Feeding habits of megrim, Lepidorhombus whiffiagonis (Walbaum, 1792), from the central Adriatic Sea

The feeding habits of the megrim, Lepidorhombus whiffiagonis , from the central Adriatic Sea were investigated with respect to fish size and seasons. Stomach contents of 510 specimens, 9.0–28.9 cm total length (TL), collected by bottom-trawl from 2004 to 2006 were analyzed. The percentage of 97 empty stomachs varied significantly with season (maximum during the winter, 32.1%; minimum during summer, 7.4%). The food composition suggests that the megrim is a carnivorous fish. Prey items identified in the stomachs belong to four major groups: Teleostei, Decapoda, Mysidacea and Cephalopoda. Teleosts were the most important (%IRI = 82.2), especially in fish larger than 14 cm TL. Mysidacea constituted the main prey for fish less than 14 cm TL. At the species level, the teleost Antonogadus megalokynodon (%IRI = 1.5) and decapod Processa canaliculata (%IRI = 0.9) were the most frequent prey. The mean weight of stomach contents increased significantly for fish larger than 14 cm TL, while the mean number of prey items did not differ significantly among size classes. Diet composition showed little seasonal variation; teleosts were the most important prey in all seasons, especially during spring. The lowest intensity of feeding recorded in winter could be related to the lower sea temperature and to the spawning period.     

Rates of gastric evacuation in piscivorous brown trout, Salmo trutta

SUMMARY. 1. The dry weight of food remaining in the stomachs of piscivorous trout decreased exponentially with time. Gastric evacuation rates increased exponentially with increasing temperature but were unaffected by predator size, meal size or type of fish prey.
2. Mathematical models were developed to estimate both the rate and time for the gastric evacuation of different meal sizes (expressed as dry weight), and were applicable to piscivorous trout of different sizes (length range 10–32 cm) feeding on trout fry or sticklebacks at different temperatures (range 5–18°C).
3. The wet weight of food in the stomachs also decreased exponentially with time, but evacuation rates both increased with temperature and decreased with increasing meal size; the latter relationship occurred because relative rates of water loss from a meal also decreased with increasing meal size. Use of wet or dry weights can therefore lead to different conclusions about the effect of meal size on evacuation rates.
4. When piscivorous trout were fed three consecutive meals of varying size, the models predicted the total dry weight of food left in the stomach, but not the weight remaining for each individual meal. Interactions between meals led to an increase in evacuation rates for meals consumed early in the series and a decrease in evacuation rates for later meals.
5. Evacuation rates for piscivorous trout were compared with those for trout feeding on invertebrates in an earlier study, and were close to those for caddis larvae as prey, higher than those for mealworms and lower than those for a variety of invertebrate prey. Although a great deal is now known about the daily food intake and growth rates of trout feeding on invertebrates, there is little comparable information for piscivorous trout.     

The basis of food selection in some estuarine fishes. Eels, Anguilla anguilla (L.), whiting, Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gasterosteus aculeatus L.

The factors influencing the selection of food by eels, Anguilla anguilla, whiting, Merlanglus merlangius, sprat, Sprattus sprattus, and stickleback, Gasterosteus aculeatus have been investigated by analysing collections made in the Severn Estuary for 1 year. Non–migratory (yellow) eels measuring from 19–5–56–5 cm in length fed mainly on either the decapod Crangon vulgaris or on the mysid Neomysis integer during the warmer months but ceased to feed in the winter. Whiting measuring between 2–5 and 15 cm fed almost exclusively on C. vulgaris, N. integer and the sand goby, Pomatoschistus minutus. Sprats fed chiefly on either the arnphipod Gammarus salinus or N. integer. Sticklebacks seldom contained any food in their stomachs despite the presence of large quantities of suitable prey and the high level of hunting efficiency. Gammarus salinus, although normally abundant in the environment, was usually ingested in disproportionately small quantities by all fishes except sprats reflecting its concealment among floating weeds and a selection against small (less than 1 cm) organisms. Because of the limitations of size and the unusually efficient escape reaction of larger animals, only young representatives of Crangon vulgaris were captured. The isopod Eurydice pulchra was rarely eaten by any of the fishes even though it was common in the environment. Burrowing polychaetes, mainly Nereis diversicolor, were never utilized possibly due to the difficulty involved in removing these organisms from the substrate. Neomysis integer was the most frequently consumed organism. Although the average length of prey ingested by the whitings increased with the size of fish, this was not the case for the other species. The proportion of non–feeding eels and the dry weight of stomach contents of this species depended on the temperature of the water but were not related to the availability of prey and tidal conditions whereas the feeding of whiting could not be related to any environmental parameter.     

