Effects of temperature and delayed initial feeding on the survival and growth of Japanese flounder larvae

The effects of the timing of initial feeding (0, 1, 2, 3 and 4 days after yolk exhaustion) and temperature (15, 18 and 21° C) on the point‐of‐no‐return (PNR), survival and growth of laboratory‐reared Japanese flounder Paralichthys olivaceus larvae were studied under controlled conditions. The larvae reached PNR on 7·7, 5·2 and 4·2 days‐post‐hatching (dph) at 15, 18 and 21° C, respectively. At each temperature, larval growth did not differ significantly among the delayed initial feedings 1 day before PNR but decreased significantly in larvae first fed after that. In the treatments where initial feeding was equally delayed, larvae grew significantly faster at 18 and 21° C than at 15° C. The larvae survived apparently better at 15 and 18° C than at 21° C when initial feeding was equally delayed. At each temperature, survival of the larvae first fed before PNR did not differ noticeably, while delayed initial feeding after that apparently reduced their survival. These results indicated that there existed a negatively temperature‐dependent PNR in the Japanese flounder larvae. Survival and growth of the larvae strongly depended on temperature as well as the timing of initial feeding. High temperature accelerated the yolk exhaustion and growth of the larvae and thus reduced their starvation tolerance and survival. To avoid potential starvation mortality and obtain good growth, the Japanese flounder larvae must establish successful initial feeding within 2 days after yolk exhaustion at 15° C and within 1 day at both 18 and 21° C.     

Effects of supplementary feeding on growth and reproduction of three carnivorous plant species in a subarctic environment

1 The effect of supplementary feeding on growth and reproduction of three carnivorous plants species was investigated over a 6‐year period. Pinguicula alpina , P. villosa and P. vulgaris populations growing at two altitudes in a subarctic environment were fed with fruit flies ( Drosophila melanogaster ).
2 Fed plants increased in size relative to control plants during the first years. Subsequently a stable size difference between feeding levels was established. The weight of the over‐wintering part was higher in fed plants than in control plants.
3 The flowering frequency (i.e. proportion of plants in a population carrying flowers) was also higher in the fed plants. The proportion of flowering plants increased in the feeding treatment compared to control plants during more‐or‐less the whole experimental feeding period (5–6 years). Seed production also increased slowly in response to feeding.
4 No feeding effect on nitrogen and phosphorus concentrations in seeds and over‐wintering parts was found.
5 In most characteristics the high‐altitude populations were less responsive than populations growing at low altitude. In the high‐altitude population reproduction failed repeatedly, suggesting that seed output may be more dependent on abiotic factors than on resource availability in cold environments.
6 Pinguicula villosa and P. vulgaris used the new resources the same summer for increased leaf rosette growth and current reproduction, showing these species to be income breeders, while the third species ( P. alpina ) allocated a larger proportion to storage and future reproduction, characteristic of a capital breeder.     

Trophically transmitted parasites in wild Atlantic salmon post‐smolts from Norwegian fjords

The community structure of trophically transmitted intestinal helminths of Atlantic salmon Salmo salar post‐smolts was highly variable among four fjords in Norway. There were no severely pathogenic parasite species. Post‐smolts from the southernmost Trondheimsfjord had a higher diversity of freshwater parasite species compared to the three northern fjords (Tanafjord, Altafjord and Malangen). In contrast, the highest diversity and proportion of marine species was found in the three northern fjords. Post‐smolts were generally more infected with marine parasites in the outer rather than inner parts of all of the fjords. The prevalence of the acanthocephalan Echinorynchus gadi (range: 13–42%) and marine trematodes (range: 14–47%) was higher in post‐smolts in outer zones of the northern fjords than in fish from Trondheimsfjord (0 and 6%, respectively). The within‐fjord variability and north‐south geographical gradient in parasite infection patterns reflected differences in marine feeding of the post‐smolts on potential intermediate hosts such as amphipods ( E. gadi ) and fish larvae (trematodes), which were higher in the northern fjords (range: 27–28 and 67–85%, respectively) than in Trondheimsfjord (5 and 19%, respectively). High intensities of marine parasites suggest that some post‐smolts from northern fjords may have a prolonged fjord‐feeding compared to those from Trondheimsfjord. Parasites of both freshwater and marine origin appear to be suitable as bio‐indicators of feeding and migratory pattern of Atlantic salmon post‐smolts and preadults during their seaward migration.     

