l ce to the authors
!
International Council f o r _ C.M. 1983/H: 3 3
_C_
the Exploration of the Sea Fish Cemmittee
GASTRIC EVACUATION RATE IN MACKEREL (Scomber scombrus L.)
Sigbjqjrn Mehl and Trond Westgård Institute of Marine Wesearch
5011 Bergen-Nordnes Norway
Abstract
About 1500 mackerel, 25-45 cm in Length, were kept in a net for l0 days. In two experiments the fish were £ed frozen euphausiids - ad. libiturn, and the wet weight of the stomach content determined every second hour for 20-30 hours. The
l' stomachs were then almost empty. Independent of fish size, the rate of digestion was related to the water temperature
(14.5
-
1 7 . 0 ~ ~ ) : f (T)= 0.005 Oexp (0.2-T). The niaximuml
stomach capacity (wet weight, grams) was a function of fish
l
size (total length, cm): w = 0.0087eL 2,21
i
i
Introduction
The present paper is a cantribution to the International Stomach Sampling Project 1989 in t h e North Sea. The project aims at producing data for a multispecies virtual population analysis (VPA) for the comercia1 fish stocks in the North Sea (Anon., 1980). Such an analysis regukes data on the consumption of each age group of the fish stocks included in the model by the other fish atocks/age groups included- Estimates of this consumption can be made from the rate of gastric evacuation and the stomach content as a function of time (e.g. Bajkov, 1935, E1Liot and Persson, 1978 and
Jobling, 1981). Data on the rate of gastric evacuation in mackerel, Scomber scombrus are to our knowledge not reported in the literature. For this reason, we conducted a preliminary field experiment in July 1982 by Eeeding euphausiids to encaged mackerel
.
Materials and Methods
In July 1982 about 500 kg of mackerel was caught in a shore seine outside Bergen, Norway. The lengtk distribution of the fish is shown in Fåg.1. 8 days after capture the fish were transfered to a keep net 4 x 4 ~ 4 m in size anchsred in a small
ba^?
___ - - .- -The fish were fed frozen Antarctic euphausiids. Euphausiids
is an important part of the diet in mackerel (Walsh and Rankine
,
1979, Mehl and Westgård, 1983).
The euphausiids were melted and spread over the surface and eaten by the fish while sinking. Krill was offered until the fish refused to take it, which took about 2.5 hours. One sample was taken immediately and then from 19-44 f ish were sampled every second hour until all or most of the stomachs in the sample were empty.
Tne estimates of the gastric evacuation rate were based on the wet weight of the stomach contents. The fish were sega-
rated into four length groups (25-29, 30-34, 35-39 and 40-45 cm).
If in the first sianiple after the fish were fed sorrie indivi- duabs in a bength group for same reason had empty skornachs they were disregarded in the calculations. In later smples the same proportion of fish with empty stomachs was subtracted.
Results
Gastric empgy&nq
---
In Figs 2 and 4 the changes in the mean stomach content in grams, for the fish in each length grsup as a function of time is shown. Figs 3 and 5 show the same, but naw relative to the mean stomach contents j u s t after the fish were fed.
The number of fish sampled at each point of tirne in each Iength group and experiment is given in Taåles I and 11. In the first experiment the temperature varied hetween 16.6°and 17. O ~ C , and in the second between 14.4' and 15. ~ O C .
Maximum stomach cagacity ---l---."--- -I--
A preliminary investigation sf maximum stomach capacåty in grams wet weight was carried out, In each length group the heaviest stomaeh was pieked out and weighted from Lhe cample taken just after the fish were fed %o satisfaetion. A total of ten fish were picked out and measured. We fikted an
ordinary power function to the data.
