Seasonal changes in diel activity of juvenile European catfish Silurus glanis (Linnaeus, 1758) in Byšická Lake,Central Bohemia

Dualism in activity has been described in many fish species, including larger individuals of European catfish (Silurus glanis), which are able to switch their activities from nocturnal to diurnal in winter and spring. During the multi‐year telemetry study, seasonal changes in diel activity of 45 juvenile European catfish were investigated. These juveniles exhibited no dualism in movement and were strictly nocturnal and crepuscular with no period of diurnal activity. During winter, the same juvenile European catfish were completely inactive throughout the 24‐hr cycle. Also investigated was the impact of temperature, dissolved oxygen levels and water clarity on fish movement, relocation of resting places and home range size. The only significant correlations were that relocation and home range size increased with rising water temperatures.     

Field metabolic rates of rainbow trout estimated using electromyogram telemetry

Field metabolic rates (FMR) of five rainbow trout were estimated using electromyogram (EMG) telemetry of the axial muscle. A series of laboratory experiments indicated that the EMG transmitter output was related strongly to total oxygen consumption of the fish over a wide range of swimming speeds and temperatures. No differences were evident when the oxygen consumption v . EMG relationship for routine swimming was compared with that for forced swimming. FMR was assessed on two time scales, revealing diel patterns and seasonal patterns. On the diel scale, the FMR pattern could be classified as crepuscular. At the upper and lower limits of temperature tolerance, the diel pattern was less distinct. On the seasonal scale, mean daily FMR was strongly dependent on mean environmental temperature. Comparisons between FMR and laboratory derived estimates of standard and maximally active metabolism indicate that the rainbow trout in the field utilize <20% of the available scope for activity.     

Explicit site fidelity of European catfish (Silurus glanis,L., 1758) to man‐made habitat in the River Meuse,Netherlands

After a century of near absence, records of European catfish (Silurus glanis, L., 1758) in the Netherlands have increased markedly since 1994. The majority of records (about 60% of the total) originate from a 12 km dammed section of the River Meuse in the province of Limburg. This paper reports on a study conducted to obtain information on the behaviour and habitat preferences of catfish at this location, whereby 20 adult Silurus glanis were implanted with both acoustic and transponder tags and their behavior monitored using a combination of passive and active methodologies. All fish remained within the study area and did not enter either the contiguous riverine sections or connected lakes. The catfish expressed schooling, nocturnal activity and strong site fidelity to a specific river section containing artificial habitat (in the form of moored boats) and were influenced by the presence and operation of nearby energy generation plants. The results are discussed in relation to the potential growth and dispersal of catfish populations and the extent to which anthropogenic activities (particularly energy generation schemes) at the site have inadvertently created favourable habitat that has assisted the colonization of catfish and impacted negatively on the wider fish community.     

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.     

Efficacy of tagging European catfish Silurus glanis (L., 1758) released into ponds

The efficacy and sub‐lethal consequences of single and double tagging European catfish Silurus glanis with Petersen disc and passive integrated transponder (PIT) tags were examined in short (laboratory) and longer‐term (field) experiments. Tag retention in the laboratory was 100%, with normal behaviour (i.e. feeding) in all fish returning within 36 h. In the field, 65 of 120 tagged S. glanis were recaptured from five small study ponds, with 85% retaining their PIT tags, though recapture rates and tagging efficacy were highly variable amongst locations. This is consistent with literature for other fishes, suggesting that tagging efficiency is variable across species and largely context dependent (fish length, tagging location, habitat).     

Prey selection by flounder, Platichthys flesus, in the Douro estuary, Portugal

Prey selection by the flounder, Platichthys flesus (Linnaeus, 1758), in an estuarine nursery was investigated and the major factors influencing food choice by this species were assessed. Diet breadth was narrow, reflecting the low prey diversity observed in the benthos. A gradual ontogenetic shift from small prey such as amphipods to larger prey like polychaetes and bivalves was observed. Amphipods had positive electivity values in the upper estuary and negative values in the lower estuary.Polychaetes showed the inverse pattern. Bivalve electivity values were always positive. Differential selectivity throughout the estuary was mainly related to spatial segregation of flounders according to size, with the smaller individuals concentrating in the upper estuary and larger individuals concentrating in the lower estuary. Amphipods such as Corophium spp. play a crucial role in the flounder diet because of their small size, low mobility and diel activity pattern. As prey, the polychaete value increases throughout flounder ontogeny since the flounder size range is compatible with the larger mouth gapes and detection ability of larger fish. Bivalve electivity values for flounder are mainly related to high calorific values. The absence of Crangon crangon (Linnaeus, 1758) in the diet may be due to low water temperature since the cost–benefit involved in the capture of highly mobile prey is too high at low temperatures. It was concluded that flounder must use several sensory features to detect and capture prey in turbid estuarine waters and that field studies provide important background information on the actual predator preferences under natural conditions.     

