A REVIEW OF METHODS USED FOR ESTIMATING GUT EVACUATION

RATES AND CALCULATING DAILY RATION FOR FISH

Richard W. Langton Northeast Fisheries Center Woods Hole Laboratory Woods Hole, Massachusetts 02543 Laboratory Reference No. 77- 07 May 1977

INTRODUCTION

In the past, little effort has been made to combine digestion rate

data and food habits studies to determine the food.turnover for a given

population of fish. Ten years ago Windell (1967) reviewed the status of

digestion studies in fish and suggested that, at that time, one of the

most outstanding needs in future research was to ~stimate food consumption

in terms of the daily ration. Since the amount of digestible food

consumed largely determines the growth and production rates in any

population, information on the daily ration is needed in order to model

natural populations or develop controlled ecosystems for fish culture.

In recent years more emphasis has been placed on combining laboratory

and field studies to determine digestion rates in fish experiencing near

natural conditions. Most of these studies have recently been reviewed by

either Kapoor et ale (1975) and/or Grove et ale (1977). The purpose of

this review is to update these previous articles where necessary and to

identify the factors which must be considered in attempting to convert

the food habits data collected by the Northeast Fisheries Center, Woods

Hole Laboratory, into estimates of the daily ration for selected Northwest

Atlantic fish species.

The review is divided into four general sections. The first

describes the methods used in determining digestion or gut evacuation

rates. It should be mentioned here that digestion rates should more

accurately be termed evacuation rates. Most of the experiments described

herein have only determined the rate of removal of food from the stomach or

gut without any reference to abscirption of the food or undigestible

materials. The fish literature uses the words digestion and·evacuation

interchangeably and no attempt has been made in this paper to distinguish

between terms. The second section of the review considers factors

influencing gut evacuation times and is. follow~d by a brief discussion

of factors which generally affect the collection of food habits data.

The final section of the paper considers the various models for determining

gut evacuation rates and the methods which have been proposed in

calculating daily rations.

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METHODS FOR STUDYING GUT EVACUATION RATES

The methods used to study gut evacuation rates in fishes have combined

a variety of laboratory and field techniques. They can, however, be broken

down into at least three general categories as out"ined by Kapoor et ale (1975).

Recovery of Stomach Contents

Fi sh have been fed known quant it i es of food and at predetermi ned i nterva 1 s

the amount of food remaining in the stomach was established by sacrificing the

, fish or pumping out the stomach. Markus (1932) followed digestion in largemouth

bass, Huro floridana (Micropterus salmoides), af~er force feeding with minnows,

by injecting a nitrous acid solution to induce' the fish to regurgitate their

stomach contents. Bajkov (1935) recovered and measured volumetrically the

partially digested food from the stomach of whitefish, Coregonus clupeaformis,

at different times after capture. Unfortunately, Bajkov's work is somewhat

compromised because he did not know the exact quantity of food consumed and

digestion rates are influenced by meal size (see next section). Hunt (1960)

determined the digestion rates for the Florida gar, Lepisosteus platyrhincus,

the warmouth, Chaenobryttus gul os us , and the 1 a l"gemouth bass, Micropterus

salmoides. The fish were allowed to feed voluntarily or else were force fed

a known quantity of mosquitofish and the volume of the stomach contents

measured at predetermined intervals. Darnell and Meierotto (1962) studied

the feeding chronology of black bullheads, Ictalurus mel~s, by using a

standard food item as an indicator of the degree of digestion for the entire

stomach contents. The amphipod, Hyalella, was selected as the standard food

item since it made up more than half the bullheads natural diet. Fish were

collected and held in the 'laboratory where the digestion rate of the amphipods

was followed under controlled conditions. More fish were then collected

over a 24 hour period and the index of digestion for the amphipods was used to

establish the feeding chronology of the fish in nature. The food habits and

digestion rates of eight species of freshwater fish were investigaged by

Seabury and t10yle (1964). Fish were collected by seining, a subsample taken

for the immediate determination of stomach contents volume-, and the remaining

fish placed in food free live boxes on the lake bottom. At specified time

intervals the fish were removed from the live boxes for stomach contents

analysis. Alternatively, the fish were force-fed a known quantity of food

and their stomachs were pumped free of food for 'volume determinations, again,

at measured inte~vals. Pandian (1967) kept his fish, Megalops cyprinoides, at

2SoC and starved them for two days before determi~ing their digestion rate

when fed prawns weighing 2% of the fishes body weight. At measured time

intervals a fish was killed and the stomach contents weighed. A near linear

relationship between the percentage of food digested and time was found after

an initial lag period during which little weight loss of the stomach contents

was recorded. Windell (1966) also starved his fish, the bluegill sunfish,

Lepomis macrochirus, for a period of three days under constant temperature

conditions.' As in Pandian's experiment, the fish were fed a known quantity

of food and the percentage decrease in stomach contents measured over time.