Food and Feeding Habits of Flounder <Emphasis Type="Italic">Paralichthys Orbignyanus</Emphasis> (Jenyns, 1842) in Bahía Blanca Estuary,Argentina

Specimens of flounder Paralichthys orbignyanus (Jenyns, 1842) were collected in Bahía Blanca estuary between February 1997 and January 1998, and their feeding habits were examined in relation to season and size class. The stomach contents of 823 specimens, ranging from 70 to 875 mm total length, were analysed. Their diet included organisms from 17 taxa. The highest vacuity index values were found during autumn and winter. The stomach fullness index indicated that flounders increased their feeding activity between October and March, reaching a highest point in February and decreasing after February. Fish were the primary prey item in frequency, number and weight, followed by crustaceans, such as shrimps and crabs. A seasonal and size class variation was detected in the diet. During summer all-size flounders consumed mainly fish. In autumn, for all-size classes the main food were fish and crustaceans even though fish were dominant in terms of biomass. In spring, crustaceans (mysids Arthromysis magellanica (Cunningham), shrimps Artemesia longinaris Bate, and prawns Pleoticus muelleri (Bate)) were the dominant prey in terms of number and biomass for flounders ≤ 450 mm TL. Size classes larger than 451 mm TL fed on crustaceans and fish though the most important prey item in terms of biomass was fish. In Bahía Blanca estuary,P. orbignyanus evidenced mainly an ichthyophagou – carcinophagous diet. The results collected from the present study lead to conclude that P. orbignyanus shows, in this region, a clear preference for fish.     

The food and feeding habits of the silver pomfret, Pampus argenteus (Euphrasen), in Kuwait waters

The food habits of the silver pomfret, Pampus argenteus (Euphrasen 1788), in Kuwait waters were investigated by examining the stomach contents of 738 specimens collected from May 1996 to April 1997. Their diet consisted of a broad spectrum of food types, but Crustacea were dominant, with copepods and their eggs constituting 39 % other non-copepod Crustacea constituted 16 %. The next major food group was Bacillariophyta (21 %), followed by Mollusca (11 %), fish scales (10 %) and, finally, fish eggs and larvae (3 %). In summer the species fed on a wider variety of food items than in winter. Copepods, other non-copepod crustaceans, and molluscs tended to occur in the stomachs in higher frequencies with an increase in P. argenteus size (up to 18.5–20.4 cm), while the bacillariophytes tended to increase in stomachs at fish sizes between 22.5–24.5 cm. Analysis of monthly variations in stomach fullness indicated that feeding intensity fluctuated throughout the year, with a low during August and September, corresponding to the spawning period.     

Estimates of daily food intake by an inshore population of Pleuronectes platessa L. off eastern Anglesey, North Wales

A sequence of trawl surveys showed that the diet of plaice off eastern Anglesey was dominated by Abra alba in spring and summer, and by Pectinaria koreni in early spring and autumn. Plaice ate little food in winter. Despite the relatively small stomach in this species, plaice were able to achieve high rates of daily food intake during bouts of heavy feeding by rapidly transferring newly-ingested prey items into the anterior intestine without full gastric digestion. Seasonal daily feeding rates (percentage body weight) varied between 5 and 10% for small fish (15–20 cm total length), 3 and 12% for medium fish (20–25 cm) and 2.8 and 4.4% for large fish (30–35 cm).     

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.     

