Evolution of feeding structure plasticity in marine invertebrate larvae: a possible trade-off between arm length and stomach size

The ability of an organism to alter its morphology in response to environmental conditions (phenotypic plasticity) occurs in several species of marine invertebrates. Examples are sea urchin and sand dollar larvae (plutei). When food is scarce, plutei produce longer food-gathering structures (larval arms and a ciliary band) and smaller stomachs than when food is abundant. However, it is unclear whether stomach size is actually induced through changes in morphogenesis or simply by food distending the stomach. Distinguishing between these two hypotheses is possible because plutei morphologically respond to food concentrations and change the length of their food-gathering structures before they are capable of feeding. More importantly, these two hypotheses provide insights to whether a trade-off exists between the response in food-gathering structures and the response in stomach size—a possible explanation for the evolution of feeding-structure plasticity in marine invertebrate larvae. In this study, I investigated whether sea urchin larvae (Strongylocentrotus purpuratus and S. franciscanus) reared in different amounts of food produced stomachs of different sizes before they were capable of feeding. Prior to having the ability to ingest food, larvae produced larger stomachs and shorter arms when food was abundant than when food was scarce, consistent with the hypothesis that food induced changes in morphogenesis. In addition, there was a strong negative correlation between the magnitude of plasticity in larval arm length and the magnitude of plasticity in stomach size. These results are consistent with the idea that a trade-off exists between the response in arm length and the response in stomach size, and at least in part, explains the evolution of feeding structure plasticity in plutei. This may also explain why feeding-structure plasticity has evolved in larvae of other taxa (e.g. other echinoderms and gastropods).     

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.     

Toxic cyanobacteria Nodularia spumigena in the diet of Baltic mysids: Evidence from molecular diet analysis

A PCR-based method was used to detect toxic cyanobacteria Nodularia spumigena in the diet of Baltic mysids, Mysis mixta and Mysis relicta. The decay in detectability of Nodularia DNA in mysid stomachs and feces following the cyanobacterium consumption was examined in laboratory with special references to (1) marker size (780 bp vs. 200 bp), (2) mysid developmental stage (juveniles vs. subadults), and (3) feeding regime after consuming the cyanobacteria (continuous vs. interrupted feeding). The Nodularia DNA could be reliably detected in mysid stomachs and feces by PCR technique. In the mysid with interrupted feeding, the calculated half-lives of N. spumigena DNA in the mysid stomachs were 1.2 and 6.1 h for 780 and 200 bp fragments, respectively. Continuous feeding, however, facilitated decay in the detectability, most likely due to increased gut evacuation rate. In stomachs of the field-collected mysids, the Nodularia DNA was detected with high frequencies, 60% in M. mixta and 51% in M. relicta. Moreover, it was higher in immature mysids than in adults and correlated with stomach fullness in age-specific manner: in juveniles and subadults, stomachs containing Nodularia were significantly fuller, while in adults, the presence of the cyanobacteria was associated with empty stomachs. This suggests greater habitat overlap for juvenile mysids and N. spumigena and thus higher encounter and consumption rates. These findings contribute to a growing body of evidence that cyanobacteria in the Baltic Sea are important food for grazers.     

Reproduction and feeding of the mountain mullet,Agonostomus monticola,in Trinidad,West Indies

Synopsis Reproduction and feeding were studied in mountain mullet,Agonostomus monticola, in northeast Trinidad during the period January 1987 to September 1988. Macroscopic and microscopic examination of the gonads indicated a single, distinct reproductive season from June to October during the wet season. Evidence implies only one spawning event per individual during the reproductive season. Females significantly outnumbered males resulting in a sex ratio of 20.4:1. The mean size at maturity for females was 135 mm fork length (FL). Fecundity (F) is related to size by the equations F = 167.3 FL^2.7 and F = 16430.7 G + 235079 (G = gutted weight).A. monticola was found to be an omnivorous feeder. The dominant food groups found in the stomachs were insects, prawns, fruits and algae, in order of decreasing importance.     

