African Journal of Biotechnology Vol. 11(17), pp. 4086-4089, 28 February, 2012
Available online at http://www.academicjournals.org/AJB
DOI: 10.5897/AJB11.3392
ISSN 1684–5315 © 2012 Academic Journals
Full Length Research Paper
Flesh quality differentiation of wild and cultured Nile
tilapia (Oreochromis niloticus) populations
Samy Yehya El-Zaeem1,4*, Mohamed Morsi M. Ahmed2,3, Mohamed El-Sayed Salama4 and
Walid N. Abd El-Kader4
1DNA Research Chair, Zoology Department, College of Sciences, P.O. Box 2455, King Saud University, Riyadh 11451,
Saudi Arabia.
2Nucleic Acids Research Department, Genetic Engineering and Biotechnology Research Institute (GEBRI), City for
Scientific Research and Technology Applications, Alexandria, Egypt.
3Biological Sciences Department, Faculty of Sciences, P.O Box 80203, King Abdulaziz University, Jeddah 21589, Saudi
Arabia.
4Animal and Fish Production Department, Faculty of Agriculture (Saba-Bacha), Alexandria University, Alexandria, Egypt.
Accepted 23 January, 2012
Variation in chemical composition and carcass traits among different wild and cultured Nile tilapia,
Oreochromis niloticus populations were analyzed to study and compare the differences among
different wild (Manzalah lake, Nile river and Edku lake) and cultured Nile tilapia populations. Data of
body composition of different Nile tilapia (O. niloticus) populations showed that, the highest mean value
of moisture content (80.32 ± 0.39%) was shown by cultured population and differ significantly (P≤0.05)
from those of other populations studied. The highest mean value of protein content (58.14 ± 0.51%) was
shown by cultured population but did not differ significantly (P≤0.05) from that of River Nile population.
Lipids content showed lower mean (21.74 ± 0.06%) by River Nile population but did not differ
significantly (P≤0.05) from that of cultured population. The results of carcass traits show insignificant
differences (P≤0.05) in all parameters among different Nile tilapia populations studied. The evaluation of
flesh quality of different wild and cultured populations of Nile tilapia studied can result in a genotype
suitable for aquaculture.
Key words: Flesh quality, wild, cultured, Nile tilapia, population.
INTRODUCTION
Tilapias are very important in world fisheries, and are the
second most important group of food fishes in the world.
Nile tilapia, Oreochromis niloticus accounted for a harvest
of nearly 2.54 million tones in 2009 (FAO, 2011), second
only to carp as a warm water food fish and exceeding the
harvest of Atlantic salmon, Salmo salar, although, the
value of the Atlantic salmon catch is more than twice that
of the tilapia catch (Maclean et al., 2002). Although,
native to Africa, tilapias are cultured in Asia and the Far
East, and occupy two rather separate market niches,
*Corresponding author. E-mail: selzaeem@yahoo.com,
selzaeem@ksu.edu.sa or samy.elzaeem@alexagrsaba.
edu.eg. Tel: +20103552398 or +966592299396.
being a poor man’s food fish in countries such as Israel
and the Southern United States (Maclean et al., 2002).
Flesh quality has gained importance among consumers
and in the aquaculture industry because it is directly
related to human health and nutrition. Flesh quality comprises
several different characteristics. Due to the large
number of traits involved and the ensuing complexity,
genetic improvement for flesh quality has been almost
neglected in breeding programs for aquaculture species.
Quality traits can usually be recorded only on dead fish,
and therefore family selection must be practiced in a
breeding program (Gjedrem, 1997).
In order to meet the increase in human fish demand,
aquaculture is increasing along the necessity of supplying
fish products of high quality and also diversified product
(Queméner et al., 2002). Generally, an important success
4086 Afr. J. Biotechnol.
Table 1. Minimum and maximum weight and total length of Nile tilapia population samples collected from
Manzalah Lake, Nile river, Edku Lake and cultured.