Feeding habits of horse mackerel, Trachurus trachurus (Linneaus, 1758), from the central Adriatic Sea

The feeding habits of the horse mackerel, Trachurus trachurus, from the central Adriatic Sea were investigated with respect to fish size and season. Stomach contents of 1200 specimens 12.9–37.6 cm total length (TL) taken at monthly intervals (January–December 1995) were analyzed. Of the total number of stomachs examined, 597 were empty (49.7%). This percentage varied significantly with season; the maximum number of empty stomachs was observed during January (80%) and February (82%) and a minimum number observed during July (15%) and August (19%). A total of 30 different prey species belonging to five major groups: Crustacea (Euphausiacea, Mysidacea, Decapoda), Cephalopoda, and Teleostei was identified in the stomach contents. Euphausiids were the most important ingested prey in all seasons as well as in small‐ and medium‐size classes (<28 cm TL). Two species of euphausiids, Nyctiphanes couchii (%IRI = 36.0) and Euphausia krohni (%IRI = 12.9), were the most frequent prey. The proportion of teleosts in stomach contents increased with the increasing size class of horse mackerel and was 15.5% IRI in >30 cm TL individuals. The mean weight of stomach contents increased significantly for fish larger than 24.1 cm TL, while the mean number of prey items significantly declined in the large‐size classes.     

Food habits of wolvesCanis lupus in Latvia

Diet of wolvesCanis lupus Linnaeus, 1758 in Latvia was studied from 1997 to 2001 based on 302 scats and 107 stomachs. Wild ungulates (cervids and wild boarSus scrofa) and beaverCastor fiber were the dominant prey. Cervids were found in 50% of samples (62% biomass), wild boar in 25% (21% biomass), beavers in 14% (12% biomass). Wolves selected for wild boar, especially in winter when its ratio in the diet increased to 34% from 20% in summer. It was a more common prey species in the east of the country. The ratio of beavers, small rodents and plant food was higher in summer, which resulted in a broader food niche in summer than in winter (B = 2.53 versus 1.81, respectively). The role of domestic animals in the wolf diet was minimal except for winter when they were consumed as carrion (13%). More than 1/3of all stomachs investigated were empty. The average weight of stomach contents was 972.8 g. The importance of the beaver as an alternative prey is discussed. We conclude that wolves in Latvia prey mainly on wild animals and conflicts with livestock owners are only occasional and/or local.     

Food and growth of arctic char, Salvelinus alpinus (L.), in the Cumberland Sound area of Baffin Island

Arctic char, Salvelinus alpinus (L.), captured during the summer, 1972, in Cumberland Sound, Baffin Island, fed mainly on planktonic amphipods (Parathemisto libellula, Pseudalibrotus glacialis), copepods (Calanus hyperboreus), and fish (Boreogadus saida, Myoxocephalus sp.), but failed to utilize coelenterates, planktonic gastropods, and epi- and infauna. The considerable variation in the species composition of the diet of char of different lengths was due primarily to size selection. The average length of all individuals in stomach contents and of representatives of most food species increased with the length of fish. The minimum and maximum length of frequently ingested organisms increased four and 90 times, respectively, as char increased from 4 to 85 cm. Char less than 10 cm in length captured in rivers tributary to the Sound fed mainly on larval Chironomidae (Eukiefferiella bavaria) during the summer, whereas those longer than 10 cm fed predominantly on other char. During the winter the stomachs of the smaller individuals were always empty while the diet of the large char was restricted to other fish. Most species available to the char were consumed in proportion to their relative abundance in the rivers. The dry weight of stomach contents, when expressed on a unit weight basis, decreased with the wet weight of char in both fresh and salt water. Thus, fish 10 g in weight contained approximately 1.5 times more food in their stomachs than those weighing 1000 g. The stomach contents of char captured in salt water weighed approximately 11 times more than those of char of comparable size captured simultaneously in fresh water. The fish fed at random intervals during the day and ceased feeding at night. Arctic char, at all sampling areas, had reached a length of approximately 9.6 cm after four years. Upon migrating to salt water, their growth rate increased sharply with the result that after eight years they were 26.5 cm in length, reflecting food availability. The growth rate gradually decreased in fish older than nine years so that 20 year olds were approximately 70.0 cm in length.     

