Aquaculture Nutrition 2000 6; 73^76
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The in¯uence of food particle size on gastric emptying
and growth rates of ®ngerling African cat®sh,
Clarias gariepinus Burchell, 1822
M.A.R. HOSSAIN, G.S. HAYLOR & M.C.M. BEVERIDGE
Institute of Aquaculture, University of Stirling, Stirling, Scotland
Abstract
This study investigates the eect of feed particle size on
gastric evacuation and growth of ®ngerling African cat®sh,
Clarias gariepinus. Fish (0.97 0.07 g) held in 40-cm
diameter tanks at a stocking density of 5 ®sh L±1 (25 ®sh
per tank) were presented with one of four sizes of food
particles (1, 1.5, 2 and 3 mm diameter). Gastric evacuation
rate could be described by an exponential function with small
feed particles being evacuated more rapidly: values of 0.076,
0.054, 0.047 and 0.029 were observed for ®sh fed 1 mm,
1.5 mm, 2 mm and 3 mm food particles, respectively.
Growth rates were highest for ®sh fed the 1.5 and 2 mm
pellets. Based on these ®ndings, recommendations are made
on the optimum food particle size for C. gariepinus ®ngerlings.
KEY WORDS: African cat®sh, Clarias gariepinus, feed size,
gastric evacuation, growth
1987; Bromley 1994), most with the purpose of determining
daily ration and food consumption. The present work is part
of a larger study aimed at developing general models for
evacuation and feed intake in African cat®sh based on feed
particle size and energy level.
Talbot & Higgins (1983) developed a radiographic X-ray
method that enabled quantitative determination of stomach
contents of ®sh. In some ®sh species the rate of passage of
X-ray dense markers appears to dier from that of other
food components (Jùrgensen & Jobling 1988; dos Santos &
Jobling 1991), but Hossain et al. (1998b) observed that
inclusion of marker in diets fed to C. gariepinus had no eect
either on ingestion or on gastric evacuation rate.
The study described in this paper was designed to examine
the eect of feed particle size on food intake, growth and
gastric evacuation rate of ®ngerling Clarias gariepinus using
X-ray radiography.
Materials and methods
Received March 1998, accepted 14 May 1999
Fish
Correspondence: Mostafa Ali Reza Hossain, Fisheries Research Station,
Kyoto University, Naga-Hama, Maizuru City, Kyoto 625-0086, Japan.
E-mail: marhossain@yahoo.com
C. gariepinus ®ngerlings, weighing 0.97 0.7 (SE) g (n
300) were obtained from broodstock maintained at the
Institute of Aquaculture, University of Stirling, Scotland.
Fish had been fed unhatched, de-cysted Artemia (Argent
Chemical Laboratories, Redmond, WA, USA) for 4 days
from 48 h after hatching, and were then weaned over a 4-day
period by substituting Artemia with a commercial trout diet,
ground and sieved to 250 lm (Trouw Aquaculture, Northwich, UK). The diet was analysed according to AOAC (1990)
methods (Table 1). After weaning, the ®sh were fed on the
ground trout diet for a further 16 days, with feed being
distributed continuously using a battery operated belt feeder
(Fiap Fish Technik, GmbH, Hohenburg, Papermell, Germany;
supplied by Aquatic Service (International) Ltd, Hans,
England).
Introduction
Although it has been suggested that food particle size is an
important factor governing gastric evacuation in ®sh (Jobling
1987), few data are available on the in¯uence of food particle
size on feed intake (Swenson & Smith 1973; Jobling 1986,
1987, 1988). Such knowledge is a prerequisite to optimizing
production of a ®sh species because the role of feed size in
determining food acceptance, growth and food eciency
(Wankowski & Thorpe 1979; Tabachek 1988).
In recent years, an extensive literature has appeared on
gastric evacuation of ®sh (FaÈnge & Grove 1979; Jobling
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Ó 2000 Blackwell Science Ltd
73
74
M.A.R. Hossain et al.
Table 1 Composition of the test diet (Trouw UK). According to the
manufacturer the dietary ingredients included cereal grains, ®sh
products, oil seed products and byproducts, land-animal products,
oils and fats, and minerals
Table 2 Sampling schedule on day 41±43 (after feeding at 09.00 h on
day 41) for African cat®sh ®ngerlings fed three dierent diets
Sampling time (h)
Proximate composition
Sample no.
