Abstract The aims of this study were to determine the effects of different levels of protein and lipid on the growth and body composition of fry of the silver dollar, Metynnis schreitmuelleri (Ahl). The fry were first fed diets containing 25, 35, 45, or 55% protein to determine the optimum protein level. The best growth, body composition, protein efficiency ratio, and food conversion ratio were obtained with the 35% protein diet. The fry were next fed diets containing 35% protein and 0, 3, 6, 9, or 12% lipid. The best growth, body composition, protein efficiency ratio, and food conversion ratio occurred with the diet containing 35% protein and 6% lipid

A K Balange

R K Singh

V R Vartak

CiteSeerX

The Israeli Journal of Aquaculture – Bamidgeh  59(1), 2007, 17-22. 17
Effects of Dietary Protein and Lipid Levels on Growth
and Body Composition of Silver Dollar 
(Metynnis schreitmuelleri) Fry
R.K. Singh*, V.R. Vartak and A.K. Balange
Taraporevala Marine Biological Research Station, New Administrative Building, Third Floor,
Bandra (E),Mumbai, 400 051, India
(Received 16.5.06, Accepted 10.10.06)
Key words: growth, protein efficiency ratio, food conversion ratio, protein level, lipid level, 
silver dollar fry
Abstract
The aims of this study were to determine the effects of different levels of protein and lipid on the
growth and body composition of fry of the silver dollar, Metynnis schreitmuelleri (Ahl). The fry
were first fed diets containing 25, 35, 45, or 55% protein to determine the optimum protein level.
The best growth, body composition, protein efficiency ratio, and food conversion ratio were
obtained with the 35% protein diet. The fry were next fed diets containing 35% protein and 0, 3,
6, 9, or 12% lipid. The best growth, body composition, protein efficiency ratio, and food conver-
sion ratio occurred with the diet containing 35% protein and 6% lipid.
Introduction
Protein and lipid nutrition is the most studied
area of fish nutrition. Lipids are critical com-
ponents of cell membranes and required in all
animal diets to provide a store of chemical
energy and for metabolic activity. Many stud-
ies have evaluated the dietary protein and
lipid requirements for edible fish and crus-
taceans but little information is available on
the dietary protein and lipid requirements of
ornamental fish.
Aquarium fish fed live food attain better
growth and survival than those fed artificial
food. However it is not always possible to pro-
vide live food due to inconsistent and limited
supply. Hence artificial feed that is nutritional-
ly balanced with protein and lipid is common-
ly fed to ornamental fishes. It is therefore
essential to evaluate the optimum nutritional
requirements for each species, as the appro-
priate amount of dietary protein and lipid ren-
der better growth and survival.
The silver dollar, Metynnis schreitmuelleri
(Ahl), is round flat freshwater ornamental fish
belonging to the Characidae family. This fish
is commercially important due to its shimmer-
ing silver color. The protein and lipid require-
ments of the silver dollar are unknown. The
present study was conducted to determine the
optimum dietary protein and lipid require-
ments of silver dollar fry.
*  Corresponding author. Tel.: +91-22-26516816, e-mail: tmbrs@rediffmail.com
18
Materials and Methods
Silver dollar fry were obtained from a local
hatchery and acclimatized for fifteen days in a
plastic pool at the Taraporevala Marine
Biological Research Station laboratory. The
fish were fed a commercial flake feed of
approximately 40% protein during acclima-
tion.
In the first experiment, protein require-
ments were evaluated. Twelve groups of 10
fry each (0.660-0.705 g) were randomly
selected, weighed, and stocked into experi-
mental glass aquaria (45 x 30 x 30 cm) pro-
vided with aeration. Three groups were
assigned to each of the four test diets.
Experimental flake diets, prepared in the lab-
oratory, contained one of four protein levels
(25, 35, 45, or 55% by dry weight) and were
nearly isocaloric (Table 1).
In the second experiment, lipid require-
ments were evaluated. Five test diets were
formulated at 3% increments of lipid (from cod
liver oil), ranging 0-12% (Table 2). The diets
contained 35% protein, based on results from
the first experiment, and were made isocaloric
by adjusting the starch content. Lipid-free
casein was used as the dietary protein
source. Metabolizable energy values for silver
dollar are unknown and were estimated