Trait Manzalah Lake Nile river Edku Lake Cultured
Average weight 124.69±46.98 184.54±41.62 179.82± 90.11 139.86±60.20
Minimum 46.60 111.90 65.00 30.00
Maximum 208.00 225.00 295.00 209.40
Average total length 18.92±2.02 21.30±1.79 20.43±3.14 19.26±3.31
Minimum 13.30 18.40 15.10 12.30
Maximum 21.70 25.00 24.50 23.20
factor is that consumers accept farmed fish to be
equivalent or superior to the wild fish (Olsson et al.,
2003). Quality terms and how they are perceived differ for
the fish farmer, processing industry and consumer. While
growth and feed conversion are of great importance to
the aquaculturist, these parameters are unlikely to be of
indirect interest to the latter. However, producing fish that
are positively received by processors and consumers
alike is naturally of major concern to the fish farming
industry (Rasmussen, 2001). The quality of farmed fish
has occasionally been reported as being lower than that
of wild fish (Sylvia et al., 1995). Although, contradictory
result have also been obtained (Jahncke et al., 1988).
Hernandez et al. (2001) reported that wild fish
acceptability is greater than that of farmed fish. The term
fish quality is all encompassing and its study is difficult
owing to the fact that specific parameters that are
recognized as being vital in one part of the world are
judged to be less important elsewhere. Salmonid
aquaculture has focused for many years on enhancing
the quantity of fish produced. However, optimization of
the quality of salmonids may lead to improvement of
consumer acceptance and higher price for the farmed
product (Rasmussen, 2001). In these connections, Sahu
et al. (2000) reported that among the commercial characteristics
of fish, flesh quality is becoming more important
to the aquaculture industry. The consumer dictates the
flesh quality and it is a very complex characteristic. An
attempt has to be made to define and analyze flesh
quality and its relation to carcass characteristics. Carcass
quality traits must be defined precisely and should be
able to be measured with a high repeatability. Some of
the quality traits vary within the carcass. Therefore, a
very precise carcass evaluation is necessary to arrive at
any useful conclusion. To have an efficient program for
improving growth and flesh quality traits of fish, it is
necessary to test 10 to 15 fishes from each family for
carcass evaluation each year and to compile a database.
The genetic gain will increase when more families are
tested in each generation.
The evaluation of flesh quality of different populations
can result in a genotype suitable for aquaculture. Therefore,
the present work aimed to evaluate and compare
the flesh quality (chemical composition and carcass
traits) of wild and cultured Nile tilapia, O. niloticus
populations collected from Manzalah lake, Nile river,
Edku lake and cultured.
MATERIALS AND METHODS
The present study was carried out at Animal and Fish Production
Department, Faculty of Agriculture (Saba-Bacha), Alexandria
University, Alexandria, Egypt.
Specimen collection
Fifty mature individuals (both sex) of each of wild and cultured Nile
tilapia, (O. niloticus) populations were randomly collected from
Manzalah Lake, Nile river, Edku Lake and cultured, by professional
fishermen (Table 1).
Chemical composition
Three samples from each population with equal number of fish
were chosen randomly for body chemical analysis. Fish body
moisture, crude protein and crude fat contents were determined
according to A.O.A.C. (1984) methods.
Flesh quality
Dressings were conducted on the same samples of fish collected
from different geographical areas. The following body traits were
recorded individually on each fish within each population:
Inedible parts traits
The following parameters were estimated as percentage values of
whole body weight (BW):
Head weight (%) = head weight / total body weight × 100.
Viscera (%) = weight of viscera / total body weight × 100.
Fins weight (%) = fins weight / total body weight × 100.
Scales weight (%) = scales weight / total body weight × 100.
Backbone weight (%) = backbone weight / total body weight × 100.
Inedible parts weight (%) = inedible parts weight/total body weight × 100.
El-Zaeem et al. 4087
Table 2. Chemical composition of different Nile tilapia (O. niloticus) populations.