Deprivation
period (h)
Ingredient
Manufacturer
stated (g kg)1)
Laboratory
analysed (g kg)1)
Crude oil
Crude protein
Crude ash
Crude fibre
N-free extract (by subtraction)
Moisture
Vitamin A
Vitamin D3
Vitamin E
70
400
100
25
ö
ö
10 000 IU kg)1
1000 IU kg)1
100 IU kg)1
77
426
89
30
288
90
ö
ö
ö
1
2
3
4
5
6
7
0
4
8
16
24
32
48
Preparation of feed marked with Ballotini
The pelleted trout diet (same diet used as in Table 1) was
ground to a ®ne powder in a hammer mill and Ballotini (0.16±
0.25 mm; Jencons Scienti®c, Leighton Buzzard, UK) added at
a concentration of 1% w/w. After several hours mixing in a
food mixer (Hobart A200; Hobart Electronic Company,
Troy, OH, USA) the feed was re-pelleted in four dierent
sizes: 1, 1.5, 2 and 3 mm (California Pellet Mill, Model CL2;
CPM Europe Ltd., West March, Daventry, Northants, UK),
freeze-dried and stored in sealed containers at 5 °C until used.
Twenty-eight samples of marked feed of known weights
(0.05±1.0 g) were X-rayed to establish a relationship between
feed weight and numbers of Ballotini (feed weight
(g) 0.00419 + 0.00209 Ballotini; r2 0.99).
Experimental procedure
Three-hundred 25-day-old ®ngerlings were randomly allocated to 12, 40-cm diameter plastic tanks with a diameter±
depth ratio of 10. The stocking density was 5 ®sh L±1 or 25
®sh per tank in a recirculation system (Hossain et al. 1998a)
with a water ¯ow rate of 0.4 L min±1. Tanks were covered by
black polythene to reduce light levels and a 12 h light/12
dark photoperiod (light period 0830 h±2030 h) was imposed.
Water temperature was maintained at 30 1 °C.
From day 26 (from the day ®sh started feeding), ®sh were
fed the marked feed to apparent satiation three times each
day (at 0900, 1300 and 1700 h). Every ®fth day, following the
morning feed, the weights (precision 0.01 g) of 15 ®sh taken
from each treatment was determined.
On day 41 (at 0900 h) the ®sh in all 12 tanks were fed to
satiation with marked pellet as usual. After various depriva-
Day 41
Day 42
Day 43
09.00
13.00
17.00
01.00
09.00
17.00
09.00
tion periods between 0 and 48 h (0, 4, 8, 16, 24, 32 and 48 h)
(see Table 2 for detailed sampling schedule), 10 ®sh from
each treatment were selected at random, anaesthetized,
weighed and X-rayed. All procedures were performed on
®sh anaesthetized with a 100 mg L±1 benzocaine solution. No
losses of ingested feed were observed in any ®sh before or
during the X-ray operation. The stomach contents were
calculated in terms of per cent body weight following the
relationship between feed weight and numbers of Ballotini.
The changes in the amount of feed present in the stomach
over time were used to estimate gastric evacuation rate
(GER). Since no X-rayed ®sh were returned to the tanks
(based on the assumption that the feeding and other behavioural patterns of ®sh would be changed following anaesthesia
and X-raying), on the last day of the experiment, day 45, the
weights of the ®ve remaining ®sh were determined.
The ®sh weight data collected every ®fth day over the
experimental period were described by the exponential
relationship Wt W0eGwt, where W0 is the initial ®sh weight
and Wt the weight at time t and speci®c growth rate is Gw.
The stomach contents of pelleted feed of dierent pellet size
from the stomach of 41-day-old ®sh after various deprivation
periods were described by the equation
St S0 eÿRt
1
where S0 stomach contents after ®rst feeding to satiation,
St stomach contents after time t, R is the rate constant,
gastric evacuation rate and t is the time in hours.
X-ray protocol
The method followed that described by Hossain et al.
(1998b), using a Machlett Aeromax 2 X-ray apparatus and
Kodak Industrex ®lm; exposure time was 2 s at 2 kV. The
numbers of Ballotini on X-ray plates were counted using a
binocular microscope (´40 magni®cation).
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Ó 2000 Blackwell Science Ltd Aquaculture Nutrition 6; 73^76
Feed and gastric evacuation
Figure 1 Speci®c growth rate in ®sh fed pellets of four dierent sizes.
Error bars represent 95% con®dence limit.