Evidence of cannibalism and bentho-pelagic coupling within the life cycle of the mussel, Perna canaliculus

The feeding ecology of the green-lipped mussel, Perna canaliculus, was investigated within three intertidal mussel beds along Ninety Mile Beach, northern New Zealand, between August 2000 and March 2001. Adult mussels of different sizes (45-105 mm in shell length) were collected from the intertidal sites about 30 min after being submerged by the incoming tide for gut content analyses. Results of these analyses indicate that mussels consume a variety of phytoplankton, micro- and mesozooplankton, including mussel larvae and post-larvae. Cannibalism of juveniles of up to 620 μm was recorded for intertidal mussels, and conspecifics of up to 2.4 mm were found within the stomachs of additional mussels collected in August 2000 from a nearby subtidal site. For all three intertidal populations, mussel larvae and juveniles contribute about 70% of the food particle consumption during the spawning peak in August, while phytoplankton and other zooplankton constitute the majority of the food source (about 99%) in March, during gametogenesis. Larger intertidal mussels tended to have more food particles in their stomachs than smaller mussels within all three populations. Distinctive differences in food consumption among intertidal populations directly coincide with variations in total particulate matter (TPM), particulate organic matter (POM) and percent organic matter (OM) in the adjacent seawater.Separate experiments designed to test the feeding behavior of mussels feeding at different times during the incoming tide were conducted at one of the intertidal sites during August 2000 and March 2001. Results from these experiments indicate a marked shift in food consumption from bivalves to other mesozooplankton in August, and from phytoplankton to mesozooplankton in March. The observed combination of mussel predatory and grazing behavior over the incoming tide and through the year provides evidence for a strong food-web link between the benthic and pelagic life stages of this species. Furthermore, the high rate of cannibalism during some months of the year suggests that this source of food may significantly contribute to the energy budget of wild populations, with potential implications for evolutionary adaptive success.     

Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil with evidence for a dormancy period

The reproductive biology and feeding habits of the hypopomid Brachyhypopomus bombilla were studied. The species has seasonal behavior, with breeding and feeding activity occurring mostly during the Southern Hemisphere spring and summer. We defined fractional spawning for the species and a relative fecundity similar to those previously reported for other gymnotiform species. According to the analysis of the food items, B. bombilla was included in the trophic category invertivorous, feeding mainly on autochthonous insects. The reproductive periods of males and females as well as female feeding activity were significantly related to the photoperiod. During a period of 5?months, when the lowest water temperatures and shortest photoperiod were recorded, all the specimens of B. bombilla were found buried in the muddy bottom of the creek, with lower electric organ discharge activity, empty stomachs, and gonads in early stages of the maturation process. This period, herein defined as a dormancy period, is reported here for the first time for a species of the Gymnotiformes order.     

Feeding habits of the bluemouth, Helicolenus dactylopterus dactylopterus (Delaroche, 1809) (Pisces: Sebastidae) in the Portuguese coast

In order to investigate the feeding habits of Helicolenus dactylopterus dactylopterus along the continental Portuguese coast, a total of 619 individuals were sampled of which 60% contained food in their stomach and 35% had more than one prey item. Among the 81 prey items that were identified in the stomachs, benthic and benthopelagic prey prevail on this species diet. Acantephyra sp, Pasiphaea sp, mysidacea, and teleostei n.i. were the prey with the higher percent index of relative importance (%IRI) value. Three length groups (5?C20?cm, 21?C27?cm, and 28?C48?cm) were defined through cluster analysis of the mean abundance of prey items. A permutational MANOVA detected significant differences in the diet and stomach fullness index for TLG, season, and maturation stage. Smaller fishes had a generalized diet, feeding mainly on mysidacea changing their diet above 20?cm TL, where a major consumption of natantia was found. The larger individuals, >28?cm TL, present a less generalized diet with pisces as dominant prey group. Seasonally, natantia and pisces were the principal prey groups during spring and winter, respectively, while mysidacea and other crustaceans were predominant during the rest of the year. Mysidacea were also the main prey group for immature individuals while natantia and pisces were the principal prey groups to the other maturity stages. The results of this study indicate that H. d. dactylopterus has a diverse diet focused on small crustaceans such as misyds and as specimens grow shrimps and fishes become more consumed, with larger specimens having a more specialized diet. The different nutritional needs during spawning season also seemed to influence the feeding habits of H. d. dactylopterus.     