Population Moisture
On dry matter basis (%)
Protein Lipid
Manzalah 74.28±0.07b 54.82±0.9d4b 23.32±0.32a
Nile 72.94±0.76b 55.88±1.56ab 21.74±0.06b
Edku 70.80±0.57c 53.59±0.28 b 23.52±0.40a
Cultured 80.32±0.39a 58.14±0.51a 21.95±0.64b
Means within each comparison in the same column with the different superscripts differ
significantly (P ≤ 0.05).
Edible parts traits
Meat yield (%) = Skin with fillet weight / total body weight ×100
(Huang et al., 1994).
Dress-out (D%) = (body weight – head – scales – viscera – gonads
– fins) / body weight x 100.
Headed–gutted body weight (HGBW%) = (gutted body weight –
head) / total body weight (g) × 100.
Head-on dress-out (HD dress%) = (body weight – scales – viscera
– gonad - fins) / body weight × 100.
Gutted body weight (GBW%) = (body weight – viscera - gonads) /
body weight × 100 (Rye and Refstie, 1995).
Statistical analysis
Data were statistically analyzed using the following model (CoStat,
1986):
Yij= μ + Ti+ eij
Where, Yij is observation of the ijth parameter measured; μ, overall
mean; Ti, effect of ith population; eij, random error.
Significant differences (P≤0.05) among means were tested by the
method of Duncan (1955).
RESULTS AND DISCUSSION
The results of chemical composition of different Nile
tilapia, O. niloticus populations on dry matter basis are
presented in Table 2. The highest mean value of
moisture content (80.32 ± 0.39%) was shown by cultured
population and differ significantly (P≤0.05) from those of
the other populations studied. Moreover, the highest
mean value of protein (58.14±0.51%) was achieved by
cultured population, but did not differ significantly
(P≤0.05) from that of Nile River population. Lipids content
showed higher mean (23.52 ± 0.40%) by Edku Lake
population, but did not differ significantly (P≤0.05) from
that of Manzalah Lake population. In these connections,
Abdel-Aziz (2006) found that Nile tilapia (O. niloticus)
from River Nile contains about 80.08% moisture. The
same results were obtained by Abo-Raya (1975) and El-
Akel (1983). Galhom (2002) reported that, moisture
content of fish from Egyptian waters ranged between
70.00 and 79.00%. On the other hand, Abd-Alla (1994)
found a range between 80.50 and 84.00% for moisture
content of fish muscles from various fish cultures. There
is a general trend towards increasing the percentage of
moisture in cultured as compared to wild fish. The results
of the present work are consistent with the ranges
reported by several other investigators that worked on
tilapia O. niloticus obtained from various water sources
and different fishing seasons (Saleh, 1986; Salama,
1990; El-Ebzary and El-Dashlouty, 1992; Keshk, 2004).
Distribution of fat in the carcass is an important economic
trait. It is very difficult to ascertain the optimum level of fat
in a carcass. Generally, it is felt that fat percentage of 16
to 18% in a fillet is too high. Excessive fat deposits
reduce the quality of the fish. Increase in fat depots
increases waste in processing. Dissection in and around
the intestine is a standard method for checking the fat
deposit of a fish. There are several other methods
available to measure fat content in a fish carcass (Wold
and Isaksson, 1997; Sahu et al., 2000). Moreover, Sahu
et al. (2000) reported that protein content and composition
are stable during development. The wide
variability in the characteristics of muscle and connective
tissues in commercial fish is related to their mode of
development. Chemical composition differences among
Nile tilapia, O. niloticus populations may be due to some
environmental factors. In these connections, Svàsand et
al. (1998), Favalora et al. (2002) and Flos et al. (2002),
reported that the quality of fish is affected by parameters
such as feed type, level of dietary intake and growth.