However, Windell measured the digestion rate as digestible organic matter

which was defined as dry weight minus tne ash plus chitin weight. Thi's

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method was again used by Kitchell and Windell (1968) and Windell and Norris

(1969) when studying gastric digestion in the pumpkinseed sunfish, Lepomis

gibbosus, and rainbow trout, Salmo gairdneri, respectively .. Windell (1967,

1968) gives details of the methods involved in using the dried digestible

organic weight technique. Magnusun (1969) fed white bait of a known average

dry weight to skip jack tuna, Katsuwonuspelamis. Over the following 24 hours

the tuna were sacrificed and the quantity of food consumed was determined by

counting the number of partially digested fish in the stomach and multiplying

. this number by the average weight for the white bait. The decrease in dry

weight .was a meaSUl"e of the digestion rate. Tyle.r (1970) acclimated .young

cod to various temperatures and starved them fbr three days prior to feedih~

a standard meal of shrimp tails. Digestion rates were determined by

measuring the decrease in the dry weight of the stomach contents over time.

Brett and Higgs (1970) feed sockeye salmon, Oncorhynchus nerka, food pellets

of known biochemical composition. Fish were periodically anaesthetized,

frozen, and the frozen stomach contents dissected into preweighed crucibles

for determination of the dry organic weight. Beamish (1972) determined the

dry weight, protein N, lipid and caloric content of the stomach contents of

thermally acclimated large mouth bass, r~icroptey'us salmoides, following a

meal of shiners. Swenson and Smith (1973) used a rather ingenious method

of coding the food items fed to walleye, Stizostedion vitreum vitreum, in

order to quantify the digestion rate. Minnows VJere weighed to 0.1 gm and

then marked with a colored thread sewn below the dorsal fin. The walleye

were force fed the marked minnows which could later be identified and weighed

after the partially digested food was remoVed from the stomach using a

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stomach pump. Steigenberger and Larkin (1974) examined the feeding activity

and digestion rate of the northern squawfish, Ptychocheilus,oregonensis, by

force feeding a quantity of redside shiners to fish that had been starved

for 72 hours. They followed the digestion rate by pumping out the stomach

contents of anesthetized fish at six hour intervals for twenty four hours

after feeding. In an attempt. to avoid starving the fish prior to determining

the digestion rate, Daan (1973) maintained cod, Gadus morhua, on a diet

of shrimp for two weeks. He then switched the diet and fed a known weight

of sprat which could easily be distinguished from the shrimp remains in

the stcimach. Jones (1974), in his study of haddock, Melanogrammus aeglefinus,

cod, Gadus morhua, and whiting, Merlangius merl~ngus, compared three methods

of determining gastric evacuation rates. He fed a single meal to previqusly

starved fish and followed the digestion time or, kept them on a regular

feeding schedule and periodically sacrificed fish or, for haddock only)

followed their digestion rate after capturing the fish from an area where

they were known to be feeding on brittle stars. The first two methods gave

different results with the single meal experiment giving consistently lower

digestion rates than the regular feeding technique. The experiment with

brittle stars was not directly comparable since the actual quantity of prey

consumed was unknown. For anyone method, however, the digestion rate i.n

all three species was similar.

Although the following method has not recently been used in fish

digestion rate studies, it warrants mentioning since Riddle (1909) quotes

it as fi~st being used in 1783 by Spallanzani and Sonebrier. Glass tubes

(Mette's Tubes) are filled with coagulated egg albumen and placed in the fishes

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stomach. After a specified time interval the tubes are removed and the

. degree of digestion of the egg albumen noted. Riddle (1909) used this

technique with Amia calva while Pegel (1950) actually prepared an intestinal

fistula for the insertion of Mette's tubes in the foregut and hindgut of

Leuciscus 1. biacalensis. Mette's tubes were also used by Chepik (1964)

to study seasonal changes in the digestive enzyme activity of carp.