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.     

The Food and Feeding Chronology of Yellow Perch (Perca flavescens) in Lake Washington

The food habits of yellow perch (Perca flavescens) in Lake Washington, Seattle, U.S.A. were studied over a period of nine months. Altogether 549 yellow perch were examined for the stomach contents. The daily activity pattern of the yellow perch in Lake Washington appears to correspond roughly with the feeding pattern. The maximum numbers of perch caught by the nets during 24 hour study periods correspond well with degree of fullness of stomachs noted for the different times of the day. The food consisted mainly of cottids, mysid shrimps (Acanthomysis awatchensis) and chironomid pupae and larvae. There was no difference in the food consumed between the different sexes and between the different size groups. Maximum feeding by perch during the day was observed just before dark and the daily ration was calculated to be about 1.4% of their wet body weight.     

Comparative feeding ecology of shortfin mako, blue and thresher sharks in the California Current

This study describes the feeding ecology of three pelagic shark species in the California Current: shortfin mako (Isurus oxyrinchus); blue (Prionace glauca); and thresher (Alopias vulpinus) sharks. Stomach contents of sharks collected from 2002 to 2008 were identified to the lowest taxonomic level and analyzed using univariate and multivariate methods. Of 330 mako sharks sampled (53 to 248?cm fork length [FL]), 238 stomachs contained 42 prey taxa, with jumbo squid (Dosidicus gigas) and Pacific saury (Cololabis saira) representing the most important prey based on the geometric index of importance (GII). In addition, 158 blue sharks were sampled (76 to 248?cm FL) and 114 stomachs contained 38 prey taxa, with jumbo and Gonatus spp. squids representing the most important prey. Lastly, 225 thresher sharks were sampled (108 to 228?cm FL) and 157 stomachs contained 18 prey taxa with northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) identified as the most important prey. Overall, mako sharks had the most diverse diet based upon Simpson??s diversity index (1/D) (8.43?±?1.16), feeding on many species of teleosts and cephalopods, followed by blue sharks (6.20?±?2.11) which consumed a wide range of prey (primarily cephalopods), while thresher sharks were most specialized (2.62?±?0.34), feeding primarily on coastal pelagic teleosts. Dietary overlap was lowest between blue and thresher sharks (S?rensen similarity index?=?0.321 and Simplified Morisita Horn index?=?0.006), and seasonal variability in diet was greatest for blue sharks (Simplified Morisita Horn index?=?0.260, Analysis of Similarity (ANOSIM) p?<?0.001). In addition, size class, and subregion were significant factors that affected diet of each species differently (ANOSIM p?<?0.001). Despite similarities in life history characteristics and spatial and temporal overlap in habitat, diets of these three common shark species are distinct in the California Current.     

Food and feeding habits of the African catfish Clarias gariepinus (Burchell, 1822) (Pisces: Clariidae) in Lake Koka,Ethiopia

The food and feeding habits of Clarias gariepinus (Burchell, 1822) were studied in Lake Koka, Ethiopia, in May 2011 (dry month) and September 2011 (wet month). Three hundred and thirty eight nonempty stomach samples were analysed using frequency of occurrence and volumetric methods of analysis. Detritus, insects, macrophytes, zooplankton and fish were the dominant food categories by occurrence, and they occurred in 79.6%, 63.6%, 63.0%, 56.2% and 15.4% of the stomachs, respectively. Volumetrically, the above food items comprised 24.3%, 14.1%, 14.5%, 19.3% and 21.8% of the total volume of food categories. Phytoplankton and gastropods were of low importance, and they occurred in 28.7% and 8.6% of the stomachs, respectively. Their volumetric contributions were 3.2% and 2.8% of the total volume of food categories. During the dry month, fish, zooplankton, insects and detritus were important food categories, while during the wet month detritus, macrophytes, insects and gastropods were important. Smaller catfish diets were dominated by detritus, macrophytes and insects, whereas larger catfish shifted to fish and zooplankton. Based on the results, C. gariepinus was found to be omnivorous in its feeding habits in Lake Koka.     

