The predation of mysids by fish of the Rockall Trough,northeastern Atlantic Ocean

The stomach contents of representatives of approximately 100 species of pelagic and demersal fish caught in the Rockall Trough, northeastern Atlantic ocean, have been examined for the occurrence of mysids. More than 40 species of fish included mysids in their diets. The majority of the 21 species of mysids identified in the stomachs live in close association with the sediment and are rarely caught in pelagic nets. Mysids contributed significantly to the diets of many demersal fish but were not apparently important constituents of the food of pelagic fish.     

Food and feeding of three Citharinus species in Lake Kainji, Nigeria

This paper provides information on the food and feeding habits of three Citharinus species in Lake Kainji. A total number of 2357 specimens made up of 1628 Citharinus citharus , 705 C. distichodoides and 24 C, latus were examined. The majority of the fish caught by gill-netting had empty stomachs unlike those caught by cast-netting and electrofishing. The main food items were planktonic and epipelic blue-green and green algae. All the three species had similar feeding habits and also fed on the same items; their food varied with the seasons. Citharinus spp. have high gut length/standard length ratios which are adaptations to the microphagous and planktivorous feeding habits.     

Food of the roughhead grenadier, Macrourus berglax, Lacepede in North Norwegian waters

Over 30 different prey species were found in the stomachs of roughhead grenadiers, Macrourus berglax , caught at depths of approximately 700 m off the coast of northern Norway. Crustaceans and fish were the principal prey categories and large, mature grenadiers are classified as being generalist feeders taking predominantly benthopelagic organisms. There is evidence for an ontogenetic shift in dietary composition, with a change from benthic prey to an increased reliance on benthopelagic prey as the fish increase in size and this results in reduced intraspecific competition for food.     

Diet and feeding of fish from Grande River, located below the Volta Grande Reservoir, MG-SP.

We compare the classic model of feeding of tropical fish by means of six bimonthly samplings using gillnets of varying mesh sizes that were inspected every twelve hours throughout a forty-eight hour period. The stomachs of the fish caught were classified in three categories according to quantity of food found. The amount of fat in the visceral cavity with respect to the energetic reserve deposition was also studied. The relative frequencies of the different categories of stomach repletion and fat deposition were examined for patterns of feeding seasonality. The stomachs considered full were examined to record diet composition. To assess the relative importance of the different food resources, we applied Feeding Importance Degree (FID), which is a useful index when difficulties exist in determining a common basis for volume, number, or weight of a given food item in different species, a common problem when dealing with fish species having different feeding habits. The fish species whose stomach contents were analyzed using the FID index were Serrasalmus spilopleura (Characidae), L. prolixa (Loricaridae), Schizodon nasutus (Anostomidae), and Pimelodus maculatus (Pimelodidae). Our findings indicate some contrasting elements, in dietary composition in relation to the classic model for tropical rivers. These factors include the importance of aquatic macrophytes, the lack of piscivorous species, and a lesser presence of allochthonous vegetation in the diet of the species studied.     

The stomach contents of Patagonian toothfish around South Georgia (South Atlantic)

The proportion of Patagonian toothfish Dissostichus eleginoides , caught around South Georgia in the south-west Atlantic, with empty stomachs was much lower in fish caught in pots compared to longlines (28 and 91%, respectively, of examined individuals). It is hypothesized that pots caused reduced levels of stress on capture. Stomach content data examined from pot-caught fish will probably therefore be more comprehensive than that from fish caught using longlines. A wide range of prey items was identified in the stomachs of D. eleginoides and stomach contents of individuals caught using the two fishing methods were significantly different. The most common prey item for D. eleginoides caught using pots was the decapod prawn Nauticaris sp., which was restricted in location and depth. However, prawns were not common in the stomachs of D. eleginoides caught from the same location using longlines. Stomach contents from the two fishing methods remained significantly different when Nauticaris sp. were eliminated from the assessment, although fishes then dominated the diet of D. eleginoides caught using either fishing gear. The study confirms that D. eleginoides is an opportunistic carnivore, and indicates that feeding habits depend on the local availability of food items, as well as factors such as depth and predator size. The potential ecological impacts of fishing for D. eleginoides on the South Atlantic ecosystem are discussed.     

The food of Charr,*Salvelinus willughbii (Günther), in Windermere

The stomach contents of 1015 charr, (Salvelinus willughbii Günther)] from Windermere, of which 658 were feeding fish, were examined. The fish were caught over a period of several years and in every month of the year. The data were analysed by two methods, by a points system, which takes into account the abundance and volume of the food organisms, and by the frequency of occurrence of each organism. Charr of all sizes had fed mainly on planktonic Crustacea (particularly Cladocera); larval and pupal chironomids and Chaoborus were also important. From November to April most stomachs of charr netted on the spawning grounds contained charr eggs. The diet of charr is compared with that of seven other fish species in Windermere. There was almost no overlap between the food of charr, which was obtained in the pelagic region, and that of the seven other species, which was mostly bottom fauna, obtained from the littoral region. Thus by occupation of these two different niches the charr and the seven other fish in no way compete for food in Windermere. Some limited data from six other lakes in the English Lake District are presented, in these planktonic Crustacea are also found to be the main food.     

