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 69

Length-weight relationship, Fulton’s condition factor and sex ratio of Bagrus docmak

(Forsskål, 1775) in Lake Chamo, Ethiopia

Buchale Shishitu Shija

Southern Agricultural Research Institute, Arba Minch Agricultural Research Center, Arba Minch,

Ethiopia

Corresponding author: buchale.shishitu@yahoo.com

Received: May 24, 2022 Accepted: December 18, 2022

Abstract: The objectives of the study were to determine the length-weight relationship, Fulton’s condition

factor, and sex ratio of Bagrus docmak in Lake Chamo. Total length (TL), total weight (TW), and sex data were

collected from 469 fish samples (268 females and 201 males) for one year (January to December 2021) from the

commercial fishery of Lake Chamo. The collected data were summarized by 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 the power function and obtained as TW = 0.0087*TL

3.0272

, (R

2

= 0.8959), TW

= 0.0052*TL

3.1412

, (R

2

= 0.9281) and TW = 0.0063*TL

3.0998

, (R

2

= 0.9152) for females, males and combined

sexes, respectively. The regression coefficient “b” was significantly different from the cubic value “3” (P <

0.05), implying that B. docmak of Lake Chamo followed a positive allometric growth pattern. There was a

significant deviation in the sex ratio of male to female (1:1.33) from the hypothetical 1:1 ratio (χ

2

= 4.79; P <

0.05). The average Fulton’s condition factor for females, males, and combined sexes was 1.01, 0.97, and 0.99,

respectively. The one-way ANOVA (P > 0.05) revealed that Fulton’s condition factor between sexes was

insignificant. But it was significantly different in the months of 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 condition factor indicated that the health condition of B.

docmak was not as good. Heavy fishing pressure and different agricultural practices were taking place around

the lake which might disturb and break the chain of food availability in addition to other biotic and abiotic

factors. Further investigations on water quality parameters and other biological aspects such as feeding habits

and reproductive biology of B. docmak shall be undertaken for the management of the fish stocks in the lake.

Keywords: Condition factor, Lake Chamo, fish sex, water quality

This work is licensed under a Creative Commons Attribution 4.0 International License

1. Introduction

Bagrus is a genus of Bagrid catfishes that are native

to Africa and Asia (Nelson, 2006). Bagrus docmak

is one of the commercially important fish species in

Ethiopia. It occurs in the most southern rift valley

lakes like Abaya and Chamo (Shibru, 1973), in the

Segen River (Risch, 1986), and in the Nile system

(Golubstov et al., 1995).

Fish length-weight relationships are useful for

converting length observations into weight

estimates to provide some measure of biomass

(Froese, 1998). Length-weight relationships have

been used frequently to estimate weight from

length because direct weight measurements can be

time-consuming in the field (Sinovcic et al., 2004).

Knowledge of length-weight relationships and

population dynamics of the fish is vital in fishery

science and management (Lizama and Ambrosio,

2002; Ahmed et al., 2003). Also, 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 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 (K) is a

quantitative parameter of the well-being, and state

of the fish and reflects recent feeding conditions

(LeCren, 1951). The growth of any fish is related to

the prevailing environmental conditions. Many

authors have explained the importance of condition

factor as a useful tool for assessing fish growth

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 70

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 length-weight relationship is

also very essential as it is possible to estimate the

average weight of fish at a given length (Lawson et

al., 2013; Ahmed et al., 2017; Getso et al., 2017;

Kumar et al., 2017; Melaku et al., 2017; Muchlisin

et al., 2017). The well-being 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 fish’s body condition (Gupta

and Tripathi, 2017).

Bagrus docmak is one of the four commercially

important fish species with 8% catch contribution

in Lake Chamo fishery (Shishitu et al., 2021). It is

highly regarded by local people as food fish

because it has few intramuscular bones. The catch

contribution and production of B. docmak was

drastically declined in Lake Chamo fishery

(Shishitu et al. 2021). Length-weight relationship

and condition factor are very important tools of

fishery management as it provides information

about the growth of the fish, its general wellbeing,

and fitness in a water body. Therefore, this study

was aimed to determine some aspects of the length-

weight relationship, sex ratio, and condition factor

of B. docmak in the lake to provide the necessary

scientific information for proper utilization and

management of the stock.

2. Materials and Methods

2.1. Description of the study area

Lake Chamo (5

o

50Ꞌ59ꞋꞋ N; 37

o

33Ꞌ54ꞋꞋ E) is located 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, 2006).