Radiographic Methods

The use of x-ray techniques can be particularly successful in studying

digestion of piscivorous fish species. The decreasing visibility of the

bony elements and swim bladder of the prey, together with a change in

position of these elements to each other, was used by Molnar et ale (1967)

to study digestion in a number of European fishes. Edwards (1971, 1973) also

used the x-ray technique to study digestion ration in plaice, Pleuron~ctes

platessa, but he fed the fish lugworms injected with barium sulphate so

that. the prey items were x-ray opaque. Other people have incorporated x-ray

markers into the fishes diet to monitor food translocation (Kevern, 1966;

Peters and Hoss, 1974). In some transparent species, ordinary photographs

may serve the same purpose as x-rays. For example, Rosenthal and Hempel

(1970) have investigated the digestion rate in transparent herring larvae

from photographs taken at two hour intervals.

Food Intake and Defecation

Various workers have estimated gut evacuation rates by observing the

time be~ween feeding and the production of faeces. This technique is farily

uncomplicated in fish like the caspian roach~ Rutilus r. caspius (Bokova, 1938),

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and the pond roach, Misgurnus(Scheuring 1928), where a small meal is

excreted as a single dropping. However, most fish larvae and miriophagous

adults will feed continuously and it is necessary to label a portion of the

diet so that it may be identified in the faeces. Rozin and Mayer (1961) fed

pellets to goldfish at a constant rate over a one hour daily feeding period.

They then substituted pellets containing carmine and timed the interval

until the production of colored faeces. The first colored faecal material

'was produced seven hours after ingesting the meal, but the remaining labelled

faecal material was produced from eight to twenty-four hours after ingestion.

Much work on larval or juvenile fishes has employed a similar technique of

feeding dye labelled food. (Lane and Jackson 1969; Blaxter 1965; and Laurence

1971.) It should be noted that measuring faecal production after a spe~ified

meal is not necessarily comparable with the previous methods described which

generally deal only with stomach evacuation times ..

FACTORS INFLUENCING GASTRIC EVACUATION

Various methodologies have been used in the digestion rate experiments

described in the first section of this review. Each of these methods result

in different experimental conditions which may have some influence on the

observed results. A number of specific factors have been identified which

are known to influence the rates of gastric digestion under experimental or

natural conditions and these are listed and discussed individually below.

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Temperature

For poikilotherms, the digestive rate, as with most metabolic processes,

is greatly influenced by temperature and the thermal history of the animal.

Temperature changes may affect the digestion rate by influencing any of the

following temperature-dependent functions: 1) feeding rate; 2) secretion

of digestive enzymes; 3) activity of digestive enzymes; 4) motility of the gut

and 5) assimilation of digested foods. Both Kapoor et. ale (1975) and Grove et ale

(1977) review most of the literature on temperature along with presenting figures

summarizing the effect of temperature on digestion in fish. (See Fig. 1)

In general Kapoor et ale (1975) concluded that every rise in temperature of

100 C wi1l increase the digestion rate by a facto~ of 3 or 4. However, not all

the fish used in his example were fully acclimated to the test temperature. If

the fish were completely thermally acclimated, the slope of the line relating

temperature and digestion rate would not necessarily be as steep. It should also

be noted that as the temperature approaches a fishes upper lethal limit the

digestion rate may be depressed and the fish wil"' not eat (Tyler, 1970).

Body Size

The relation between body size and digestion rate has been established for

a number of, different fish species. In general, bigger fish will digest a

greater amount of food than smaller fish. However, if the size of the fish is

taken into consideration, and the amount of food digested is expressed as per

gram of fish, smaller fish have a higher evacuation rate. For example, Pandian

(1967) found that a 5.12 g fish digested the same amount ~f food as a 90.6 g

fish in approximately one third the time. Since small fish have a relatively

hi~her digestion rate it might also be expected that they will consume

relatively more food per day. This has been found to'be true for at least

Curve til>.

1 2 3 4 :> 6 7

8 {}

0.4r--"""I"'-""-O--,.--.--...----.---.

