J. Agric. Environ. Sci. Vol. 5 No. 2 (2020) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 44
Length-Weight Relationship and Fulton’s Condition Factor of the Nile Tilapia
(Oreochromis niloticus L., 1758) in Lake Chamo, Ethiopia
Buchale Shishitu Shija
Arba Minch Agricultural Research Center, Arba Minch, Ethiopia
*Corresponding author: buchale.shishitu@yahoo.com
Received: September 6, 2020 Accepted: November 5, 2020
Abstract: The objectives of the study were to determine the length-weight relationship and Fulton’s condition factor
of O. niloticus in Lake Chamo, Southern region of Ethiopia. Data for total length (TL), total weight (TW) and sex
were collected from 5,778 fish samples (3577 females and 2201 males) for nine months (February to October 2018)
from commercial fishery of Lake Chamo. The collected data were summarized using descriptive statistics (graphs
and tables) and analyzed with the application of Microsoft Excel 2010 and SPSS Software. The length-weight
relationship was calculated using power function and obtained as TW = 0.0112*TL
3.14
, (R
2
= 0.96), TW =
0.0102*TL
3.19
, (R
2
= 0.98) and TW = 0.0102*TL
3.18,
(R
2
= 0.97) for male, female and pooled sexes, respectively. The
b value in this study was greater than the cubic (b > 3) value and indicates that both males and females of O.
niloticus in Lake Chamo followed positive allometric growth pattern. The average Fulton’s condition factor (K)
value for male, female and combined sex was 1.78, 1.96 and 1.85, respectively. The one-way ANOVA (P > 0.05)
revealed that Fulton’s condition factor by month’s interaction was insignificant. But the condition factor of both
sexes in Lake Chamo was significantly different (ANOVA, p < 0.05). There was highly significant differences
between sexes interaction (t-test, P = 0.000) which indicates the presence of temporal variation between both sexes
in Fulton’s condition factor. All the values of Fulton’s condition factors of male, female and combined sex of O.
niloticus were above 1.6 and indicates that O. niloticus of Lake Chamo was in a very good condition throughout the
study period. Future studies including other species of fish are also recommended.
Keywords: Fulton’s condition factor, Lake Chamo, Length-weight relationship
This work is licensed under a Creative Commons Attribution 4.0 International License
1. Introduction
Nile tilapia (Oreochromis niloticus L., 1758)
contributes more than 50% of the total landings of
fish caught per year in Ethiopian water bodies
(Tesfaye and Wolff, 2014). In addition to this, the
Nile tilapia are the most important fish species in
both tropical and subtropical freshwater bodies and
often playing a significant role of commercial
fisheries in various African countries (Mohammed
and Uraguchi, 2013). This is most probably due to
their high range of tolerance to environmental
conditions and the ability to accept artificially
formulated and naturally available food items that
make them commercially feasible (Adeyemi, 2009).
In Ethiopian context, O. niloticus is the most edible
fish species (Wudneh, 1998; Mitike, 2014). The O.
niloticus is widely found in the Rift valley lakes,
Abay, Awash, Baro-Akobo, Omo-Gibe, Tekeze and
Wabishebele-Genale basins (Golubtsov and Mina,
2003; Awoke, 2015). Furthermore, it is also found in
some other Ethiopian highland lakes and rivers
(Golubtsov and Mina, 2003).
Length-weight relationships data of fishes are useful
tools for biologists in fishery assessment and proper
management of fish population (Martin-Smith, 1996).
In addition, the length-weight relationship is used to
obtain information about the condition of fishes to
determine whether somatic growth is isometric or
allometric (Gurkan and Taskavak, 2007; Ujjania et
al., 2012).