Abundance–body mass relationships in size-structured food webs

In communities sharing a common energy source, the energetic equivalence hypothesis predicts that numerical abundance (N) scales with body mass (M) as M^?0.75. However, in size‐structured food webs all individuals do not share a common energy source, and the energy available (E) to larger individuals is constrained by inefficient energy transfer through the food chains that support them. This is expected to lead to steeper scalings of N with M. Here, we formalize and test an existing model for predicting abundance–body mass scaling, where the decline in E with M is calculated from the mean predator–prey body mass ratio (from size‐based nitrogen stable isotope analysis) and trophic transfer efficiency. We show that the steep predicted scalings of abundance and body mass (N scales as M^?1.2, B scales as M^?0.2) in a marine food web are consistent with empirical estimates and can be attributed to the small predator–prey body mass ratio (106 : 1). As a previous study has shown that environmental stability may favour low predator–prey mass ratios and long food chains, we predict that steeper abundance–body mass relationships will be found in more stable environments.     

Can species‐specific prey responses to chemical cues explain prey susceptibility to predation?

The perception of danger represents an essential ability of prey for gaining an informational advantage over their natural enemies. Especially in complex environments or at night, animals strongly rely on chemoreception to avoid predators. The ability to recognize danger by chemical cues and subsequent adaptive responses to predation threats should generally increase prey survival. Recent findings suggest that European catfish (Silurus glanis) introduction induce changes in fish community and we tested whether the direction of change can be attributed to differences in chemical cue perception. We tested behavioral response to chemical cues using three species of freshwater fish common in European water: rudd (Scardinius erythrophthalmus), roach (Rutilus rutilus), and perch (Perca fluviatilis). Further, we conducted a prey selectivity experiment to evaluate the prey preferences of the European catfish. Roach exhibited the strongest reaction to chemical cues, rudd decreased use of refuge and perch did not alter any behavior in the experiment. These findings suggest that chemical cue perception might be behind community data change and we encourage collecting more community data of tested prey species before and after European catfish introduction to test the hypothesis. We conclude that used prey species can be used as a model species to verify whether chemical cue perception enhances prey survival.     

Diel activity of adult pikeperch <Emphasis Type="Italic">Sander lucioperca</Emphasis> (L.) in a drainage canal in the Mediterranean basin during spring

Pikeperch (Sander lucioperca L.) is a broadly distributed fish species in Europe but little is known about its ecology in the southern part of its distribution area in warm climatic conditions. The aim of this study was to analyse pikeperch rate of movement and to assess whether it displayed a diel pattern related to temperature. Thus acoustic telemetry was used to track adult pikeperch in a drainage canal located in south of France. The survey was carried out in spring, during the spawning period. The results showed that females were more active than males. This is in accordance with previous data on the nest guardian behaviour of the males. For both genders, the activity rates increased during the study period as water temperature rose. Males and females displayed the same diel activity with a maximum at dusk, thereby confirming many indirect observations. Nevertheless, inter-individuals variations were observed. Thus, these results on diel activity are rather a general trend than a strict rule and suggest the involvement of other factors than light intensity in the control of diel activity. This diel rhythm is positively correlated to water temperature for females. Pikeperch activity may be the result of a trade-off between physiological requirements of temperature and light, satisfaction of energy needs and avoidance of predators.     

