Gut evacuation and absorption efficiency of walleye larvae

Gut evacuation and absorption efficiency in zooplanktivorous walleye Stizostedion vitreum larvae (10–19 mm; 0.53–6.8 mg dry weight) were examined in the laboratory. The decline in dry weight of whole digestive tract contents was examined at 15, 20, and 25) C in discontinuous feeding larvae. The observed relationship between short-term evacuation rate and gut fullness indicated that evacuation approximated most closely an exponential decline. When gut evacuation rate, R , was calculated as the slope of loge gut fullness v . time there were significant effects of temperature and walleye size on R . Gut evacuation rate was higher at 20° C than at 15 or 25° C and declined with increasing walleye dry weight. Absorption efficiency at 20° C was examined by qualitative analysis of food and faeces. Apparent digestibility, D _a, of crustacean zooplankton increased with gut retention time and declined with walleye dry weight. Maximum D _a was estimated to be 79% of organic matter from food retained in the gut for 6 h.     

Ingestion,Digestion and Assimilation Efficiency of the Sea-Anemone Aiptasia pallida Fed Zooplankton Prey

Ingestion time, digestion time, and assimilation efficiency by the sea anemone Aiptasia pallida were studied in the laboratory by feeding individual anemones preweighed pellets of freeze-dried Artemia salina nauplii. There was no significant correlation between anemone size, measured as dry weight, and either ingestion time, digestion time or assimilation efficiency. Similarly, there was no significant correlation between meal size (i.e., dry weight of ingested brine shrimp pellet) and either ingestion time, digestion time or assimilation efficiency. These results suggest that, under these conditions, assimilation efficiency is unaffected by either “meal” size or anemone size.     

Food choice,feeding rates,and the turnover of macrophyte biomass by a surf-zone inhabiting amphipod

The amphipod Allorchestes compressa Dana inhabits large accumulations of detached macrophytes in the surf-zone of sandy beaches in southern Western Australia. A. compressa is most abundant on branching red algae and least abundant on intact thalli of the kelp Ecklonia radiata (Turn.) J. Agardh., yet the major component of the gut contents is brown algae (probably E. radiata) and decomposing E. radiata ranked first in laboratory food preference experiments. Observations on the feeding behaviour of Allorchestescompressa indicated that the amphipods obtain their food by feeding on small pieces (< 3 cm) of macrophyte tissue trapped within the highly branched algae, or amphipods may move with and feed on the plant particles as they are swept around in the surf. In a particle selection experiment, using plant particles 1–3 mm sieved from the surf, A. compressa selected particles of Ecklonia radiata, leached Ulva sp., Sargassum spp., and seagrass leaves but avoided branching red algae. The influence of potential foods on the darwinian fitness of Allorchestes compressa was assessed on the basis of adult survival, the percentage of females which carried eggs, growth rates, and time to maturity measured in laboratory rearing experiments. Fitness increased in the order red algae → intact seagrass leaves → mixed particles (1–3 mm) sieved from the surf → Eckloniaradiata tissue. Given the constraints of fish predation and the fluctuating supply of E. radiata, amphipods in the surf consume close to their theoretically optimum diet by feeding mainly on E. radiata from amongst the available particles of different macrophytes. Estimates of the significance of the Allorchestes compressa population in the turnover of Ecklonia radiata biomass in the surf-zone (estimated as g Ecklonia consumed per g Ecklonia per day) showed that amphipods could turnover E. radiata biomass twice per month in summer and once every 1 to 2 months during spring and autumn. These rates are comparable with those measured for the physical breakdown and microbial decomposition of E. radiata and, except during winter, grazing by Allorchestes compressa must, therefore, be considered an important process during the remineralization of nutrients tied up in kelp biomass in the surf-zone.     

