J. Agric. Environ. Sci. Vol. 7 No. 2 (2022) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 1
Length-Weight Relationship, Fulton’s Condition Factor and Sex Ratio of Nile Perch
(Lates niloticus, Linnaeus- 1762) in Lake Abaya, Ethiopia
Buchale Shishitu Shija
Southern Agricultural Research Institute Arba Minch Agricultural Research Center, Arba Minch, Ethiopia
Corresponding author: buchale.shishitu@yahoo.com
Received: June 11, 2022 Accepted: October 21, 2022
Abstract: The length-weight relationship of fish is an important fishery management tool. The objectives of the
study were to determine the length-weight relationship, Fulton’s condition factor and the sex ratio of Lates
niloticus in Lake Abaya. Total length (TL), total weight (TW), and sex data were collected from 755 fish samples
(377 females and 378 males) for one year (January to December 2021) from the commercial fishery of Lake
Abaya. The collected data were summarized by using descriptive statistics and analyzed with the application of
Microsoft Excel 2010 and SPSS software. There was no significant deviation in sex ratio (M: F) from
hypothetical 1:1 ratio (χ
2
= 0.00; P > 0.05). The length-weight relationship was calculated using power
function and obtained as TW = 0.0077*TL
3.1176
, (R
2
= 0.8834), TW = 0.0078*TL
3.1372
, (R
2
= 0.8548) and TW =
0.0098*TL
3.0723
, (R
2
= 0.8713) for females, males and combined sexes, respectively. The regression coefficient
“b” was significantly different from the cubic value “3” (P<0.05) and implied that L. niloticus of Lake Abaya
follows a positive allometric growth pattern. The one-way ANOVA (P > 0.05) revealed that Fulton’s condition
factor between sexes was insignificant but highly significant by month’s interaction (ANOVA, P < 0.05). The t-
test also revealed a highly significant difference in a month’s interaction (t-test, P = 0.000) indicating the
seasonal variation in the mean monthly condition factor. The average value of Fulton’s condition factor was
higher than one and indicates that L. niloticus in Lake Abaya was in good health condition. The present study
was focused only on L. niloticus and recommends that similar studies including feeding and reproductive
biology should be conducted to determine the status of other fish species in Lake Abaya.
Keywords: Allometric growth pattern, Commercial fishery, Fishery management, freshwater fish, Lake Fishery
This work is licensed under a Creative Commons Attribution 4.0 International License
1. Introduction
The growth of fish is a mathematical function of
length and weight which varies due to biological
changes and seasonal dynamics (Das, 2004). The
length-weight relationship of fish is an important
fishery management tool. The relationship is
pronounced in estimating the average weight at a
given length group and assessing the relative well-
being of a fish population (Abowei et al., 2009).
Length-weight relationships of freshwater fishes
are useful in determining weight and biomass when
only length measurements are available and are
required in fishery management and conservation
(Froese, 1998; Oscoz et al., 2005). Knowledge of
the sex ratio of fish is important to ensure
proportional fishing of two sexes and provides
information necessary for assessing the
reproductive potential of a population (Vazzoler,
1996).
The condition factor (K) is a method by which the
physical condition and seasonal variation in the
well-being of an individual fish could be known
(King, 1995). The condition factor is a quantitative
parameter of the well-being and state of the fish
that reflects recent feeding conditions (Le cren,
1951). The growth of any fish is related to the
prevailing environmental conditions. Many authors
have explained the importance of the 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 well-being of fish is considered
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 fish’s body condition (Gupta and Tripathi,
2017).
J. Agric. Environ. Sci. Vol. 7 No. 2 (2022) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 2
The L. niloticus is one of the four commercially
important fish species in Lake Abaya. Lakes Abaya
and Chamo are the main sources of L. niloticus. It
is a widely accepted fish species as a food
commodity and is economically important for the
fishing societies in Lake Abaya. The biology of
fish from different water bodies in Ethiopia has
been studied by various scholars. But such
important information in Lake Abaya is null or
little. Therefore, the present study aimed to
generate crucial information on length-weight
relationships, sex ratios and Fulton’s condition
factor of L. niloticus in the lake to provide the
necessary scientific information for proper
utilization and management of the lake fishery.
2. Materials and Methods
2.1. Description of the study area
Lake Abaya is one of the two southernmost Rift
Valley lakes in Ethiopia. It is the second largest
lake in the country next to the highland lake, Lake
Tana. It is located between 5˚55'9"N to 6˚35'30"N
latitude and 37˚36'90"E to 38˚03'45"E longitude.
The lake, including its islands, has a total area of
1108.9 km
2
. It is located at an average altitude of
1235 meters above sea level (Bekele, 2007). It has
a maximum length of 79.2 km with a maximum
width of 27.1 km. The mean and the maximum
depths are 8.6 m and 24.5 m, respectively (Arne,
2013).