Hatchery-reared fish have less consistent behavioral pattern compared to wild individuals,exemplified by red tilefish studied using video observation and acoustic telemetry tracking

The behavior of wild and hatchery-reared red tilefish Branchiostegus japonicus was analyzed using two different methods: video observation and acoustic telemetry tracking. In the laboratory, digging and swimming activity of seven wild and five hatchery-reared fish were recorded for 2–4 days in an experimental aquarium and related to changes in light intensity. The activity of wild individuals increased with light intensity, while hatchery-reared individuals were active during both day and night. In the field, 18 wild and 9 hatchery-reared fish were released and tracked using an acoustic telemetry system during the winter and the summer in Maizuru Bay, Kyoto (Japan). Seven wild and three hatchery-reared fish settled within 2 km of the release point for 21–200 days whilst 11 wild and 6 hatchery-reared fish were detected in the central part of the bay within 13 days. The settled fish demonstrated a diel pattern of behavior; most of them probably stayed outside their burrows in the daytime but inside their burrows during the nighttime. During the winter wild fish tended to stay near the release site for longer periods than the hatchery-reared fish. However, in summer the hatchery-reared fish tended to remain close to the release site for longer than the wild fish. Based on these two experiments, we suggest that the activity of wild red tilefish respond to changes in low levels of light intensity (0–0.1 μmol m⁻² s⁻¹) at dawn and display a diel behavior. Hatchery-reared fish may differ from wild fish with regard to their behavior, response to water temperature and light conditions. Electronic supplementary material Supplementary material is available for this article at and accessible for authorized users     

Relationships between metabolic rate, muscle electromyograms and swim performance of adult chinook salmon

Oxygen consumption rates of adult spring chinook salmon Oncorhynchus tshawytscha increased with swim speed and, depending on temperature and fish mass, ranged from 609 mg O₂ h^?1 at 30 cm s^?1 (c. 0·5 BL s^?1) to 3347 mg O₂ h^?1 at 170 cm s^?1 (c. 2·3 BL s^?1). Corrected for fish mass, these values ranged from 122 to 670 mg O₂ kg^?1 h^?1, and were similar to other Oncorhynchus species. At all temperatures (8, 12·5 and 17° C), maximum oxygen consumption values levelled off and slightly declined with increasing swim speed >170 cm s^?1, and a third‐order polynomial regression model fitted the data best. The upper critical swim speed (U_crit) of fish tested at two laboratories averaged 155 cm s^?1 (2·1 BL s^?1), but U_crit of fish tested at the Pacific Northwest National Laboratory were significantly higher (mean 165 cm s^?1) than those from fish tested at the Columbia River Research Laboratory (mean 140 cm s^?1). Swim trials using fish that had electromyogram (EMG) transmitters implanted in them suggested that at a swim speed of c. 135 cm s^?1, red muscle EMG pulse rates slowed and white muscle EMG pulse rates increased. Although there was significant variation between individual fish, this swim speed was c. 80% of the U_crit for the fish used in the EMG trials (mean U_crit 168·2 cm s^?1). Bioenergetic modelling of the upstream migration of adult chinook salmon should consider incorporating an anaerobic fraction of the energy budget when swim speeds are ≥80% of the U_crit.     

Exogenous control of diel locomotor activity in the whitefish Coregonus clupeaformis: effects of light and temperature

Summary Data on factors determining activity cycles of nearctic fishes are scarce overall, and nonexistent for Coregoniae (family Salmonidae), a group with closely related and somewhat better known palaearctic species. We studied effects of photoperiodicity, light intensity and temperature on diel locomotor activity of lake whitefish Coregonus clupeaformis (Mitchill). Under LD 12:12, a day-active pattern was evident. Under continuous light (LL) and continuous dark (DD), rhythmicity was greatly suppressed or absent, respectively. Day-time activity levels were positively correlated with illuminance over the range tested (0.005 to 500 lux). At the three temperatures tested, activity was lowest at 7° C, highest at 12° C (a reported temperature optimum), and intermediate at 17° C. Our results suggest that level and diel pattern of lake whitefish activity are under overriding external control, and we find similarities with published data on the European species Coregonus lavaretus.     

Time-related predator/prey interactions between birds and fish in a northern Swedish river

Summary Seasonal and diel activity patterns of mergansers, gulls, and terns along a river in northern Sweden were documented, as were those of their fish prey. The seasonal and diel activity patterns of goosandersMergus merganser and gulls (Larus canus, L. argentatus, andL. fuscus) were closely related to that of the river lampreyLampetra fluviatilis. During the peak spawning of the river lamprey, birds showed a nocturnal peak in fishing activity. During the summer solstice, birds were active for 24 h. The activity patterns of red-breasted merganserMergus serrator, ternsSterna spp., and three-spined sticklebacksGasterosteus aculeatus were also similar. Activity pattern of the prey apparently influenced breeding time, diel activity and foraging area of the twoMergus species. Social relations between gulls probably corrdinated their peak in fishing, which coincided with the time lampreys were most efficiently exploited.     