Accumulation of mercury in estuarine food chains

To understand the accumulation of inorganic mercury and methylmercury at the base of the estuarine food chain, phytoplankton (Thalassiosira weissflogii) uptake and mercury speciation experiments were conducted. Complexation of methylmercury as methylmercury-bisulfide decreased the phytoplankton uptake rate while the uptake rate of the methylmercury-cysteine and -thiourea complexes increased with increasing complexation by these ligands. Furthermore, our results indicated that while different ligands influenced inorganic mercury/methylmercury uptake by phytoplankton cells, the ligand complex had no major influence on either where the mercury was sequestered within the phytoplankton cell nor the assimilation efficiency of the mercury by copepods. The assimilation efficiency of inorganic mercury/methylmercury by copepods and amphipods feeding on algal cells was compared and both organisms assimilated methylmercury much more efficiently; the relative assimilation efficiency of methylmercury to inorganic mercury was 2.0 for copepods and 2.8 for amphipods. The relative assimilation is somewhat concentration dependent as experiments showed that as exposure concentration increased, a greater percentage of methylmercury was found in the cytoplasm of phytoplankton cells, resulting in a higher concentration in the copepods feeding on these cells. Additionally, food quality influenced assimilation by invertebrates. During decay of a T. weissflogii culture, which served as food for the invertebrates, copepods were increasingly less able to assimilate the methylmercury from the food, while even at advanced stages of decay, amphipods were able to assimilate mercury from their food to a high degree. Finally, fish feeding on copepods assimilated methylmercury more efficiently than inorganic mercury owing to the larger fraction of methylmercury found in the soft tissues of the copepods.     

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.     

Food, feeding and growth rates of peracarid macro-decomposers in a Ria Formosa salt marsh, southern Portugal

The diet, feeding rates and growth rates of three species of isopod and three species of amphipod from a Ria Formosa salt marsh in southern Portugal are compared to test the hypotheses that the relative success of amphipods as macro-decomposers in salt marshes worldwide can be a) attributed to their utilizing a distinctly different range of potentially available food resources and b) attributed to them using similar food resources but at different rates.The first hypothesis was tested using a combination of gut contents analysis, stable isotope analysis and multiple-choice food preference tests. The results of all three analyses showed that there was a very broad overlap in the resource utilization curves for these species for the most abundant potential foods available in the upper salt marsh. The first hypothesis was therefore rejected.The second hypothesis was tested with palatability experiments in which consumption rates of each of the test animals were compared for each potential food offered alone. The amphipods ate all five of the foods significantly faster, consuming from 3-73× more food per unit mass than the isopods.Analyses of their relative growth rates from when released from the marsupium until first breeding, showed that amphipods have a faster growth rate than isopods in the field which is consistent with other traits in their rapid development-high fecundity life-history strategy. We conclude that these data support the second hypothesis and that their morphological adaptations to a shredding, high ingestion-rate rapid gut turnover digestive strategy enable them to have a more efficient resource acquisition rate than the slower growing, lower fecundity and slower ingestion-rate longer gut throughput time strategy of most isopods.     

Feeding chronology,daily ration,and the effects of temperature upon gastric evacuation in the pipefish,Syngnathus fuscus

Synopsis Feeding chronology, daily ration, and the effects of temperature upon gastric evacuation were examined in the pipefish,Syngnathus fuscus, from field and laboratory data.S. fuscus displayed a pattern of diurnal feeding, characteristic of syngnathids. Daily ration calculations yielded estimates of 4.0 and 4.4% body weight per day, which are comparable to estimates for other teleosts. Evacuation rate was found to be temperature dependent. with more rapid evacuation with increasing temperature. In addition, evacuation rate was found to be positively correlated with gut content. Slowing of evacuation rate with decreasing gut content may allow for increased assimilation efficiency during periods of low food availability. Daily ration, although controlled by the temperature dependence of evacuation rate, may also be controlled by prey abundance; fish maximize food intake during periods of high prey availability, and maximize upon assimilation during periods of low prey availability.Contribution number 1035 of the Virginia Institute of Marine Science of the College of William and Mary.     

Filtration and digestion responses of an elementally homeostatic consumer to changes in food quality: a predictive model

In the study of the stoichiometric relationship between autotrophs and herbivores, attention has been largely focused on effects of the encountered mismatch between needs and supplies of an element on herbivore growth and ecosystem processes. Herbivore adaptation to poor food quality has rarely been investigated. This study presents a predictive model of feeding, assimilation, digestion and excretion of Daphnia facing a dietary deficiency in phosphorus. Biochemical compounds in the food were divided into phosphorous and non-phosphorus compounds. It was assumed that Daphnia is able to differently assimilate both types of compounds by regulation of target specific digestive enzymes. Feeding rate was regulated by optimal gut residence time of food particles, and assimilation efficiency by gut residence time and optimal secretion of both classes of gut enzymes. The model predicted the optimal strategy for a consumer facing an elementally imbalanced diet: (1) increase the ingestion rate, and (2) increase the secretion rate of both classes of gut enzymes. It resulted in decreased C and nutrient assimilation efficiencies, increased C feeding costs, and reduced growth rate. Sensitivity analysis showed that these predictions were qualitatively not influenced by parameter values. An alternative model was tested that includes an additive term allowing the direct excretion of C assimilated in excess. Results showed that this strategy is not optimal for the consumer growth rate. In conclusion, the model supports the hypothesis that carbon ingested in excess may generate energy that can be used to obtain more nutrients by increased feeding rate.     