Geographical differences in marine feeding of Atlantic salmon post‐smolts in Norwegian fjords

Stomach content analyses were conducted on Atlantic salmon Salmo salar post‐smolt (average size, 119–154 mm fork length, L _F) caught in eight large Norwegian fjord systems along a north–south geographical axis during 1998–2001. In general, post‐smolts from southern Norway showed low feeding intensity in the fjords, whereas extensive feeding was observed in fjords in the northern and middle parts of Norway. The marine diet mainly included different crustaceans and in particular marine pelagic fish larvae (sand-eels Ammodytes spp., herring Clupea harengus and gadoids), but with a substantial spatial and annual variation in prey diversity and feeding intensity. Insects were most frequently taken in the estuary, although fishes often made a large contribution in mass. In contrast, fishes, and to some extent various crustaceans (particularly Hyperiidae, Gammaridae, Euphausiacea and Copepoda) dominated the diet in the middle and outer parts of the fjords, where post‐smolts also fed more extensively than in the inner part. The results indicate that extensive feeding immediately after sea entrance may be more common for post‐smolts in the northern and middle parts of Norway, than in the southern fjords. The observed differences in post‐smolt feeding may be due to spatial and temporal differences in prey availability within and between the different types of fjord systems, and this might influence post‐smolt growth and survival.     

On the interaction of turbulent flow and feeding behaviour of juvenile Atlantic Salmon (Salmo salar)

Anthropogenic activities can dramatically modify the riverine habitat of juvenile Atlantic salmon ( Salmo salar ). In the perspective of protecting and restoring the fluvial habitat, bioenergetic models are often used to estimate fish habitat quality. These models determine the habitat quality as the ratio between the energetic gains (food) and costs (growth, metabolism) of a fish. The energetic costs of swimming in a river are generally estimated using the average flow velocity without consideration of the effect of turbulence. Juvenile Atlantic salmon (JAS) live in rivers characterized by intense velocity fluctuations, which are often described as a succession of high‐ and low‐speed flow regions. These flow structures are likely to affect the JAS activity that consists of long periods of sit‐and‐wait at the top of a protuberant rock interrupted by short bursting motions to capture drifting food particles. To minimize the energetic costs, it is hypothesized that JAS use low‐speed flow regions to initiate and undertake their feeding motions.  To improve bioenergetic modelling, this study aimed at analyzing the relation between turbulent flow structures and the feeding behaviour of JAS in a natural gravel‐bed river. We filmed eight JAS during 30 min with a submersible video camera while simultaneously measuring velocity fluctuations close to the fish in the St. Marguerite River, Quebec, Canada. Our results show that the proportion of time used for feeding motions decreases with increasing turbulent intensity and mean flow velocity; and that JAS do not seem to prefer low‐speed flow regions to initiate their feeding motions.     

Feeding preference and deterrence in rabbitfish Siganus fuscescens for the cyanobacterium Lyngbya majuscula in Moreton Bay, south‐east Queensland, Australia

