Gastric digestion and evacuation in whiting, Merlangius merlangus (L.)

Three meal sizes of sandeels were fed to whiting in order to monitor the evacuation of food out of the stomach. The stomach contents were sampled at intervals after feeding, using a stomach pump. In such experiments, the proportion of fish with empty stomachs tends to increase with time and, since stomach contents are limited to zero or positive values, the variance of the stomach contents becomes censored at zero. This tends to produce a curved relationship between mean stomach content and time, which gives the impression that evacuation rate slows down at low levels of stomach fullness. By taking account of censoring, it was shown that the evacuation curve generated for whiting was consistent with and could be generated from a linear model in which the rate of gastric evacuation exhibited by the fish was constant and independent of meal size, level of stomach fullness and time after feeding. The parameters of the linear model were estimated by maximum likelihood and then applied in a second model to predict the observed mean stomach content. The average gastric evacuation rate of whiting of mean weight 268 g at 10°C was 0.31 g h⁻¹.     

Effects of pre- and post-prandial starvation on meal size and evacuation rate of juvenile Atlantic salmon, Salmo salar L.

After a pre-prandial period of starvation or feeding with unlabelled food, 0+ salmon parr (0.8–11.7 g) were fed a test meal of iron particle labelled food and subsequently were again either starved or fed unlabelled food. The quantity of labelled food consumed and the evacuation rate was determined by serial radiographs. In fish of all sizes, pre-prandial starvation causes a larger test meal (as a percentage of body weight) to be consumed when compared to pre-prandially fed fish. In addition, pre-prandial starvation results in relatively larger meals as a percentage of body weight being taken by smaller compared to larger fish. This result was not evident for pre-prandially fed fish. Evacuation rate was unrelated to body size irrespective of feeding history. Post-prandial starvation decreased evacuation rate but this effect was inversely related to the quantity of food consumed. Larger meals were not evacuated differently from smaller meals if feeding occurred post-prandially, irrespective of pre-prandial starvation.     

Stomach pH,feeding rhythm and ingestion rate in Oreochromis niloticus L. (Pisces: Cichlidae) in Lake Awasa,Ethiopia

Fish were caught in February and October, 1985 with gill and trawl nets at different time intervals. The length and weight of the fish, the stomach pH and the weight of the stomach contents were determined. The feeding pattern of O. niloticus was observed to have a diel rhythm. The stomach became more acidic towards the afternoon and most of the evening. The pH of the stomach had a significant regression on stomach fullness. The feeding rate of O. niloticus in Lake Awasa was estimated from daily feeding periodicity and rate of gastric evacuation. The fish ingests 11.5% of their wet body weight daily at an average water temperature of 21.5 °C. It is believed that the fish ingests and assimilates adequate supply of energy (9.1 KJ/day) for growth, maintenance and other energy requiring activities of the fish.     

Temperature and state‐dependence of feeding and gastric evacuation in juvenile Pacific halibut

Relationships between nutritional state, behavioural response to prey and gastric evacuation rates were examined in juvenile Pacific halibut Hippoglossus stenolepis feeding on squid. Pacific halibut reared at 2, 6 and 10° C were fasted for 1 or 7 days to generate variation in energetic state. The 7 day fast resulted in measurable declines in condition indices at 10 and 6° C but not at 2° C. At 10° C, all Pacific halibut consumed the first meal offered, but fish previously fasted for 7 days took significantly longer to locate and consume the meal than fish fasted for only 1 day. At 2° C, Pacific halibut fasted for 7 days did not generally consume the first meal offered, but resumed feeding 2·1 days sooner, on average, than fish fasted for only 1 day. The gastric evacuation rate of the squid meal was best described by a power model with near‐exponential curvature ( a  = 1·011). The evacuation rate was strongly temperature‐dependent ( Q ₁₀ = 3·65) but displayed the same degree of variability at each temperature. The evacuation rate in Pacific halibut was not affected by feeding history, body size or energetic state. Furthermore, individual variation in gastric evacuation rate was not correlated with feeding responsiveness at any temperature. These results indicate a general plasticity in the behavioural but not physiological aspects of energy acquisition.     