Feed composition has a major influence on the proximate
composition of salmonids. In particular, whole body lipids
as well as the lipid content in the edible fillet are directly
related to dietary fat content, while the fatty acid
composition of the fish flesh is also strongly influenced by
the dietary fatty acid profile. Fish body composition
appears to be largely influenced by feed composition. An
increase in other parameters such as feeding rate and
fish size also result in enhanced adipose deposition and
decrease water content in the fish body. The protein
content, however, remains more or less stable. An
increase in body fat content is generally accompanied by
reduction in slaughter yield, owning to an increase in the
weight of viscera in relation to body weight. The levels of
4088 Afr. J. Biotechnol.
Table 3. Carcass traits (% of body weight) of different Nile tilapia (O. niloticus) populations.
Trait
Population
Manzalah Nile Edku Cultured
Head 23.05±1.62 22.05±1.87 25.01±2.73 23.49±2.21
Viscera 12.48±1.42 12.78±1.58 9.78±2.95 12.25±1.40
Fins 2.73±0.17 2.68±0.17 2.58±0.50 2.95±0.73
Scales 3.65±0.51 3.78±0.45 3.90±0.54 3.80±0.54
Back bone 8.73±0.51 9.05±4.12 9.15±0.47 8.65±0.37
Inedible parts 50.58±2.00 49.70±2.36 50.43±3.35 51.69±2.20
Meat yield 47.27±2.11 47.25±3.41 46.30±2.97 46.33±1.40
Dress out 58.15±2.12 56.08±2.70 55.93±5.60 55.30±3.98
HGBW 63.38±2.97 64.30±2.94 64.30±3.37 63.35±2.66
HD Dress 80.08±1.20 80.38±1.09 82.83±3.90 80.06±0.99
GBW 86.43±1.73 86.75±1.54 90.28±4.36 86.80±1.75
Dress-out (D %) = (body weight – head – scales – viscera – gonads – fins) / body weight × 100; headed – gutted
body weight: (HGBW %) = (gutted body weight– head)/ body weight × 100; head-on dress-out: (HD dress %) =
(body weight with skin-scales-viscera-gonad-fins)/body weight × 100; gutted body weight: (GBW %) = (body
weight–viscera–gonads) / body weight × 100.
proximate constituents in the whole body as well as the
fillet are readily manipulated by feed composition and
feeding strategies, whereas the sensory parameters are
less affected by these variables. Different rearing
systems generate products having variable quality level
which differ from wild fish in color.
Carcass traits of different Nile tilapia, O. niloticus
populations are presented in Table 3. The results show
that insignificant differences (P≤0.05) were detected in all
carcass traits studied among different Nile tilapia
populations tested. Head weight as percentage of body
weight ranged from 22.05 ± 1.87 to 25.01 ± 2.73. Viscera
percentage ranged from 9.78 ± 2.95 to 12.78 ± 1.58. Fins
percentage varied between 2.58 ± 0.50 and 2.95±0.73.
Scales percentage ranged from 3.65 ± 0.51 to 3.90 ±
0.54. Back bone percentage ranged from 8.65 ± 0.37 to
9.15 ± 0.47. Meat yield percentage ranged from 46.30 ±
2.97 to 47.27 ± 2.11. Dress out percentage varied
between 55.30 ± 3.98 and 58.15±2.12. HGBW
percentage ranged from 63.35 ± 2.66 to 64.30 ± 3.37. HD
dress percentage ranged from 80.06 ± 0.99 to 82.83 ±
3.90. GBW percentage varied between 86.43 ± 1.73 and
90.28 ± 4.36. Non-edible parts percentage varied
between 49.70 ± 2.36 to 51.69±2.20. The results of
carcass traits of the present work are consistent with the
ranges reported by several other investigators who
worked on tilapia O. niloticus obtained from various water
sources and different fishing seasons (El-Sagheer, 2001;
Khalifa, 2003; Keshk, 2004; Johnston et al., 2006; Abdel-
Aziz, 2006). The evaluation of flesh quality of different
wild and cultured populations of Nile tilapia studied can
result in a genotype suitable for aquaculture.
ACKNOWLEDGMENT
This Project was supported by King Saud University,
Deanship of Scientific Research, College of Science
Research Center.
