Composition Of Stomach Contents Research Articles

Body size mediates trophic interaction strength of novel fish assemblages under climate change.

Ecological similarity plays an important role in biotic interactions. Increased body size similarity of competing species, for example, increases the strength of their biotic interactions. Body sizes of many exothermic species are forecast to be altered under global warming, mediating shifts in existing trophic interactions among species, in particular for species with different thermal niches. Temperate rocky reefs along the southeast coast of Australia are located in a climate warming hotspot and now house a mixture of temperate native fish species and poleward range-extending tropical fishes (vagrants), creating novel species assemblages. Here, we studied the relationship between body size similarity and trophic overlap between individual temperate native and tropical vagrant fishes. Dietary niche overlap between vagrant and native fish species increased as their body sizes converged, based on both stomach content composition (short-term diet), stable isotope analyses (integrated long-term diet) and similarity in consumed prey sizes. We conclude that the warming-induced faster growth rates of tropical range-extending fish species at their cool water ranges will continue to converge their body size towards and strengthen their degree of trophic interactions and dietary overlap with co-occurring native temperate species under increasing ocean warming. The strengthening of these novel competitive interactions is likely to drive changes to temperate food web structures and reshuffle existing species community structures.

Historical trophic ecology of some divergent shark and skate species in the Dutch coastal North Sea zone

Over the last century the fish community of the Dutch coastal North Sea zone has lost most its shark and skate species. Whether their disappearance has changed the trophic structure of these shallow waters has not been properly investigated. In this study historical dietary data of sharks and skates, being in the past (near)-residents, juvenile marine migrants and marine seasonal visitors of the Dutch coastal North Sea zone were analyzed for the period 1946–1954. Near-resident and juvenile marine migrant species were demersal while all marine seasonal visitors species were pelagic. Based on stomach content composition, the trophic position of four of the various shark and skate species could be reconstructed. The (near)-resident species, the lesser spotted dogfish, the marine juvenile migrant, the starry smooth hound, and the benthopelagic marine seasonal visitor, the thornback ray, had a benthic/demersal diet (polychaetes, molluscs and crustaceans), while the pelagic marine seasonal visitor, the tope shark, fed dominantly on cephalopods and fishes. Diet overlap occurred for fish (tope shark and lesser spotted dogfish), for hermit crabs (lesser spotted dogfish and starry smooth hound) and for shrimps (thornback ray and starry smooth hound). Trophic position ranged from 3.2 for thornback ray preying exclusively on crustaceans to 4.6 for the tope shark consuming higher trophic prey (crustaceans and fish). The analysis indicates that most of the shark and skate species were generalist predators. The calculated trophic positions of shark and skate species indicate that those species were not necessarily at the top of the marine ecosystem food web, but they might have been the top predators of their particular ecological assemblage.

Importance of non‐native isopods and other terrestrial prey resources to steelhead/rainbow trout Oncorhynchus mykiss in coastal streams in Big Sur, California

AbstractTerrestrial invertebrates provide important prey subsidies to many stream fishes. Non‐native invertebrates are widespread in many ecosystems, yet they have received little attention in studies of subsidies to stream food webs. We sampled coastal basins in Big Sur, California, to determine the importance of non‐native isopods and other terrestrial invertebrates in the summer diet of steelhead/rainbow trout (Oncorhynchus mykiss) and to estimate the density of isopods along streambanks. Terrestrial invertebrates contributed more than 40% of the energetic value of O. mykiss stomach contents at most sites and up to 75% at some locations. Non‐native isopods Armadillidium vulgare or Porcellio scaber occurred at all sites, reaching mean densities of up to 13 individuals/m2 on streambanks, and accounted for up to 20% of the energy in the diet. The proportion of non‐native isopods in the diet was positively correlated with their density at a site, and the frequency and energetic value of terrestrial invertebrates and non‐native isopods in O. mykiss diets increased with fish size. In terms of the broader diet, the energetic value and taxonomic composition of stomach contents varied among sites but there was no major geographic pattern or trend to the variation, and overall O. mykiss diets were generally similar across the region. Our results highlight that non‐native terrestrial invertebrates may provide a considerable but overlooked subsidy to stream fishes.