Condition factor (K) is an important biological
parameter, which indicates the suitability of a
specific water body for growth of fish and an index
of species average size (Alam et al., 2014). Many
authors have also explained the importance of
J. Agric. Environ. Sci. Vol. 5 No. 2 (2020) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 45
condition factor as a useful tool for assessing fish
growth rate, age and feeding intensity (Abowei,
2006; Kumolu-Johnson and Ndimele, 2010;
Oribhabor et al., 2011; Onimisi and Ogbe, 2015; Abu
and Agarin, 2016). The relationship is also very
essential for proper fish exploitation and management
schemes and it is possible to estimate the average
weight of fish at a given length (Lawson et al., 2013;
Assefa, 2014; Ahmed et al., 2017; Getso et al., 2017;
Kumar et al., 2017; Melaku et al., 2017; Muchlisin et
al., 2017). The wellbeing of the fish is considered as
a good indicator of various water bodies‟ health in
relation to water pollution due to its cheapest means
of determining the stress of water pollution on the
fishes‟ body condition (Gupta and Tripathi, 2017).
O. niloticus is one of the edible fish species in Lake
Chamo and is economically important with high
acceptability by the consumers in Arba Minch as well
as in the country. According to Shija et al. (2019),
93.1% of the total annual catch of O. niloticus was
reported as immature and drastically reduced in yield.
So, it is important to determine the growth pattern
and conditions of fish in Lake Chamo. Therefore, the
present study was aimed at determining the length-
weight relationship and Fulton‟s condition factor of
O. niloticus in Lake Chamo. The finding of this study
would serve as an essential input for intervention in
fish resource management and environmental
conservation.
2. Materials and Methods
2.1. Description of the study area
Geographically Lake Chamo is located at 5
o
50Ꞌ59ꞋꞋ N
and 37
o
33Ꞌ54ꞋꞋ E in Southern Nations Nationalities
and People‟s Regional State of Ethiopia (Figure 1).
The catchment and surface area of Lake Chamo is
1,109 km
2
and 329 km
2
, respectively (Awulachew,
2006a, b). The catchment of the lake is characterized
by a humid to hot semi-arid tropical climate with a
bimodal rainfall pattern including two wet seasons
(the first from end-March to mid-June, and the
second from mid-September to late November) and
two dry seasons (the first from December to mid-
March, the second from end-June to mid-September)
(Makin et al., 1975; Wagesho, 2014). Lake Chamo
receives water from the rivers Kulfo, Sile and Elgo
(Makin et al., 1975; Teklemariam, 2005). The flood
plains and the deltas of the lake are fertile and hence
have been under extensive agricultural cultivation
since the last three decades (Fassil et al., 2018).
The fishery on Lake Chamo is almost exclusively
conducted with a surface gillnet, although long–lines
are also used to some extent to Clarias gariepinus
and Bagrus docmak. The nets are prepared locally by
fishers themselves or by some other people involved
in fishing gear making activity. Also, monofilament
is highly applicable in the fishery. The mesh size of
gillnet used in the present study ranged from 3 to 8
cm.
Figure 1: Location of Lake Chamo, Southern Ethiopia (Utaile and Sulaiman, 2016)
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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 46
Table 1: Water quality parameters of Lake Chamo and recommended water quality limits for the protection of aquatic
life
Variables
(Mean + SD)
Recommended
limits
Sources
Explanations
Temperature
(
º
C)
29.41+1.67
26-30
Boyd, 1990
The range for optimal growth of
tropical fishes
pH
9.15+0.08
5-10
USEPA, 1986
Fishes may die if 5 <pH > 10
TSS (mg/L)
112.77+63.19
20-80
Alabaster and Lloyd, 1980
Suitable range for diverse fish
species
DO (mg/L)
6.41+0.48
5
Akporhonor and Asia, 2007
The minimum concentration that
allows survival of freshwater
fishes
BOD (mg/L)
2.59+0.80
<5
US EPA 1997
Indicate the absence of
biodegradable organic pollution
TDS (mg/L)
1232.80+13.04
1340
SETAC 2004
May cause adverse effects to
fishes
Source: Utaile and Sulaiman (2016)
2.2. Methods of sampling and data collection
Samples of O. niloticus were collected monthly from
February to October 2018 in randomly selected three
days in a week from the fisheries of Lake Chamo.