Food and feeding habits of Ilisha africana (Bloch) (Pisces: Clupeidae) off the Lagos coast, Nigeria

A total of 2215 specimens of Ilisha africana (Bloch) were examined for the food habits of the species off the Lagos coast, Nigeria. Their food consisted mainly of crustaceans, fish and molluscs; less important in the stomach contents were insects, annelids, chaetognaths, coelenterates, urochordates and phytoplankton. The incidence of nematodes in the stomachs was low. Monthly variation of food as well as variation with fish size and water depth were examined, as was the relationship of food composition to components of the plankton fauna. Feeding habits of I. africana were compared with those Sardinella maderensis (Lowe), Galeoides decadatylus (Bloch), Brachydeuterus auritus (Val.) and Vomer setapinnis (Mitchill); there was an overall diversity in the diets of these fish species.     

Diet of post-smolt and one-sea-winter Atlantic salmon in the Bothnian Sea, Northern Baltic

Until July, post-smolt salmon Salmo salar ( n =337; 129–375 mm L _T, mean 225 mm) in the Bothnian Sea relied largely on surface fauna (mainly terrestrial insects). From August onwards, fish was the principal food type. The smallest piscivorous post-smolts were <200 mm, but the main shift to piscivory occurred at sizes of 240–320 mm. Piscivory was promoted by a large smolt size. Almost all one-sea-winter (1-SW) salmon ( n =316; 278–524 mm, mean 397 mm) were piscivorous. Over 70% of the post-smolt and 96% of the 1-SW salmon with identifiable fish species in their stomachs had preyed on herring Clupea harengus. Other fish prey included the ten-spined Pungitius pungitius and three-spined sticklebacks Gasterosteusaculeatus but no sprats Sprattus sprattus. The results support earlier observations of a close relationship between recruitment of herring and production of salmon in the Bothnian Sea, and of the crucial role of smolt size in determining the ability of feeding salmon for utilizing the food resources of the area.     

The diet of Brycinus nurse (Pisces: Characidae) from Asa reservoir,Ilorin, Nigeria

From November 1991 to October 1993, 980 specimens of the characid Brycinus nurse were collected from Asa reservoir to examine its diet. The diet was analyzed using the frequency of occurrence, numerical and gravimetric methods. Two hundred and sixty nine (27.45%) of the stomachs examined were empty. The fish was an omnivore feeding extensively on a wide array of plant and animal food items. These consisted of 9 families, 10 genera and 10 species. The most extensively consumed plant food item was aquatic plant parts which occurred in 63.88% of the stomachs, and accounted for 6.06% by number and 12.10% by weight while the ephemeropteran, Povilla adusta was the most dominant animal food item, occurring in 50.92% of the stomachs, and accounting for 11.98% by number and 11.86% by weight. Conversely, the least consumed plant food item was Volvox occurring in 4.49% of the stomachs and accounting for 0.18% by number and 0.35% by weight, while the fish Barbus sp. was the least consumed animal food item occurring in 0.51% of the stomachs, accounting for 0.03% by number and 1.62% by weight. New food items not previously recorded such as a watermite. Aspatharia sinuata and Barbus callipterus were found in the stomach contents. The nonspecific feeding regime of the fish and its ability to utilize different food items effectively was what accounted for the prominence and wide distribution of the fish in the lake.     

Temporal variation in chum salmon, Oncorhynchus keta, diets in the central Bering Sea in summer and early autumn

Seasonal, ontogenetic, and diel variations in the diets of chum salmon, Oncorhynchus keta, were examined by analyzing the stomach contents of 1398 fish (300–755 mm fork length) collected in the Bering Sea during summer and early autumn of 2002. Whereas mesozooplankton, including euphausiids, hyperiids, and gastropods, constituted the greatest portion of the stomach contents during the summer, forage fishes (Stenobrachius leucopsarus and Atka mackerel, Pleurogrammus monopterygius) were the most important items during early autumn. Although no apparent diel trend was found in feeding intensity, distinct diel differences in prey composition were observed. Chum salmon caught in the morning contained Stenobrachius leucopsarus, whereas those caught in the afternoon had mainly fed on euphausiids. Thus, chum salmon diets change temporally because of changes in prey availability that result from differences in the annual life cycles and diurnal vertical migrations of prey species.     