0.2

0.1

0.05

0.02

-":- 0.01 :! ::J o . e O•005 e

f c ~ 0.002 et ., en

. :; 0.C01 '--~5-':-'.:O--:-!15:--"""2."..O--::2c1=5--::3..i:.·)-'

temp. (Oe)

Fish species Food

Fundtdus heteroclitus clam mantles M isgufnus jossilis .. Oligochaetes and Gammarus ltf ulltts barbatu8 Polychaetes ],1 icropterus salmoides Alburnus alb. Sebastes inermis 7 % of body weight Lucioperca lucioperca Alburnu8 alb. lctaluru~ pu.nctalu~ pellets

(Calculated from time of 50% depletion of stomach cont~nts)

shrimp tails Gadus morhua Oncorhynchus nerka canned salmon and pellets

Author

Nicholls, 1933 Scheuring, 1928 . Lipskaya, 1959 Fabian et al., 1963 Kariya, 1969 Molnar a.nd Tolg, 1962 Shrable et al .• 1969

Tyler. i970 Brett and Higgs, 1970'

Figure 1. Digestion rate in relation to temperature.

(From: Kapoor et. a1. 1975)

sockeye salmon. Brett (1971) fed different size ~roups of salmon an artificial

diet to determine the maximum daily voluntary food intake. When expressed as a

percentage of the dry body weight, he found that the diet dropped from an

average of 16.9% for a 4 g fish to 4.3% for a 216 g fish. In absolute

terms, though, the small fish consumed 0.68 g while the large fish ate

9.29 g.

Meal Size

In evaluating the effect of meal size on digestion, it is· important to

consider how various authors have presented theil~ data. The effects of meal

size have usually been expressed as the time t~kento empty the stomach or as

a percentage decrease against time. For example, Windell (1966) found that the

time for the stomach of a bluegill sunfish to empty following a small or large

meal of Tenebrio was similar. Clearly, however, the rate of digestion of the

larger meal (expressed as weight/unit time) must be greater. In general then, .~

it has been found that a larger meal i~ digested at a greater rate than a smaller

meal of a similar type (Hunt 1960; Beamish 1972; Swenson

and Smith, 1973; Joblinget a1. 1977). It may also be true that a smaller meal

is digested sooner than a larger meal, as suggested by Barrington (1957), because

of a larger surface to volume ratio. For example, a fourfold increase in the

ration size of a large mouth bass, Micropterus, only doubled the time required for the

fish's stomach to empty (Beamish, 1972). Likewise, an increase in ration size

from 1 g to 5 g for a 100 g dab, Limanda, caused a 3.8 fold increase

in the time for the stomach to empty (Jobling et ale 1977). In both examples,

however, the digestion time for the larger meal was offset by a greater rate of

digestion, perhaps due to a greater stimulation of enzyme secretion (Norris

et ale 1973) Dr gastric motility (Burnstock 1958).

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The rate of stomach evacuation has been found by Jdnes (1974) to be

related to meal size in three gadoids by the exponent O.46~ i.e., digestion

rate = (meal size)0.46. Windell et ale (1969), Mc Kone (1971), and Beamish (1972)

have found that digestion rate is related to meal size raised to the power 0.6,

0.7 and 0.75 for Salmo gairdneri, Prosopium and Micropterus respectively. In

one instance digestion rates have been found to be directly proportional to

the meal size (Windell, 1966) while Steigenberger and Larkin (1974) showed that

the digestion rate of Plychochei'lus actually decreased with.an increase in

meal size. As Grove et ale (1977) mentioned, many more species need to be

studied before this fish can be called anomalous.'

Diet Composition

Data on digestion of different food items suggests that the composition

of a fish's diet will have a substantial influence,on the rate of gastric

evacuation. There is apparently a lag period of variable duration after most

any food item enters the stomach and before it begins to be digested. For

example, Jones (1974) fed several gadoids a variety of fish and crustaceans in

an attempt to compare the digestion rate for different foods. Pollack was 'used

as the standard diet and it was found by extrapolation of a fitted regression line,

that the pollock remained in the stomach for approximately l~ hours, at 120 C,

before the stomach contents lost weight. Most other fish tested had similar lag

times except for Centronotus VJhich remained intact for up. to 20 hours. The

crustaceans, Crangon, Carcinus and Nephrops were similarly tested and remained in

the stomach unchanged anywhere from 10-40 hours. The differences in digestion

rate between fish and crustacea may be attributed to the presence of the hard and

thick exoskeleton of shrimps and crabs. Hard food parts have been observed by

Windell (1966, 1968), Edwards (1971), and Kionka and \'Jindell (1972), to take longer

to be evacuated from the stomach than softer more easily digestible food items.