Rabbitfish Siganus fuscescens preferences for Lyngbya majuscula collected from three bloom locations in Moreton Bay, Queensland, Australia, were tested along with a range of local plant species in the laboratory. Consumption of L. majuscula by fish did not differ between wild and captive‐bred fish ( P  = 0·152) but did differ between bloom location ( P  = 0·039). No relationship was found between consumption rates and lyngbyatoxin‐a concentration ( r ² = 0·035, P  = 0·814). No correlation existed between C : N and proportion of food consumed when all food types were analysed statistically, whereas a clear correlation was observed when L. majuscula was removed from the calculations. In simulated bloom conditions, fish avoided ingestion of L. majuscula by feeding through gaps in the L. majuscula coverage. Both wild and captive‐bred S. fuscescens showed a distinct feeding pattern in 10 day no‐choice feeding assays, with less L. majuscula being consumed than the preferred red alga Acanthophora spicifera . Lyngbya majuscula however, was consumed in equal quantities to A. spicifera by wild S. fuscescens when lyngbyatoxin‐a was not detectable. Wild fish probably do not preferentially feed on L. majuscula when secondary metabolites are present and are not severely impacted by large L. majuscula blooms in Moreton Bay. Furthermore, poor feeding performance in both captive‐bred and wild S. fuscescens suggests that they would exert little pressure as a top‐down control agent of toxic L. majuscula blooms within Moreton Bay.     

Gustatory responses to feeding‐ and non‐feeding‐stimulant chemicals, with an emphasis on amino acids, in rainbow trout

Specific receptor and fibre types of rainbow trout Oncorhynchus mykiss involved in the detection and discrimination of amino acids and a heterogeneous collection of compounds were investigated by recording the electrical activity of the maxillary branch of the facial nerve innervating taste buds inside the upper jaw. Proline (Pro), alanine (Ala), leucine (Leu), betaine (Bet) and 2‐amino‐3‐guanidinopropionic acid (Agp) were the major amino acids detected by the gustatory system. The two experimental approaches, concentration‐response curves and cross‐adaptations, showed that all amino acids were detected by three independent receptor types: Pro ‐, Agp/Bet ‐ and Leu ‐receptors. Bile acids, the most potent stimulants recorded, were detected by a single receptor type independent of those for amino acids, with threshold concentrations of 10⁻¹² M. Strychnine, quinine and tetrodotoxin may have partially shared a single receptor mechanism. The gustatory sensibility narrowly tuned towards the amino acid spectrum compared to those for a diverse array of non‐feeding stimulant chemicals, combined with feeding behaviour triggered primarily by vision and olfaction, suggest that in rainbow trout, and possibly other salmonid species, gustatory chemical cues, in addition to food finding and intake, play an important role in detecting poisonous prey and substances.     

Does light intensity affect self‐feeding and food wastage in group‐held rainbow trout and white‐spotted charr?

The self‐feeding rhythms of rainbow trout Oncorhynchus mykiss and white‐spotted charr Salvelinus leucomaenis were studied when group‐held fishes ( n  = 10 per group) were fed using self‐feeders under two different light intensities (50 lx, 16 μW cm⁻² and 700 lx, 215 μW cm⁻²) during the light phase of the light‐dark cycle. Food wastage was also measured. At 50 lx, all groups of rainbow trout learned to operate the self‐feeder within 4 days, whereas it took up to 25 days for all groups at 700 lx. In contrast, all groups of white‐spotted charr learned self‐feeding within 17 days, irrespective of light intensity. These results, although non‐significant, suggest that lower light intensities can stimulate instrumental learning in rainbow trout, but not white‐spotted charr. In rainbow trout, the total number of trigger actuations for the entire experimental period was significantly higher at 50 rather than 700 lx, although this may have been related to delayed learning at 700 lx. There was no significant effect in white‐spotted charr. Growth rate (assessed using the thermal growth coefficient) was also higher in rainbow trout but not white‐spotted charr at 50 rather than 700 lx, although this difference was non‐significant. Light intensity had no significant effect on food wastage in either rainbow trout or white‐spotted charr, and it did not appear to affect the proportion of trigger actuations during the light phase. Clear diurnal feeding rhythms were observed in both species and these were classified into four categories: uniform, dawn, dusk and crepuscular. At 50 lx, fish from both species generally fed in temporally localized periods at either dawn and dusk, whilst feeding was predominantly uniform during the light phase at 700 lx.     

