The characteristics of feeding of Diaphus theta (Myctophidae) in the northwestern part of the Pacific Ocean in the Summer-Autumn period

The feeding of Diaphus theta in the zone of the subarctic front and in Pacific waters off the Kuril Islands in November 2001 and in July–August 2002 was studied. Interzonal plankton [euphausiids (mainly Euphausia pacifica), copepods (Metridia pacifica), and amphipods (Themisto pacifica)] dominated in the food bolus. As fish grow, the proportion of copepods decreases, the proportion of euphausiids and amphipods increases in stomachs, and the food spectrum extends. One considerable peak in the feeding (in both the summer and autumn periods) occurring in the nighttime was revealed. The most intensive feeding takes place in the dark time of the day in the epipelagial due to euphausiids and amphipods; in the light time of the day, the feeding activity declines. Fish feed mainly on copepods in the upper pelagial. The daily ration of D. theta was 1.5% of the weight of fish in the summer period and 3.2% in the autumn period.     

Sound production during competitive feeding in the grey gurnard

The acoustic repertoire of captive grey gurnard Eutrigla gurnardus during competitive feeding consisted of three types of sound: knocks, grunts and growls. Knocks were audible as a single sound, whereas grunts and growls were perceived as longer, pulsed sounds to the human ear. Typically, knocks were composed of 1–2 pulses, grunts of 4–8 pulses and growls >10 pulses. Growls were longer and had shorter pulse periods than grunts. All sound types had peak frequencies of c . 500 Hz. The sequences of behaviours observed during feeding interactions suggest that grey gurnard obtain food both by scramble and contest tactics. Competing fish emitted knocks mainly while grasping a food item and also during other non‐agonistic behaviour, suggesting that knock production may reflect a state of feeding arousal but could also serve as a warning of the forager's presence to nearby competitors. Grunts were mainly emitted during frontal displays, which were the most frequent behavioural act preceding grasps, suggesting that they may play a role in deterring other fish from gaining access to disputed food items.     

Ontogeny of Acoustic and Feeding Behaviour in the Grey Gurnard, Eutrigla gurnardus

Although sound production in teleost fish is often associated with territorial behaviour, little is known of fish acoustic behaviour in other agonistic contexts such as competitive feeding and how it changes during ontogeny. The grey gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during competitive feeding and seems to adopt both contest and scramble tactics under defensible resource conditions. Here we examine, for the first time, the effect of fish size on sound production and agonistic behaviour during competitive feeding. We have made sound (alone) and video (synchronized image and sound) recordings of grey gurnards during competitive feeding interactions. Experimental fish ranged from small juveniles to large adults and were grouped in four size classes: 10–15, 15–20, 25–30 and 30–40 cm in total length. We show that, in this species, both sound production and feeding behaviour change with fish size. Sound production rate decreased in larger fish. Sound duration, pulse duration and the number of pulses increased whereas the peak frequency decreased with fish size, in both sound types (knocks and grunts). Interaction rate and the frequency of agonistic behaviour decreased with increasing fish size during competitive feeding sessions. The proportion of feeding interactions accompanied by sound production was similar in all size classes. However, the proportion of interactions accompanied by knocks (less aggressive sounds) and by grunts (more aggressive) increased and decreased with fish size, respectively. Taken together, these results suggest that smaller grey gurnards compete for food by contest tactics whereas larger specimens predominantly scramble for food, probably because body size gives an advantage in locating, capturing and handling prey. We further suggest that sounds emitted during feeding may potentially give information on the motivation and ability of the individual to compete for food resources.     

Growling for food: acoustic emissions during competitive feeding of the streaked gurnard

The streaked gurnard Trigloporus lastoviza produced only one sound type, a growl, lasting up to 3 s and consisting of repeated groups of typically one to three pulses. The foraging fish followed two different strategies. In the first, the fish circled the feeding area, grasped a food item and fled, sometimes displaying aggressively to competitors. With this foraging strategy, fish usually made sounds as they circled, grasped and fled. Fish that growled while circling were more likely to grasp a food item subsequently than were silent fish. The second feeding strategy occurred when a fish had already ingested food or failed to get any. In this case, typically fish searched for food on the substratum or approached and touched other individuals that were feeding, sometimes grabbing food that was spat out during food handling by the other fish. Although payback experiments would be needed to draw firm conclusions on the communicative function of growling during competitive feeding in the streaked gurnard, the results suggest that sound production confers advantages to individuals competing for limited food resources.     