The trained fishermen were involved in data
collection with regular following up by the
researcher. The total length and total weight of fresh
fish samples were measured to the nearest 1 mm and
1 g using measuring board and sensitive electronic
balance, respectively. Length-weight relationship was
calculated using power function (Le Cren, 1951).
  [1]
Logarithmic transformation of the formula indicated
above [1] gives a linear equation as indicated below.
      [2]
Where,
TW = total weight (g)
TL = total length (cm)
a = the intercept
b = the slope of length-weight regression
The confidence limit for the slope (b) was estimated
using the formula described by King (1995), which is
indicated below.
     [3]
Where,
b = slope in length weight relationship
t = table value of t (t test at 95 % confidence)
Sb = the standard error of slope b
The Fulton‟s condition factor (K) is often used to
reflect the nutritional status or well-being of an
individual fish. It was calculated by using the formula
described by Fulton (1904) which indicated below.


   [4]
Where,
TW = total weight of fish in gram (g)
TL = total length of fish in centimeter (cm)
2.3. Data analysis
The data analyses were done using
Microsoft Office Excel (2010) and SPSS
software.
3. Results and Discussion
3.1. Length-weight relationship
A total of 5,778 fish samples comprising 3,577
females and 2,201 males were collected from the
landing sites for the study. Based on the collected
data, the length-weight relationship of O. niloticus in
Lake Chamo was curvilinear. The relationship
representing male, female and pooled (both sexes)
J. Agric. Environ. Sci. Vol. 5 No. 2 (2020) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 47
are presented in Figure 2, 3 & 4, respectively.
According to the results, the rate of increase in body
weight was inversely proportional to length. It is the
same relationship as has been reported by earlier
authors for the same species in Lake Chamo (Teferi
and Admassu, 2002), in Lake Hayq (Worie and
Getahun, 2014), in Lakes Koka, Ziway and Langano
(Tesfaye and Tadesse, 2008).
The 95% confidence limits for the slope (b) of
length-weight relationship of male, female and
pooled data were estimated following the formula in
equation [3] and indicated below.
Male: 3.11 – 3.16
Female: 3.17 – 3.20
Pooled: 3.16 – 3.19
Figure 2: Length-weight relationship of male O. niloticus in Lake Chamo
TW = total weight; R
2
= coefficient of determination; n = number of sample
TW= 0.0112TL
3.1388
R² = 0.9656
n= 2201
0
200
400
600
800
1000
1200
1400
1600
0 10 20 30 40 50
Weigth (g)
Length (cm)
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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 48
Figure 3: Length-weight relationship of female O. niloticus in Lake Chamo
TW = total weight; R
2
= coefficient of determination; n = number of sample
Figure 4: Length-weight relationship in both sexes (pooled) of O. niloticus in Lake Chamo
TW = total weight; R
2
= coefficient of determination; n = number of sample
TW = 0.0102TL
3.185
R² = 0.9799
n=3577
0
200
400
600
800
1000
1200
0 10 20 30 40
Weigth (g)
Length (cm)
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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 49
There is high significant difference between b and the
cubic value (b
3
) in both sexes and pooled data (Table
2). The calculated t-value was much higher from the
tabulated t-value, which justifies that the b value
calculated based on length-weight data of O. niloticus
was significant. The exponential value of all cases
was tested against „3‟ and was found to be
significantly different at the 5% confidence interval
level. When the value of b was smaller, equal and
larger than 3, it indicates negative allometry,
isometry and positive allometry, respectively
(Nehemia et al., 2012). Fish can attain an isometric,
negative or positive allometric growth pattern. In
isometric growth, the fish does not change the shape
of its body as it continues to grow while negative
allometric growth shows the fish becomes thinner as
its body weight increases as opposed to a positive
allometric growth that implies the fish becomes
relatively broader and fatter as its length increases
(Riedel et al., 2007). As the b value in this study was
greater than the cubic value, both males and females
of O. niloticus in Lake Chamo follows positive
allometric growth pattern. The b value (3.18)
obtained in the present study was higher than the
values obtained in the earlier studies for the same
species in some lakes of Ethiopia.