A radiographic estimation of the effect of temperature on gastric emptying time in Sarotherodon niloticus (L) × S. aureus (Steindachner) hybrids

A radiographic technique was used to determine temperature effects on gastric emptying time in S. niloticus/aureus hybrids. Stomach evacuation times for 30 g fish fed 3% of their body weight were 8.5 h at 30° C, 10.8 h at 25° C and 16.4 h at 20° C. Hence, there was a negative correlation between stomach evacuation time and temperature. The Q ₁₀ between 20 and 30° C was calculated to be 1.92. Similar relationships were found for intestinal evacuation and total evacuation.
The data were used to estimate maximum daily feed intake levels of fish within the size range studied. Levels for 30 g fish were 8.5% body weight at 30° C, 6.6% at 25° C and 4.4% at 20° C. However, the optimum feeding regime should take account of the feeding behaviour of the animals.     

Rates of gastric evacuation in piscivorous brown trout, Salmo trutta

SUMMARY. 1. The dry weight of food remaining in the stomachs of piscivorous trout decreased exponentially with time. Gastric evacuation rates increased exponentially with increasing temperature but were unaffected by predator size, meal size or type of fish prey.
2. Mathematical models were developed to estimate both the rate and time for the gastric evacuation of different meal sizes (expressed as dry weight), and were applicable to piscivorous trout of different sizes (length range 10–32 cm) feeding on trout fry or sticklebacks at different temperatures (range 5–18°C).
3. The wet weight of food in the stomachs also decreased exponentially with time, but evacuation rates both increased with temperature and decreased with increasing meal size; the latter relationship occurred because relative rates of water loss from a meal also decreased with increasing meal size. Use of wet or dry weights can therefore lead to different conclusions about the effect of meal size on evacuation rates.
4. When piscivorous trout were fed three consecutive meals of varying size, the models predicted the total dry weight of food left in the stomach, but not the weight remaining for each individual meal. Interactions between meals led to an increase in evacuation rates for meals consumed early in the series and a decrease in evacuation rates for later meals.
5. Evacuation rates for piscivorous trout were compared with those for trout feeding on invertebrates in an earlier study, and were close to those for caddis larvae as prey, higher than those for mealworms and lower than those for a variety of invertebrate prey. Although a great deal is now known about the daily food intake and growth rates of trout feeding on invertebrates, there is little comparable information for piscivorous trout.     

Consumption and gut evacuation rate of laboratory‐reared spotted seatrout (Sciaenidae) larvae and juveniles

The temperature and mass dependence of maximum consumption rate was measured for larval and early juvenile spotted seatrout Cynoscion nebulosus . Maximum consumption ( C _MAX) estimates were obtained from feeding and gut evacuation experiments on larvae (3·8–19 mm standard length, L _S) at three temperatures (24, 28 and 32° C), and maximum consumption experiments on juveniles at three temperatures (20, 26 and 32° C). Feeding levels were determined for larvae fed live prey ( Brachionus plicatilis and Artemia salina ) ad libitum . The midgut and total evacuation times were estimated for fish feeding continuously and discontinuously using alternate meals of tagged and untagged live prey. Temperature and fish size had significant effects on gut evacuation and consumption. The gut evacuation time increased with increasing fish size, and decreased with increasing temperatures. Mass‐specific midgut contents increased for small larvae <0·156 mg dry mass ( M _D)( c . 4 mm L _S), and decreased for larger larvae and juveniles. Maximum consumption was modelled by fitting a polynomial function to a reduced dataset of individuals feeding at high levels. The C _MAX model predicted an initial increase in specific feeding rate from 70 to 155% M _D day⁻¹ for small larvae, before declining for larger larvae and juveniles.     

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.     

东、黄海鳀鱼的胃排空率及其温度影响

在室内受控条件下,以卤虫幼体为饵料,测定了不同温度下鳀鱼的胃排空率,并比较了线性、指数和平方根3种常用数学模型对其排空曲线的拟合程度.统计结果表明,3种数学模型均可较好地描述鳀鱼的胃排空曲线 (df =10, r2=0.7820～0.9629, P<0.01),综合评价结果则进一步表明,指数模型最适于定量描述其胃排空曲线,平方根模型次之,直线模型较差.在研究温度范围内,鳀鱼的胃排空率随着温度的升高而加速增大,二者之间的定量关系可以用指数函数Rt=0.0354e0.0766T (R2=0.9770)加以定量描述.     