Trophic structure and resource utilization of the coastal fish community in the western Wadden Sea: evidence from stable isotope data analysis

We studied the trophic structure of the western Wadden Sea fish community through stable isotope analysis (δ13C and δ15N) of 1658 samples from 57 fish species collected between 2012 and 2016. Stable isotope values differed between species but did not vary between years or seasons, and only for some species with fish size. Stable isotope values were not different between immigrating (spring) and emigrating (autumn) fish, suggesting a similar trophic niche of the various fish species in the coastal zone and inside the Wadden Sea. For the majority of species, average δ13C values were within the range of -12 to -20.5‰, showing that both (marine) pelagic and benthic primary producers were at the base of the food web. Average δ15N values varied among species from 13-18‰, resulting in estimated trophic positions (TPs) of 2.1-5.5 with the majority between 2.2 and 3.5. Thick-lipped grey mullet Chelon labrosus, golden grey mullet C. aurata, greater pipefish Syngnathus acus and pilchard Sardina pilchardus had the lowest TP (2.2-2.4). Among the common species (>10 observations), the highest TP values (3.4-3.5) were found for twaite shad Alosa fallax, smelt Osmerus eperlanus, bull-rout Myoxocephalus scorpius, bass Dicentrarchus labrax and cod Gadus morhua. For all species, estimated TPs based on isotope values were lower than those based on stomach content composition (2.0-4.7), which could be explained by species-specific differences in trophic fractionation or by underestimation of the contribution of smaller prey species in the stomach content analysis. The trophic niche space of benthopelagic species was the smallest and overlapped with that of the pelagic and benthic species. In terms of area use, trophic niche space was smaller for juvenile marine migrant species (nursery-type species) and overlapped with that of the (near-)resident species and marine seasonal visitors. Potentially, trophic competition is highest for the functional group of benthopelagic species and the guild of juvenile marine migrant species (nursery-type species).

Diet Composition of Bluefish Pomatomus saltatrix (Linnaeus, 1766) in the Sea of Marmara

In this study, diet composition of bluefish Pomatomus saltatrix (Linnaeus, 1766) was investigated. A total of 512 bluefish samples were monthly collected from commercial fishing boats operating in the Sea of Marmara between January and December 2014. It was determined that the total length distribution of the samples varied between 12.3-47.3 cm. 367 of them (71.67%) were found to be the full of the stomach. The nutritional composition of stomach contents only two main prey groups (teleostei and crustacean) were identified. In evaluation, relative importance indexes (IRI) food groups were calculated. According to the relative importance index (IRI=91.8%) anchovy (Engraulis encrasicolus) has been found to be the most preferred food group. The number of individuals whose stomachs were found to be full was low in the winter months; it started to rise with spring and reached the highest level in the autumn months. It was determined that the increase in the total number of stomachs occurred between August and October in relation to the reproductive period. It was found that stomach fullness rates significantly relationship between sex and seasons (p<0.01).

Dietary Composition and Trophic Niche Partitioning of Spotty‐bellied Greenlings Hexagrammos agrammus, Fat Greenlings H. otakii, Korean Rockfish Sebastes schlegelii, and Japanese Seaperch Lateolabrax japonicus in the Yellow Sea Revealed by Stomach Content Analysis and Stable Isotope Analysis

AbstractStable nitrogen and carbon isotope ratios of fish tissues, in combination with stomach content analysis, provide insights into how energy flows through marine food webs. Using these techniques, we investigated the diets and trophic niches of four important fish species of the Yellow Sea: the Spotty‐bellied Greenling Hexagrammos agrammus, Fat Greenling H. otakii, Korean Rockfish Sebastes schlegelii, and Japanese Seaperch Lateolabrax japonicus. The stomach content analysis revealed that Spotty‐bellied Greenlings mainly fed on crabs and fish; Fat Greenlings mainly preyed on fish, crabs, and shrimps; Korean Rockfish primarily consumed fish and shrimps; and Japanese Seaperch mainly fed on fish. Korean Rockfish had the highest dietary breadth index among the four fish species. Dietary composition of the four species did not overlap significantly, as indicated by Schoener's index. Prey category composition varied across fish species and differed between species pairs (except Korean Rockfish and Japanese Seaperch), as suggested by permutational ANOVA tests. The stable isotope analysis suggested that Japanese Seaperch had significantly higher δ13C and δ15N and had a significantly different centroid position, both of which indicated a higher trophic position. The corrected standard ellipse area on the δ15N–δ13C (‰) biplot varied in size among species and significantly overlapped in the three rockfishes, with the largest overlap area observed between Fat Greenlings and Korean Rockfish. The results, in general, suggested that the three rockfish species, especially Korean Rockfish and Fat Greenlings, had similar trophic niches, but they were partitioned by prey resources according to the stomach content composition. Our study provides novel insights into the dietary niches and trophic dynamics of these four exploited species, which could help to improve ecosystem‐based fisheries management in the Yellow Sea.