Daily feeding rhythm and rations of Pacific salmon of the genus Oncorhynchus in the period of marine prespawning migrations

The daily feeding rhythm and rations of the humpback salmon Oncorhynchus gorbuscha, the sockeyed salmon O. nerka, and the chum salmon O. keta during marine prespawning migrations is investigated with consideration of materials collected at daily stations in waters off eastern Kamchatka in June–July 1999 and 2001 (from catches of drift nets). The bulk of humpback salmon and sockeyed salmon food consists of euphausiids, hyperiids, large copepods, pteropods, and fish juveniles. In the food of chum salmon, pteropods dominated. In a 24-h period, salmon manifest a pronounced evening peak of stomach fullness, while at night feeding discontinues. Samples collected in the morning consisted of fish who had just started feeding after the night pause. In addition to nightly period of rest, all species manifested a daytime decrease in foraging activity, though less pronounced than in the night. The daily rhythm of Pacific salmons’s feeding depends on the vertical migrations of their food items (representatives of sound-scattering layers). During the marine feeding period, the most intensive feeding is recorded in the humpback salmon and chum salmon. The daily ration of the humpback salmon is lower than that of the chum salmon but includes animals of higher food value. Due to a high digestion rate in combination with a large stomach volume, the chum salmon can consume a large quantity of low-calorific food in a short time. The daily ration of the sockeyed salmon is considerably lower than that of other salmon species.     

The functional roles of different muscle fibre types identified in the myotomes of marine teleosts: a behavioural, anatomical and histochemical study

Norway pout ( Trisopterus esmarkii ) were collected during a trawling survey of inshore waters of the west coast of Scotland. 0–group fish were first taken by the bottom trawl in late summer and since there was no evidence of local spawning it was inferred that a migration from the open sea had occurred. The distribution and age composition of the stock was related to depth. The young fish migrated from the shallower stations during their first winter but persisted for a second winter at some of the deeper stations.
There was a marked seasonal variation in the quality of the diet and in the intensity of feeding. The most important food organisms were copepods, decapod larvae, mysids and euphausiids. Diurnal variations in the intensity of feeding were minimal in August but the quality of the food in the stomachs was dependent on the time of sampling. The converse was observed in January when feeding was at a maximum between dusk and dawn but the quality of the food remained fairly constant.     

Long‐term changes in the feeding of Pollachius virens on the Scotian Shelf: responses to a dynamic ecosystem

The diet and feeding ecology of pollock Pollachius virens from the Scotian Shelf and Bay of Fundy in the north‐west Atlantic changed over the last few decades, which was associated with decreases in euphausiid abundance. Stomach contents data for 2078 pollock collected during the 1958–1967 period and for 1230 pollock collected during the 1996–2002 period indicated that pollock diet contained fewer euphausiids and feeding activity decreased. During the early period, euphausiids were present in 65% of the pollock stomachs that contained food and only 9% of these stomachs in the recent period. The decrease of euphausiids was not wholly offset by an increase in piscivory, since there was little increase in the frequency of fish prey in the diet or in the fullness index for this prey type. Empty stomachs were significantly more common in the recent period during both the winter and summer. The decreased occurrence of euphausiids in stomach samples coincided with a significantly decreased abundance of this prey, suggesting that the near‐absence of euphausiids in recently collected pollock stomachs reflected prey abundance. Concurrent with changes in diet and feeding intensity, the condition or 'plumpness' of pollock significantly declined from the early to the late sampling periods.     

Distribution and abundance of euphausiids and pelagic amphipods in Kongsfjorden,Isfjorden and Rijpfjorden (Svalbard) and changes in their relative importance as key prey in a warming marine ecosystem

