Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
REPLACEMENT VALUE OF DUCK WEED (LEMNA MINOR)
IN NILE TILAPIA (OREOOCHROMIS NILOTICUS) DIET
Christianah Oludayo Olaniyi, PhD
Isaac Omoniyi Oladunjoye, PhD
Ladoke Akintola University of Technology, Ogbomoso, Nigeria
Abstract:
A twelve - week feeding trial was conducted to determine the nutritive potential of duck
weed meal (DWM) as an animal protein concentrate in fish feeding by evaluating growth
response
and
nutrient
utilization.
Two
hundred
and
twenty
five
Tilapia
(Oreochromisniloticus ) fingerlings of 50g average weight were assigned randomly in groups
of fifteen to control diet (CD) and four other diets. D2,D 3, D4 andD5 containing DWM. The
treatments were replicated three times.
Diets had significant effects (p<0.01) on Mean Weight Gain (MWG), Average Daily Weight
Gain (ADWG), Percentage Weight Gain (PWG), Feed Conversion Ratio (FCR), protein
Efficiency Ratio (PER) total protein intake(TPI). Initially, fish increases in weight as feed
intake increased and the dietary inclusion of DWM increases up to 25% with an improved
feed conversion however, the reverse was the case as the DWM dietary inclusion level
increased beyond this level in the Tilapia diet. 100% DWM inclusion recorded the least
MWG, PER and highest FCR followed by 75% DWM inclusion.
The study clearly showed that fish fed diet with 25% duckweed dietary inclusion (treatment
II)
perform
excellently
well
compared
to
other
treatments.
Therefore
Oreochromisniloticuscan tolerate up to 25% duckweed in its diet.
Keywords: Inclusion level, Nile Tilapia, feed conversion, growth
Introduction:
Tilapia is a fast growing fish widely cultured in about 100 countries in the tropical
and subtropical region. The production of farmed tilapia has increased from 383,654 mt in
1990 to 1,505,804 mt in 2002 representing about 6 % of total farmed finfish in 2002 (FAO,
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
2004). In the developing countries, the major challenge facing aquaculture industry is high
cost of production. Even though the feed takes the lion share of the total operating cost in
intensive fish culture, protein alone represents about 50% of this cost. Fish meal is the major
source of protein in aquaculture feeds because it is a good source of essential amino acids,
fatty acids, vitamins , minerals and enhance palatability (Daving and Armold, 2000).
Although, fish meal is highly demanded, it is however limited in supply and the price is very
high. For this reason, alot of studies have been conducted on finding an alternative to fish
meal that are less competitive and with low cost. (Yilmazet al,. 2004). A wide varieties of
non conventional protein of both animal and plant origin have been evaluated and used
recently. The use of plant protein materials in fish diets is desirable due to their low prices
and regular availability (Fagbenro, 2000). In adition, Tilapia protein requirements and
herbivorous feeding habit and tolerance for plant protein sources in its diet can be employed
to reduce feed expenses.
Duckweed is a small green floating flowering plant of the Lemnaceae family. The
plant grow well in different climates and has a high concentration of trace minerals,
potassium , phosphorus and protein content of about 40-43% dry weight (Lenget al., 1995)
with better
amino acids profile than other vegetable protein (Hillman and Culley 1978).
Comparing duck weed with other plants, its leaves contain lower fiber (5% in dry matter)
and highly digestible (Chaturvedet al., 2003). Duck weed can produce between 10-30 tons
dry matter/ha/year, depending on the species, climatic conditions, available surface area,
amount of nutrient and management (Tavares et al., 2007)
The possibility of using duckweed in Nile tilapia feeding as a source of protein and
energy in place of fishmeal is quite prominent, therefore this study was conducted to evaluate
the nutritive value of duckweed as alternative protein feed stuff and its effect on growth
performance of tilapia.
Materials and methods
Experimental site:
The experiment was carried out at the fishery unit of the LadokeAkintola University
of Technology (LAUTECH) Teaching and Research Farm, Ogbomoso.
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
Collection and processing of duckweed meal:
The duckweeds (Lemna minor) were collected from the surface of earthen ponds at
Ijede, Ikorodu Lagos. It was drained and sundried for minimum of 6 hours per day until it
became crispy to touch after which it was milled.
Experimental diets:
Five diets were formulated in which duck weed meal replaced 25% (diet 2), 50%
(diet 3), 75 % (diet 4) and 100% (diet 5) fish meal and diet 1also seved as control diet The
diets were isonitrogenous (30% crude protein), other ingredients used in diets preparation
were obtained from a local supplier in Ogbomoso township of Oyo state, Nigeria. The
ingredients were thoroughly mixed into a paste by adding water and pelletized into 1mm size.
The resulting pellet was air dried to about 13% moisture content.
Table 1: Gross composition of the experimental diets.