Finless porpoises (Neophocaena asiaeorientalis) in the East China Sea: insights into feeding habits using morphological, molecular, and stable isotopic techniques

Describing feeding habits of cetaceans is crucial to understanding their feeding strategies and conservation status. Here, both morphological and molecular techniques were employed to identify the stomach contents of 122 finless porpoises (Neophocaena spp.) in the East China Sea for insight into their short-term feeding habits, and stable isotopes of δ13C and δ15N were used to analyze prey resource use and trophic position as a manifestation of their long-term feeding habits. In total, 33 prey species consisting of 19 teleosts, seven crustaceans, five cephalopods, and two gastropods were identified. In both short- and long-term analyses, teleosts represented primary prey, cephalopods and crustaceans were secondary prey, and gastropods were occasional prey; but the primary prey species composition differs between the short- and long-term diets. The composition of stomach contents showed sexual and age-related variation. This finding is supported by stable isotopic analyses, which indicated the separation of trophic position of adult males, adult females, and young males. In general, finless porpoises prey on species that are primarily caught by fisheries.

Spatio-temporal variability in the winter diet of larval and juvenile Antarctic krill, Euphausia superba, in ice-covered waters

Antarctic krill Euphausia superba is an ecological key species in the Southern Ocean and a major fisheries resource. The winter survival of age class 0 (AC0) krill is susceptible to changes in the sea-ice environment due to their association with sea ice and their need to feed during their first winter. However, our understanding of their overwintering diet and its variability is limited. We studied the spatio-temporal variability of the diet in 4 cohorts of AC0 krill in the Northern Weddell Sea during late winter 2013 using stomach contents, fatty acids (FAs) and bulk stable isotope analysis (BSIA). Stomach contents were dominated by diatoms in numbers and occasionally contained large volumes of copepods. Many of the prey species found in the stomachs were sea ice-associated. Our results show that the diet of overwintering AC0 krill varies significantly in space and time. Variability in stomach content composition was related to environmental factors, including chlorophyll a concentration, copepod abundance and sea-ice cover. In contrast, FA composition mainly varied between cohorts, indicating variation in the long-term diet. The condition of the AC0 krill was reflected in FA and BSIA analysis, suggesting that the availability of sea ice-derived food sources over a long period may impact the condition of developing AC0 krill significantly. The spatio-temporal availability of sea-ice resources is a potentially important factor for AC0 krill winter survival.

The influence of feeding behaviour on growth of Atlantic cod (Gadus morhua, Linnaeus, 1758) in the North Sea

The objective of this study was to resolve key mechanisms driving individual growth patterns of Atlantic cod (Gadus morhua). Growth dynamics were analysed by linking growth patterns with stomach content composition and environmental temperature. Samples were collected in August/September of the years 2009, 2010 and 2011 in the north-eastern part of the central North Sea. Prey selection was assessed by identification of individual prey items in the stomach content to species. Ten feeding groups were identified consisting of individuals with one prey type dominating their stomach contents (≥75% by mass), of which six were used for growth analyses: “Sandeel”, “Clupeids”, “Norway pout”, “Flatfishes”, “Crustaceans” and “Brittle stars”. For each group, growth patterns were estimated based on measures of otolith growth increments. The stomach contents showed that cod as a species are opportunistic in their prey selection, but at the same time indicated that the total, broad feeding niche width of the population is dominated by individual diet specialization and that many individuals temporally show a preference for a particular prey type. The contribution of invertebrates and particularly crustaceans decreased with increasing cod size, whereas that of fish and predominantly herring increased. Prey type had a significant effect on growth, while temperature had no effect. Slowest growth was observed in the cod group preying on sandeel, while cod preying on Norway pout showed the fastest growth. No significant difference was observed between groups preying on brittle stars, crustaceans, flatfishes and herring. Growth in the year before capture did however not differ between any of these groups. Across sampling years, growth chronology patterns were similar but not significantly influenced by temperature.