2.2. Methods of sampling and data collection
Samples of L. niloticus were collected from the
three commercial fisheries that are actively
practicing fishing in Lake Abaya. Fishes were
randomly collected for three days a week at four
landing sites of the commercial fisheries from
January to December 2021. The trained fishermen
were involved in data collection with regular
following-up of the researcher. The total length and
total weight of fresh fish samples were measured to
the nearest 1 mm and 1 g using a measuring board
and sensitive electronic and hanging balances,
respectively. Small-sized fish was weighed with
sensitive electronic balance while the larger sized
was weighed with hanging balance. Sex
determination was made visually based on external
sexual characteristics as well as dissecting the
abdomen and observing the gonads.
2.3. Data analysis
The length-weight relationship was calculated
using the power function described by Le Cren
(1951).
 
[1]
Where
TW = total weight (g)
TL = total length (cm)
a = the intercept
b = the slope of length-weight regression
The Fulton’s condition factor (K) is often used to
reflect the nutritional status or well-being of an
individual fish and was calculated by using the
formula described by Fulton (1904) which is
indicated below.

 [2]
Where
TW = total weight of fish in gram (g)
TL = total length of fish in centimeter (cm)
The data analyses were done using Microsoft
Office Excel (2010) and SPSS (Version 16.0)
software. A chi-square test (ꭓ
2
test) was employed
to determine if the sex ratio varies between the
male and female L. niloticus.
3. Results and discussion
3.1. Sex ratio
About 755 samples of L. niloticus were collected.
Among these samples, 377 (49.93%) were females
and 378 (50.07%) were males (Table 1). The
monthly sex ratio (M: F) was statistically
insignificant between males and females except for
August, October and December. But the total sex
ratio (M: F) was 1:1 and statistically insignificant
(χ
2
= 0.00; P > 0.05). The finding indicates the
presence of a normal and expected sex ratio of one
male to one female of L. niloticus in Lake Abaya.
Sex ratio is one of the reproductive parameters to
determine the availability of mature males and
females expected to spawn. In normal conditions,
the male-to-female ratio is indicated as a 1:1 ratio.
It is therefore evident that the L. niloticus in Lake
Abaya tends to have an equal population of males
and females. Unlike the present study, the sex ratio
of L. niloticus was dominated by males in Lake
Chamo (Dadebo et al., 2005) and in Lake Victoria
(Edwine et al., 2017).
J. Agric. Environ. Sci. Vol. 7 No. 2 (2022) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 3
Table 1: Sex ratio of L. niloticus in Lake Abaya
Month
Female
Male
Total
Expected frequency
Sex ratio (M: F)
Chi-square (χ
2
)
P-value
January
20
18
38
19
1:1.11
0.05
0.75
February
20
20
40
20
1:1
0.00
1.00
March
17
24
41
20.5
1:0.70
0.60
0.27
April
37
31
68
34
1:1.19
0.26
0.47
May
43
41
84
42
1:1.05
0.02
0.83
June
48
57
105
52.5
1:0.84
0.39
0.38
July
20
17
37
18.5
1:1.18
0.12
0.62
August
72
106
178
89
1:0.69
3.25
0.01
*
September
25
23
48
24
1:1.09
0.04
0.77
October
27
10
37
18.5
1:2.7
3.91
0.01
*
November
28
22
50
25
1:1.27
0.36
0.40
December
20
9
29
14.5
1:2.22
2.09
0.04
*
Total
377
378
755
377.5
1:1
0.00
0.97
* Significant value
3.2. Length-weight relationship
The values of the regression coefficient “b” for
females, males and combined sexes were 3.1176,
3.1372, and 3.0723, respectively, where the
relationships are presented in Figures 1, 2, and 3,
respectively. Based on the analysis of variance
(one-way ANOVA), there was a significant
difference between the regression coefficient “b”
and the expected cubic value of “b” (P < 0.05). The
t-test revealed the presence of a significant
difference between the regression coefficient “b” in
female, male and combined sexes (P < 0.05).
According to the results of this study, the growth
patterns of L. niloticus was positive allometric and
curvilinear in Lake Abaya. The positive allometric
growth patterns implied that the fish became
relatively stouter and deep-bodied as they increased
in length.
A similar relationship has been reported by Edwine
et al. (2017) for L. niloticus in Lake Victoria and
Pendjari River (Simon et al., 2009). Fishes 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 length 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).
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 (Bagenal
and Tesch, 1978; Arslan et al., 2004; Froese, 2006;
Yilmaz et al., 2012; Ali et al., 2016). Furthermore,
variations in fish growth patterns could also be
related to the condition of the species itself, its
phenotype, specific geographic location, and its
environment (Tsoumani et al., 2006).