Gastric evacuation in the sandbar shark, Carcharhinus plumbeus

Sandbar sharks maintained in an enclosure in the natural environment were fed meals of soft blue crab, Callinectes sapidus , or menhaden, Brevoortia lyrannus , and were sacrificed at intervals after feeding to measure rates of gastric emptying. Regression analysis was used to evaluate the adequacy of various models in describing the decrease in stomach contents with time after feeding. A Gompertz growth curve provided the best fit to the data for both food types. This model suggests that gastric emptying is characterized by an initial lag phase during which evacuation rate increases, a period of maximal evacuation, and a decreasing evacuation rate during the later stages of digestion. Passage of food from the stomach was slow relative to other species of fish studied. The time required to evacuate 98% of a meal was 92–3 and 70–7 h for sharks fed menhaden and blue crab respectively. Evacuation rates did not differ between day and night periods.     

The effects of temperature and different food organisms on the rate of gastric evacuation in perch (Perca fluviatilis)

SUMMARY. The rate of gastric evacuation in perch Perca fluviatilis was studied at different mean temperatures (range 4.0–21.7°C). Gastric evacuation rates were empirically described by an exponential function and the relationship between the instantaneous evacuation rate ( R ) and temperature was also exponential. Evacuation rates were not significantly different ( P > 0.1) for the following food organisms: Gammarus pulex, Chaoborus , chironomids and zooplankton. The effects of temperature, different food organisms and fish size on the evacuation rates in different fish species are discussed.     

Recovery of gastric evacuation rate in Atlantic cod Gadus morhua L surgically implanted with a dummy telemetry device

The current study investigated how the gastric evacuation rate (GER) was affected after surgically introducing dummies of a blood flow biotelemetry system into the abdominal cavity of Atlantic cod, Gadus morhua. Gastric evacuation experiments were performed two and 10 days postsurgery on surgically implanted and control G. morhua force-fed sandeel, Ammodytes tobianus. The results were compared with previously obtained estimates from unstressed conspecifics voluntarily feeding on a similar diet. After two days, GER was significantly lower in the group of fish with the dummy implants compared with the control group, but following 10 days of recovery no significant difference was seen between the two groups. The difference between implanted and control fish observed two days postsurgery may have resulted either from surgery, postsurgical stress and/or the presence of the implant. The conclusion is that 10 days of postsurgical recovery will stabilize GER in G. morhua, thus indicating that at this point the implant per se did not affect GER. Both the fish with surgical implants and controls in this study evacuated their stomachs much slower and with much higher interindividual variation compared with G. morhua feeding voluntarily on similar prey items. The lower GER and higher interindividual variation for force-fed fish indicate that handling, anaesthetization and force-feeding impair GER and that individual fish respond differently to the suppressing effects.     

Diel feeding habits of juveniles of Mullus surmuletus (Linneo 1758) in the lagoon of the Stagnone di Marsala (Western Sicily, Italy)

Diet composition, feeding rhythm, gastric evacuation rate and daily ration were investigated in juvenile Mullus surmuletus (Linneo 1758). Fish were collected in the lagoon of the Stagnone di Marsala in western Sicily, in July 1995, during a 24 h sampling period. Copepoda, Polychaeta, Amphipoda and Tanaidacea were shown to be the most frequent prey items. The feeding index values showed two different daily feeding times. A unimodal trend in the daily rhythm of food consumption was derived, with a peak in feeding between 1200 and 2000 h. Gastric evacuation in juvenile M. surmuletus is best described by an exponential model, with a gastric evacuation rate R  = 0.66 g h⁻¹ ( r = 0.88) ( T  = 24.45 ± 0.64°C). The amount of food consumed daily, calculated according to the Elliott and Persson model, was 0.079 g, equal to about 8% of the average dry weight of the fish.     