where
"max = maximum stomach capacity in grams
L = total length in em
A m a t h e m a t i e a l deceiripti.cl3n af t h e b a l a n c e of mas8 ire a fish stomaeh c a n talite v a r i s u s Sarms. A n expanential d e c r e a s e irn stomach c o n t e n t as a func;tian of tiarie h a s c o m a n l y been
found ( T y l e r , 1970, E l l i s t and Percssn, 1 9 4 8 ) . O t h e r a u t h s r s r e p o r t e d the r a t e of e v a c u a t i o n t o be p r o p s r ' t i o n a l t o the stomach c o n t e n t r a i s e d t o a ,power bekwaen Q and l (Fånge and Grove, 1 9 7 9 , Jobling, 1981). F o r t h e time being. we h a v e
a d o p t e d t h e e x p o n e n t i a l model a s a good E i t t o o u r m a c k e r e l d a t a . The balance e g u a t i o n of the stomach e o n t e n t s i s t h e r e - f o r e :
- - -
dW - F ( T ) * W+
i (t)d t where,
t . = t i m e i n h s u r s
W ( t )
-
w e t w e i g h t of stomach c o n t e n t s i n gramc a t t i m e ti ( t ) = I n s t a n t a n e o u s r a t e o f f o o d uptake i n grams/hour
f ( T )
-
The r a t e o % d i g e s t i o n (Func drlnn of t e m p e r a t u r e ) T-
Temperature i n Q CAs i s s e e n i n F i g a . 3 and 5 t h e r e seerns t o be a t i m e l a g b e f o r e the e x p o n e n t i a l d e c r e a s e of atamach e o n t e n t s e t s i n . T h i s m i g h t b e a n a r t i f a c t siizca the k r i l l , , was . c o l d e r %han t h e a m b i e n t water t e r n p e r a t u r e when o f f e r e d to t h e fish, The r a t e o f d i g e s t i o n seems to be similar for all s i z e y r o u p s of f i s h . Prey s p e c i e s arid s i z . e c l ~ s s e s may have a n e f f e c t on t h e r a t e o f d i g e s t i o n , but w e do not have any data t o c o n f i r m o r e n f e e b l e t k a - i s . 1t.s p o s s i b l e e f f e c t i s t h e r e f o r e left ut
in e q u a t i o n 2.
To r e a c h 10% of t h e mean sksmaeh contents a% the s u t s e t of t h e e x p e r i m e n t t o s k 16 h s u r s in t h e f i r s t experiment and 26 h o u r s i n t h e s e o n d ( F i g s 3 amid 5 ) . The t e m p e r a t u r e d i f f e r e n c e was about 2"6,
P a b i a n e t
-
a l (1963) arglaed t h a % an enzymatic k i n e t i e r e a c t i o n o f t h e A r r h e n s u s t y p e s h s u l d be used f a r the dependence o f t h e r a t e o f e v a c u a t i s n on t e m p e r a t u r e . This e q u a t i o a c o u l d beapproximated by an o s d i n g r y e x p o n e n t i a l f u n c t i o n , Such a f u n c t i o n i s found t o d e c c s i b e t h e e f f e c t o f t e m p e r a t u r e on t h e r a t e d i g e s t i o n q u i t e weL1 i n brown t r o u t ( E l l i s t , 1 9 7 2 ) . W e have two measurernents s e p e r a t e d o n l y by a 2Oc t e m p e r a t u r e d i f f e r e n c e . T h e r e f o r e t h e c s n f i d e n c e we c a n put i n t o t h e r e s u l t i s l i m i t e d . W e g o t t h e r e s u l t e
f ( T ) = -Q.005 exp (0.2.T) ( 3 )
D i s c u s s i o n and c o n c l u s i o n s
The p r e s e n t r e s u l t c are t o our knowledge t h e f i r s t t o d e s c r i ' b e t h e g a s t r i c e v a c u a t i o n r a t e o f rnackerel. T k i s may be due %o t h e d i f f i c u l t i e s i n k e e p i n g m a c k e r e l i n s r d i n a r y a q u a r å a o v e r
e x t e n d e d t i m e p e r i o d s . Due t o this we w e r e a b l e t o c a r r y out two e x p e r i m e n t s on2.y and t h e water temperatures were t o o c l o s e t o d e c c r i b e t h e t e m p e r a t u r e 8 a effect on d i g e s t i o n in any d e t a i l . U n f s r t u n a t e l y , w e were u n a b l e t o i n v e s t i g a t e t h e effect of
food t y p e and p a r t i c l e s i z e on t h e r a t e o f d i g e s t i o n . The f i s h * h a d o n l y s m i i l l d a m a g e s - a t the end o f t h e a x p e r i m e n t , m o s t l y wsunds om t h e sn%aut, and there w a s a åaw m o r k a l i t y in t h e keep n e t . Most o f t h e f i c h were wi,EPing t a e a t a t o n c e when f o s d were s f f e r e d i n b ~ & h experiments. T h i s i n d i c i i t e s
t h a t t h e f i s k were i n good c o n d i t i o n . The experirnen& should t h e r e f o r e g i v e a f a i r l y good d e s e r i p t i a n sf the m a c k e r e l ' s r a t e o f d i g e s t i o n of k r i l å .