Diet and Feeding Habits of the Eurasian Otter (Lutra lutra): Experiences fromPost mortemAnalysis

The diet composition and feeding habits of the Eurasian otter (Lutra lutra) were studied by post mortem examination of individuals (n = 236) found dead in Hungary in order to test the dietary differences between sample types (stomach and rectum), calculation methods and different factors. A relationship was found between the summarized wet weight (W) and occurrence number (O) of food remains detected in the stomach. Otters preyed primarily on small-sized (< 100 g) cyprinids, mainly on non-commercial fish. The composition of stomach contents differed according to different factors: season — in autumn and winter fish were eaten in higher proportions but in spring and summer there were more amphibians; sex — males prey on fish in higher proportions; age group — juveniles consumed invertebrates in higher proportions; and cause of mortality — otters found dead on roads had consumed fish in higher ratios. The composition of rectum content showed a relationship according to the three calculation methods considered (W, O and B — estimated biomass composition). In the otters examined the composition of food items in the stomach (which is the nearest to the actual food ingested) and the rectum content (which relates to the composition in non-invasive collecting spraints) were basically similar.

Studi Komposisi Isi Lambung Dan Kondisi Morfometri Untuk Mengetahui Kebiasaan Makan Ikan Manyung (Arius thalassinus) Yang Diperoleh Di Wilayah Semarang

Manyung fish (Arius thalassinus) is one of the bottom fish (demersal), which has significant economic potential. One of the measures that can be done to preserve the habitat of fish manyung is a rational exploitation. Information on the biological aspects can be provide additional information on the food and feeding habits and the condition of fish manyung morphometry, to gain a better understanding on the survival and growth of fish. The study was conducted to examine the contents of the stomach and the type of food eaten and the condition of morphometry of manyung fish were caught from the waters around Semarang, manyung fish samples obtained from collectors of Semarang in the krobokan. Manyung fish samples taken on July, August, September and October 2011, with total sample of 50 fish. Retrieval of data in this study conducted in the field and in the laboratory by measuring the weight, total length of fish, fish food organisms manyung frequency, and calculate the volume food organisms of fish manyung. Manyung major food fish (Arius thalassinus) by his preponderance index is a kind of fish with a value of 28.7%. Base of composition of stomach contents, types of mouth (sub terminal), the presence of tentacle, and the length of intestines (1,7-2 times length of the body ) can be concluded manyung fish (Arius thalassinus) is omnivores which tend to be carnivores. The results of 50 samples Manyung fish (Arius thalassinus) gained the most long range artifacts in the interval 55-61 cm (23 fish), weight range for most numerous in the interval 1.6 to 2.7 kg (30 fish).

Feeding of twaite shad, Alosa fallax (Lacépède, 1803), during the upstream spawning migration in the River Ulla (NW Spain)

In order to contribute to a better understanding of feeding behaviour of adult twaite shad, Alosa fallax, in freshwater, we studied the stomach content composition of 147 A. fallax during their upstream spawning migration in the River Ulla (Galicia, NW Spain). The diet composition included 34 types of prey, aquatic invertebrates being the most important food. The present study is, to the best of our knowledge, the first record of A. fallax feeding on potamodromous Pseudochondrostoma duriense.

Effect of corn oil and perilla oil intake by rats during pregnancy and lactation on composition of stomach contents and plasma lipids concentration of pups

We studied the effects of corn oil and perilla oil intake by rats during pregnancy and lactation on the composition of the stomach contents and plasma lipids concentration in their pups. Two groups of dams were fed either a corn oil diet (CD) or a perilla oil diet (PD) during their pregnancy and lactation. On days 8, 21 and 33 after birth, two pups each from the litters of all dams were killed and their blood and stomach were collected. A long chain polyunsaturated fatty acid (LCPUFA; C20-22) not presented in the dams diet was detected in the stomach breast milk of both groups. Although the n-3 fatty acids of LCPUFA in the stomach of the PD group was higher than that of the CD group, no significant difference in the arachidonic acid (AA; 20:4) and docosahexaenoic acid (DHA; 22:6) was observed between the two groups. The plasma lipid concentration in the pups of the PD group was lower than that of the CD group, but there was no significant difference in the two groups after weaning. Therefore, α-lindenic acid (ALA; 18:3) in the PD was synthesized into eicosapentaenoic acid (EPA; 20:5) and DHA in the dam's body and added to the breast milk, which indicated that the plasma lipids concentration in the pups nursed by the dams fed the PD decreased during lactation.