Gut evacuation rates and ingestion rates of Eudiaptomus graciloides measured by means of the gut fluorescence method

Diel variation in feeding rates of Eudiaptomus graciloides wasmeasured in situ with the gut fluorescence method during Mayand June in the eutrophic Frederiksborg Slotss Pronounced dielperiodicity occurred in both periods with highest feeding ratesduring the night. The food concentration as well as the periodicitywas almost constant with depth, indicating that the feedingactivity represents a behavioral periodicity. The gut evacuationmeasured in the laboratory on field-collected copepods was exponentialand temperature-dependent. The exponential decline in gut contentwas found for both copepods feeding continuously and when feedinghad ceased. Considering spatial and temporal variation in feedingactivity, daily ratios were 61–68 body carbon per day,and higher than if calculated from existing laboratory dataof short-term feeding dates.     

Energy partitioning in the Antarctic collembolan Cryptopygus antarcticus

Abstract. 1. Consumption, production and assimilation rates were determined for two age groups of Crypropygus antarcticus to give an estimate of energy utilization, and to investigate low temperature adaptation in its energy partitioning.
2. Feeding selectivity shown in laboratory preference tests was supported by gut analysis of field animals from contrasting sites. Although moulting rate was not significantly affected by food type, rates of growth were slowest and mortality highest when fed on a non-preferred substrate.
3. Both a radio labelling and a more direct method for measuring dry weight consumed gave similar results for Cvpropygus feeding on algae. The consuniption rate for animals when feeding on algae was lower than that on moss peat. The assimilation efficiency for immature animals feeding on algae was 46% and for mature animals was 19%; the values when feeding on moss peat were 7% and lo%, respectively, The net production efficiency ranged from 35%(inimatures) to 13% (matures) and was similar on both substrates.
4. Food consumption exceeded assimilation over the range 2.5–10°C, but the two converged from 2.5 to 0°C. Immature Cryptopygus maintained a net positive energy balance over 0–10°C, whilst below 1S°C respiration exceeded assimilation for mature individuals.
5. An estimate of the annual dry matter consumption (7 g m^-1 y^-1) by Ctypropygus in a moss turf at Signy Island agrees with one based on respiration data alone (Davis, 1981). The consumption at an alga-dominated site was c . 26 g m^-2 y^-l, and Crypropygus may have a locally limiting effect on net priniary production at such sites.     

Food habits of small fishes in a common reed <Emphasis Type="Italic">Phragmites australis</Emphasis> belt in Lake Shinji,Shimane, Japan

To clarify the feeding habits of reed fishes, the gut contents of 13 fish species collected in a Phragmites australis belt in Lake Shinji were examined. Six species showed ontogenetic and/or seasonal changes in food use patterns. Smaller individuals generally preyed on small planktonic items (e.g., calanoid and cyclopoid copepods) or small crustaceans (gammaridean amphipods), subsequently changing to other prey items (e.g., mysids and filamentous algae) with growth. The most important dietary items for the reed fish assemblage comprised planktonic copepods, gammaridean amphipods and mysids. However, the relative importance of these changed seasonally, gammaridean amphipods being the most important in autumn and winter, and planktonic copepods and mysids the most important in spring and in summer. Cluster analysis based on dietary overlaps showed that the reed fish assemblage comprised five feeding guilds (planktonic-copepod, mysid, gammaridean-amphipod, filamentous-algae, and detritus feeders). Of these, the three former guilds were the most abundantly represented, whereas detritivores were represented by a single species.     

Are digestive characteristics important contributors to the profitability of prey?