Figure 2 Gastric evacuation rate in Claris gariepinus ®ngerlings fed
pellets of four dierent sizes. The y-axis represents the gastric
evacuation rate (±R). Error bars represent 95% con®dence limit.
Statistical analyses
These data are summarized in Fig. 2, evacuation rate was
highest in ®sh fed 1 mm pellet diet and lowest in ®sh fed
3 mm pellet diet; however, there was no signi®cant dierence
between the ®sh fed 1.5 and 2 mm pellet diets.
Ninety-®ve percent con®dence limits (CL) were calculated as,
CL X t0.05 (n±1) (S/Ön); where X mean, t0.05 (n)1)
=value from a two-tailed t table where 0.05 is the proportion
expressing con®dence and n ± 1 is the degree of freedom and
S standard deviation. The percentage body weight data
were arcsine transformed and a Bartlett's test used to con®rm
homogeneous variance (Sokal & Rohlf 1981). A single
classi®cation ANOVA was carried out to investigate dierence
in stomach content at various deprivation periods between 0
and 48 h. Exponential regression between the deprivation
time and stomach content were carried out using computer
program Excel (Version 4 Windows NT, from Microsoft).
Results
Weights changes over time (measured every 5 day) were not
signi®cantly dierent (P < 0.05) in ®sh fed 1.5 and 2 mm
pellet but were signi®cantly higher than those of ®sh fed 1
and 3 mm diets:
1 mm: Wt 1.04 ´ e0.087t, R2 0.95, n 6, P < 0.01;
1.5 mm: Wt 1.04 ´ e0.099t, R2 0.98, n 6, P < 0.01;
2 mm: Wt 1.12 ´ e0.099t, R2 0.97, n 6, P < 0.01;
3 mm: Wt 0.95 ´ e0.077t, R2 0.98, n 6, P < 0.01.
Speci®c growth rates (Gw) did not dier between the ®sh
fed 1.5 and 2 mm pellets but were higher than those of ®sh
fed with 1 and 3 mm pellets (Fig. 1).
The relationships between stomach content and time for
the four pellet sizes were:
1 mm: St 4.67 ´ e±0.077t, r2 ±0.96, n 6, P < 0.01;
1.5 mm: St 6.47 ´ e ±0.054t, r2 ±0.97, n 6, P < 0.01;
2 mm: St 6.54 ´ e±0.046t, r2 ±0.97, n 6, P < 0.01;
3 mm: St 3.89 ´ e±0.029t, r2 ±0.92, n 6, P < 0.01.
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Ó 2000 Blackwell Science Ltd Aquaculture Nutrition 6; 73^76
Discussion
Growth rate was found to be closely related to food particle
size, and the fact that the highest growth rate occurred
among ®sh fed 1.5 and 2 mm pellets indicates that there is an
optimum, intermediate particle size range (Fig. 1). The
largest food items that ®sh can manipulate and ingest are
not necessarily the most pro®table (Wanzenboeck 1995) and
although large ®sh may be able to consume small particles,
the net energy may be low (Pandian & Vivekanandan 1985).
Thus, intermediate sized feed particles may result in greater
net energy gain and promote best growth, as found here and
in studies on other species, such as young Atlantic salmon
(Salmo salar) (Wankowski & Thorpe 1979), Arctic charr
(Salvelinus alpinus) (Tabachek 1988) and common carp
(Wang et al. 1994).
There is wide agreement that an exponential model can
describe the evacuation of small easily digestible feed particles
from the stomach (Persson 1986; Jobling 1987; Macpherson
et al. 1989; Haylor 1993). In the present experiment, small feed
particles were evacuated more rapidly than large Ð ®ndings
that are similar to those reported previously (Swenson & Smith
1973; dos Santos & Jobling 1991).
The present trials demonstrated that feeding ®sh small
food particles results in faster stomach evacuation rates, and
this may be expected to lead to an increase in meal frequency,
even though growth may be poorer.
In contrast, when the cat®sh were fed larger particles, both
feed intake and growth rates were observed to be lower.
75
76
M.A.R. Hossain et al.
Highest feed eciency and growth rates occurred when ®sh
were fed the intermediate pellet sizes (1.5±2 mm).
Acknowledgements
The ®rst author thanks the British Council for funding this
research and K. Ranson, W. Hamilton, A. Porter and
I. Elliott for technical support.
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Ó 2000 Blackwell Science Ltd Aquaculture Nutrition 6; 73^76