W e want t o t h a n k Erling Bakleen, Ingeanund Scii%go%.k and flyvind U l l t a n g f o r kind assistanse and a d v i c e ,
The project was granted financiål support frank the Norwegian Fisheries Researck Council..
Literature
Anon 1980. Report of the & working group on multispecies assessment made1 testing. ICES C.MeE988/Go2
18 pages, Mimeo
.
Bajkov, A.D. 1935. How to estimate the daily food consumption of fisk under natural conditions. Trans.Am,Fish.Soc.
65: 288-289.
c
Elliot, J.M. 1972. Rates of gastric evacuation h brown trout, Salmo trutta L. Freshw .Biol. L s 1-18
Elliot, J.M. and Persson, L. 9978. The estirnation of daily rates of food consumption for fish. Journal of Animal Ecology 47: 977-991.
FabiSn, Gy., Molnar, Gy.andT8lg11. 1963. Gomparative data and enzymatic kinetic calculations on changec caused by temperature in the duration of gastric digestion of sorne predatory fishes. Acta Bio1.Hung. 14 (2) :L23-12/.
Fange, R. and Grove, D.J. 1979. Digestion. In Fish Physiology
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(W.S.Hoar, D.J. Randall and J.R. Brett, eds)
,
Vol VIII,I
pp.161-260. New York and London: Academic Press.
Jobling, M. 1981. Mathematical rnodebs of gastric emptying and
the estimation of food consumption for fish.
I
Mehl, S.and Westgård, T,1983. The daet and consumption - .
1
of rnacketel in the North Sea. IGES, CeM.1983/H:34.
l
Tyler, A.V. 1970. Rates of gastrlc ernptying in young cod.
J'.Fiah.Res.Bd.Can. 27: 9197-1189.
Walsh, M. and Rankine, P . 1979. O b s e r v a t i o n s on t h e d i e t o f
mackerel i n t h e North Sea and t o t h e w e s t of B r i t a i n . ICES C.M.1949/H:$5. 1 8 pages, Mimeo
.
I T a b l e 1. Number of f i s h sampbed ( i n e a c h 5 cm l e n g t h g r o u p a t e a c h p o i n t o f t i m e ) 4-5 August 1 9 8 2 .
l
I T a b l e 2. Number o f f i s h sampled ( i n e a c h l e n g t h g r o u p a t e a c h p o i n t o f t i m e ) 11-12 August 1 9 8 2 .
I F i g . 2. The stomach c o n t e n t s i n grams wet w e i g h t f o r t h e l e n g t h
I groups 25-29 cm, 30-34 cm, 35-39 cm, 40-45 cm and-
l
25-45 cm a s a f u n c t i o n o f time i n h o u r s a f t e r t h e f i s hl were f e d . 4-5 August 1982.
F i g . 3. The w e i g h t of stomach c o n t e n t s measured r e l a t i v e t o t h e stomach c o n t e n t s j u s t a f t e r t h e f i s h were f e d a s a f u n c t i o n o f t i m e i n h o u r s a f t e r t h e f i s h were f e d . The l e n g t h g r o u p s were 25-29 cm, 30-34 cm, 35-39 cm, 40-45 cm and 25-45 cm. 4-5 August 1982.