Estimating oxygen exchange across the air–water interface of a hypereutrophic lake

Patterns of estimates of oxygen flux (J) across the air–water interface of hypereutrophic Onondaga Lake, NY, U.S.A., are characterized for time scales ranging from diel to seasonal for an 8-month period. The analysis is supported by a high frequency (most often hourly) monitoring program, conducted with a robotic buoy, that included measurements of dissolved oxygen (DO), temperature, and fluorometric chlorophyll a in the lake's surface waters, vertical profiles of DO through the epilimnion, and wind speed and solar radiance. The magnitude and direction of J is demonstrated to vary dramatically at diel, day-to-day, and seasonal time scales. Thus, large errors in estimates of J may result from extrapolating flux calculations made from short-term data to longer time periods. The variations in J were driven by variations in metabolic activity and meteorology, and were mediated by departures from equilibrium DO concentrations and wind-driven turbulence. Extended periods of high J values are shown to coincide with intervals of large departures from equilibrium DO concentrations, but day-to-day differences are driven mostly by variations in wind. A distinct diel pattern of J estimates is manifested for average conditions, with substantially higher J values during daylight hours. This pattern reflects the common diel patterns of the drivers of both higher DO oversaturation and wind speed over those hours. It is demonstrated that the magnitude of J is substantial relative to net changes in the epilimnetic DO pool, and thus must be accommodated accurately in estimates of primary production and community respiration that are to be based on diel monitoring of DO in the water columns of productive lakes.     

Does the non‐native European catfish Silurus glanis threaten French river fish populations?

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Susceptibility of European catfish (Silurus gianis) to Edwardsiella ictaluri

European catfish (Silurus glanis) were tested for their susceptibility to the bacterium Edwardsiella ictaluri. The LD₅₀ of E. ictaluri when injected into European catfish was 5.4 × 10⁶ compared to 7.1 times; 10⁴ for channel catfish (Ictalurus punctatus). E. ictaluri was isolated from dead and moribund European catfish and the bacterium was also detected in kidney smears by an indirect fluorescent antibody (FA) technique. The bacterium was not isolated or detected by FA from surviving fish 15 days after injection. No clinical signs of E. ictaluri infection were noted in European catfish, but these were prevalent in the channel catfish. These experiments indicate that under experimental conditions European catfish are not as susceptible to E. ictaluri as channel catfish.     

Diel activity pattern of juvenile Atlantic salmon (Salmo salar) in early and late winter

Radiotelemetry was used to investigate the diel activity pattern of juvenile Atlantic salmon (Salmo salar) in early and late winter. Fish were active throughout the diel cycle. However, there was significantly less daytime than nighttime movement and movement declined significantly with increasing fork length. Maximizing winter growth rate, through an overall increase in foraging activity, may reduce the risk of starvation in smaller fish. The results of the present study provide evidence that the activity patterns of juvenile salmonids are quite complex and support the suggestion that individual variation in activity patterns are, at least, partially driven by body size.     

Tracking and mapping sun-synchronous migrations and diel space use patterns of Haemulon sciurus and Lutjanus apodus in the U.S. Virgin Islands

The spatially explicit diel movement patterns of fish using coral reef ecosystems are not well understood, despite the widespread recognition that many common species undergo distinct migrations to utilize different resources during night and day. We used manual acoustic telemetry coupled with global positioning technology to track the detailed spatially explicit daily movements (24 h) of multiple individuals of two common Caribbean fish species, Haemulon sciurus (bluestriped grunt) and Lutjanus apodus (schoolmaster snapper). Movement pathways and day and night activity spaces were mapped and quantified in a Geographic Information System (GIS). Directional sun-synchronous migrations occurred close to astronomical sunset and sunrise. Site fidelity within day and night activity spaces was high. Nine of twelve individuals exhibited overlap of day and night activity spaces and three fish (L. apodus) exhibited complete spatial segregation. Night activity spaces (H. sciurus: 11,309?±?3,548 m²; L. apodus: 9,950?±?3,120 m²) were significantly larger than day activity spaces (H. sciurus: 2,778?±?1,979 m²; L. apodus: 1,291?±?636 m²). The distance between sequential position fixes (step lengths) was significantly greater at night than day, indicative of nocturnal foraging and day resting behavior. Integrating acoustic telemetry, GIS techniques and spatial statistics to study fish movement behavior revealed both individual variability and some broader generality in movement paths and activity spaces suggestive of complex underlying behavioral mechanisms influencing diel movements.     

