An in situ estimate of daily food consumption and alimentary canal evacuation rates of common carp, Cyprinus carpio L.

Daily food consumption and alimentary canal evacuation rates for common carp, Cyprinus carpio L., were estimated at 4-week intervals from April to October 1979. Both the rate of food evacuation and its relationship to temperature were described by an exponential function. Gut evacuation rates ranged from 6.0% of gut contents per hour at 9°C to 32.7% h⁻¹ at 26.5°C. Temperature accounted for 72–91% of the variation in gut evacuation rate among months. Daily food consumption varied from a low of 3.87 mg g⁻¹ of fish wet wt per day in April at 14°C (0.39% of wet body wt) to a high of 40.75 mg g⁻¹ (4.08%) in August at 26.5°C. Although a greater quantity of food appeared to be consumed during the morning in spring and early summer and a greater amount in the evening after July, there was not a statistically significant time of day for peak feeding activity. The field method described here seemed to provide reasonable estimates of food consumption compared with other field and laboratory studies.     

Gut morphology,feeding rate and gut clearance in five species of caddis larvae

Feeding rate, the rate of movement of food through the gut and gut morphology of large larvae of five caddis species (Halesus radiatus, Hydropsyche instabilis, Polycentropus kingi, Rhyacophila dorsalis and Potamophylax cingulatus) were investigated in the laboratory. Following 72 hr starvation, P. cingulatus and H. radiatus larvae became satiated (refused prey offered directly to the mouthparts) after consuming 8–11 and 9–13 mayfly nymphs (Baetis rhodani, 3.5–4.6 mm) respectively. Hunger level affected prey consumption. In P. cingulatus, the number of prey consumed over 24 h (at 9.5–12 °C) increased with starvation periods from 0–72 h, but declined following longer starvation periods. Six clearly recognisable gut states (defined by the position of food material in various parts of the gut) can be identified at different times since commencement of a meal. As environmental temperature increased (from 8–12 °C to 15–17 °C), the rate of change of the gut state increased and the food retention time decreased in all species. Feeding periodicity (i.e. nocturnal/diurnal activity) in the field was estimated based on the evacuation rate and the gut state and environmental temperature at the known time of collection. Initiation of consumption of prey appeared to coincide with emptying of the foregut and proximal midgut, whereas actual feeding continued until complete satiation when some threshold fullness of the foregut had been reached. The length of time food was held in the foregut was positively correlated with increasing specialisation of the foregut (particularly elaboration of the proventriculus).     

Food limitation in a nursery area: estimates of daily ration in juvenile scalloped hammerheads, Sphyrna lewini (Griffith and Smith, 1834) in Kāne'ohe Bay, ō'ahu, Hawai'i

Gastric evacuation and daily ration were studied in juvenile scalloped hammerhead sharks in Kāne'ohe Bay in order to better understand their ecology and role as apex predators in the marine environment. Three major variables known to affect the rate of gastric evacuation were manipulated: meal size, prey species, and temperature. Rates of gastric evacuation were faster than have previously been measured for sharks. The time for 80% of the meal weight (dry) to be evacuated ranged from 5.4 to 22.1 h. Daily ration was estimated using two different methods based on gastric evacuation rates and stomach content data. Estimates ranged from 2.12% to 3.54% of the body weight, which is relatively high compared to other elasmobranchs, but lower than estimates of maintenance ration for juvenile scalloped hammerheads. Data available for diet and growth of juvenile scalloped hammerhead sharks in Kāne'ohe Bay as well as data for their prey species suggest that these sharks may be surviving much of the time at consumption levels below maintenance ration.     

Gastric evacuation rates and daily ration of piscivorous coho salmon, Oncorhynchus kisutch Walbaum

Effects of temperature and meal size on gastric evacuation rates of juvenile coho salmon, Oncorhynchus kisutch , consuming sockeye salmon, O. nerka , fry were examined and used in the estimation of daily meal, daily ration and number of fry consumed by coho in Chignik Lake, Alaska. Evacuation of fry by coho was best described by a negative exponential model (average R² = 0.93). A square root model also provided a good fit (average R² = 0·93), but the y-intercepts deviated more from the expected value than did the y-intercepts of the exponential model. The effect of temperature ( T , 5–13° C) and meal size (MS, 0·166–0·367 g) on the exponential evacuation rate (r_e, h^-1) could be described as
In the lake, coho fed continuously during the 24-h period in early June 1986 and 1987. Estimates of daily meal and ration of coho calculated by the Eggers method and the geometric mean of prey weight ranged from 0·224 to 0·435 g (2.1–4.4% body wt) depending on location and year. The Elliott & Persson method provided similar estimates of food consumption, whereas estimates based on the Pennington method and square root evacuation of prey differed from the exponential models. Sockeye fry represented 93% of the total prey weight. The average number of sockeye fry consumed per coho per 24 h, based on the arithmetic mean of prey weight, was 3·0–3·9 fry.     