Euphausiid (krill) and amphipod dynamics were studied during 2006–2011 by use of plankton nets in Kongsfjorden (79°N) and adjacent waters, also including limited sampling in Isfjorden (78°N) and Rijpfjorden (80°N). The objectives of the study were to assess how variations in physical characteristics across fjord systems affect the distribution and abundance of euphausiids and amphipods and the potential for these macrozooplankton species to reproduce in these waters. The abundances of euphausiids and amphipods were higher in Kongsfjorden than in Rijpfjorden and Isfjorden, and the highest abundances were observed at the innermost stations of Kongsfjorden, where Thysanoessa inermis and Themisto libellula dominated. The Atlantic species Thysanoessa longicaudata, Meganyctiphanes norvegica and Themisto abyssorum dominated at the outside Kongsfjorden. Inter-annual and seasonal variability in abundances of euphausiids and amphipods were evident. The presence of ripe euphausiids outside Kongsfjorden indicates that they may reproduce in these areas. Mature individuals of T. abyssorum were recorded mainly outside Kongsfjorden, whereas no mature or ripe T. libellula were present in both the inner and outer parts of this fjord. If the warming trend persists, as seen during the last decade, this would favour the Atlantic/boreal euphausiid species, while Arctic species, such as the amphipod T. libellula, may decline. Euphausiids and amphipods are major food of capelin (Mallotus villosus) and polar cod (Boreogadus saida), respectively, in this region, and changes in prey abundance will likely have an impact on the feeding dynamics of these important fish species.     

The food supply of the Pacific salmon of the genus Oncorhynchus in the northwestern Pacific Ocean. 2. Comparative characterization and general state

The interannual variations and general state of the food supply of Pacific salmon (Oncorhynchus spp.) in the 2000s in the northwestern Pacific Ocean (including the Bering Sea and the Sea of Okhotsk) were analyzed based on indirect characteristics that indicate the variability of their forage base, feeding habits, growth, and biomass. A new index for the quantitative evaluation of food supply was suggested. The food supply of the Pacific salmon during the 2000s was found to be sufficient to maintain the normal functioning of populations. With high abundance of Pacific salmon, the food supply tended to decrease. However, this caused no negative consequences for the survival of major salmon stocks during the marine period of life and, as a rule, no marked decrease in the food consumption and growth rates of fish. A relative increase in food competition was compensated by adaptive changes in the diet and diel feeding rhythm of salmon. With the shortage of preferred food organisms (amphipods, euphausiids, and pteropods), Pacific salmon changed to consuming minor prey (copepods and chaetognaths), and numerous mesopelagic species of macroplankton and micronekton in the evening hours.     

Seasonal variation of food and feeding in burrowing goby <Emphasis Type="Italic">Parapocryptes serperaster</Emphasis> (Gobiidae) at different body sizes

Diet composition and feeding habits of the burrowing fish Parapocryptes serperaster were investigated on different fish sizes across dry and wet seasons in the Mekong Delta, Vietnam. The gut length was positively related to fish length; the gut length was 1.57 ± 0.30 times the total length, which is in the range for omnivore (1–3). Detritus, algae and copepods were the main food items in the foregut. The diet composition showed seasonal and intraspecific variations in all fish sizes. The diet diversity varied with fish size and the dry-wet season pattern, and small fish had a higher diet diversity than large fish. The diet evenness index and Costello graphic analysis indicate that this goby is a generalist feeder and feeds mainly on detritus, followed by diatoms, and could obtain food from the bottom and the water column. The feeding intensity of P. serperaster was higher in the wet season than in the dry season, but was not significantly affected by fish size. The P. serperaster fed on Navicula spp. in the wet season, but on Nitzschia spp. in the dry season. The understanding of food and feeding habits of P. serperaster contributes to our knowledge on feeding adaptation of small-bodied bottom-dwelling gobies to the mud flat habitats in tropical monsoonal regions.     

Vocalisation Repertoire of Female Bluefin Gurnard (Chelidonichthys kumu) in Captivity: Sound Structure,Context and Vocal Activity

Fish vocalisation is often a major component of underwater soundscapes. Therefore, interpretation of these soundscapes requires an understanding of the vocalisation characteristics of common soniferous fish species. This study of captive female bluefin gurnard, Chelidonichthys kumu, aims to formally characterise their vocalisation sounds and daily pattern of sound production. Four types of sound were produced and characterised, twice as many as previously reported in this species. These sounds fit two aural categories; grunt and growl, the mean peak frequencies for which ranged between 129 to 215 Hz. This species vocalized throughout the 24 hour period at an average rate of (18.5 ± 2.0 sounds fish^-1 h^-1) with an increase in vocalization rate at dawn and dusk. Competitive feeding did not elevate vocalisation as has been found in other gurnard species. Bluefin gurnard are common in coastal waters of New Zealand, Australia and Japan and, given their vocalization rate, are likely to be significant contributors to ambient underwater soundscape in these areas.     