Diets and food consumption rates of pelagic fish in Lake Malawi, Africa

• 1 Studies of diel feeding periodicity, rates of food consumption and diet composition of pelagic fish were undertaken to resolve the dispute regarding the existence of a vacant niche for a pelagic zooplanktivore in Lake Malawi.
• 2 Six species of zooplanktivore were abundant in the offshore pelagic zone, these were: Diplotaxodon limnothrissa, D.‘bigeye’, Rhamphochromis longiceps and Copadichromis quadrimaculatus (all haplochromine cichlids), Synodontis njassae (Mochokidae) and Engraulicypris sardella (Cyprinidae). The main piscivores were cichlids of the genus Rhamphochromis.
• 3 All cichlids were daytime feeders; some showed peaks in feeding activity at dawn and dusk that were related to vertical migration patterns of their prey. Synodontis njassae was able to feed throughout the day, but fed most actively at night.
• 4 Food consumption: biomass ratios (Q/B yr^-1) calculated from diel stomach contents data were 5.87–7.13 for D. limnothrissa, 12.79 for D.‘bigeye’, 4.20–24.7 for R. longiceps and 6.45 for S. njassae. Annual Q/B ratios for other species, which ranged from 4.74 to 9.28, were obtained from an empirical model relating food consumption to fish morphology. Published estimates were used for E. sardella and Opsaridium microcephalum (Cyprinidae). An estimate of total prey consumption by the pelagic fish population was obtained from Q/B ratios and fish biomass estimates from acoustic surveys covering the entire offshore pelagic zone of the lake (24 000 km²).
• 5 Diplotaxodon limnothrissa, R. longiceps and C. quadrimaculatus had a broad range of diets, with the ability to switch from crustacean zooplankton to larvae and pupae of Chaoborus edulis (Diptera) or larval and juvenile E. sardella. Diplotaxodon‘bigeye’ and S. njassae fed almost exclusively on fourth-instar larvae and pupae of C. edulis. Engraulicypris sardella fed mainly on crustacean zooplankton. The main prey of the large piscivorous Rhamphochromis species were Diplotaxodon spp. and E. sardella.
• 6 The fish community consumed only 3% of estimated crustacean zooplankton production directly. Predation pressure was intense (> 80% of estimated production consumed by predators) on late instars of the zooplanktivorous C. edulis larvae and on E. sardella larvae. Rhamphochomis spp. consumed 22–43% of estimated production of the zooplankton-eating fishes.
• 7 Although many members of the fish community do not feed directly on crustacean zooplankton, so that the food-chain supporting fish production involves an extra trophic level, it is considered that the endemic fish community is well adapted to feeding on the low-density prey in the pelagic zone, and that there is no vacant feeding niche.

     

Trophic relationships between primary producers and fish yields in Lake Balaton

Relationships between chlorophyll a content of the water, the shoreline-length: water area ratio and the annual total fish yield as catch per unit effort (CUE: kg ha^–1 100 h^–1 as annual mean values) have been calculated by multivariable regression. The determination coefficient (r ² = 0.913) showed a significant dependence of fish yield on morphometry of different lake areas. Accordingly, fish carrying capacity of the open water areas, calculated from chlorophyll a content and S/A, ranged from 12 to 34%, but that of the littoral zone between 66 and 88%. These findings have also been supported by echo-sounding records of the horizontal distribution of fish.Bream (Abramis brama L.) contributes the majority (70–80%) of fish stock and yield. Its food mainly consists of zooplankton and benthic invertebrates in ratios that are widely variable with season and depend on the age of fish. Average daily food consumption of individuals (age group 3 + and over) varies between 2 and 5 g. Bream consumes two- to three-times more food in the SW basin than in the NE one. This means that the present stocks inhabiting areas from NE to SW consume annually 13249–20085 t yr^–1 of food. According to estimated calorific values, the annual energy consumption of local populations along the longitudinal axis of the lake varies between 93 and 141 kJ m^–2 yr^–1. The efficiency of energy transfer from primary producers to fish is low and varies from 0.04 to 0.1%.