Gastric evacuation of mixed stomach contents in predatory gadoids: an expanded application of the square root model to estimate food rations

A mechanistic gastric evacuation model of mixed stomach contents was established. Its simple generic nature should prove useful for studying predator‐prey interactions in fish communities. Only prey lengths were required as additional input. Surface dependent digestive processes were considered to act on equal fractions of individual prey‐cylinder surfaces. Primary and interactive effects of size, energy density and resistance to digestion of individual prey in a stomach were described by the model. Model predictions of results from experiments on gastric evacuation of meals composed of different prey types demonstrated the capability of this model, as opposed to previously applied model principles, to predict evacuation of mixed stomach contents involving the three above‐mentioned prey characteristics. The study furthermore illustrated that estimates of food ration might be severely biased by using improperly formulated effects of prey characters on gastric evacuation, and demonstrated that the new model holds the potential to predict food ration and diet composition for wild populations of predatory fishes.     

Seasonal change in the gastric evacuation rate of rainbow trout feeding on natural prey

Seasonal changes in the gastric evacuation rate ( R ) and gut contents of a wild population of rainbow trout Oncorhynchus mykiss feeding on natural prey at four water temperatures (2, 7, 9 and 12° C) were measured. The R and mass of the gut contents increased with water temperature, and prey items changed seasonally. These results suggest that the R of fish feeding on natural food depends primarily on water temperature, with their consumed prey being a secondary factor.     

Diel food utilization by woundfin,Plagopterus argentissimus,in Virgin River,Arizona

Synopsis Woundfin, Plagopterus argentissimus, fed predominantly on simuliid larvae during the day, and shifted to the larger Hydropsyche spp. at night. Ephemeropteran larvae were eaten nearly uniformly throughout the 24 hour period. Mean weight of food consumed varied from 20–40 mg per individual (0.7–2.5% body weight) throughout the 24 h period. Our estimated daily ration of about 8% body weight, at temperatures that varied between 15–25°C, is based upon our measure of mean gut contents over a 24h period, combined with intestinal evacuation rates suggested for other cyprinids in the literature. The relatively continuous feeding pattern suggests a foraging strategy that would minimize competition with other species for food during June, a period of minimum annual food abundance in Virgin River.     

Diel feeding periodicity, daily ration and vertical migration of juvenile Cape hake off the west coast of South Africa

Feeding periodicity, daily ration and vertical migration of juvenile Cape hake Merluccius capensis are investigated from midwater and bottom trawl collections taken during a 42-h period between 29 February and 2 March 1992 at a fixed position off the west coast of South Africa. Feeding of 10-20 cm hake intensified during the night when they ascended into subsurface layers to prey on recruits of anchovy Engraulis capensis. Larger hake remained close to the bottom, were partially cannibalistic and exhibited no diel feeding periodicity. M. capensis appear to migrate vertically and feed asynchronously in midwater, as individuals, and not as a population, returning to the bottom when satiated. Based upon the exponential rate of decline in stomach fullness throughout the day, the evacuation rate by hake <20 cm was estimated as 0.054 h⁻¹; 90% evacuation of anchovy prey required an estimated 43 h. Using the Elliott & Persson and Eggers methods, the daily ration was estimated as 5.51 and 4.15% of wet body weight respectively. The effect of the foraging behaviour of M. capensis on the appropriateness of acoustic sampling for estimates of their abundance is discussed.     

Development and application of a bioenergetics model for juvenile walleye Pollock

A bioenergetics model was parameterized for age-0 walleye pollock, Theragra chalcogramma , based on a synthesis of literature data. The sensitivity of the new parameters was tested by individual parameter perturbation (IPP) analysis. The model was applied to estimate individual and total cohort food consumption of age-0 pollock in two areas of high pollock density in the Gulf of Alaska during the summer of 1990. Total cohort consumption was compared with zooplankton biomass and production estimates for the same areas and times of the year. The model was also used to examine the bioenergetic implications of age-0 pollock diel vertical migration through a thermal gradient. During a 1-month bioenergetics simulation, individual daily consumption decreased from 16·0 to 6·0% of wet body weight. Daily ration estimates corresponded well with independent field estimates of daily ration for the same areas and time of the year. Comparison of total cohort consumption with prey availability (production and biomass) indicated minimal potential for food limitation. Bioenergetic optimization of growth can be a potential benefit of diel vertical migration to age-0 pollock, however more information on prey density and distribution is needed to test this hypothesis thoroughly.     