Growth and food consumption of 0+ Arctic charr fed pelleted or natural food at six different temperatures

The effects of temperature and diet on the specific growth rate and food consumption of 1-summer-old Arctic charr Salvelinus alpinus were studied. Fish were reared singly in aquaria at six different constant temperatures (5, 9, 13, 16, 18 and 20°C). They were fed Neomysis integer or commercial pelleted food for 2 weeks and growth and food consumption were measured. In both experiments, growth rate increased to an optimum at 15°C. Growth rates were high in the range 13–18°C, with no significant ( P >0·05) differences between temperatures. No significant ( P> 0·05) differences in growth were found between fish at 9 and 20°C. There were no effects of diet on size-adjusted growth rates. The growth efficiency decreased with increasing temperature in both treatments, but the decrease was faster in the Neomysis treatment. Charr seemed to compensate for the high water content (79·5%) of Neomysis by having a higher food intake.     

Occurrence of stones, sediment and fish scales in stomach contents of demersal fish of the Rockall Trough

The occurrence of stones, sediment and fish scales was determined among the stomach contents of some 5000 fish. These fish comprised representatives of more than 70 different demersal species, sampled at 250 m bathymetric intervals, from the Rockall Trough, northeastern Atlantic Ocean, at depths ranging from 500 to 2900 m. Stones only occurred in stomachs of fish caught at 500–1000 m depth, their incidence in stomachs with food present being 4.6% at 500m, 1.1% at 750 m and 1.3% at 1000m depth. Sediment occurred in 9%, fish scales in 7%, of stomachs with contents. Sediment and scales co-occurred in the stomachs of primarily benthopelagic feeding fish. The sediment, however, was associated with the less dominant epibenthic components of the diets while the scales occurred with the more common benthopelagic components. The co-occurrence of sediment, scales and benthopelagic prey may arise through the former items having longer residence times in the stomachs than, for example, epibenthic prey. There is no evidence of increased occurrence of sediment (and its associated meiofauna) in the diets of fish on the lower slope at depths of 1500–2900 m in the Rockall Trough.     

The feeding strategy of dab Limanda limanda in the southern North Sea: linking stomach contents to prey availability in the environment

The feeding strategy of dab Limanda limanda was investigated within a predefined research area in the southern North Sea for 2 years. The aims were: 1) to establish the relationship between prey availability and dab abundance, distribution, body condition and prey selection, and 2) to determine the underlying functional processes of prey choice in dab. Temporal and spatial trends of prey availability in relation to dab abundances, distribution, condition and prey selection were analysed. Temporal trends in dab condition, percentage of empty stomachs and numbers of ingested prey were apparent. In particular in the winter period 2000–2001 dab were in poor condition and prey items were only rarely found in stomachs. Similarly prey availability decreased in the environment while the abundance of dab increased. Thus, temporal changes in the nutritive state were partly thought to be attributed to density‐dependent effects. The stomach composition of dab during the two consecutive summers was mainly dominated by Pariambus typicus and Ophiura albida while in the winter period only O. albida made a significant contribution to the stomach content. Analysis of prey characteristics indicated that only prey densities in the environment significantly influenced prey choice in dab, while other characteristics such as the position of the prey in the habitat, its palatability or mobility did not have significant effects. The feeding strategy of dab thus was highly opportunistic, although trends were apparent that suggested that buried living fauna was less likely to be ingested, which was also observed in previous studies.     

Diet of Atlantic cod in the southern Gulf of St Lawrence as an index of ecosystem change, 1959–2000