according to protein 4.5 kcal/g (Smith, 1971),
carbohydrate 3.49 kcal/g (Chiou and Ogino,
1975), and lipid 8.51 kcal/g (Austreng, 1978).
In both experiments, fish were fed twice a
day (at 10:30 and 16:30-17:00) at 5% of their
body weight, close to the maximum amount
consumed by the fry during the acclimation
period. Every ten days, the fish were weighed
and counted, their lengths were recorded,
weight gains determined, and feed allowan-
ces adjusted. Calculation of the total feed
allowance was initially based on the average
weight of the fish in all treatments. Sub-
sequently, they were adjusted according to
the average weight of the fish in each treat-
ment and the number of fish in each aquari-
um. The fish were given the experimental
diets for 30 days. Half the water in the aquar-
ia was changed twice daily, at 10:00 and
16:00, before the fish were fed, and the aquar-
ia were cleaned thoroughly every morning
before the removal of the water. Water tem-
perature, pH, and DO were measured daily.
At the end of each experiment, ten fish
were randomly sampled from each treatment.
They were pooled, ground, and freeze-dried,
and body crude protein, lipid, moisture, and
ash contents were determined (AOAC, 1984).
Singh et al.
Dietary protein (%)
25 35 45 55
Ingredient
Casein 17.0 27.0 37.0 47.0
Fish meal 17.0 27.0 37.0 47.0
Corn flour 33.0 23.0 13.0 3.0
Egg (whole) 33.0 23.0 13.0 3.0
Proximate analysis
Moisture 6.0 5.5 5.0 5.0
Crude protein 25.1 34.9 44.8 55.3
Crude lipid 4.8 4.8 4.9 4.8
Ash 8.5 9.0 10.5 11.0
Table 1. Composition and proximate analysis (% dry weight) of the
experimental diets in the protein requirement test.
19Effects of dietary protein and lipid levels on silver dollar fry
Dietary lipid (%)
0 3 6 9 12
Ingredients
Casein 47.0 47.0 47.0 47.0 47.0
Starch 50.5 41.0 32.0 22.5 13.0
Lipid a 0.0 3.0 6.0 9.0 12.0
Vitamin mix 0.1 0.1 0.1 0.1 0.1
Carboxymethyl cellulose 1.9 1.9 1.9 1.9 1.9
Cellulose 0.5 7.0 13.0 19.5 26.0
Metabolizable energy b 315 315 315 315 315
P/E ratio (mg/kcal) 111.11 111.11 111.11 111.11 111.11
Proximate analysis
Moisture 14.5 15.0 13.9 14.0 15.0
Crude protein 35.1 35.2 35.1 34.9 35.1
Crude lipid 0.0 3.1 6.1 9.1 12.0
Ash 4.1 4.0 4.0 4.2 4.1
Table 2. Composition and proximate analysis (% dry weight) of the experimental diets in the
lipid requirement test.
a Lipid source: cod liver oil
b Metabolizable energy estimated according to protein 4.5 kcal/g (Smith, 1971), carbohydrate
3.49 kcal/g (Chiou and Ogino, 1975), and lipid 8.51 kcal/g (Austreng, 1978).
Dietary protein (%)
25 35 45 55
Initial avg length (cm) 3.51±0.08 3.47±0.04 3.49±0.02 3.50±0.04
Final avg length (cm) 4.09±0.02 4.46±0.08 3.98±0.08 3.98±0.06
Length gain (%) 16.50±0.08a 28.67±012b 14.04±0.04c 13.55±0.02d
Initial avg wt (g) 0.70±0.08 0.66±0.04 0.68±0.08 0.66±0.02
Final avg wt (g) 1.48±0.09 1.73±0.06 1.34±0.08 1.18±0.04
Wt gain (%) 110.63±2.16a 162.12±1.08b 96.35±2.24c 78.19±2.36d
FCR 1.34±0.04a 0.92±0.04b 1.55±0.06c 1.93±0.04d
PER 2.97±0.06a 3.08±0.08b 1.42±0.02c 1.21±0.04d
Table 3. Growth, feed conversion ratio (FCR), and protein efficiency ratio (PER) of silver dol-
lar, Metynnis schreitmuelleri (Ahl), fry fed different levels of dietary protein (means±SE).
Values in a row with different superscripts are significantly different (p<0.05).
20
Weight gain (%), feed conversion ratio (FCR),
and protein efficiency ratio (PER) were deter-
mined according to the following formulas: wt
gain = 100[(final wt - initial wt)/initial wt], FCR
= dry wt of food consumed/increase in wet wt
of animal, and PER = increase in wet wt of
fish/dry wt of protein fed. Data were analyzed
using one-way analysis of variance (Snedecor
and Cochran, 1967).
Results
Weight gains, FCR, and PER in the protein
experiment are given in Table 3. Water para-
meters were favorable: temperature ranged
24-26ºC, pH 7.1-7.2, and dissolved oxygen
5.3-5.8 mg/l. Fish fed 35% protein had the
highest weight gain, length gain, and PER and
the lowest FCR. The protein level in the tissue
of the fish significantly differed among treat-
Singh et al.
Initial body Dietary protein (%)
composition
25 35 45 55
Moisture 80.90±0.60 82.00±0.60a 81.50±0.50a 80.50±0.50a 80.60±0.50a
Crude 
protein 11.12±0.06 11.15±0.06b 11.45±0.05c 11.45±0.06d 11.50±0.05e
Crude 
lipid 1.35±0.01 1.35±0.01a 1.36±0.01a 1.37±0.01a 1.38±0.01a
Ash 4.00±0.05 3.99±0.04b 3.45±0.02c 3.45±0.03d 4.01±0.03e
Table 4. Proximate body composition (%) of silver dollar fry fed different levels of protein