Interactions between developmental processes,growth, and food selection in the larvae and juveniles of Rutilus rutilus (L.) (Cyprinidae)

Summary The aim of this study was to assess the effects of developmental events, occurring in fish during the first weeks after hatching, on the quantity and quality of the ingested food and on growth. The investigation was carried out with the larvae and juveniles of Rutilus rutilus, the single cyprinid species occurring in an oligotrophic subalpine lake in Tirol, Austria. Comparison between availability of prey in the water and gut contents suggests that the selection of food by the young fish is strongly influenced by developmental processes. For example, the prevalence of indigestible phytoplankton in the gut of young larvae can be taken as a sign of the not yet fully developed sensory and locomotory capacities of the young fish (El-Fiky et al. 1987). Furthermore, quantitative and qualitative changes in the gut contents correlate strongly with changes in the form and relative length of the gut, but reflect only weakly the availability of prey in the water. In the Seefelder See population of R. rutilus the switch from a phytoplankton to a cladoceran dominated diet is accompanied by an increase in relative growth rate by nearly one order of magnitude (Wieser et al. 1988).     

Comparison of field-based and indirect estimates of daily food consumption in larval perch and zander

Since bioenergetics models for 0+ fish have seldom been validated by field consumption estimates, field-based and indirectly estimated daily food rations were compared in larval perch Perca fluviatilis and zander Stizostedion lucioperca. Field-based estimates were calculated with linear and exponential evacuation rates based on gut fullness data during a 24-h cycle, with hourly field samplings instead of the normally recommended 3-h intervals. Indirect calculations used bioenergetics modelling with variable activity multipliers ( A ). Field-based estimates of daily rations ranged between 0·21 and 0·27 g g⁻¹ day⁻¹ in perch (mean L _T 13·1 mm) and 0·31–0·40 g g⁻¹ day⁻¹ in zander (mean L _T 10·6 mm). The higher values were calculated by using the exponential model. Daily rations calculated by bioenergetics modelling with A = 1 were only slightly higher than direct estimates in both species. However, if A values >1 were used, calculated daily rations were substantially higher than direct estimates. Estimates of daily ration based only on every third value ranged between 41 and 72% compared with 1-h intervals, mainly because of lower estimates of evacuation rate.     

Resource allocation in Tomocerus flavescens (Insecta,Collembola): a study with C-14-labelled food

Summary Individuals of the collembolan species Tomocerus flavescens from a beech wood on limestone near Göttingen (West Germany) were fed with C-14-labelled algae in the laboratory. On an average, T. flavescens exchanged almost all of its endogenous carbon after 3.4 moults. In periods of starvation the interval between two ecdyses increased from 5.2 to 6.1 days (17°C). The assimilation efficiency was determined in three independent ways (carbon use of different algal components; A=C-FU; C=P+R+FU, A=P+R): it ranged from 0.34 to 0.40 (converted to energy values 0.30 to 0.45). It could be raised in phases of high mobility and in periods of food shortage by lowering the gut passage rate. The decrease in feeding activity (demonstrated by gut contents analyses) in case of a detoriation of the food quality and the food availability can be partly compensated in this way. For individuals which did not reproduce, the ratio of production to assimilation was 0.24 (converted to energy values 0.31). T. flavescens showed an increased body growth in connection with reaching sexual maturity. Specific demands of nutritive substances in periods of physiological changes could possibly be compensated by a more efficient resource use as well as by differences in resource allocation. The studied population of T. flavescens was compared both with that of a Danish beech forest and general data from the literature. The production of few eggs rich in energy, the high weight of newly hatched individuals, the high growth as well as the storage of carbon connected with egg production, the comparatively low respiration metabolism and the high amount of energy invested in search for food have to be regarded as an adaptation to the habitat. According to conservative estimates climbing individuals of this species consume 0.83 g of the algal dry mass growing on one beech tree during one summer. T. flavescens mainly uses the ethanol-soluble components of the algae.     