Major temporal changes in the importance of euphausiids and Atlantic herring Clupea harengus in the diet of Atlantic cod Gadus morhua , 10–75 cm L _F, occurred in shallow waters (<100 m depths) of the southern Gulf of St Lawrence between 1959 and 2000. Euphausiids represented 6–70% of prey mass for Atlantic cod 31–60 cm L _F from 1959 to 1987 but only trace amounts were detected in stomachs collected from 1990 to 2000. Mysids and gammarid amphipods (for Atlantic cod ≤45 cm L _F), and Atlantic herring (for Atlantic cod >45 cm L _F) largely replaced euphausiids in the Atlantic cod diets from 1990 to 2000. This diet change suggested there has been a major perturbation of the food web of the southern Gulf of St Lawrence. The importance of fishes (mostly Atlantic herring) in the diet of Atlantic cod >45 cm L _F increased significantly between the periods 1959–1980 and 1987–2000. Atlantic herring comprised 0–4% (mean 1.3%) of prey mass of Atlantic cod 46–60 cm L _F from 1959 to 1980 and increased to 2–42% (mean 19.6%) of the diet from 1987 to 2000. Atlantic herring comprised 0–25% (mean 9.4%) of the prey mass of Atlantic cod 61–75 cm L _F from 1959 to 1980 and increased to 42–81% (mean 54.2%) of prey mass from 1987 to 2000. This increased consumption of Atlantic herring was consistent with observed changes in abundance of Atlantic herring in the ecosystem between the late 1970s and 2000. The large changes in consumption of euphausiids and Atlantic herring represent highly significant changes and would need to be included in the development and interpretation of ecosystem-based management models for this ecosystem.     

Increasing turbidity significantly alters the diet of brown trout: a multi‐year longitudinal study

The stomach contents of adult brown trout Salmo trutta from Lake Sorell, Tasmania, were analysed during 6 years of increasing turbidity to follow changes in the diet associated with dramatic changes in water clarity. Brown trout were sampled from 1996, when turbidity was 26 NTU, to 2001 when turbidity was 141 NTU. The mean relative volume of stomach contents decreased progressively to 2001, by which time it was only one sixth of that in 1996, and the mean diversity of prey in stomachs decreased from an average of more than six species per stomach in 1996 to one species in 2001. The species composition of stomach contents shifted from domination by the phreatoicid isopod Colubotelson sp., to the galaxiid fish Galaxias auratus and the amphipod Austrochiltonia australis , and then the cladoceran Daphnia carinata . To give an indication of diet changes over a typical yearly cycle in the current turbid state of the lake, a sample was taken from each season from December 2000 to September 2001. Two basic diets were found during the year; brown trout specialized on D. carinata in summer and autumn, and G. auratus in winter and spring. Mean diversity of prey was less than two species per stomach in all samples from 2000 to 2001, except for the sample from spring 2001 when it was 2·2 species per stomach, and the mean relative volume of stomach contents was more than three times greater in winter than any other season. The ways in which high turbidity may have influenced the changes in the brown trout diet observed since 1996 and the patterns evident during the seasons of 2000–2001 are discussed.     

Diet of the Worm Lizard,Diplometopon zarudnyi (Nikolsky, 1907), in Riyadh province,Saudi Arabia (Reptilia: Trogonophidae)

We analysed the diet composition of 133 specimens of the Worm Lizard, Diplometopon zarudnyi, in Riyadh province, Saudi Arabia. Analysis of stomach contents revealed that 90 specimens (66.6%) had prey items in their gut. The stomach content consisted mainly of small invertebrate prey (beetles), mainly larvae of Dermestes sp., but also imagines of Dermestes maculatus and Rhynchophorus ferrugineus. Dermestes sp. constitutes over 99% of the total food items, showing a high selectivity in food intake. The high number of beetles in the stomach contents indicates that this lizard forages very frequently. Specimens collected during winter had empty stomachs. The high proportion of fossorial prey items and the occasional records of other stomach contents show that D. zarudnyi only occasionally forages on the surface.     

Feeding Habits of Four Species of Istiophoridae (Pisces: Perciformes) from Northeastern Brazil

Billfishes from the Brazilian oceanic northeastern region feed on a large food spectrum composed mainly of epipelagic species of fish and cephalopods, with occasional occurrences of mesopelagic organisms and crustaceans. The oceanic pomfret, Brama brama, and the squid, Ornithoteuthis antillarum, were the main prey items in the diet of the four species, occurring in at least 50% of the stomachs containing food. There was no correlation between body length of prey and predator, or between mass of stomach content and body mass in the individuals from 100 to 330cm fork length. The feeding of the four species was characterized by constant ingestion of small quantities of food, and constant presence of food in the stomachs, with a predominance of epipelagic organisms of small sizes with an average of 8.0cm. The reduced stomach size forces the predators to feed constantly on several meals during the day, and consequently provide constant energy for migration.     