Cheliped morphological variation of the intertidal crab Eriphia verrucosa across shores of differing exposure to wave action

Understanding the effects of predator–prey interactions at a community level requires robust information on the mechanisms determining these interactions at the individual level. Here we use the intertidal crab Eriphia verrucosa (Forskål) as a model species to examine patterns of association between functional morphology (cheliped size and form) and patterns of prey consumption on shores of differing exposure to wave action. The size and form of the cheliped of crabs are known to be related to feeding performance and thus influence the outcomes for prey assemblages. Multivariate analyses showed that the claw size and shape of E. verrucosa varied between shores of differing exposure to wave action. Individuals from exposed locations had larger claws than those from sheltered locations. This shift in size was accompanied by differences in the composition of stomach contents between locations. Crabs from exposed shores had ∼ 55% more hard shell prey (mussels and limpets) in their diet than those from sheltered shores. Crabs were more abundant on sheltered shores, but those from exposed locations were larger in carapace width. The relative abundance of prey varied between shores of differing exposure. Patterns of claw functional morphology provided a mechanistic explanation for the differences in prey consumption along the wave exposure gradient, although it remains to be tested whether there is a phenotypic plasticity response of crab claw to patterns of prey consumption. The interaction between prey abundance and morphology of the cheliped will likely shape the diet of this crab species, and this may have implications for the relative impact of this predator between shores of differing exposure.

Effect of Dietary Lard and Fish-oil Intake by Rats during Pregnancy and Lactation on the Composition of Stomach Contents and Plasma Lipid Concentration in Pups

Effect of Dietary Lard and Fish-oil Intake by Rats during Pregnancy and Lactation on the Composition of Stomach Contents and Plasma Lipid Concentration in Pups

Feeding niche segregation among the Northeast Atlantic community of oceanic top predators

In the Northeast Atlantic, off the Bay of Biscay, the pelagic top predator community is mainly composed of the blue shark Prionace glauca, the swordfish Xiphias gladius, the albacore tuna Thunnus alalunga, the common dolphin Delphinus delphis and the striped dolphin Stenella coeru- laeoalba. The present study is aimed at determining the patterns of feeding niche segregation among this oceanic top predator assemblage. Overlaps were measured in terms of prey taxa and prey sizes. Preferred foraging depth ranges and diel patterns were inferred from prey compositions and diges- tion conditions. In terms of prey taxa, the blue shark, the albacore and the swordfish segregated fairly well from each other and from the 2 dolphins, whereas the 2 dolphins showed considerable overlap. In terms of prey sizes, substantial overlap was found between the blue shark and the swordfish, but these predators differed from the 2 dolphins and the albacore, which, in turn, overlapped consider- ably. Spatio-temporally, the blue shark and the swordfish appeared to be predominantly diurnal mesopelagic predators, while the albacore and the dolphins were mostly nocturnal epipelagic feed- ers. Prey diversity was higher in the 2 dolphins, which also showed a lower interindividual variabil- ity in stomach content composition. The 2 dolphins have the highest energy needs and are bound to the surface for breathing; the albacore is also bound to the surface layer for physiological reasons (swim bladder development and body temperature control): all 3 rely on small gregarious epi- to ver- tically migrating mesopelagic prey species of high energy content. The swordfish and the blue shark have much lower energy needs and are not restricted to the surface layer; they are better able to for- age on scattered, deep-living, large-size and low-energy prey. Hence, within the whole community, the energetics of predation and constraints relative to the sea surface are the main structuring factors, and not the relationship between predator size and prey size.

Spatio-temporal variability in fatty acid trophic biomarkers in stomach contents and muscle of Iberian sardine (Sardina pilchardus) and its relationship with spawning