Estimation of evacuation rates in the field

Two methods are presented to calculate evacuation rates based on observed diel changes in occurrence and mean mass of prey in predator stomachs. The methods do not require predators to exhibit prolonged non‐feeding periods, but the ingestion of each particular prey type must be restricted to certain diel periods. Data from >7500 whiting Merlangius merlangus collected at five locations in the North Sea were used to demonstrate the methods. The evacuation rates estimated from field data were similar to laboratory results, though a tendency for estimates to exceed literature values slightly was noted. Bias was introduced if a large proportion of the prey was evacuated completely in the interval between subsequent samples and if significant amounts of other food were present in the stomach together with the prey in question. The methods can be used to supplement laboratory estimates of evacuation rates or provide first estimates for species that are not easily maintained in the laboratory.     

Effect of sampling interval and temperature on the accuracy of food consumption estimates from stomach contents

The effect of temperature and sampling interval on the accuracy of food consumption estimates based on stomach contents was studied using simulation. Three temporal patterns of feeding were considered (scattered throughout the day, one 5 h period or two 5 h periods) and gastric evacuation was modelled according to published values. Sampling intervals of 3 h gave reasonable food consumption estimates (2 to 19% error) at all temperatures. Comparably, sampling intervals as large as 12 h gave reasonable estimates of food consumption (1 to 20% error) when temperature was set to ≤10° C. At temperatures <5° C, even 24 h intervals (equivalent to one daily sampling) provided reasonable estimates of daily food consumption (2 to 19% error) for all but the highest gastric evacuation rate combined with one daily feeding period (47% error). The temperature effect on estimation error resulted from diminishing temporal fluctuations in stomach contents with slower gastric evacuation rates. It follows that sampling effort may be considerably minimized when estimating food consumption from stomach contents during periods with low temperatures such as the winter time experienced by temperate fishes.     

A gastric evacuation model for three predatory gadoids and implications of using pooled field data of stomach contents to estimate food rations

The general applicability of the square root model to describe gastric evacuation in predatory gadoids independently of meal size was verified through experiments on whiting Merlangius merlangus , saithe Pollachius virens and cod Gadus morhua fed different fish and crustacean prey. Gastric evacuation rate was related by a negative power function to energy density of fish prey over an extended range from 3·4 to 11·5 kJ g^-1 of the effector variable. Gastric evacuation of crustacean prey seemed to depend on the characteristics of their exoskeleton. Gastric evacuation of mixed meals composed of fish prey with different energy densities could be described as a function of the overall energy density. The evacuation rate of each of the prey could be described directly by their share of the stomach content. A full gastric evacuation model including predator size, temperature and prey energy density was established for whiting, saithe and cod. It was demonstrated that estimates of food rations might be severely biased by use of mean values for prey composition and total mass of stomach contents.     

Food consumption of yellowfin tuna,Thunnus albacares, in Sri Lankan waters

Synopsis A total of 4181 stomachs of yellowfin tuna,Thunnus albacares (22–164 cm FL), mainly caught by gillnets in the period from July 1984 to June 1986 were analyzed. Food consumption of yellowfin tuna in nature was determined using the values of the average stomach content, incorporating laboratory measurements of gastric evacuation rates in a feeding model. The diet of yellowfin tuna around Sri Lanka comprised a variety of macro zooplanktonic and nektonic organisms. Juveniles < 39 cm FL, are planktivores. Tuna > 40 cm FL gradually increase their consumption of fishes with increasing size. Among fish speciesAuxis sp. are the most important. The daily food consumption of juvenile yellowfin tuna (22–59 cm FL) range from 1.8 g to 136.2 g, increasing to about 284.7 g to 551.9 g for the medium size tuna (60–99 cm FL). The adult tuna (100–>130 em FL) consume around 513 g to 538.8 g of prey per day. Daily ration estimates increase from 2.1% to 5.5% of body weight with increasing size up to 70 cm FL, beyond which it decreases. The predatory pressure of yellowfin tuna on commercially important fishes and other species is discussed.     

Winter feeding: an adaptive strategy broadening the niche of the central mudminnow,Umbra limi

Synopsis Mudminnows, Umbra limi, were euryphagic carnivores during the ice-free period consuming invertebrates of terrestrial and aquatic origins. In winter, diversity and amount of food eaten were reduced. Age 0 fish consumed aquatic invertebrates as did males aged 1 and 2+ but females aged 1 and 2+ consumed mainly fishes. In the laboratory mudminnows were able to capture small fish at temperatures of 12.6° C and less. Their rates of digestion of fish prey varied directly with temperature and estimates of time for 100%, gastric evacuation ranged from 161 h at 1.1° C to 26 h at 12.6° C. The ability to forage actively during winter and to digest food relatively rapidly at cold temperatures are seen as mechanisms to broaden the niche along dimensions of resources utilized and time, thereby increasing the chances of survival and reproduction in an environment with high temporal heterogeneity.     