On the problem of ecological groups formation in European perch Perca fluviatilis populations

Simulation model of the intraseasonal growth dynamics of young-of-the-year European perch Perca fluviatilis has been developed and studied. The model has been constructed based on the principles of bioenergetics and covers all the main physiological utilization processes of energy that come with food, including somatic growth, expenses on metabolism, and partial loss of energy with egestion and excretion. It is assumed that there are two space-separated biotopes called “inshore” and “pelagial” with different feeding conditions. Fish move from inshore to pelagial as the amount of food in the inshore biotope gets lower, provided that the actual ration is reduced down to the predetermined threshold level. It is demonstrated that the combined distribution of fish specimens belonging to one generation according to weight by the end of their growth period mainly depends on the intensity of exchange process between the biotopes. The ratio between the abundance values of young fish localized in different biotopes is determined by the threshold ration level, which motivates fish to move, as well as the duration of spawning, and, accordingly, length of hatching period.     

Feeding patterns of post-larval and juvenile notothenioids in the southern Weddell Sea (Antarctica)

Summary The food of 163 juvenile specimens of 13 species of notothenioid fishes collected in the southern Weddell Sea (Antarctica) was analyzed. Investigated fish size range was 3–13 cm SL. Principal food items were calanoid copepods Metridia gerlachei, Calanoides acutus, and Calanus propinquus; all developmental stages of Euphausia crystallorophias, and post-larval nototheniid fish Pleuragramma antarcticum. Diet of juvenile channichthyids is limited to few species of euphausiids and fish in the size > 10 mm, but does not include significant numbers of copepods. Pelagic stages of nototheniids feed on copepods and/or larval euphausiids smaller than 10 mm. At similar size, nototheniids and bathydraconids take smaller prey items than channichthyids.     

Feeding ecology of capelin (Mallotus villosus Müller) in West Greenland waters

Capelin (Mallotus villosus Müller) is a key pelagic mediator of energy from lower to higher trophic levels in arctic waters. This is also the case in Greenland waters, but little is known of its feeding behaviour in this region. By analysing stable nitrogen isotopes and stomach content of capelin collected along 1500?km of the Greenland west coast, this study aims to provide knowledge on capelin feeding ecology and the role that diet composition and biomass may have in generating the observed latitudinal growth differences in Greenland capelin. In total, 572 stomachs were sampled. The most dominant prey by wet weight was euphausiids (61?%) followed by amphipods (18?%) and copepods (10?%). The most common species were Thysanoessa raschii, Themisto libulla, Calanus finmarchicus and Calanus hyperboreus. Copepods dominated in smaller capelin but were replaced by euphausiids in larger fish. A similar prey shift towards euphausiids along with an increase in prey weight (relative and absolute) was seen with increasing latitude. The spatial variation in feeding pattern was supported by stable nitrogen analyses. The mean δ¹⁵N values of capelin muscle tissue for the south (60–64°N) and north (68–72°N) were 9.54?‰?±?0.72 and 12.47?‰?±?0.38 (mean?±?SD), respectively. However, when differences in isotopic baseline values (C. finmarchicus δ¹⁵N, 2.47?‰) in the two areas were taken into account, the isotope values suggest that capelin in the northern areas fed on a slightly higher trophic level higher than in the south, as would be expected with increasing importance of euphausiids. These significant feeding differences along the Greenland west coast are likely impacting capelin growth and condition as they show parallel trends along the same gradient.     

Diet composition in summer of rosefish Helicolenus hilgendorfii on the southeastern coast of Korea

The feeding habits of Helicolenus hilgendorfii were studied using 93 specimens (35–135 mm in standard length) collected from the southeastern coast of Korea during the summer season (June–August) from 2005 to 2007. Helicolenus hilgendorfii is a carnivore that mainly consumes shrimps and fishes. Its diet also includes small quantities of mysids, amphipods, euphausiids, copepods, and isopods. Our graphical method for feeding habits revealed that H. hilgendorfii is an opportunistic and specialized predator on shrimps, especially Crangon hakodatei, although H. hilgendorfii showed an ontogenetic dietary shift, the proportion of shrimp decreasing and the consumption of fishes gradually increasing with the increase of fish size.     