Predator–prey interactions between larval damselflies and mining larvae of Glyptotendipes gripekoveni (Chironomidae): reduction in feeding activity as an induced defence

1. The feeding methods and intensity of predation by larvae of the damselfly Erythromma najas on leaf‐mining larvae of the chironomid Glyptotendipes gripekoveni were examined in artificial habitats differing in complexity. The experiments assessed the influence of chemical stimuli from the predator, light and the concentration of suspended food on the feeding activity of G. gripekoveni inside and outside of the mine.
2.  Erythromma najas preyed upon G. gripekoveni as the latter grazed outside mines. The intensity of this predation decreased significantly at night in a habitat offering alternative prey.
3. When the food concentration for the chironomid was high, it significantly reduced both filtering activity and activity outside mines in response to the kairomone produced by E. najas . Feeding activity did not change when food was scarce.
4. The induced reduction in filter‐feeding and deposit‐feeding activity probably reduced predator success by reducing the probability of long‐distance detection of a mine and location of the chironomid's hole.
5. The predator can detect and catch mining prey in either the light (visually) or dark (mechanically). This may explain the lack of diel periodicity in the chemically induced differences in prey activity.
6. Reduced feeding activity of mining larvae in the chemically simulated presence of a larval damselfly can be explained as an induced antipredator behaviour, illustrating the trade‐off between feeding demands and predation risk in a poorly known link of the littoral foodweb.     

The influence of temperature on the stage at hatch of laboratory reared Gadus morhua and implications for comparisons of length and morphology

A staging table for yolk‐sac larvae of Atlantic cod Gadus morhua was developed and applied to determine the development stage at hatch. Larvae ( n  = 20) were sampled during the period from 50% hatch to first‐feeding from four temperature treatments ( c . 2, 4, 8 and 12° C). Data recorded included standard length, development stage, yolk‐sac area and evidence of feeding by larvae. The results indicated that the stage of development at hatch was positively correlated to larval size. Furthermore, developmentally based changes in morphology shortly after hatch reduced much of the initial difference in size, although some difference still existed. No relationship between size at hatch and the incidence of first‐feeding larvae was found. Based on these observations, it is recommended that the development stage of hatching larvae be reported in studies investigating size and morphological differences when observing individual larval fish that originate from different populations, batches or species.     

Behavioural interactions between native smokey dace and introduced yellowfin shiner: implications from habitat selection theory for an ongoing invasion

The occupation of adjacent, non‐overlapping positions along environmental gradients by closely related and ecologically similar species has drawn considerable attention from ecologists over the past decades. Condition‐specific competition, wherein competitive superiority varies with the abiotic environmental gradient, has been proposed as the major structuring force behind such distributions. These concepts, however, are generally applied to explain the contemporary distribution of organisms that share an evolutionary history. Our aim was to apply these concepts to the naive interactions between native and introduced fishes. In 1990 yellowfin shiner ( Notropis lutipinnis ) were introduced into the headwaters of the Little Tennessee River of western North Carolina, U.S.A. where it exhibits microhabitat preferences that overlap significantly with those of a threatened native minnow, the smokey dace ( Clinostomus funduloides raneyi ). Previous research has established that these drift‐feeding minnows: (1) differ in their average ability to intercept drifting prey as a function of water velocity; (2) generally occupy focal‐point velocities that maximize the rate of prey capture; and, (3) occasionally defend the forward positions in foraging aggregations that form in high quality patches. We present the results of a series of experiments designed to: (1) evaluate the role of aggression in the establishment and maintenance of preferred foraging positions in drift‐feeding minnows; (2) test the effects of prey availability, group size, and velocity on dominance rank, spatial position in groups, and feeding rates of individuals; and, (3) evaluate the potential for condition‐specific competition to establish competitive refugia for the native within the natural heterogeneity of mountain streams.     