Warming Ocean Conditions Relate to Increased Trophic Requirements of Threatened and Endangered Salmon

The trophic habits, size and condition of yearling Chinook salmon (Oncorhynchus tshawytscha) caught early in their marine residence were examined during 19 survey years (1981–1985; 1998–2011). Juvenile salmon consumed distinct highly piscivorous diets in cold and warm ocean regimes with major differences between ocean regimes driven by changes in consumption of juvenile rockfishes, followed by several other fish prey, adult euphausiids and decapod larvae. Notable, Chinook salmon consumed 30% more food in the warm versus cold ocean regime in both May and June. Additionally, there were about 30% fewer empty stomachs in the warm ocean regime in May, and 10% fewer in warm June periods. The total prey energy density consumed during the warmer ocean regime was also significantly higher than in cold. Chinook salmon had lower condition factor and were smaller in fork length during the warm ocean regime, and were longer and heavier for their size during the cold ocean regime. The significant increase in foraging during the warm ocean regime occurred concurrently with lower available prey biomass. Adult return rates of juvenile Chinook salmon that entered the ocean during a warm ocean regime were lower. Notably, our long term data set contradicts the long held assertion that juvenile salmon eat less in a warm ocean regime when low growth and survival is observed, and when available prey are reduced. Comparing diet changes between decades under variable ocean conditions may assist us in understanding the effects of projected warming ocean regimes on juvenile Chinook salmon and their survival in the ocean environment. Bioenergetically, the salmon appear to require more food resources during warm ocean regimes.     

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.     

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 diet of blue whiting, hake, horse mackerel and mackerel off Portugal

This paper deals with the diets of blue whiting Micromesistius poutassou (Risso 1810), hake Merluccius merluccius (L. 1758), horse mackerel Trachurus trachurus (L. 1758), and mackerel Scomber scombrus (L. 1758) off Portugal and explores variations in fish length, water depth, latitude and season. All four species feed on fish; however, hake and mackerel are the first and second most important predators, respectively, blue whiting being the most important fish prey for both species. The diets of blue whiting and horse mackerel are composed mainly of crustaceans. Diet variations according to predator fish size are more important than either latitude or depth. In the diets of blue whiting, hake and horse mackerel, prey importance increases with predator size. For blue whiting and horse mackerel, diet variations with fish length and water depth are correlated: small fish are closely associated with coastal areas where they feed on copepods and decapod larvae. Seasonality in the diet is apparent for blue whiting, hake and mackerel. For blue whiting, the decapod Pasiphaea sivado is the most important prey in summer and autumn, being replaced by the euphausid Meganyctiphanes norvegica in winter. In the diet of hake, seasonality was characterised by the major importance of Macroramphosus scolopax in autumn, whereas the diet of mackerel consisted of zooplankton in summer, fish and decapods in autumn and decapod larvae in winter. Seasonal changes in the diet of horse mackerel correspond to a higher diversity of prey in autumn compared to other seasons (although euphausids are the main prey in all seasons). Seasonality in feeding activity is not as marked for the other species as it is for horse mackerel; the percentage of empty stomachs of horse mackerel is greatest in winter, when spawning takes place at the Portuguese coast.     

Feeding and prey-selection of wild Atlantic salmon post-smolts

The diet of post-smolt Atlantic salmon Salmo salar caught in the Trondheimsfjord and Frohavet in central Norway, based on stomach contents analysis, showed a gradual change during migration from the river to the estuary, fjord and coastal areas. Post-smolts caught in the estuary had eaten intertidal gammarid amphipods, while post-smolts caught further seawards preyed upon available marine prey such as Calanus spp., adult euphausiids and fish larvae. The frequency of adult insects was high in all post-smolt stomachs. The gradual change in diet suggested that feeding conditions in the early marine phase were important for post-smolt survival and growth. With the exception of the copepods, there was no overall similarity between species composition of the plankton samples and the stomach contents. Although the hypothesis that the post-smolts are opportunistic feeders cannot be rejected, the composition of the stomach contents suggests a possible selectivity of advantageous prey.     

The seasonal trophic link between Great Cormorant <Emphasis Type="Italic">Phalacrocorax carbo</Emphasis> and ayu <Emphasis Type="Italic">Plecoglossus altivelis altivelis</Emphasis> reared for mass release

The feeding ecology of Great Cormorants (Phalacrocorax carbo) during the breeding season in the Kano River basin, central Japan, was examined to clarify the trophic relationship between the cormorants and ayu (Plecoglossus altivelis altivelis) reared for mass release in the river. The ayu was most frequently found in stomachs of cormorants culled during the breeding season, despite relatively poor catch in the year-round fish fauna research in the watershed. Carbon and nitrogen stable isotope ratios of some ayu individuals extracted from the stomachs of the culled cormorants were similar to the isotopic values of ayu caught in the watershed, whereas the other stomach-content ayu showed peculiarly high nitrogen isotopic values, clearly distinct from the values of the ayu caught in the watershed, and overlapped with the values of mass-release ayu. Furthermore, isotopic values of past diets inferred by the isotope analysis of livers of the culled cormorants were closer to the values of the mass-release ayu, relative to the past diet values inferred by the analysis of the cormorant muscles. This suggests that the food supply from the mass-release ayu had increased in the breeding season, since the isotopic turnover rate is faster in livers than in muscles. The huge number of formula-fed ayu released in the watershed create an anthropogenic food chain which is assumed to significantly support the breeding of the cormorants.     