J. Agric. Environ. Sci. Vol. 7 No. 2 (2022) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 4
Figure 1: Length-weight relationship of female L. niloticus from Lake Abaya
Figure 2: Length-weight relationship of male L. niloticus from Lake Abaya
Figure 3: Length-weight relationship of combined sex L. niloticus from Lake Abaya
J. Agric. Environ. Sci. Vol. 7 No. 2 (2022) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 5
3.3. Fulton’s condition factor
The monthly mean Fulton’s condition factor ranged
from 0.92 to 1.47 for females, 0.89 to 1.56 for
males and 0.93 to 1.53 for combined sexes (Table
2). The average K value for females, males and
combined sexes were 1.29, 1.34 and 1.31,
respectively. The lowest condition factor for
females (0.92) was recorded in October, and the
highest (1.47) was in August. For males, the lowest
value, 0.89 was recorded in December and the
highest value (1.56) was in August. For combined
sexes, the lowest value (0.93) was recorded in
December and the highest (1.53) in August. The
results indicated that there was no significant
difference between the mean condition factor of
males and females L. niloticus (P > 0.05; Fig. 4).
But the mean condition factor by month’s
interaction in Lake Abaya was significantly
different (P < 0.05). The t-test also revealed a
highly significant difference in a month’s
interaction (t-test, P = 0.000) indicating the
seasonal variation in the mean monthly condition
factor.
In the study of fish, the condition factor is used in
comparing its condition, size or well-being
(Ndimele et al., 2010). Condition factor is also
important in the monitoring of feeding intensity,
age and growth rates in fish (Anene, 2005). Related
studies had also shown that the condition factor is
strongly influenced by both biotic and abiotic
environmental conditions, and can be used to
assess the ecological habitat of fish species
(Ayoade, 2011; Onimisi and Ogbe, 2015; Abu and
Agarin, 2016). Morton and Routledge (2006)
divided the K values into five categories 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 a condition factor
higher than one is a good fish health condition.
It was observed in the present study, that the
average condition factor of L. niloticus in Lake
Abaya was 1.29, 1.34 and 1.31 for females, males
and combined sexes, respectively. Variations in
condition factors are influenced by many biotic and
abiotic factors such as phytoplankton abundance,
predation, and water temperature and dissolved
oxygen concentrations among others (Ahmed et al.,
2011). Morton and Routledge (2006) state that the
fish with condition factor values ranging from 1.2-
1.4 is considered to be in balance condition; while
Ayoade (2011) suggests the condition factor higher
than one is in good health condition. Hence, the
condition factor in the present study was higher
than one and L. niloticus in Lake Abaya was in
good health condition.
The average condition factor of the fish species in
the current study was similar to the condition
factors reported by Edwine et al. (2017) in Lake
Victoria, Olapade, et al. (2019) in River Jong, and
Simon et al. (2009) in the Pendjari River for the
same fish species. The condition factor of fish can
vary based on the species type, prevailing
environmental conditions, and food availability in
their occupied habitats (Okach and Dadzie, 1988;
Wanyanga et al., 2016). The condition factor of
fish can also be affected by season, reproductive
cycles and water quality parameters (Khallaf et al.,
2003).
Table 2: Mean monthly condition factor of females, males and combined L. niloticus in Lake Abaya during 2021
Months
Female
Male
Combined sex
January
1.20
1.20
1.2
February
1.42
1.47
1.44
March
1.43
1.49
1.47
April
1.37
1.37
1.37
May
1.23
1.27
1.25
June
1.46
1.53
1.5
July
1.39
1.45
1.42
August
1.47
1.56
1.53
September
1.18
1.43
1.3
October
0.92
1.02
0.95
November
1.41
1.36
1.39
December
0.95
0.89
0.93
Average
1.29
1.34
1.31
J. Agric. Environ. Sci. Vol. 7 No. 2 (2022) ISSN: 2616-3721 (Online); 2616-3713 (Print)
Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 6
Figure 4: Monthly Fulton’s condition factor (FCF) between females and males L. niloticus in Lake Abaya
4. Conclusion
The sex ratio of L. niloticus did not deviate from
the expected sex ratio of one male to one female
and the length-weight relationship follows a
positive allometric growth pattern. The body
condition of L. niloticus was showing seasonal
variability in the monthly condition factor and it
was generally good in health condition. The present
study was focused only on L. niloticus and
recommends that similar studies including feeding
and reproductive biology should be conducted to
determine the status of other fish species in Lake
Abaya.
Conflict of interest
The author declares that there is no conflict of
interest in publishing the manuscript in this journal.
Acknowledgment
The author would like to acknowledge the
Ethiopian Institute of Agricultural Research
(EIAR) for the financial support and Arba Minch
Agricultural Research Center for accessing the
necessary facilities.
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