Feeding activity of Callinectes ornatus Ordway, 1863 and Callinectes danae Smith, 1869 (Crustacea, Brachyura, Portunidae) in Ubatuba, SP, Brazil

The feeding activity along the day cycle and the time consumed for extracellular digestion were evaluated in the portunids C. ornatus and C. danae. Swimming crabs were obtained from trawling in Ubatuba bay, São Paulo, Brazil, during both the rainy and dry seasons. In each season, daily scheduled samples were taken at dawn (±6 h), noon (±12 h), dusk (±18 h) and midnight (±24 h). All individuals were dissected and the degree of stomach replenishment was recorded. In order to estimate the time elapsed for extracellular digestion, crabs were fed, and groups were dissected at 30 min intervals to check the conditions of their stomachs. In general, both species show a higher feeding activity during periods of lower light intensity, as evidenced by an increased percentage of full stomachs in dusk and midnight samples. The obtained results support higher feeding activity at night in these species and indicate short time for extracellular digestion, not exceeding 8 h. Nevertheless, full stomachs were recorded in all sampling schedules. In this case, it should be considered that elimination of certain food items such as fish bones, mollusk shells and carapace fragments of crustaceans could take more time than other items. Additionally, some crab species could require a cycle of cell replacement in the midgut gland epithelium until they can take their next meal.     

The feeding habits of Sargochromis Codringtonii in Lake Kariba, Zimbabwe

The food of adult Sargochromis codringtonii in Lake Kariba was dominated by prosobranch snails with pulmonate snails forming an insignificant dietary component. S. codringtonii does not show particular preference for any snail species, feeding on those species that are readily available. Morphometrical analysis of the feeding structures of S. codringtonii showed that the fish is well adapted to handling a molluscivorous diet. The pharyngeal jaws with their flat crowned teeth are well adapted to crushing molluscs. The daily food consumption rate of S. codringtonii was estimated over different seasons. Estimates of food consumption indicate that the fish consumed 13.96% of their dry body weight per day in summer falling to 4.46% in winter. The low consumption of pulmonate snails suggests that S. codringtonii can not be a successful biological control agent against the vectors of schistosomiasis.     

Nutritional ecology of the invasive freshwater mysid Limnomysis benedeni: field data and laboratory experiments on food choice and juvenile growth

The introduction of alien species leads to changes in species composition and therefore the trophic structure. The highly invasive freshwater mysid Limnomysis benedeni is established and abundant in Lake Constance since 2006. Our aim was to confirm the assumption that L. benedeni feds on small particles and to identify their food web position. We examined the feeding mode and food preference of adult L. benedeni collected from the field and from laboratory feeding experiments by analysing their stomach contents. Stable isotope analyses (SIA) confirm an omnivorous feeding of L. benedeni. In laboratory growth experiments, we determined the growth of juveniles by feeding juveniles with different natural food sources. Growth was supported by natural biofilm, dreissenid biodeposited material and an algal suspension. Stomach analyses showed clearly that L. benedeni fed on small particles of both benthic and pelagic origin and fed by both filtering and grazing. Absence of high numbers of animal structures in the stomachs and SIA supported the lack of predatory impact in the field, but the mysid probably affects the nutrient cycles in the littoral. L. benedeni seems to play an important role in the trophic relations in Lake Constance and all other water bodies they invaded.     