Feeding behaviour in some teleosts is triggered by single amino acids primarily through olfaction

The present study investigated behavioural responses of naïve rainbow trout Oncorhynchus mykiss , lake charr Salvelinus namaycush , lake whitefish Coregonus clupeaformis and goldfish Carassius auratus to food extracts as well as selected amino acids (at 10⁻⁶ M) and related chemicals in a flow‐through behaviour trough. Cysteine, the most potent olfactory stimulating amino acid determined electrophysiologically, enhanced locomotor activity, an initial arousal behaviour, in all species examined, in exactly the same fashion as did food extracts. The increased locomotor activity was followed by distinct species‐specific search behavioural patterns: 1) bottom searching in rainbow trout; 2) surfacing and jumping in lake charr; 3) exploratory behaviour against the trough window in lake whitefish; 4) gravel pecking in goldfish. Olfactory‐stimulating neutral amino acids alanine and serine and gustatory‐stimulating imino acid proline were effective, to varying degrees, in eliciting feeding behaviour. Arginine and glutamate suppressed the locomotor activity in rainbow trout, but triggered feeding behaviour in the other species. Agmatine, a decarboxylated arginine, stimulated feeding behaviour in all species tested, except rainbow trout. The observed behavioural responses were in close accordance with the electrophysiological threshold and specificity. Together, the present data demonstrate that single amino acids and closely related chemicals initiate feeding behaviour primarily by olfaction, and interchangeably and complemented by gustation, in naive fishes.     

Muscle development in cultured blackspot seabream Pagellus bogaraveo: preliminary histochemical and immunohistochemical data on the fibre types

We studied muscle ontogeny and fibre type characteristics in the blackspot seabream, a new species for commercial aquaculture. Myosin ATPase and SDH histochemistry and immunohistochemistry were tested at different ontogenetic stages, using a panel of antibodies to myosin isoforms and parvalbumin. In general, deep white muscle was parvalbumin‐positive, and superficial 'red' muscle was parvalbumin‐negative at all ages examined. At 6 days of age (transition from endogenous to exogenous feeding) three layers of muscle fibres were observed with different antimyosin reactivities: superficial monolayer, presumptive slow red (present only as a small group of fibres adjacent to the lateral line nerve), and presumptive fast‐white (forming the bulk of the muscle). The superficial monolayer and presumptive slow fibres were positive for SDH. At 60 days of age (transition from live to artificial feeding) an additional fibre type was identified: a typical 'pink' or intermediate layer. In juveniles, the axial muscle consisted mainly of fast white fibres covered by a slow‐red layer and between them a pink layer. Surprisingly, the red layer could be resolved into two distinct types by myosin immunostaining. Red fibres were also present along the horizontal septum, near the notochord. Both red and white muscle layers showed a mosaic appearance, which was confirmed by ATPase reaction. The work was financed by British Council, CRUP, and FCT (PhD Grant SFRH‐BD‐14068–2003).     

Fasting modulates metabolic responses to cortisol, GH and IGF‐I in Arctic charr hepatocytes

Hepatocytes in primary culture from fed and 2 month fasted Arctic charr Salvelinus alpinus were exposed to physiological doses of either cortisol, salmon growth hormone (GH), salmon insulin‐like growth factor‐I (IGF‐I) or a combination of salmon GH and salmon IGF‐I. Fasting significantly lowered medium glucose levels compared to the fed fish, but had no significant effects on hepatocyte glycogen content or on the activities of enzymes involved in the intermediary metabolism. Cortisol treatment had no effect on hepatocyte glycogen content or on the enzyme activities investigated, but resulted in a significant increase in medium glucose concentration in hepatocytes isolated from fasted, but not fed fish. GH and IGF‐I treatments, both singly and in combination, significantly increased the glycogen content of hepatocytes isolated from fed fish, with less pronounced effects on hepatocytes isolated from fasted fish. The combination of GH and IGF‐I significantly increased lactate dehydrogenase activity regardless of the feeding state and significantly reduced the phosphenolpyruvate carboxykinase activity and medium glucose concentration in hepatocytes isolated from fed fish. Further, GH and IGF‐I significantly increased the activities of alanine aminotransferase and aspartate aminotransferase in hepatocytes isolated from fasted fish, but not fed fish. There were no effects of GH, IGF‐I, or their combination, on glucose 6‐phosphate dehydrogenase or 3‐hydroxyacyl‐CoA dehydrogenase activities. The results demonstrated that nutritional status of the animal modulates hepatocyte responsiveness to metabolic hormones, and suggested a role for GH and IGF‐I in hepatic glycogen conservation.     