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The difference in the digestion rate for the various fish species may relate to

differing biochemical composition or even hydrolysis of the food once it is in the

stomach. Karpevitch and Bokova (1936, 1937) showed that different foods are

digested at different rates and that fat retarded digestion. ,Windell (1967)

suggested that fat might influence the digestion rates observed in bluegill

sunfish while Windell et ale (1969) showed that diets with increasing fat levels

decreased the gastric evacuation rate in rainbow trout. Hydrolysis of a food

item has also been observed under experimental conditions'which resulted in an

initial depression of the observed digestion rate (Herting and Witt, 1968;

Steigenberger and Larkin, 1974).

A number of other workers have detected a decrease in digestion rate for

different food items. Elliott (1972) found that b~own trout evacuate gammarids

or oligochaetes in approximately 22 hours (l20 C) while Protonemura, Hydropsyche,

and Tenebrio took 26, 30 and 49.5 hours respectively. Pandian (l967) feeding

Megalops on Gambusia or Metapenaeus and Hestern (1971) feeding Cottus and Enophrys on

Tubifex, Calliphora or semifluid meals also found differential rates of digestion.

"Feeding'FreguencyandForce-Feeding

Experimental determination of digestion rates usually involves handling

the fish, a period of starvation in order to completely empty the stomach and,

either letting the fish feed voluntarily or force-feeding anesthetized animals.

These conditions all deviate from what a fish usually experiences in nature and

consequently the merits and disadvantages of various experimental techniques

have been discussed. Windell (1967) sites a number of papers describing the

physiological effects of handling fish and these may vary anywhere from

hyperglycemia to death. In any experimental situation, handling cannot be

avoided and one has to be satisfied that it is kept to a minimum.

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When measuring digestion rates, starvation of experimental animals should be ,

kept to a minimum, lasting only long enough to allow the animals to clear their

stomachs, or else avoided completely by feeding easily distinguishable food items.

The influence of starvation and feeding frequency in adult fi·sh have most recently

been investigated by Windell (1967), Tyler (1970) and Jones (1974). In general,

it was found that the digestion rates measured in previously starved fish were

only 50 to £0% of those in fish which were on a regular feeding schedule. Similar

results have been found for larval fish by Blaxter ~nd Holliday (1963), Laurence

(1971), Rosenthal and Paffenhofer (1972) and Nobel (1973).

Force-feeding is often used to insure that the fish consumed a known quantity

of food ~t a specified time. Few workers hav~ critically evaluated the effect that

force-feeding has on the fish. Hunt (1960), during a study of the digestion rate

of the Florida gar, warmouth and largemouth bass observed little difference

between fish that fed voluntarily and those that were force-fed. The influence of

forced versus voluntary feeding was compared statistically during a study of the

walleye by Swenson and Smith (1973). They concluded that force-feeding does in

fact bias the results obtained on digestion rates. Force-feeding decreased

the rate of gastric evacuation,as had been suggested by Windell (1966).

FACTORS AFFECTING FOOD HABITS DATA

The food supply for a fish population is one of the primary factors controlling

production. The purpose of collecting data on digestion rates is usually to use

the information together with estimates of the average amount of food in the fishes

stomach to establish the daily or yearly ration. In carrying out laboratory or

even field experiments to determine either the food habits or digestion rates, a

number of factors which may influence the results have to be considered. Some of

the major difficulties in studies of this type are discussed below.