Summary In the field, Spinachia fed on four types of prey; copepods, isopods, mysids and amphipods. As fish size increased, mysids gradually succeeded amphipods as the most important food type in the diet. Prey dimensions and morphometry of the fish's mouth most accurately predicted capture efficiency for amphipods, whereas for mysids capture efficiency was determined by the prey's escape response and the fish's fast-start capability. Responses to model prey revealed the ability of fish to differentiate among contrasting prey characteristics, resulting in the adoption of appropriate predatory tactics. Amphipods were associated with a shorter gut evacuation time than mysids, although approximately equal proportions of energy were absorbed from each. Similar rations of mysids and amphipods were required to satiate fish. The lower energy content per unit dry mass of amphipods was off set by their lower water content. From pre-digestive behaviour, we predicted that mysids were more profitable than amphipods, and this was reflected in the fish's choice. Conversely, incorporating the net rate of energy uptake by the gut led us to predict that amphipods were more profitable. Although physiological constraints clearly influence the net rate of energy uptake, it appears that dietary preferences are based on pre-digestive predatory behaviour and hence on time minimisation.     

A comparison of gut evacuation models for larval mackerel (Scomber scombrus) using serial photography

A novel technique is described, using serial photography of the gut contents of transparent living larval fishes, to generate individual gut evacuation time series. This technique was applied to Atlantic mackerel Scomber scombrus larvae to compare three widely used models of gut evacuation: linear, exponential and square-root. Regression r ² for the exponential model exceeded those for the linear and square root models in 20 of 21 time series, strongly supporting the exponential model. At the initial gut fullness for each time series, total gut evacuation rates calculated with the exponential model averaged 2·2 and 1·3 times greater than those calculated with the linear and square-root models, respectively, and would produce correspondingly higher estimates of feeding rates for field-collected larvae with similar levels of gut fullness. The results highlight the importance of choosing the appropriate evacuation model in feeding studies, particularly those intended to examine short-term changes in larval fish feeding rates, a contributing factor to the highly variable yearly recruitment of many marine fish species.     

Gastric emptying and the return of appetite in juvenile turbot, Scophthalmus maximus L., fed on artificial diets

Gastric emptying time in Scophthalmus maximus , when fed friable artificial pellets based on fishmeal, is composed of two phases:
(a) a delay time (t_d) during which the meal forms a bolus and which shortens with temperature, and
(b) an emptying phase (duration t_end ) which varies with meal size ( S ), body weight ( W ) and temperature (71 according to:
(where t _end is in h, S is in g, W is in g and T is °C). During the emptying phase, stomach contents decrease curvilinearly according to:
(where S_t , & S_o is in g and t is in h) in which the instantaneous digestion rate, K , varies with fish weight and temperature as:
Food pellets were prepared which remained separate and did not form a bolus in the stomach; K increased if a given meal size was subdivided to increase surface area. If meal size was increased by ingestion of identical pellets, K decreased. After a satiation meal, appetite in young turbot returns in direct relation to the degree of stomach emptiness. When food is regularly available, young turbot feed steadily at a rate which maintains their stomachs at c. 85% maximum fullness. When trained to use demand feeders, the fish interact as a group to feed rhythmically, but feeding rate falls 33% to only two-thirds of the previous rate since stomach fullness, and hence digestion rate (g h⁻¹), is maintained at a lower level. Reduction in dietary energy density below 1 kCal g⁻¹ increases gastric emptying rate and the turbot demonstrate partial compensation by increasing food intake. On energy-rich diets, protein nitrogen and energy assimilation efficiencies remain high (97 5% and 91% respectively) irrespective of feeding rate and frequency.     

Prey envenomation does not improve digestive performance in western diamondback rattlesnakes (Crotalus atrox)

Although the toxic properties of snake venoms have been recognized throughout history, very little is known about the adaptive significance of these powerful mixtures. This study examined the popular hypothesis that prey envenomation enhances digestion by influencing the energetic costs of digestion and assimilation, gut passage time, and apparent assimilation efficiency (ASSIM) in western diamondback rattlesnakes (Crotalus atrox), a species whose venom is recognized for its comparatively high proteolytic activities. A complete randomized block design allowed repeated measures of specific dynamic action and gut passage time to be measured in eight snakes ingesting four feeding treatments (i.e., artificially envenomated live mice, artificially envenomated prekilled mice, saline injected live mice, and saline injected prekilled mice). A second experiment measured ASSIM in eight snakes ingesting a series of six artificially envenomated or six saline injected mice meals over an 8-week period. Contrary to expectations, the results of both these experiments revealed that envenomation had no significant influence on any of the measured digestive performance variables. Gut passage time averaged 6 days and ASSIM averaged 79.1%. Twenty-one hours following ingestion, postprandial metabolic rates exhibited factorial increases that averaged 3.9-fold greater than resting metabolic rate. Specific dynamic action lasted on average 88 hr and accounted for 26% of the total ingested energy. The results of this study reinforce the need to systematically examine the potential adaptive advantages that venoms confer on the snakes that produce them.     