Individual‐level analysis of pre‐ and post first‐feed growth and development in Atlantic salmon

Atlantic salmon Salmo salar were followed from egg to smoltification using genetic analysis to identify individuals and to link observations from pre‐ and post first feeding. Egg size and hatch timing significantly influenced alevin size at first feed but neither egg size, hatch timing or alevin sizes were correlated to size, condition factor or smolt status post first feed. In a hatchery environment the potential advantage gained by early hatching, larger alevin does not persist after first feeding. Different physiological and genetic complexes appear to influence growth in these two distinct phases of the Atlantic salmon's life‐cycle.     

Swim or hide: predator cues cause species specific reactions in young fish larvae

The anti‐predator behaviour of first‐feeding (9 mm total length) hatchery‐reared pike Esox lucius larvae and wild‐caught three‐spined stickleback Gasterosteus aculeatus larvae was studied in the presence of chemical and visual signals from a fish predator. The results clearly showed that both fish species detected the predator by chemical signals alone but the combined chemical and visual signals caused stronger and more diverse reactions. Subsequent to predator detection, their swimming activity decreased, they attacked zooplankton less frequently and spent more time in the vegetation. Fishes differed in their anti‐predator responses. Pike reacted more clearly to chemical signals alone while three‐spined stickleback needed both chemical and visual cues to assess the predation risk. The strongest reaction was the reduction in swimming activity in the three‐spined stickleback (38% decrease) and a decrease in attack rate of the pike (39% decrease), but only when a refuge was available. Pike were more dependent on the vegetation cover showing almost no anti‐predator responses in the absence of a refuge. In addition, there was a difference in the refuge use of three‐spined stickleback between different macrophytes, indicating a complex or dense structure, which was difficult to penetrate or chemical excretion in one of them.     

Does diet in Celtic Sea fishes reflect prey availability?

Feeding preferences of Celtic Sea fishes were investigated using a database of stomach content records, collected between 1977 and 1994. The diet of cod Gadus morhua , hake Merluccius merluccius , megrim Lepidorhombus whiffiagonis , whiting Merlangius merlangus and saithe Pollachius virens changed markedly as the animals grew larger, and although large predators generally chose larger bodied prey, the variability of prey sizes consumed also increased. Large predators continued to select small, low value, benthic prey ( e.g . Callionymus spp. and Trisopterus spp.) which were easier to catch, rather than larger, more energy lucrative pelagic prey ( e.g . mackerel Scomber scombrus ), even though these pelagic prey‐fishes were nearly always available and were often very abundant. Stock estimates of the International Council for the Exploration of the Sea and U.K. groundfish survey catches were used as indices of prey abundance. Blue‐whiting Micromesistius poutassou and other small pelagic fishes ( Argentina spp. and clupeoids) were identified as being particularly important, and were consumed by some predators more often than would be expected given the abundance of these prey in the environment. There was no evidence for density‐dependent feeding by predators on mackerel and only hake exhibited density‐dependent feeding on horse‐mackerel. Hake, cod and megrim consumed more blue‐whiting when this prey was at higher abundance in the environment. In choosing what prey to consume, predators must balance costs and benefits, considering the quality of prey and the energy expended during search, capture and handling.     

The feeding behaviour of juvenile Atlantic salmon in relation to turbulent flow

The feeding behaviour of juvenile Atlantic salmon Salmo salar in the Sainte‐Marguerite River, Quebec, Canada, varied with the characteristics of turbulent flow. Simulations indicated that juveniles would decrease their swimming costs during attacks by 19·8% in low and by 31·1% in high turbulent conditions by initiating movements in low‐speed flow events. The real swimming costs did not differ from the swimming costs estimated for a situation where fish initiate their movements at randomly selected flow velocities. The juvenile Atlantic salmon did not seem to prefer low‐speed flow events when initiating their movements. The proportion of time used for movements by fish decreased with an increase in the mean and the s . d . of the flow velocity.