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Feeding Chronology

The accurate determination of the daily feeding chronology requires sampling

of a fish population over a number of 24 hour periods. Consequently, this type of

experiment has only rarely been carried out successfully. Darnell and Meierotto

(1962) suggested a methodology for determining the 24 hour chronology of feeding

intensity in natural fish populations based on stomach contents analysis and

digestion rates for a standard food item. Using. this method they identified two

distinct feeding periods, one just before dawn and one shortly after dark, in a

population of black bullheads. Swenson and Smith (197~) evaluated the diel feeding

periodicity of walleye by collecting fish at t\AJO hour intervals over a total of

16 days." They calculated the percentage of the total meal consumed for each two

hour period and found that feeding was rhythmic at least from July through

September. Daily patterns of feeding intensity for other fish populations have

been observed by Keast and Welsh (1968), Holton (1969), Olla et al.(1969, 1974),

Narver (1970), Steigenberger and Larkin (1974), Merrett and Roe (1974), Timokhina

(1974), Thijssen et ale (1974), Baird et ale (1975), Girsa (1975), and

Ebeling and Bray (1976).

Sea~onal fluctuations in food habits have been observed for both freshwater

and marine fish. Seaburg and Moyle (1964) found a decrease in the quantity of

food in the stomach of some Minnesota lake fish over a summer long study of food

habits. For marine fish, difficulties in sampling the same population over a year.

compromise studies of seasonal changes in food habits. Despite this problem

Wigley and Theroux (1965), Vinogradov (1971) and Tyler (MS 1971) have found a

seasonal change in food habits for various marine fish.

Apart from daily and seasonal changes in food habits, sampling technique is

pro~ably the biggest factor influencing the estimates of daily rations made from

field samples. If the average amount of food in the ·siomach is used in calculating

. the ration, then two major sources of error may affect the results. First is the

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sample size. If, for example, fish feed ver'y intensely over a short period during

the day, too sm~l a sample could either grosslY overestimate or underestimate

the mean stomach contents weight. The second source of error is caused by the

length of time the fish are retained in the gear before the stomachs are removed

and the contents preserved. Food intake presumably ceases once the fish are caught

(Hopkins and Baird 1975) but gastric evacuation will continue. There are undoubtedly

other factors influencing the average stomach contents such as regurgitation and

swallowing other fish after being caught in the'gear, but these are difficult to quantify ...

The first two factors mentioned above have recently been incorporated into a simple

.differential equation model describing the level of food in the stomach (Eggers 1977).

CALCULATING DIGESTION RATES AND O'AILY RATIONS

A variety of techniques have been utilized 'in analyzing gastric evacuation

rates. Magnuson (1969), Kitchell (1970), and Swenson and Smith (1973) fitted a

first or second order polynomial regression to their data while Tyler (1970),

Brett and Higgs (1970) and Elliott (1972) found that an exponential regression

best described their results. In contrast, Daan (1973) fitted a straight line

regression to his data on gastric evacuation in cod. In comparing his data to

Tyler's (1970) data on cod, Daan states that the curvilinear fit described by Tyler

was primarily due to the last 10% of the stomach contents, and for at least the

initial phase of digestion a linear fit to the data would be adequate. Windell

et ala (1976) compared various methods in describing their data on gastric

evacuation by rainbow trout. Different regressions produced different predictions

with the greatest variation occurring when predicting the length of time necessary

to completely empty the stomach. They found that the time for complete stomach

evacuation could range from 22 to 35 hours ~epending entirely on the method used

to analyze the data. Because of the variability between methods) it was suggested

that the actual type of regression equation chosen to describe any data on evacuation

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rates be chosen statistically using an analysis of variance and F statistics.

In the case of Windell IS rainbow trout, a semilbg relationship of the form:

% evacuation = a + b log Time was chosen as the best fit regression.

Four equations have been proposed which may be used to c.alculate estimates

of the daily ration. Bajkov (1935) suggested the following formula:

where: D = the daily ration

D = A 24 n

A = the average amount of food in the stomach

n = the number of hours necessary to completely empty the stomach

Bajkov's formula assumes that feeding is effectively continuous, that

digestion continues at the same rate throughout the day and that the amounts

and kind of food do not influence the rate of gastric evacuation. Since most

of these assumptions are not valid, Davis and Warren (1968) do not recommend the

use of Bajkov's formula. Nevertheless, this methodology had been adopted and

modified slightly by Darnell and Meierotto (1962) and Seaburg and Moyle (1964)

in their calculation of the daily ration of some freshwater fishes.