(means of three replicate groups±SEM).
Values in a row with different superscripts are significantly different (p<0.05).
Dietary lipid (%)
0 3 6 9 12
Initial avg length (cm) 3.88±0.05 3.86±0.02 3.87±0.02 3.84±0.04 3.87±0.03
Final avg length (cm) 4.30±0.02 4.37±0.02 4.51±0.01 4.32±0.02 4.28±0.01
Length gain (%) 10.82±0.20a 13.21±0.25b 16.38±0.2c 12.63±0.2d 10.59±0.2e
Initial avg wt (g) 1.08±0.01 1.08±0.01 1.10±0.01 0.99±0.01 0.98±0.01
Final avg wt (g) 1.45±0.02 1.51±0.01 1.73±0.03 1.46±0.02 1.42±0.01
Wt gain (%) 34.25±0.10a 39.81±0.20b 56.10±0.10c 47.47±0.20d 44.67±0.10e
FCR 2.62±0.02a 2.26±0.02b 1.59±0.01c 1.89±0.03d 2.01±0.04e
PER 1.08±0.01a 1.26±0.02b 1.79±0.01c 1.51±0.01d 1.41±0.02e
Table 5. Growth, feed conversion ratio (FCR), and protein efficiency ratio (PER) of silver dol-
lar fry fed different levels of dietary lipid (means±SE).
Values in a row with different superscripts are significantly different (p<0.05).
ments and increased as the dietary protein
level rose (Table 4).
Weight gains, FCR, and PER in the lipid
experiment are given in Table 5. Growth,
PER, and FCR were significantly superior with
the diet containing 6% lipid while the poorest
growth  was obtained in fish fed the lipid-free
diet. Lipid body contents rose significantly
with higher lipid diet contents (Table 6).
Discussion
The majority of fish species require 40-50%
dietary protein (Cowey et al., 1975). The pro-
tein requirement for optimum growth of
Cyprinus carpio fingerlings is around 40%
(Ogino and Saito, 1970) and for carp fry
around 45% protein (Sen et al., 1978). The
highest weight gain in grass carp
(Ctenopharyngodon idella) was obtained with
a dietary protein level of 40% (Dabrowski,
1977) while the optimum dietary protein level
for Pleuronectus platessa is approximately
50% (Cowey et al., 1972). The weight gain of
milk fish fry is directly related to the dietary
protein level, with a 40% protein diet produc-
ing the highest weight gain (Lim et al., 1979).
In Clarias batrachus fingerlings, diets contain-
ing 37.72-35.69% protein produced best
results in terms of weight gain and feed con-
version (Cruz and Laudencia, 1976).
The positive correlation between dietary
lipid and body lipid contents may indicate that
when dietary lipid is supplied in excess, a pro-
portion of this lipid is deposited as body fat. Our
results are in agreement with results for other
fish species such as rainbow trout (Lee and
Putnam, 1973), channel catfish (Garling and
Wilson, 1977), common carp (Takeuchi et al.,
1979), red drum (Ellis and Reigh, 1991), and
hybrid Clarias catfish (Jantrarotai et al., 1994). 
Both protein and lipid are important in fish
diets. Lipids are well utilized by most fishes,
but may reduce fish growth at high dietary lev-
els (Garling and Wilson, 1977; El Sayed and
Garling, 1988; Ellis and Reigh, 1991). Similar
results were observed in the present study.
Fatty acids, which are not synthesized by the
organism, are necessary for cellular metabo-
lism as well as for maintenance of membrane
structure integrity. Lipid also serves as a vec-
21Effects of dietary protein and lipid levels on silver dollar fry
In
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 6
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V
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22
tor during intestinal absorption of liposoluble
vitamins and carotenoid pigments (Jean et al.,
2001). This is very important in ornamental
fishes as the quality of the fish depends on its
color. The silver dollar is known for its shim-
mering silver color. In fish fed the lipid-free
diet, blackishness shed over the silver, affect-
ing its appearance.
In summary, the diet containing 35% pro-
tein and 6% lipid maximized weight gain and
food conversion in silver dollar fry. Hence, this
is the most effective diet, producing maximum
growth in minimum time.
Acknowledgements
The authors are thankful to Dr. P.C. Raje,
Associate Dean, and Dr. S.G. Belsare, Senior
Scientific Officer, of the Faculty of Fisheries in
Ratnagiri for critical review of the manuscript.
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Effects of Dietary Protein and Lipid Levels on Growth and Body Composition of Silver Dollar (Metynnis schreitmuelleri) Fry

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Effects of Dietary Protein and Lipid Levels on Growth and Body Composition of Silver Dollar (Metynnis schreitmuelleri) Fry

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