Ingredients
Diet
1 Diet 2
Diet 3
Diet 4
Diet
(%)
(0%)
(25%)
(50%)
(75%)
(100%)
Yellow maize
20.55
16.55
12.55
7.55
1.55
Wheat offal
10.28
6.28
2.28
1.28
1.28
Fish meal
38.5
28.88
19.25
9.62
-
DWM
-
9.62
19.25
28.88
38.5
SBM
12.83
15.83
18.83
18.83
26.83
GNC
12.83
17.83
22.83
28.83
27.83
Vitamin premix
2.00
2.00
2.00
2.00
2.00
Bone meal
1.50
1.50
1.50
1.50
1.50
Oyster shell
0.50
0.50
0.50
0.50
0.50
Vegetable oil
0.50
0.50
0.50
0.50
0.50
Salt
0.50
0.50
0.50
0.50
0.50
TOTAL
100
100
100
100
100
Cp (%)
41.90
39.60
39.65
41.02
41.06
ME (Meg/Joule)
3.67
3.06
3.89
3.71
3.40
5
GNC=groundnut cake , SBM=soya bean meal, DWM=duckweed meal: CP=crude protein;
ME= Metabolizable energy
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
Experimental Animal, Procedure and Management
Tilapia fish (Orochromisniloticus)fingerlingswere acclimatized for 2 weeks and two
hundred and twenty five were distributed into 15 bowls, each containing 15 fingerlings. The
five dietary treatments were in triplicates. They were fed twice daily at 8.00hrs and 16.00hrs,
at the rate of 5% body weight per day,feed were divided into two equal feedings. The
fingerlings were weighed every two weeks after which the feeding were adjusted to body
weight; the experiment lasted for 12weeks.
Data collection
The parameters measured were the weight change, feed intake while the followings
parameters were determined: Mean Weight Gain (MWG), Average Daily Weight Gain
(ADWG), Percentage Weight Gain (PWG), Feed Conversion Ratio (FCR), protein Efficiency
Ratio (PER) total protein intake(TPI).
Chemical analysis
The proximate analysis of the duckweed meal, diets and the fish carcass were carried
out using the procedure outlined by AOAC (2000) and from whuch the followings were
determined: Crude protein, crude fibre, moisture content, nitrogen free extract, ether extract
and ash.
Statistical analysis
The data collected were subjected to one way analysis of Variance (ANOVA) using
the General Linear Model of SAS, (1999) and where significance was indicated Duncan’s
Multiple Range Test option of the package was used to separate the means. Significance was
determined at P<0.05.
Results
Final weights of all the treatments were significantly different (p> 0.05) except for
treatments III and IV even though highest final weight of fingerlings was promoted by
treatment II (25% inclusion level).Mean weight gain for all the treatments were significantly
different (p >0.05).highest mean weight gain (44.00g) was recorded in treatment II (25%
inclusion) and treatment V has the lowest value (29.93g).Percentage weight gain was
different (p>0.05), highest value of 88.53% was recorded by treatment II compared with
other treatments; however treatment V recorded the least value of 59.75%. There was no
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
significant difference (p>0.05) among the total feed intake of the five treatments, treatment II
had the highest total feed intake (119.13g), compared with treatment V which had the least
value (116.00g).All the treatments had low feed conversion ratio, the treatment II had the
least feed conversion ratio while treatment V had the highest (3.87).Protein efficiency ratio
were significantly different (p>0.05) among the treatments, even though there is no difference
between treatment I and II. Fish fed 25% duckweed had the highest protein efficiency ratio
(0.88) and treatment V had least value (0.63).Total protein intake also follows the same trend.
Table 2: Proximate composition of experimental diets and test ingredient (duckweed meal)
Diets
Moisture (%)
Ash(%)
CF (%)
CP (%)
EE (%)
NFE (%)
1 (0%)
10.00
7.40
2.60
30.90
2.40
46.70
2 (25%)
11.60
11.80
2.00
29.60
2.60
42.70
3 (50%)
10.50
10.60
2.10
29.65
2.10
45.05
4 (75%)
10.80
9.20
2.10
30.02
2.10
45.78
5 (100%)
10.00
7.80
1.70
30.06
2.30
48.14
DWM
9.20
8.80
1.30
40.23
2.30
38.17
60% Crude protein Fish meal was used in formulating the five diets.
CF= Crude fibre; CP=Crude protein; EE= Ether extract,
NFE =Nitrogen free extract
DWM = Duckweed meal; Diet1= Control (0%); Diet 2= 25% DWM; Diet 3= 50% DWM;
Diet 4=75% DWM; Diet 5= 100% DWM.
Table 3: Growth performance of Nile tilapia fed Duckweed meal.
Diets
Parameters
2
3
4
5
SEM
50.00
50.00
50.00
50.00
-
live 91.77b
93.83a
85.03c
84.30c
79.93d
0.73
MWG (g)
41.67b
44.00a
35.03c
34.30d
29.93e
1.04.