Observations on the feeding behaviour of the Antarctic Gammarid Eusirus perdentatus Chevreux, 1912 (Crustacea: Amphipoda) in aquaria

Summary The feeding behaviour of adult Eusirus perdentatus was observed in aquaria. These observations and the analysis of gut contents of preserved specimens demonstrate that this species is a carnivorous predator feeding on polychaetes, amphipods and other small crustaceans. Apparently the localization and capture of prey in aquaria follows a fixed pattern.     

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.     

A stable isotope approach to the eastern Weddell Sea trophic web: focus on benthic amphipods

Stable isotope (¹³C/¹²C and ¹⁵N/¹⁴N) analyses were performed on 90 species belonging to different benthic communities sampled in the eastern Weddell Sea. The study focused on eight amphipod species whose isotopic composition was compared to their previously described respective gut contents. Amphipod stable isotope ratios correspond fairly accurately to the trophic classification based on gut contents and attest to their wide spectrum of feeding types. Since the fundamental difference between the isotope and the gut content approaches to diet studies is the time scale each method addresses, this coincidence indicates that there would be no significant changes in feeding strategies over time. Three levels of the food web are covered by the eight species and, instead of belonging strictly to one trophic category, amphipods display a continuum of values from the suspension-feeder to scavengers.     

Assimilation efficiencies of slugs on different food materials

Summary The relative assimilation efficiencies of two common British species of slug, Limax flavus (L.) and Arion hortensis (Fér.), were studied in the laboratory using a gravimetric method. Results are given for adult slugs feeding on carrot root and potato tuber at 5°, 10°, 15°, and 20° C, and for L. flavus juveniles of known age feeding on potato at 10° and 15° C. A few results are also provided for Agriolimax reticulatus (Müller) feeding on both potato and carrot at 15° C.High mean assimilation efficiencies of 76.94 and 76.87% were obtained for L. flavus feeding on carrot and potato respectively. The equivalent results for A. hortensis were 88.60 and 89.42%. For A. reticulatus at 15° C the figures were 76.1 and 71.9%. Ingestion rates and assimilation rates are given for the first two species at all temperatures. Assimilation efficiency was found to be independent of temperature for L. flavus but not for A. hortensis. Ingestion rate and assimilation rate were temperature dependent in all cases except for A. hortensis feeding on potato. A. hortensis was more efficient at consuming both carrot and potato per gram live weight. All species consumed more potato than carrot per gram live weight.Juvenile L. flavus were found to have higher assimilation efficiencies and ingestion rates than the adults per gram live weight.Linear regression equations were determined from the relationship between dry weight of food consumed, and dry weight of faeces produced from that food for L. flavus.It is concluded that food quality and age of slug may be the factors most strongly influencing assimilation efficiency in this group.     

A Mechanistic Individual-Based Model of the Feeding Processes for Oikopleura dioica

A mechanistic physiological model of the appendicularian Oikopleura dioica has been built to represent its three feeding processes (filtration, ingestion and assimilation). The mathematical formulation of these processes is based on laboratory observations from the literature, and tests different hypotheses. This model accounts for house formation dynamics, the food storage capacity of the house and the gut throughput dynamics. The half-saturation coefficient for ingestion resulting from model simulations is approximately 28 and is independent of the weight of the organism. The maximum food intake for ingestion is also a property of the model and depends on the weight of the organism. Both are in accordance with data from the literature. The model also provides a realistic representation of carbon accumulation within the house. The modelled half-saturation coefficient for assimilation is approximately 15 and is also independent of the weight of the organism. Modelled gut throughput dynamics are based on faecal pellet formation by gut compaction. Model outputs showed that below a food concentration of 30 , the faecal pellet weight should represent a lower proportion of the body weight of the organism, meaning that the faecal pellet formation is not driven by gut filling. Simulations using fluctuating environmental food availability show that food depletion is not immediately experienced by the organism but that it occurs after a lag time because of house and gut buffering abilities. This lag time duration lasts at least 30 minutes and can reach more than 2 hours, depending on when the food depletion occurs during the house lifespan.