Food capture, appetite, digestion rate and efficiency in hatchling and juvenile Crocodylus porosus

Juvenile estuarine crocodiles captured insects and crabs at or above the water surface by leaps and lunges powered by the hind limbs and tail. The mouth opened as the head cleared the water; most prey were held by sidesnaps of the jaws. Such prey capture was accurate, deliberate and preceded by stalking. In contrast, submerged prey (e.g. prawns) appeared to be detected mainly by touch and detection was followed by undirected, inaccurate 'snapping frenzies' which were usually ineffective. Small prey items were swallowed whole under water. Large dense prey (e.g. crabs) were handled and swallowed on land or in very shallow water; large less dense prey (e.g. cockroaches) were swallowed during vigorous water-treading in deep water, the head being maintained above the water surface.
Young crocodiles ate satiation meals of 9–10% body weight (on a fresh food weight basis) at 30°C, and appetite returned over about 40 h as the stomach emptied. Total gut clearance time for a meal was 4–5 d. Evidence was obtained which demonstrated that young Crocodylus porosus Schneider deliberately eat gastroliths from an early stage. Such gastroliths are retained within the stomach (as were barium/polystyrene spheroids of 1 mm diameter) presumably by the action of the well-developed pyloric sphincter. X-radiographs demonstrated that gastroliths are dispersed throughout the stomach contents after a meal and presumably aid digestion.
Assimilation rates for dry mass (77.5%), energy (85.2%) and protein-N (97.4%) were high in normal juveniles. Animals exhibiting 'runt syndrome' showed strong appetite but slow food processing by the gut, together with poor assimilation, especially of protein (35.7%).     

Feeding ecology of Oreochromis niloticus (Linnaeus) & Tilapia Zillii (Gervias) in a Nile canal

Fish stomachs, 1149 for Tilapia zillii and 1698 for Oreochromis niloticus, were collected from April 1984 till April 1985 from a Nile canal in the Egyptian delta. Both species showed a significant overlap of diet (Schoener's index) among individuals ranging from 12 to 17.9 cm standard length. Outside this range differences in the importance of food of animal origin occurred. Macrophytes were the main food of O. niloticus and aquatic insects of the food of T. zillii. This initial diet overlap may have contributed to irregularity in the increase of full stomachs with increasing length, and to a decline of the stomach index (SI = stomach weight × 100/fish weight) with increase in length in O. niloticus. The stomach of either species correlated significantly with water temperature, but with daily photoperiod in O. niloticus only.     

Comparison of growth, diet and food consumption of sea-run and lake-dwelling Arctic charr

Sea-run post-smolt Arctic charr Salvelinus alpinus , (15–26 cm) from Storvatn, northern Norway (70°39'48"N) had significantly higher average specific growth rates in two years (1·64 and 1·66) than the corresponding lake-dwelling charr (0·53 and 1·20). The post-smolts displayed fast compensatory growth in the first 2–3 weeks of their sea residency, but then almost stopped growing prior to their return to fresh water. Lake-dwelling charr grew more evenly during the same time period. Thus, the anadromous charr may return to the lake after only 5–6 weeks in the sea, because the potential to maintain a high growth rate in the sea is reduced. The marine diet consisted mainly of the two crustacean plankton species Calanus finmarchicus , and Thysanoëssa , sp. (88%), and less of fish (6%), insects (4%) and benthos (2%). The diet of lake-dwelling charr consisted mainly of insects (58%, mostly chironomid pupae) and zoobenthos (29%), and less of zooplankton (13%) during the same time period. Although post-smolts had the highest growth rates, they had significantly lower food consumption rates and higher frequencies of empty stomachs than the corresponding lake-dwelling fish. Possible explanations for this paradox are discussed in relation to stomach evacuation rates, water temperature, feeding behaviour and the energy content of the food in the two environments.