Temporal variation in the fatty acid (FA) composition of stomach contents of Iberian sardines was compared to the relative contribution to dietary carbon made by different prey types for fish from two areas off Portugal. The effect of the FA content of the diet on sardine muscle FA composition was also studied, aiming at (1) analysing if FA biomarkers can be used as a complementary technique for the study of sardine diet and (2) to relate spatial and temporal variations of prey FA content with sardine condition and reproduction. Significant spatial differences in the FA composition of sardine diet occurred with concentrations of n-3 polyunsaturated FA, namely eicosapentaenoic acid [EPA, 20:5n-3] and linolenic acid 18:3n-3, being significantly higher in the diet of sardines from the west coast, whilst the diet of sardines from the south coast was richer in monounsaturated fatty acids (MUFA), namely the carnivory biomarker oleic acid 18:1n-9. These results are in agreement with the higher contribution made by diatoms and dinoflagellates to the diet of sardines off the west coast. Spatial variation in sardine dietary FA was also detected in their muscle composition, specifically for EPA, and the eicosapentaenoic/docosahexaenoic acid and (n-3)/(n-6) ratios, which were higher in sardines from the west coast. No difference in FA composition was detected between sexes, and the seasonal variability in sardine total FA concentration was primarily related to the seasonality of spawning. Sardines accumulate high concentrations of FAs during the resting stage of reproduction when the feeding intensity is similar or lower to that observed during the spawning season. Additionally, sardines show a high selective retention of MUFA and polyunsaturated FA (PUFA) throughout the year except at the beginning of the spawning season, when these FAs are largely invested in the formation of the gonads. Therefore, temporal and regional differences of prey environments are strong enough to be reflected in fish body composition, namely on the accumulation of essential FAs, which can have a strong impact on reproduction success for this species.

Effect of feed texture, meal frequency and pre-slaughter fasting on behaviour, stomach content and carcass microbial quality in pigs

In this study, behaviour in lairage, weight and composition of stomach contents and carcass microbial contamination were studied in 96 barrows assigned to the following treatments: feed texture (FT; mash vs. pellets), meal frequency (MF; 2 vs. five meals per day) and fasting time (WT; 4, 14 and 24 h) according to a 2 × 2 × 3 factorial design. Pigs fed two meals had heavier stomach weights at slaughter than those fed five times per day (P = 0.01). An interaction was found between WT and FT (P = 0.002) for stomach weight. With respect to the contamination of the mouth, total aerobic mesophilic counts were higher than 104 cfu cm-2 but not significantly different between treatments. Coprophagy behaviour in lairage was not correlated with mouth contamination at slaughter. The treatment resulting in the lowest Escherichia coli counts on the thoracic area was feeding the pigs pellets five times per day followed by a 24-h fast. In contrast, the highest E. coli counts were observed in pigs fed mash five times per day followed by a 4-h fast. Comparison a posteriori of these two extreme scenarios yielded a P value of 0.03. Key words: Animal behaviour, carcass hygiene, fasting, feeding, pigs, stomach

Diet and feeding behaviour of the Neotropical parrot snake (Leptophis ahaetulla) in northern Brazil

Specimens (289) of Leptophis ahaetulla from northern Brazil and western Maranhão were examined for the composition of stomach contents. Most prey items were tree frogs, especially those of the family Hylidae (90%). Most of the anurans identified belong to the Scinax ruber species group (27%) and Scinax sp. (25%). Prey size was significantly related to snake length but not to head length. There was no significant difference related to sex in either case. Both sexes preyed on small to medium‐sized items (3–10% of snake snout–vent length). Leptophis ahaetulla seems to manipulate captured prey before ingestion since most of the prey items (83.6%) were swallowed head‐first. Leptophis ahaetulla is primarily diurnal and semi‐arboreal, inhabits disturbed and undisturbed forest, and forages primarily on the ground and in fallen vegetation, where its prey items are likely to be found at rest. †In memoriam.

Opportunistic predation in tuna: a size-based approach

To test whether predation is an opportunistic size-based process within a tuna community, analyses were carried out on the size composition of stomach contents of bigeye tuna Thunnus obesus (Lowe, 1839) and yellowfin tuna T. albacares (Bonnaterre, 1788) caught in 1995 to 1997 during longline scientific surveys in the French Polynesian Exclusive Economic Zone (EEZ). Prey size distributions were compared with the size distribution of organisms collected by pelagic trawls carried out during the same programme. Relationships between prey size and predator size were studied using quantile regressions, and were related to tuna mouth-gape measurements. The results showed that mean and maximum sizes of prey increased with increasing predator size, and that maximum prey sizes (versus tuna size) were below those predicted by tuna mouth-gape size. Minimum prey size varied little with tuna size, and the size distributions of prey in tuna stomachs were very asymmetrical (lognormal type), confirming that during growth, tunas continue to feed on small prey. Comparison with previous studies on other piscivorous species from different ecosystems underlined that tunas feed on very small prey in relation to their own size. However, comparison of size distributions of prey in stomach contents and prey in pelagic trawls revealed that bigeye tuna select larger prey than yellowfin tuna when such prey are available.