The earlier studies showed that the O. niloticus in
Lake Chamo, Ziway, Hawassa, and Tana was found
to have b values of 2.98 (Teferi and Admassu, 2002),
3.03 (Tadesse, 1988), 2.90 (Admassu, 1990), and
2.74 (Tadesse, 1997), respectively, which indicate
negative allometric growth pattern except for Lake
Ziway. The b value in this study opposes the value in
the previous study in Lake Chamo and the variation
in growth pattern could be due to different ecological
parameters during the study periods which comprises
of several biotic and abiotic interactions depending
on seasonality. According to Bagenal and Tesch
(1978) and Froese (2006), the variation in the value
of b takes place due to season, habitat, gonad
maturity, sex, diet, stomach fullness, health,
preservation techniques and annual differences in
environmental conditions.
The b value in the present study was comparable to
that of Lake Victoria (3.20) (Njiru et al., 2006), 3.16
(Steve and Okeyo, 2019). The R
2
values estimated in
the present study was very close to 1 that shows the
accuracy of data and methodology followed for the
estimation of relationship.
Parameters
Male
Female
Pooled
a value
0.0112
0.0102
0.0102
b value
3.1388
3.185
3.1779
Std. error (S
b
)
0.013
0.008
0.007
r
2
0.9656
0.9799
0.972
t value
(calculated)
10.68
23.13
25.41
t critical at 5%
1.96
1.96
1.96
Number of
observations
2201
3577
5778
Significance
Highly
significant
Highly
significant
Highly
significant
The analysis of variance of the regression coefficient
(ANOVA) for testing regression coefficient of length
and weight of O. nilotcus were presented in Table 3.
Table 3: ANOVA table of regression analysis
Regression
Residual
Total
Male
Female
Combined
Male
Female
Combined
Male
Female
combined
SS
663.92
1215.86
1934.10
23.68
26.67
55.74
687.61
1242.53
1989.84
DF
1
1
1
2199
3575
5777
2200
3576
5778
MS
663.92
1215.86
1934.10
0.011
0.007
0.01
F
61639.66
162993.58
200446.74
Sig.
0.000
0.000
0.000
The calculated value of the coefficient of correlation
(r) along with the coefficient of determination (r
2
),
adjusted r
2
and Standard Error of the estimate is
presented in Table 4. The result shows that there is a
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Journal of the College of Agriculture & Environmental Sciences, Bahir Dar University 50
high degree of correlation between r and r
2
parameters which justifies the fact that there was a
strong significant relationship between length and
weight.
Table 4: Calculated values of correlation (r) and
determination (r
2
) coefficient, adjusted r
2
and Std. error
Sex
R
r
2
Adjusted
Std.
error
Male
0.983
a
0.966
0.966
0.104
Female
0.989
a
0.979
0.979
0.086
Combined
0.986
a
0.972
0.972
0.098
3.2. Fulton’s condition factor
Monthly mean Fulton‟s condition factor (K) values
ranged from 1.75 to 1.79 for males, 1.85 to 1.97 for
females and 1.81 to 1.90 for combined sex (Table 5).
The average K value for male, female and combined
sex was 1.78, 1.92 and 1.87, respectively. Unlike the
present study, Teferi and Admassu, (2002) reported a
high value of K (2.35) in Lake Chamo. The average
K value of O. niloticus in this study was lower than
the values reported for the same fish species from
Lakes Koka (1.87) (Tesfaye and Tadesse, 2008),
Hawassa (2.03) (Abebe and Tefera, 1992).
The variation in the K value might be due to changes
in the environmental conditions of the lake and
thereby changes in the nutritional status of the fish.
For instance, there are different agricultural activities
taking place around the lake and these activities
might disturb and break the chain of food availability
for the fish.
The study of condition assumes that heavier fish of a
given length is in a better condition. The indices have
been used by fishery biologists as indicators of the
general “well-being” or “fitness” of the population
under consideration (Jones et al., 1999). The
condition factor is used to evaluate the sensitivity and
healthy condition of fish (Jin et al., 2015). The values
of condition factor depend on physiological features
of fish especially maturity, spawning, life cycle,
environmental factors and food availability in a water
body (Ujjania et al., 2012; Dan-Kishiya, 2013).
