at night. Fish biomass was distributed alonga strong increasing onshore–offshore gradient at night,whereas crustacean prey showed a decreasing gradient. This onshore–offshorenegative gradient in crustacean distribution, expressed on ashorter scale during the day, shifted toward the surface watersat night. A distinct kinetic of diel vertical migration (DVM)patterns was exhibited by daphnid and cyclopoid populationsand resulted in distinct vulnerability to perch predation. Spatio-temporaldistribution of crustaceans in Lake Annecy during the diel cyclestudy was probably shaped both by predation loss to YOY perchand by anti-predator behaviour (DVM, DHM) by zooplankton. Theimplications for fine-scale studies of fish-zooplankton interactionsare discussed.     

The structure and organization of an eelgrass fish fauna

Summary Ten species of fish made up more than 95 percent of the standing crop of the total fish assemblage of a shallow-water eelgrass meadow in southeastern Australia. The relative abundance of each species remained fairly constant from year to year during a four and a half year period. Four species were permanent residents, three moved over the meadow at high tide, and the juveniles of three species changed residence status as they grew. Most species exhibited distinct diel patterns of activity, four species were diurnal and five were nocturnal. Species foraged in different microhabitats and dietary overlap was very low amongst all but two species which had overlapping habitat, prey and prey size preferences, but had different diel activity periods. Data on production by prey and consumption of prey by these two fish species indicated that competition for food was probably responsible for the temporal separation of feeding niches. Predation by birds and fish appeared to be the major influence on the diel activity period of one fish species. The maintenance of the patterns of resource allocation among the remaining species is discussed and the organization of different seagrass fish faunas is compared.This is publication number 265 in the Ministry for Conservation, Victoria publication series. — Present address: Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada     

Diel variation of phytoplankton functional groups in a subtropical reservoir in southern Brazil during an autumnal stratification period

A knowledge of diel variation and the vertical distribution of phytoplankton communities may contribute to a better understanding of the driving factors of key species. Applying functional-group classification provides important information on the causes of species selection in the pelagic community. The diel variation of phytoplankton functional groups was analysed during an autumnal stratification period with the aim of understanding their changes in the vertical position related to light, mixing regime and grazing pressure. Phytoplankton and zooplankton communities were sampled every 4 h during a 24-h period in a vertical profile in a subtropical meso-eutrophic reservoir. Strong stratification during a 24-h cycle and a mixed clear epilimnion with partial atelomixis marked the autumn season in the Faxinal reservoir, southern Brazil. The highest phytoplankton densities and biomass were found during the second part of the day, a general pattern reported in the literature, and may be explained by zooplankton dynamics. During the 24-h cycle, phytoplankton functional groups lacking a self-regulating capacity and those able to regulate their vertical position were vertically segregated in the lake. The diel behaviour of both groups was driven by the mixing regime (including atelomixis), light and zooplankton grazing pressure.     

Spatial and Temporal Variation of Macroinvertebrate Drift in Two Neotropical Streams1

The detection of spatial variation in macroinvertebrate drift depends on the spatial scale of investigation in streams of the La Selva Biological Station, Costa Rica. Drift samples were taken in a spatially nested design, with two streams, two reaches per stream, two riffles per reach, and four replicate samples per riffle. Drift showed little variation among streams, but varied significantly at the scales of reach and riffle, with variation among samples also high. In addition, sampling took place at two temporal scales: diel and at two different periods that differed in rainfall conditions. Drift diel periodicity was a clear pattern, while only density of individuals varied among sampling periods. This is the first study of macroinvertebrate drift at multiple spatial scales, despite the recognition that multi‐scale studies are essential for a more complete understanding of community patterns and processes.     

Diel changes in resource use and diet overlap in temperate stream fishes

Interspecific variation in diel-scale temporal niches is common in natural communities. Such variation changes population dynamics via effects on the growth and reproduction of individuals. Also at the community level, theory predicts that animals can reduce competition for shared resources by changing diel activity in certain situations. However, the role of diel activity at the community-level has not been examined sufficiently. In this study, to examine whether the diel-scale temporal niche act as a competition-mitigating mechanism for stream fishes at the community level, we surveyed diel changes in microhabitat use and foraging, and the pattern of interspecific diet overlap in the middle reaches of a temperate stream where various fish species that seemed to be either nocturnal or diurnal coexisted. Our results suggest that the fishes forage during both daytime and night, but change their foraging mode at different times of the day, so that the foraging habits of these fish species cannot be divided simply into nocturnal and diurnal. Furthermore, fishes appeared to aggregate in the vicinity of common food resources during time zones with high availability of the resources, and therefore, inter-guild diet overlap was high during certain time zones. On the other hand, when inter-guild diet overlap was low, each fish species used foods or microhabitats that did not any have the potential to be used by species of another guild. Therefore, we conclude that variation in diel niche use is influenced by variation in the fundamental niche and food supply or availability rather than by competitive interaction between fishes in the stream fish community.     

First feeding diet of young brown trout fry in a temperate area: disentangling constraints and food selection

Trophic interactions are important factors structuring animal communities. We assessed the trophic relations of four fish species that live in sympatry in the River Ladra (NW Spain), and cluster analysis differentiated two feeding strategies: (1) species with omnivorous feeding habits, feeding mainly on detritus and plant material but with aquatic macroinvertebrates as an important complement (Achondrostoma arcasii and Pseudochondrostoma duriense) and (2) species feeding mainly (Salmo trutta) or exclusively (Gasterosteus gymnurus) on aquatic macroinvertebrates. Concerning ingested macroinvertebrates, the trophic overlap was quantified using Schoener’s index and the results obtained revealed a high diet overlap among the species (from 81.3 up to 99.2%). In order to get a deeper insight into mechanisms of fish species coexistence, we used ten biological and ecological traits of macroinvertebrate prey to discriminate feeding preferences. As a result, despite the high similarity among the diets, our analyses suggest that differences in diel activity patterns and drift behaviour of preys, as well as differences in the prey size, are important adaptive features that may reduce the inter-specific competition in the fish community and permit the partitioning of food that allows coexistence.