Feeding ecology of dominant groundfish in the northern Bering Sea

We investigated current diets of the six most abundant benthic fish in the northern Bering Sea. Our objective was to explore feeding strategies and potential competition with other top predators as ecosystem changes occur in the northern Bering Sea ecosystem. Our approach used stomach content data collected from field sampling during spring 2006 and 2007. Calanoid copepods and ampeliscid amphipods were important prey of Arctic cod (Boreogadus saida) but in different proportions depending upon fish size, feeding location, and local environmental conditions. Snailfish (Liparidae) occupied a broad niche and fed on a variety of benthic amphipods. Arctic alligatorfish (Ulcina olrikii) and Arctic staghorn sculpin (Gymnocanthus tricuspis) consumed ampeliscid amphipods predominantly. Shorthorn sculpin (Myoxocephalus scorpius) had a less-diverse diet, with snow crab (Chionoecetes opilio) most important by weight. Finally, all Bering flounder (Hippoglossoides robustus) sampled had empty stomachs. Our results indicate that ampeliscid amphipods, which have high biomass in the central region of the northern Bering Sea, are the most important prey for the dominant groundfish in the Chirikov Basin. Generally, all dominant benthic fish in the northern Bering Sea had narrow feeding niches, except snailfish. High diet overlap was found among many of the fish species, including Arctic cod and snailfish, snailfish and Arctic alligatorfish, and Arctic alligatorfish and Arctic staghorn sculpin. These findings are consistent with a relatively short food chain for benthic fish that are for the most part specialized feeders with narrow preferences for food and may be affected by changes in benthic prey distributions.     

Dietary niche differentiation among three species of invasive rodents (Rattus rattus, R. exulans, Mus musculus)

The diets of sympatric rodents partially define their realized niches. Identifying items in stomachs of introduced rodents helps determine rodents’ trophic positions and species most at risk of consumption. In the Hawaiian Islands, which lacked rodents prior to human arrival, three rodents (Rattus rattus or black rat, R. exulans or Pacific rat, Mus musculus or house mouse) commonly coexist in native habitats where they consume a wide range of plants and animals. These three rodent species were trapped in montane forest for 2.5 years; their stomach contents were analyzed to determine short-term diets (n = 12–95 indiv. per species), and isotopic fractions of δ¹⁵N and δ¹³C in their bone collagen were analyzed to further estimate their trophic positions (n = 11–20 indiv. per species). For all three species, >75 % of individuals had plants and >90 % had arthropods in their stomachs, and significant differences in mean relative abundances were found for food items in stomachs among all three rodents. Rodents may be dispersing some native and non-native seeds, including the highly invasive Clidemia hirta. Most identifiable arthropods in rodent stomachs were non-native, and no stomachs contained birds, snails, or lizards. The δ¹⁵N and δ¹³C signatures were consistent with trophic feeding differences revealed from stomach contents. Dietary niche differentiation by coexisting rodent species is evident in this forest, with Pacific rats being intermediate between the mostly carnivorous house mouse and the mostly herbivorous black rat; such findings can help forecast rodent impacts and direct management efforts in ecosystems where these invasive animals coexist.     

Feeding ecology and daily ration of the pelagic armorhead,Pseudopentaceros wheeleri,at Southeast Hancock Seamount

Synopsis The unusual life history of pelagic armorhead, Pseudopentaceros wheeleri, includes occupation of epipelagic subarctic and transitional waters of the northeast Pacific Ocean and Gulf of Alaska as subadults and subsequent recruitment to the southern Emperor and northern Hawaiian Ridge (SE-NHR) seamounts in the central North Pacific Ocean where they assume a demersal existence and begin maturation as adults. Feeding ecology and daily ration were examined in pelagic armorhead during field studies conducted at Southeast Hancock Seamont (29°48′ N,179°04′ E) in the SE-NHR seamounts. A total of 1133 stomachs collected during June-July 1985, January 1988, and July 1988 were examined for contents; only 19.7% contained food items. The diet consisted of pelagic tunicates and other micronektonic animals that are associated with the vertically migrating sonic scattering layer that is advected over the seamount from the adjacent oceanic environment. Peak feeding occurred in the early morning on migrating organisms likely trapped by the expanse of the seamount summit during the morning descent. Newly recruited armorhead had lower feeding rates than older, previously recruited fish. Estimates of daily ration for previously recruited armorhead were 1.17 g (0.26% of body weight) in the summer of 1985 and 12.87 g (2.86% of body weight) in the summer of 1988. Since estimated values for the evacuation coefficient and the duration of the daily feeding period did not differ between sampling periods, the increase in daily ration was due to an increase in feeding rate. The proportion of the diet composed of pelagic tunicates was also higher in 1988.     