Morton and Routledge (2006) divided the K values
into five categories as follows: very bad (0.8–1.0),
bad (1.0–1.2), balance (1.2–1.4), good (1.4–1.6) and
very good (> 1.6). On the other hand, Ayoade (2011)
suggests that the condition factor higher than one is a
good fish health condition. Thus, all the values of
Fulton‟s condition factors of male, female and
combined sex of O. niloticus were above 1.6 and
indicates that O. niloticus of Lake Chamo was in a
very good condition throughout the study period.
Variations in the condition factor of many fishes is
believed to be related to their reproductive cycle
(Narejo et al., 2002), feeding rhythms, physio-
chemical factors of environment, age, physiological
state of fish or some other unknown factors (Dar et
al., 2012).
Table 5: K values of male and female O. niloticus in
Lake Chamo sampled from February 2018 to October
2018
Months
Male
Female
Combined
February
1.78
1.96
1.89
March
1.78
1.97
1.89
April
1.78
1.94
1.88
May
1.79
1.96
1.90
June
1.79
1.93
1.89
July
1.75
1.94
1.88
August
1.75
1.89
1.84
September
1.75
1.85
1.81
October
1.76
1.86
1.82
The K values by month‟s interaction was
insignificant (one-way ANOVA, P > 0.05; Table 6)
but the condition factor of both sexes in Lake Chamo
was significantly different (ANOVA, p < 0.05; Table
7). The t-test also revealed high significant difference
between sexes interaction (t-test, P = 0.000)
indicating that K temporal variation of both sexes
was different in the present study.
Table 6: One-way ANOVA table of K by months
K
Sum of
squares
df
Mean
square
F
Sig.
Between
groups
0.013
8
0.002
0.139
0.995
Within
groups
0.109
9
0.12
Total
0.123
17
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Journal of the College of Agriculture & Environmental Sciences, Bahir Dar University 51
Table 7: One-way ANOVA of K by sex
K
Sum of
squares
df
Mean
square
F
Sig.
Between
groups
0.104
1
0.104
90.891
0.000
Within
groups
0.018
16
0.001
Total
0.123
17
The condition of fish can be affected by several
factors such as the environment, availability of food,
stress, food quality, feeding rate, degree of parasitism
and reproductive activity (Tefera, 1987; Stewart,
1988; Tadesse, 1997). It is also a useful index for
monitoring feeding intensity, age, and growth rates in
fish (Ujjania et al., 2012). Maternal mouthbrooders
like O. niliticus take less food during the early stages
and probably throughout the brooding period (Fryer
and Iles, 1972). The males are also busy in building
and guarding nests and fertilizing many females
(Tadesse, 1997).
In general, the K values of females were higher than
males in all the studied period and it might be due to
the higher gonad weight of females than males which
result in higher total body weight as well as
mobilization of energy for building and guarding of
nests which might reduce total body weight in males.
4. Conclusion
The O. niloticus of Lake Chamo followed positive
allometric growth pattern which implies that the fish
became relatively broader and fatter as its length
increased. The body condition of the fish was found
to be insignificantly different between months but
significantly different between sexes and indicates
that the FCF temporal variation of both sexes was
different. The values of Fulton‟s condition factors of
male, female and combined sex of O. niloticus were
above 1.6 and indicates that O. niloticus of Lake
Chamo was in a very good condition throughout the
study period. Even if the K value of O. niloticus in
Lake Chamo was in a better condition, it was lower
than the values from earlier studies conducted on the
same fish species in the same study area. As the
differences in the K value indicate the changes in the
general conditions of the lake, it is advised to
undertake conservation and rehabilitation of the
buffer zone of the Lake. Moreover, considering other
species of fishes of Lake Chamo is also
recommended in future research.
Conflicts of Interest
The author declares that there is no conflict of
interest in publishing the manuscript in this journal.
Acknowledgements
I am grateful to the Southern Agricultural Research
Institute for providing financial support and access to
fish samples.
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