A first test of a new modelling approach to estimate food consumption in particle-feeding fish

Models for estimating food consumption in fish by analysing changes in stomach fullness over time are invariably based on a stomach evacuation rate obtained when the fish is fasting, on the assumption that this rate also applies to when the fish is feeding. However, this often is not the case in fish that feed on small particles. A new modelling approach was therefore tested, which is based not only on stomach fullness but also on gut contents. To eliminate errors arising from assimilation in the gut, titanium(IV) oxide (TiO₂) was used as an indigestible marker. When applied to a dataset obtained from tilapia given several equal doses of pelleted feed over a 2.5‐h period, the new approach gave a closer true consumption estimate than a conventional model. The evacuation rate proved to be a more sensitive parameter than the ingestion rate, but the former was no longer required by the new approach for estimating ingestion, thus liberating the food consumption estimate from any errors and dependencies inherent in the evacuation rate. The new approach assumes that the digesta of previous feedings can be distinguished from those of the feeding phase being analysed and therefore needs further refinement for those cases when this does not apply. Suggestions for such refinements are also given. This new approach is expected to be equally suitable for estimating consumption in stomachless fish.     

Estimation of food consumption from field observations of fish feeding cycles

The available methods of estimating food consumption by fish require that experiments be performed on confined animals and that experimental results may be validly applied to free fish. A method is described by which food consumption in periodically feeding fish may be estimated without performing laboratory experiments. A relatively simple input–output model of stomach contents is fitted to the observed time trajectory of stomach fullness, and food consumption is calculated from the estimated model parameters. Feeding is considered to be restricted to a distinct feeding period, and the rate of feeding during that period can be either constant or linearly decreased with the quantity of food already present in the stomach.
The method is applied to three examples. The model appears robust, and generally provides very similar food consumption estimates to those obtained from methods requiring an independent estimate of gastric evacuation rate. However, the described method is sensitive to violation of the assumption that feeding occurs only during a discrete feeding period.     

鱼类的胃排空率及其影响因素

鱼类的胃排空率是研究鱼类能量学的重要参数,近年来国外有关研究结果表明,鱼类的胃排空率除了受鱼体自身生理状况和实验方法的影响以外,还受许多其它因素,如：鱼的种类,鱼体重,温度,食物,摄食频率以及饥饿时间等的影响。这些资料将为我国开展该方面的研究工作提供有价值的参考作用。     

The effects of predator size, temperature, and prey characteristics on gastric evacuation in whiting

No effect of prey size on gastric evacuation rate was found in whiting Merlangius merlangus .Prey energy density explained most of the data variation among fish prey, and evacuation time increased by a factor 1·6–1·7 with prey energy density increasing from 3·4 to 5·6 kJ g⁻¹. The power model expanded to include predator size, temperature, and prey energy density could describe gastric evacuation in whiting fed fish prey. Krill Meganyctiphanes norvegica was evacuated at a rate similar to fish prey of equal energy density, while the evacuation of brown shrimp Crangon crangon took almost twice as long.     

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.     

Effects of temperature, prey type and prey size on gastric evacuation in small cod and whiting

Gastric lavage was used to investigate the effects of temperature, prey type and prey size on gastric evacuation in small cod Gadus morhua and whiting Merlangius merlangus . The fish were fed to satiation and subsequently the stomach contents were sampled to determine the rate at which food was evacuated. Satiation meal size was positively related to temperature and differed between prey types. The gastric evacuation rate (GER) also tended to increase with temperature and varied with prey type. GER at temperatures of 11.3–12.7° C averaged 1.5–1.7 times higher than at 6–9.5° C. There was no significant difference (P>0.05) in the evacuation of lugworm Arenicola marina , sandeel Ammodytes spp., and herring Clupea harengus , but the GER of brown shrimp Crangon vulgaris was much slower (P<0.05). No significant changes in GER were observed when fish were fed on three different size groups of either herring or brown shrimp. In whiting, there was no significant difference in the GER of individual herring or brown shrimp when they were fed as single species meals or incorporated in meals containing a mixture of prey species.     

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.