A second formula has been suggested by Daan (1973):

where: ~L = daily ration for a given length fish

wL = average weight of the stomach contents for a given length fish

DL ; digestion time in days for a given length fish

Rewriting the equation in Bajkovls terms, it becomes:

D = 2 • A n

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From the resul ts of 1 aboratory experiments, Daan assumed that gastr.i c evacuati on was

a linear function of time and therefore the daily ration was twice the average

amount of food in the stomach divided by the time for gastric evacuation. This

assumption, however, does not consider feeding periodicity and the possibility that

there is a differential rate of digestion for the various prey items. The formula,

therefore, suffers from some of the inadequacies which were discussed in reference

to Bajkov's equation.

The third method for calculating the daily ration has been. proposed by Swenson

and Smith (1973) and is of the form:

C - Lt Lt (-L·f SC)

F

where: C = daily food consumption in grams for the .average fish

SC = weight of the undigested stomach contents for foods of a given

size and not more than 90% digested, during a specified time period

Lf = summation'of corrected weight of stomach contents for all the

fish in the sample, having consumed food nf a given size, during a

specified time period

F = number of fish in the sample which could have contained food of a

given size, not more than 90% digested, during a specified time period

LS = summation of food sizes

Lt = summation of time

The use of Swenson and Smith's method requires the determinafion of the degree of

digestion of the food items in the stomach and the establishment of length-weight relation­

ships for the various prey items so that the original weight of an item may be estimated

from the partially digested ramains. This technique is similar to that of Fortunatova

(1950, 1951, 1955; See also Popova 1967) and has apparently been used extensively by Russian

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workers (see Davis. and Warren, 1968). The major difficulty in ,using this

technique would be establishing accurate estimates of the "reconstructedll

weight for the variety of prey items eaten by various fish. It is most

appropriate for piscivorous fish which feed infrequently.

Another approach for calculating the daily ration would be to measure

growth rate and metabolic rate and then calculate the ration necessary to

sustain the fish. Winberg (1956) proposed the following formula for calculat­

ing food consumption:

where: C = consumption

R = respiration

LlB = growth

c = 1 .25 (R + AB)

Estimating food consumption in nature from laboratory growth studies using

coho salmon has been attempted by Carline and Hall (1973). They held fish in

an outdoor stream tank, where natural social behavior patterns were established,

and compared the growth with fish held individually in restrictive aquaria. The

growth rate of the groups fed identical rations was similar and it was concluded

that laboratory growth data could be useful in field extrapolations as had been

suggested by Davis and Warren (1968). This technique may be used in conjunction

with the methods estimating daily consumption based on stomach contents as a

check on some of the assumptions and apparent shortcomings of those methods

(Backiel 1971; Adams 1974).

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REFERENCES

Adams, S. M. 1974. Structural and Functional Analysis of Eelgrass Fish Communities. Ph.D. thesis, The University of North Carolina at Chapel Hill. 131 pp. '

Backiel, T. 1971. Production and Food Consumption of Predatory Fish in the Vistula River. J. Fish Biol. 3, 369-405.

Bajkov, A.D. 1935. How to Estimate the Daily Food Consumption of Fish Under Natural Conditions. Trans. Am. Fish. Soc. 65, 288-289.

Baird, R. C., T. L. Hopkins and D. F. Wilson. 1975. Diaphus taaningi Norman in the Cariaco Trench.

Feeding Chronology of Copeia 1975, 356-365.

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Carline,'R.F. and J. D. Hall. 1973. Evaluation of a Method for Estimating Food Consumption Rates of Fish. J. Fish. Res. Bd. Can. 30. 623-629.

Chepik, L. 1964. Activity of Carp Digestive Enzymes at Different Seasons of the Year. Biological Abstracts 47, (1966) 60747.

Daan, N. 1973. A Quantitative Analysis of the Food Intake of North Sea Cod, Gadus morhua. Neth. J. Sea Res. 6, 479-517.

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Davis, G. E. and C. E. Warren. 1968. Estimation of Food Consumptinn Rates. In: W. E. Ricker (ed.). Methods for Assessment of Fish Production in Fresh Waters. Chapter 10, pp 204-225. IBP Handbook No.3 B1.ackwell Scientific Publications, Oxford and Edinburgh.

Ebeling, A. W. and R. N. Bray. 1976. Day Ver~usNight Activity of Reef Fishes in a Kelp Forest off Santa Barbara, California. Fish Bull. 74, 703-717.