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Available online at http://www.academicjournals.org/AJB
DOI: 10.5897/AJB11.3392
ISSN 1684–5315 © 2012 Academic Journals
Full Length Research Paper
Flesh quality differentiation of wild and cultured Nile
tilapia (Oreochromis niloticus) populations
Samy Yehya El-Zaeem1,4*, Mohamed Morsi M. Ahmed2,3, Mohamed El-Sayed Salama4 and
Walid N. Abd El-Kader4
1DNA Research Chair, Zoology Department, College of Sciences, P.O. Box 2455, King Saud University, Riyadh 11451,
Saudi Arabia.
2Nucleic Acids Research Department, Genetic Engineering and Biotechnology Research Institute (GEBRI), City for
Scientific Research and Technology Applications, Alexandria, Egypt.
3Biological Sciences Department, Faculty of Sciences, P.O Box 80203, King Abdulaziz University, Jeddah 21589, Saudi
Arabia.
4Animal and Fish Production Department, Faculty of Agriculture (Saba-Bacha), Alexandria University, Alexandria, Egypt.
Accepted 23 January, 2012
Variation in chemical composition and carcass traits among different wild and cultured Nile tilapia,
Oreochromis niloticus populations were analyzed to study and compare the differences among
different wild (Manzalah lake, Nile river and Edku lake) and cultured Nile tilapia populations. Data of
body composition of different Nile tilapia (O. niloticus) populations showed that, the highest mean value
of moisture content (80.32 ± 0.39%) was shown by cultured population and differ significantly (P≤0.05)
from those of other populations studied. The highest mean value of protein content (58.14 ± 0.51%) was
shown by cultured population but did not differ significantly (P≤0.05) from that of River Nile population.
Lipids content showed lower mean (21.74 ± 0.06%) by River Nile population but did not differ
significantly (P≤0.05) from that of cultured population. The results of carcass traits show insignificant
differences (P≤0.05) in all parameters among different Nile tilapia populations studied. The evaluation of
flesh quality of different wild and cultured populations of Nile tilapia studied can result in a genotype
suitable for aquaculture.
Key words: Flesh quality, wild, cultured, Nile tilapia, population.
INTRODUCTION
Tilapias are very important in world fisheries, and are the
second most important group of food fishes in the world.
Nile tilapia, Oreochromis niloticus accounted for a harvest
of nearly 2.54 million tones in 2009 (FAO, 2011), second
only to carp as a warm water food fish and exceeding the
harvest of Atlantic salmon, Salmo salar, although, the
value of the Atlantic salmon catch is more than twice that
of the tilapia catch (Maclean et al., 2002). Although,
native to Africa, tilapias are cultured in Asia and the Far
East, and occupy two rather separate market niches,
*Corresponding author. E-mail: selzaeem@yahoo.com,
selzaeem@ksu.edu.sa or samy.elzaeem@alexagrsaba.
edu.eg. Tel: +20103552398 or +966592299396.
being a poor man’s food fish in countries such as Israel
and the Southern United States (Maclean et al., 2002).
Flesh quality has gained importance among consumers
and in the aquaculture industry because it is directly
related to human health and nutrition. Flesh quality comprises
several different characteristics. Due to the large
number of traits involved and the ensuing complexity,
genetic improvement for flesh quality has been almost
neglected in breeding programs for aquaculture species.
Quality traits can usually be recorded only on dead fish,
and therefore family selection must be practiced in a
breeding program (Gjedrem, 1997).
In order to meet the increase in human fish demand,
aquaculture is increasing along the necessity of supplying
fish products of high quality and also diversified product
(Queméner et al., 2002). Generally, an important success
4086 Afr. J. Biotechnol.
Table 1. Minimum and maximum weight and total length of Nile tilapia population samples collected from
Manzalah Lake, Nile river, Edku Lake and cultured.