The effect of temperature on digestive and assimilation efficiency,gut passage time and appetite in an ambush foraging lizard,<Emphasis Type="Italic"> Cordylus melanotus melanotus</Emphasis>

In ectotherms, an increase in body temperature increases metabolic rate and may increase rates of digestive processes. We measured the thermal dependence of the apparent digestive and apparent assimilation efficiencies (ADE and AAE), gut passage time (GP) and appetite in Cordylus melanotus melanotus, a medium sized Crag Lizard, which is endemic to South Africa. Trials were conducted at 20, 22, 25, 30, 32 and 35 °C under controlled conditions. Trials lasted 14 days, during which, lizards were fed ca. 1 g mealworms per day. Glass beads were used as markers to determine GP at the beginning and end of trials. Faeces and urates were collected daily and oven dried at 50 °C. The energy content of egested matter was then measured using bomb calorimetry. ADE and AAE were not affected by temperature for either males or females. The mean±SE ADE and AAE were 94.4±0.3% and 87.2±0.6%, respectively. GP was not significantly different between males and females at any temperature, but decreased significantly with increasing temperature. Appetite was significantly different between the different temperatures measured. The decrease of gut passage time with increasing temperature was expected, since the digestive and assimilation efficiencies are similar over the range of temperatures tested. Lizards are thus assimilating a similar proportion of ingested energy, but at faster rates at higher temperatures. The results indicate that the digestive physiology of this species results in maximum energy gain per meal in environments where food is scarce.Abbreviations AAE apparent assimilation efficiency - ADE apparent digestive efficiency - AE assimilation efficiency - DE digestive efficiency - GP gut passage rate - NEA net energy absorbed through gut - NER net usable energy retained - SVL snout-vent length - T _b body temperature Communicated by G. Heldmaier     

Predator gut state and prey detectability using electrophoretic analysis of gut contents

Abstract. I. An investigation of the effects of position of food in the gut (gut state), time since feeding, meal size and environmental temperature on the detection of prey using the electrophoretic separation of proteins with esterase activity was undertaken. The waterbug Notonecta glauca Linn (Hemiptera/Heteroptera) was used as the model predator.
2. Seven easily recognizable gut states can be identified at different times since commencement of a meal.
3. Specific prey esterase 'fingerprint' bands can be detected whilst food remains in the foregut.
4. Meal size and environmental temperature (affecting digestion and assimilation rates) both affect the rate of filling and emptying of the foregut, and hence the time period over which prey proteins can be detected by electrophoresis following a meal. Small meals and high temperatures lead to quite rapid changes in gut state with time and thus reduce the time period over which prey can be identified from gut contents (20 h). Large meals and low temperatures extend this period (48 h).
5. Predator gut state is the most important parameter in prey detectability from gut contents, and from a visual examination of the gut state it is immediately evident whether or not prey detection by electrophoresis will be possible.
6. There is further evidence in support of a twocompartment food processing model for Nofoonecru , and the significance of this type of processing in relation to gut content analysis of sucking predators is discussed.     

Effects of temperature and ration level on the growth and food conversion efficiency of Salmo gairdneri, Richardson

The effects of temperature and ration size on the growth rate and gross efficiency of food conversion of juvenile rainbow trout Salmo gairdneri were evaluated during 25-day seasonal experiments. Rations ranged from near-starvation to repletion levels. Test temperatures were 3 and 6°C higher than the controls which fluctuated dielly and seasonally. At rations near maintenance, elevated temperatures decreased trout growth. As the feeding rate increased the detrimental effect of temperature on growth was ameliorated. At repletion feeding levels, elevated temperature up to 17°C improved trout growth by increasing the maximum food consumption rate. With a temperature increase from 6.9 to 22.5°C maintenance rations increased from 2.2 to 7.5 % body weight per day. Gross efficiency was dependent upon ration level and temperature. As the food consumption rate increased, efficiency increased to a maximum, then generally declined at repletion levels. Elevated temperatures resulted in reduced efficiencies at low consumption rates but temperatures had little effect at high ration levels. A field study provided estimates of the food consumption relationships established in the laboratory, suggested any substantial increase of stream temperature without a concomitant increase of food abundance would result in decreased trout production.