Diets of sympatric flatfishes, Hippoglossoides platessoides, Pleuronectes ferrugineus, Pleuronectes americanus, from Sable Island Bank, Canada

Prey exploitation was documented for Hippoglossoides platessoides, Pleuronectes ferrugineus , and P. americanus collected from southeast Sable Island Bank in February and June 1989. Diets varied significantly by sample and with fish species and length. Of 239 species consumed by flatfishes, 66 were determined to be principal prey. Crustaceans, particularly amphipods, were the most frequently exploited prey of all three flatfish species. Small H. platessoides fed on suprabenthic fauna, while larger fish exploited epifauna and hyperiid suprafauna. P. ferrugineus exploited epibenthic fauna, consuming crustaceans and tunicates when small and polychaetes when larger. P. americanus preyed on epifauna; smaller fish exploited polychaetes while larger fish usually consumed crustaceans associated with ectoproct colonies. Feeding intensity was dramatically lower in February, food being found in stomachs of only 36% of H. platessoides and 49% of P. ferrugineus , and lacking in the stomachs of P. americanus . In June, stomachs of 86% of H. platessoides , 94% of P. ferrugineus and 96% of P. americanus contained food. Results indicate that prey resources for the three flatfish species are partitioned by specific habitat and prey type preferences.     

Resource seasonality and fish diets in an Illinois stream

Synopsis The purpose of this study was to evaluate the intensity of competition for food among 9 species of stream fishes that primarily eat aquatic invertebrates. The taxonomic and size composition, and numerical abundance of aquatic invertebrates were monitored for one year using drift and benthic samples. Diet data were obtained from stomachs of fishes captured at the same time and place that invertebrate sampling was done. Diet characteristics examined included taxonomic and size composition, number of prey per fish, and diet breadth. Drifting invertebrates were more abundant early in the year (March–June) than later (July–January). The summer-early fall scarcity of invertebrates was especially notable among those>3.6 mm long, which comprised the bulk of prey found in fish stomachs. Average prey size eaten by a fish species was positively correlated with fish mouth size, but interspecific overlap in prey size was extensive. Cyprinids as a group (5 species) ate proportionally fewer small (< 3.6 mm long) prey from July to January than did the centrarchids and stonecat. Taxonomic compositions of available invertebrates and fish diets varied markedly among sampling dates, but the use of prey taxa by fishes was not correlated with the availability of those taxa. Use of aquatic prey taxa was generally similar among fish species, but cyprinids as a group ate proportionally more terrestrial prey from July to January than did the centrarchids and stonecat. Diet breadths for all species increased as food levels declined, indicating that these fishes experienced resource depression. Food scarcity was evidently more severe for cyprinids since their stomachs contained few prey through the summer and fall relative to the centrarchids and stonecat. Though the fish species studied probably compete for food in the summer and fall, this competition did not account for the community structure observed.     

Factors that influence the cutaneous synthesis and dietary sources of vitamin D

The major sources of vitamin D for most humans are casual exposure of the skin to solar ultraviolet B (UVB; 290-315 nm) radiation and from dietary intake. The cutaneous synthesis of vitamin D is a function of skin pigmentation and of the solar zenith angle which depends on latitude, season, and time of day. In order to mimic the natural environment of skin to sunlight exposure, we therefore measured serum 25-hydroxyvitamin D levels in volunteers with different skin types following repeated UV irradiation. Because melanin pigment in human skin competes for and absorbs the UVB photons responsible for the photolysis of 7-dehydrocholesterol to previtamin D3, we also studied the effect of skin pigmentation on previtamin D3 production in a human skin model by exposing type II and type V skin samples to noon sunlight in June when the solar zenith angle is most acute. Vitamin D is rare in food. Among the vitamin D-rich food, oily fish are considered to be one of the best sources. Therefore, we analyzed the vitamin D content in several commonly consumed oily and non-oily fish. The data showed that farmed salmon had a mean content of vitamin D that was approximately 25% of the mean content found in wild caught salmon from Alaska, and that vitamin D2 was found in farmed salmon, but not in wild caught salmon. The results provide useful global guidelines for obtaining sufficient vitamin D3 by cutaneous synthesis and from dietary intake to prevent vitamin D deficiency and its health consequences, ensuing illness, especially, bone fractures in the elderly.