Trait Manzalah Lake Nile river Edku Lake Cultured
Average weight 124.69±46.98 184.54±41.62 179.82± 90.11 139.86±60.20
Minimum 46.60 111.90 65.00 30.00
Maximum 208.00 225.00 295.00 209.40
Average total length 18.92±2.02 21.30±1.79 20.43±3.14 19.26±3.31
Minimum 13.30 18.40 15.10 12.30
Maximum 21.70 25.00 24.50 23.20
factor is that consumers accept farmed fish to be
equivalent or superior to the wild fish (Olsson et al.,
2003). Quality terms and how they are perceived differ for
the fish farmer, processing industry and consumer. While
growth and feed conversion are of great importance to
the aquaculturist, these parameters are unlikely to be of
indirect interest to the latter. However, producing fish that
are positively received by processors and consumers
alike is naturally of major concern to the fish farming
industry (Rasmussen, 2001). The quality of farmed fish
has occasionally been reported as being lower than that
of wild fish (Sylvia et al., 1995). Although, contradictory
result have also been obtained (Jahncke et al., 1988).
Hernandez et al. (2001) reported that wild fish
acceptability is greater than that of farmed fish. The term
fish quality is all encompassing and its study is difficult
owing to the fact that specific parameters that are
recognized as being vital in one part of the world are
judged to be less important elsewhere. Salmonid
aquaculture has focused for many years on enhancing
the quantity of fish produced. However, optimization of
the quality of salmonids may lead to improvement of
consumer acceptance and higher price for the farmed
product (Rasmussen, 2001). In these connections, Sahu
et al. (2000) reported that among the commercial characteristics
of fish, flesh quality is becoming more important
to the aquaculture industry. The consumer dictates the
flesh quality and it is a very complex characteristic. An
attempt has to be made to define and analyze flesh
quality and its relation to carcass characteristics. Carcass
quality traits must be defined precisely and should be
able to be measured with a high repeatability. Some of
the quality traits vary within the carcass. Therefore, a
very precise carcass evaluation is necessary to arrive at
any useful conclusion. To have an efficient program for
improving growth and flesh quality traits of fish, it is
necessary to test 10 to 15 fishes from each family for
carcass evaluation each year and to compile a database.
The genetic gain will increase when more families are
tested in each generation.
The evaluation of flesh quality of different populations
can result in a genotype suitable for aquaculture. Therefore,
the present work aimed to evaluate and compare
the flesh quality (chemical composition and carcass
traits) of wild and cultured Nile tilapia, O. niloticus
populations collected from Manzalah lake, Nile river,
Edku lake and cultured.
MATERIALS AND METHODS
The present study was carried out at Animal and Fish Production
Department, Faculty of Agriculture (Saba-Bacha), Alexandria
University, Alexandria, Egypt.
Specimen collection
Fifty mature individuals (both sex) of each of wild and cultured Nile
tilapia, (O. niloticus) populations were randomly collected from
Manzalah Lake, Nile river, Edku Lake and cultured, by professional
fishermen (Table 1).
Chemical composition
Three samples from each population with equal number of fish
were chosen randomly for body chemical analysis. Fish body
moisture, crude protein and crude fat contents were determined
according to A.O.A.C. (1984) methods.
Flesh quality
Dressings were conducted on the same samples of fish collected
from different geographical areas. The following body traits were
recorded individually on each fish within each population:
Inedible parts traits
The following parameters were estimated as percentage values of
whole body weight (BW):
Head weight (%) = head weight / total body weight × 100.
Viscera (%) = weight of viscera / total body weight × 100.
Fins weight (%) = fins weight / total body weight × 100.
Scales weight (%) = scales weight / total body weight × 100.
Backbone weight (%) = backbone weight / total body weight × 100.
Inedible parts weight (%) = inedible parts weight/total body weight × 100.
El-Zaeem et al. 4087
Table 2. Chemical composition of different Nile tilapia (O. niloticus) populations.