Edwards, D. J. 1971. Effect of Temperature on Rate of Passage of Food' through the Alimentary Canal of the Plaice Pieuronectes Platessa L. J. Fish. Biol. 3,443-439.

1973. The Effects of Drugs and Nerve-Section on the Rate of Passage of Food through the Gut of the Plaice, Pleuronectes Platessa L. J. Fish Biol. 5,441-446.

Eggers, D. M. 1977. Factors in Interpreting Data Obtained by Diel Sampling of Fish Stomachs. J. Fish. Res. Bd. Can. 34, 290-294.

Elliott, J. M. 1972. Rates of Gastric Evacuation in Brown Trout, Salmo trutta L. Freshwater Biology 2, 1-18.

Fabian, G., Molnar and I. Tolg. 1963. Comparative Data and Enzyme Kinetic Calculations on Changes Caused by Temperature in the Duration of Ga~tric Digestion of some Predatory Fishes. Acta Biologica Academiae Scientiarum ' Hungaricae 14, 123-129.

Fortunatova, K. R. 1950. (Biology of Feeding of Scorpaena Porcus L.) Trudy secastopol. biol. Sta. 7, 193~235.

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Girsa, I. I. 1975. The diurnal Rhythm in the Feeding of Underyear1ings of' some White Sea Fish at Different Photoperiods. J. Ichthyo1. USSR 15, 102-110.

Grove, D. J. et ale 1977. Manuscript in Preparation.

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Holton, A. A. 1969. Feeding Behavior of Vertically Migrating Lanternfish. Pac. Sci. 23, 325-331.

Hopkins, T. L. and R. C. Baird. 1975. Net Feeding in Mesopelagic Fishes. Fishery Bulletin 73, 908-914.

Hunt, B. P. 1960. Digestion Rate and Food Consumption of Florida Gar, Warmouth and Largemouth Bass. Trans. Am. Fish. Soc. 89, 206-210.

Jobling, J., D. Gwyther and D. J. Grove. 1977. Some Effects of Temperature, Meal Size and Body weight on Gastric Evacuation in the Dab Limanda 1imanda (L). J. Fish Biol. 10, 291-298.

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Kariya,'T. 1969. The Relationship of Food Intake to the Amount of Stomach Contents in Mebaru, Sebastes inermis. Bull. Jap. Soc. Scient. Fish. 6, 533. Abstract only.

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Karpevitch, A. F. and E. N: Bokova .. 1937. The Rate of Digestion in Marine Fishes, Pt. II. Zoblogicheskij Zhurnal 16, 21-44. In Russian with English summary.

Keast, A. and L. Welsh. 1968. Daily Feeding Periodicities, Food Uptake Rates, and Dietary Changes with Hour of Day in Some Lake Fishes. J. Fish. Res. Bd. Can. 25, 1133-1144.

Kevern, N. R. 1966. Feeding Rate of Carp Estimated by a Radiosotopic Method. Trans. Am. Fish. Soc. 95, 363-371.

Kionka, B. C. and J. T. Windell.· 1972. Differential Movement of Digestable and Indigestable Food Fractions in Rainbow Trout, Salm0 gairdneri. Trans. Am. Fish. Soc. 101, 112-115.

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Kitchell, J. F. and J. T. Hindell. 1968. Rate of Gastric Digestion in Pumpkinseed Sunfish, Lepomis gibbosus. Trans. Am. Fish. Soc. 97, 498-492.

Lane, T. H. and H. M. Jackson. 1969. Voidance Time for 23 Species of Fish. U.S. Bur. Sport. Fish. Wildl. Inv. in Fish COhtrol No. 33. 9 pp.

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Molnar, G. and I. Tolg. 1962. Experiments Concerning Gastric Digestion of Pike Perch (Lucioperca lucioperca L.) in relation to water temperature. Acta Biologica Academiae Scientiarum Hungaricae 13, 231-239.

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Wigley, R. L. and R. B. Theroux. 1965. Seasonal Food Habits of Highland Ground Haddock. Trans. Am. Fish. Soc. 94, 243-251.

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References

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Bowman, R. E ., R. O. Maurer and J. A. Murphy. 1976.." Stomach contents of twenty-nine fish species from five regions in the Northwest Atlantic -data report. Laboratory Reference No. 76-10.

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