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.     

Diet and trophic niche of Macrourus spp. (Gadiformes, Macrouridae) in the Ross Sea region of the Southern Ocean

Both Macrourus caml and M. whitsoni are probably abundant and widespread in the Ross Sea region at depths between approximately 500 and 2100 m. We present the analysis of stomach contents (including regurgitated stomach contents) from an undifferentiated mixture of 33 specimens of these species (henceforth Macrourus spp.) in the Ross Sea region of the Southern Ocean. Samples of stomach contents were obtained from the Ross Sea slope (between about 71° and 73° S) and on the Scott Island and seamount chain. Overall, amphipods were the dominant prey found in Macrourus spp. stomachs with an index of relative importance (IRI) of 43%. About half the amphipods were Eurythenes gryllus and about half could not be identified. Based on stable isotope results, unidentified amphipods were probably herbivorous rather than carnivorous. Other important prey were copepods (especially for fish with total length less than 30 cm), krill (mainly Euphausia superba for larger fish) and fishes (Pleuragramma antarcticum and Gymnoscopelus opisthopterus). Minor prey found in stomachs included isopods, mysids, salps and polychaetes, with rocks and fragments of coral, echinoderm and shell also found. Stomach contents data provide evidence of both pelagic and benthic feeding. Carbon and nitrogen stable-isotope analysis of 161 Macrourus spp. muscle tissue samples from the Ross Sea slope, Admiralty and Scott seamounts and two parts of the Pacific-Antarctic fracture zone (near 65° S) are presented. Nitrogen isotope results (??¹⁵N = 10.6 ± 1.0??, mean ± SD) were generally consistent with stomach contents. Carbon isotope results (??¹³C = ?24.7 ± 0.8??) were consistent with Southern Ocean residence but higher than phytoplankton values (?29.9 ± 1.2??). We found that Macrourus spp. in the Ross Sea region have a trophic level of 3.8 ± 0.3, placing them well below the top of the food chain. Trophic level of Macrourus spp. was significantly affected by location and by size of fish (especially for fish less than 30 cm), whereas sex, fatness and bottom depth were not significant.     

Physiological responses to short-term fasting among herbivorous,omnivorous, and carnivorous fishes

We explored the integrated role of dietary specialization and feeding periodicity on the response of the gastrointestinal tract of teleosts fishes to short-term (7–10 days) fasting and refeeding. Fasted and fed herbivorous grass carp (Ctenopharyngodon idella), omnivorous channel catfish (Ictalurus punctatus), and carnivorous largemouth bass (Micropterus salmoides) were compared for digestive organ masses, intestinal morphology, gastrointestinal pH, and the specific activities and total intestinal capacities of the intestinal hydrolases aminopeptidase (APN) and maltase and intestinal nutrient transporters. All three species experience intestinal hypertrophy with feeding as noted by significant increases in enterocyte dimensions. Of the three, only I. punctatus experienced a postprandial increase in intestinal length, and only C. idella experienced significant modulation of intestinal microvillus length. Feeding resulted in acidification of the stomachs of I. punctatus and M. salmoides. Predicted to exhibit a relatively modest set of postprandial responses because of their more frequent feeding habits, C. idella only experienced increases in APN and maltase activity with feeding and no significant regulation of nutrient uptake. Significant regulation of hydrolase activities and nutrient uptake were exhibited by I. punctatus and M. salmoides, with I. punctatus experiencing the most comprehensive set of responses. As predicted by food habits, there was an interspecific gradient in intestinal length and glucose uptake extending from longer intestines and greater glucose uptake for the herbivorous C. idella, intermediate lengths and glucose uptake for the omnivorous I. punctatus, and shorter intestines and reduced glucose uptake for the carnivorous M. salmoides. Among teleosts fishes, short episodes of fasting lead to significant alterations in intestinal form and function that are rapidly restored with feeding.