Population Moisture
On dry matter basis (%)
Protein Lipid
Manzalah 74.28±0.07b 54.82±0.9d4b 23.32±0.32a
Nile 72.94±0.76b 55.88±1.56ab 21.74±0.06b
Edku 70.80±0.57c 53.59±0.28 b 23.52±0.40a
Cultured 80.32±0.39a 58.14±0.51a 21.95±0.64b
Means within each comparison in the same column with the different superscripts differ
significantly (P ≤ 0.05).
Edible parts traits
Meat yield (%) = Skin with fillet weight / total body weight ×100
(Huang et al., 1994).
Dress-out (D%) = (body weight – head – scales – viscera – gonads
– fins) / body weight x 100.
Headed–gutted body weight (HGBW%) = (gutted body weight –
head) / total body weight (g) × 100.
Head-on dress-out (HD dress%) = (body weight – scales – viscera
– gonad - fins) / body weight × 100.
Gutted body weight (GBW%) = (body weight – viscera - gonads) /
body weight × 100 (Rye and Refstie, 1995).
Statistical analysis
Data were statistically analyzed using the following model (CoStat,
1986):
Yij= μ + Ti+ eij
Where, Yij is observation of the ijth parameter measured; μ, overall
mean; Ti, effect of ith population; eij, random error.
Significant differences (P≤0.05) among means were tested by the
method of Duncan (1955).
RESULTS AND DISCUSSION
The results of chemical composition of different Nile
tilapia, O. niloticus populations on dry matter basis are
presented in Table 2. The highest mean value of
moisture content (80.32 ± 0.39%) was shown by cultured
population and differ significantly (P≤0.05) from those of
the other populations studied. Moreover, the highest
mean value of protein (58.14±0.51%) was achieved by
cultured population, but did not differ significantly
(P≤0.05) from that of Nile River population. Lipids content
showed higher mean (23.52 ± 0.40%) by Edku Lake
population, but did not differ significantly (P≤0.05) from
that of Manzalah Lake population. In these connections,
Abdel-Aziz (2006) found that Nile tilapia (O. niloticus)
from River Nile contains about 80.08% moisture. The
same results were obtained by Abo-Raya (1975) and El-
Akel (1983). Galhom (2002) reported that, moisture
content of fish from Egyptian waters ranged between
70.00 and 79.00%. On the other hand, Abd-Alla (1994)
found a range between 80.50 and 84.00% for moisture
content of fish muscles from various fish cultures. There
is a general trend towards increasing the percentage of
moisture in cultured as compared to wild fish. The results
of the present work are consistent with the ranges
reported by several other investigators that worked on
tilapia O. niloticus obtained from various water sources
and different fishing seasons (Saleh, 1986; Salama,
1990; El-Ebzary and El-Dashlouty, 1992; Keshk, 2004).
Distribution of fat in the carcass is an important economic
trait. It is very difficult to ascertain the optimum level of fat
in a carcass. Generally, it is felt that fat percentage of 16
to 18% in a fillet is too high. Excessive fat deposits
reduce the quality of the fish. Increase in fat depots
increases waste in processing. Dissection in and around
the intestine is a standard method for checking the fat
deposit of a fish. There are several other methods
available to measure fat content in a fish carcass (Wold
and Isaksson, 1997; Sahu et al., 2000). Moreover, Sahu
et al. (2000) reported that protein content and composition
are stable during development. The wide
variability in the characteristics of muscle and connective
tissues in commercial fish is related to their mode of
development. Chemical composition differences among
Nile tilapia, O. niloticus populations may be due to some
environmental factors. In these connections, Svàsand et
al. (1998), Favalora et al. (2002) and Flos et al. (2002),
reported that the quality of fish is affected by parameters
such as feed type, level of dietary intake and growth.