ADWG (g/day)
0.46b
0.48a
0.38c
0.38c
0.33d
0.33
Initial
1
weight 50.00
(g)
Final
weight (g)
b
a
PWG (%)
83.53
88.53
TFI (g)
118.27b 119.13a
70.07
c
118.10b
68.60
d
116.96c
e
59.75
0.60
116.00d
0.01
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
FCR
2.83d
2.70e
3.34c
3.44b
3.87a
PER
0.88a
0.88a
0.75b
0.71c
0.63d
d
TPI (g)
46.77
d
46.38
47.67
c
48.44
b
0.02
0.01.
a
49.92
0.02.
abcde: Means bearing different superscripts along the same row are significantly different
(p<0.05)
MWG: mean weight gain, ADWG: average daily weight gain, PWG: percentage weight gain
TFI: Total feed intake, FCR: feed conversion ratio, PER: protein efficiency ratio
TPI: total protein intake
Figure 1: relationship of final weight, mean weight gain and percentage weight Gain
between treatment I- V. This table
Discussion
The proximate composition of the feeds and duckweed meal is presented in Table 2.
The crude protein content value obtained for the DWM used in this study is high (42.23%)
which makes it a potential protein source for fish. The protein content of DWM is
comparable to that of soybean meal which is used in fish formulation to reduce cost. The
value is however higher than the value obtained by Tavares et al 2008. The fiber content of
duckweed meal (1.30%) is considerably lower than that reported by the same author.
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
The crude protein content of the feeds ranged between 29.60% for diet 2 (25%DWM)
and 30.90% for the control (0%DWM) which is adequate for tilapia fish.
The performance characteristic of the fish fed DWM is shown in Table 3.
Substitution of DWM for 25% fish meal promotes higher (P<0.05) final live weight than
feeding only fish meal as the main source of protein in the tilapia fish. However, the final live
weight of the fish that were fed control diet were higher than those that received 50%, 75%
and 100% DWM. The same trend was observed in mean weight gain, average daily weight
gain and percentage weight gain. This result was in support of the work of Fasakinet al.,
(2001) who reported 10%DWM replacement of fishmeal in the diet of Nile tilapia without
adverse effect on their growth. Yilmazet al (2004) also observed no weight difference when
20% DWM was substituted for commercial fish meal in common carp (Cyprinuscarpio). The
growth depression that was observed at 50%, 75% and 100% substitution aggrees with the
work of Tavares et al, 2008 who also observed growth depression when only DWM was fed
to Niletilapia.This effect can be attributed to poor feed utilization that was observed at these
substitution levels.
Diet 2 (25%DWM) was more consumed than the control (0%DWM) and diet 3 (50%
DWM). This may be due to better palatability. However, diets 4 (75%DWM) and diet 5
(100%DWM) were less consumed than the control diet. This could be due to change in
texture or taste at higher replacement level. Substitution of 25% fish meal with DWM
promotes better (p<0.05) feed utilization than feeding only fish meal as the main source of
protein in tilapia fish . Feed utilization however becomes progressively depressed with
increased level of substitution as evident by higher (p<0.05) feed: gain ratio. The implication
of this is that complete replacement of fishmeal with duckweed is detrimental to fish
production. This is supported by the work of Fasakinet al,(2001) and Tavares.et al., (2008)
who reported that 100% inclusion of duckweed does not favour growth performance of Nile
Tilapia.
Efficiency of protein utilization was similar for tilapia fish that had 25% fish meal in
their diet
and those that were fed only fish meal as main source of protein. Protein
utilization however decreased progressively with increased level of DWM substitution in the
diet from 50% to 100%. This could be due to poor quality of plant protein compared to that
of fish meal.
Fish that were fed 0% (control diet) and 25% DWM (diet 2) were comparable in
terms of protein intake but they consumed less (p<0.05) protein compared to those that were
fed 50%, 75% and 100% DWM.
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
The study clearly showed that fish fed diet with 25% duckweed (treatment II) perform
excellently well compared to other treatments. Therefore Oreochromisniloticuscan tolerate up
to 25% duckweed in its diet.
Conclusion:
The results of this study showed that substitution of 25% fish meal with duckweed
meal in the diet of Oreochromisniloticus promotes better growth with better feed utilization
than feeding only fish meal which can lead to reduction in cost of feeding fish and profit
margin. Exceeding this limit however depress weight gain.
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Daving, D. A and Arnold, C.R. 2000.Replacement of fish meal in practical diets for the
Pacific white shrimp, Litopenaeusvannamei. Aquaculture, 185:291- 298.
Fagbenro, O.A 2000..Validation of the essential amino acid requirements of Nile tilapia,
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Transnational Journal of Science and Technology
October 2012 edition vol.2, No.9
Yilmaz, E; Akyurt, I and Gunal, G (2005) sUse of duckweed Lemna minor as a protein
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