Otolith oxygen and carbon stable isotopes in wild and laboratory-reared plaice (Pleuronectes platessa)

The relationship between water temperature, growth rate, and otolith isotopic ratios was measured for juvenile plaice (Pleuronectes platessa) reared at two temperatures (11 and 17°C) and two feeding regimes (1 and 3 prey items·ml^?1). The otolith isotope ratios in individual fish ranged from ?2 to ?4 for carbon isotope ratios (δ¹³C) and from 0.2 to 1.9 for oxygen isotope ratios (δ¹⁸O). The otolith oxygen isotope ratios were significantly affected by water temperature, but not by feeding level, and there were no significant synergistic effects. The fractionation of oxygen isotopes during otolith growth was independent of individual growth rate. Carbon isotope ratios were not significantly affected by food ration or water temperature, but were related to fish growth rate. The carbon isotope ratios were negatively correlated with fish length in the colder water treatments, and tended to increase with fish length in the warm water treatments. The laboratory-determined relationship between otolith oxygen isotope ratio and water temperature was applied to individuals of five species (plaice, cod, whiting, haddock, gurnard) collected in a single trawl sample. The otolith derived temperatures often overestimated measured water temperatures. The difference between real and estimated water temperatures varied between species, and the closest fit was for field-caught plaice.     

The consumption of euphausiids by the pelagic fish community off southwestern Vancouver Island, British Columbia

The consumption of adult euphausiids was estimated for the sevenmost abundant fish species found on the continental shelf offsouthwestern Vancouver Island, British Columbia, Canada. Empiricaldata on fish feeding rates, diets and biomass were used to estimateeuphausiid consumption in August for each year from 1985 to1997. The fish community in August was estimated to consumean average 297 kt of euphausiids (124 t km^–2). Pacifichake (Merluccius productus) and Pacific herring (Clupea harengus)accounted for 60% and 30%, respectively, of the total euphausiidsconsumed by fish. The total estimated consumption of euphausiidsper tonne of fish averaged 0.93, and there was no significanttrend in the time series. In addition, there was no significantrelationship between the total fish community consumption oreuphausiids consumed per tonne of fish and euphausiid biomass,and there was no change in the fraction of euphausiids in thediet of small or large Pacific hake. Thus, it appears that predationpressure from the pelagic fish community was relatively constantand not responsible for the apparent fivefold decline in adulteuphausiid biomass observed in the 1990s.     

Feeding of Polar cod <Emphasis Type="Italic">Boreogadus saida</Emphasis> in the Kara Sea

In the summer–autumn period of 2007, 2010, and 2013, the peculiarities of Polar cod feeding Boreogadus saida in the Kara Sea were considered. In these years, the intensity of feeding of adult individuals was quite similar. Spatial and interannual differences in the composition of the food have been observed. Copepoda, Euphausiacea, and tunicates (Oikopleura sp.) dominated in the food of young fish. The main preys of adult individuals are Hyperiidea, Copepoda, Euphausiacea, and fish. As the length of Polar cod increases, the weight percentage of copepods decreases and the portion of fish increases.     

Feeding habits of the African bagrid,Chrysichthys filamentosus in a Nigerian lake

The feeding ecology ofChrysichthys, a commercially important freshwater bagrid in Nigeria, is described from a southeastern lake. Over a year period, 779 stomachs were examined. The main food items were chaoborid and chironomid larvae, ostracods, copepods and detritus. Larger fish fed mostly on insect larvae and detritus while the smaller individuals consumed mostly microcrustacea. Feeding intensity was lowest during the height of the flood. There was little diel change in the amount of food consumed. The fish are morphologically pre-adapted for their benthic omnivorous feeding habits.     

Interspecific variations in the surface ultrastructure of the gills of freshwater mullets

SEM studies were made on the gills of freshwater mullets,Rhinomugil corsula andSicamugil cascasia, to correlate surface ultrastructure of various gill units with their probable functions. Two types of lamellated gill rakers of the former fish are suited for plankton feeding and the short, stumpy and transversely beaded gill rakers of the latter reflect the varied food and feeding habit of the fish.R. corsula has numerous mucous glands on the epithelium covering the gill arch and gill filaments,S. cascasia has fewer. In accordance with the differences in the density and distribution of the mucous glands, the microridged epithelial cells also show variations in their architectural plan. In both species the epithelium of the secondary lamellae is smooth, probably an adaptation for better gaseous exchange.