Feed composition has a major influence on the proximate
composition of salmonids. In particular, whole body lipids
as well as the lipid content in the edible fillet are directly
related to dietary fat content, while the fatty acid
composition of the fish flesh is also strongly influenced by
the dietary fatty acid profile. Fish body composition
appears to be largely influenced by feed composition. An
increase in other parameters such as feeding rate and
fish size also result in enhanced adipose deposition and
decrease water content in the fish body. The protein
content, however, remains more or less stable. An
increase in body fat content is generally accompanied by
reduction in slaughter yield, owning to an increase in the
weight of viscera in relation to body weight. The levels of
4088 Afr. J. Biotechnol.
Table 3. Carcass traits (% of body weight) of different Nile tilapia (O. niloticus) populations.
Trait
Population
Manzalah Nile Edku Cultured
Head 23.05±1.62 22.05±1.87 25.01±2.73 23.49±2.21
Viscera 12.48±1.42 12.78±1.58 9.78±2.95 12.25±1.40
Fins 2.73±0.17 2.68±0.17 2.58±0.50 2.95±0.73
Scales 3.65±0.51 3.78±0.45 3.90±0.54 3.80±0.54
Back bone 8.73±0.51 9.05±4.12 9.15±0.47 8.65±0.37
Inedible parts 50.58±2.00 49.70±2.36 50.43±3.35 51.69±2.20
Meat yield 47.27±2.11 47.25±3.41 46.30±2.97 46.33±1.40
Dress out 58.15±2.12 56.08±2.70 55.93±5.60 55.30±3.98
HGBW 63.38±2.97 64.30±2.94 64.30±3.37 63.35±2.66
HD Dress 80.08±1.20 80.38±1.09 82.83±3.90 80.06±0.99
GBW 86.43±1.73 86.75±1.54 90.28±4.36 86.80±1.75
Dress-out (D %) = (body weight – head – scales – viscera – gonads – fins) / body weight × 100; headed – gutted
body weight: (HGBW %) = (gutted body weight– head)/ body weight × 100; head-on dress-out: (HD dress %) =
(body weight with skin-scales-viscera-gonad-fins)/body weight × 100; gutted body weight: (GBW %) = (body
weight–viscera–gonads) / body weight × 100.
proximate constituents in the whole body as well as the
fillet are readily manipulated by feed composition and
feeding strategies, whereas the sensory parameters are
less affected by these variables. Different rearing
systems generate products having variable quality level
which differ from wild fish in color.
Carcass traits of different Nile tilapia, O. niloticus
populations are presented in Table 3. The results show
that insignificant differences (P≤0.05) were detected in all
carcass traits studied among different Nile tilapia
populations tested. Head weight as percentage of body
weight ranged from 22.05 ± 1.87 to 25.01 ± 2.73. Viscera
percentage ranged from 9.78 ± 2.95 to 12.78 ± 1.58. Fins
percentage varied between 2.58 ± 0.50 and 2.95±0.73.
Scales percentage ranged from 3.65 ± 0.51 to 3.90 ±
0.54. Back bone percentage ranged from 8.65 ± 0.37 to
9.15 ± 0.47. Meat yield percentage ranged from 46.30 ±
2.97 to 47.27 ± 2.11. Dress out percentage varied
between 55.30 ± 3.98 and 58.15±2.12. HGBW
percentage ranged from 63.35 ± 2.66 to 64.30 ± 3.37. HD
dress percentage ranged from 80.06 ± 0.99 to 82.83 ±
3.90. GBW percentage varied between 86.43 ± 1.73 and
90.28 ± 4.36. Non-edible parts percentage varied
between 49.70 ± 2.36 to 51.69±2.20. The results of
carcass traits of the present work are consistent with the
ranges reported by several other investigators who
worked on tilapia O. niloticus obtained from various water
sources and different fishing seasons (El-Sagheer, 2001;
Khalifa, 2003; Keshk, 2004; Johnston et al., 2006; Abdel-
Aziz, 2006). The evaluation of flesh quality of different
wild and cultured populations of Nile tilapia studied can
result in a genotype suitable for aquaculture.
ACKNOWLEDGMENT
This Project was supported by King Saud University,
Deanship of Scientific Research, College of Science
Research Center.
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