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

(a first from end-March to mid-June, a second from

mid-September to late November) and two dry

seasons (a first from December to mid-March, a

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 floodplains

and the deltas of the lake are fertile and hence have

been under extensive agricultural cultivation for the

last three decades.

There are four commercially important fish species

in Lake Chamo which are Nile tilapia

(Oreochromis niloticus), African catfish (Clarias

gariepinus), Nile perch (Lates niloticus) and

Bagrus docmak. The fishery on Lake Chamo is

almost exclusively conducted with a surface gillnet,

although long–lines are also used to some extent

for African catfish (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, a monofilament

gillnet is used and it is obtained from abroad

illegally and it is dangerous as it causes

overfishing.

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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 71

Figure 1: Location of onshore and offshore sampling stations at Lake Chamo, Southern Ethiopia (Utaile and

Sulaiman, 2016)

2.2. Methods of sampling and data collection

Six legal cooperatives are organized on Lake

Chamo fisheries and four cooperatives (Arba

Minch, Chamo, Sego and Harura Boche) were

selected for data collection. Out of the selected

cooperatives, eight landing sites (Ganta fora,

Bedena 1, Grawa, Wedeb, Bole, Ashewa, Chika,

and Mehal) were selected and used as sampling

sites. Samples of B. docmak were collected from

the commercial fisheries of Lake Chamo randomly

selected three days a week from January to

December 2021. 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 a measuring board and

sensitive electronic balance, respectively. Sex

determination was distinguished manually based on

external sexual characters. Males have two

openings which are present just before the anal fin

and females have three body openings. The length-

weight relationship was calculated using the power

function (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. It was calculated by using the

formula described by Fulton (1904) which is

indicated below.

  







  [2]

Where

 TW = total weight of fish in grams (g)

 TL = total length of fish in centimeters (cm)

2.3. Data analysis

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 males

and females B. docmak.

3. Results and Discussion

3.1. Length-weight relationship

The values of the regression coefficient “b” for

females, males, and combined sexes obtained from

the length-weight relationship by using the best-fit

regression of power function gave 3.0272, 3.1412,

and 3.0998, respectively. The relationship was

presented in Fig. 2, 3, and 4, respectively. Analysis

of variance (one-way ANOVA) showed significant

differences between the regression coefficient “b”

and the expected cubic relationship between length

and weight for an ideal fish which maintains the

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 72

same shape “b” (3) (Table 1; P<0.05). As indicated

in Table 2, the t-test revealed the presence of a

significant difference between the regression

coefficient “b” in females, males and combined

sexes (P < 0.05). According to the results of this

study, the growth patterns of B. docmak were

positive allometric and curvilinear in Lake Chamo.

Figure 2: Length-weight relationship of female B. docmak from Lake Chamo

Figure 3: Length-weight relationship of male B. docmak from Lake Chamo

TW = 0.0087TL

3.0272

R² = 0.8959

n = 268

TW = Total weight

TL = total length

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 20 40 60 80 100 120

Weight (g)

Length (cm)

TW = 0.0052TL

3.1412

R² = 0.9281

n = 201

Tw = Total weight

TL = Total length

0

2000

4000

6000

8000

10000

12000

0 20 40 60 80 100 120

Weight (g)

Length (cm)

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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 73

Figure 4: Length-weight relationship of combined sexes of B. docmak from Lake Chamo

Table 1: Analysis of variance (ANOVA) of length-weight relationship of B. docmak from Lake Chamo

Source of Variation

SS

df

MS

F

P-value

F-critical

Between Groups

0.0144

1

0.0144

36

0.027

18.513

Within Groups

0.0008

2

0.0004

Total

0.0152

3

Table 2: Regression static parameters of female, male and combined sexes

Parameters

Females

Males

Combined sexes

a value

0.0087

0.0052

0.0063

b value

3.0272

3.1412

3.0998

Std. Error (S

b

)

0.063

0.062

0.043

R

2

0.8959

0.9281

0.9152

t-calculated

48.33

50.45

71.29

t-critical (5%)

1.962

No of observation

268

201

469

Significance

0.0000

A similar relationship has been reported by earlier

studies for B. docmak (Anja et al., 2009).

According to the reports of some authors, the

growth patterns of B. docmak were negative

allometric (Ikongbeh et al., 2012; Edwin and

Simon, 2021). Fish can attain an isometric,

negative or positive allometric growth pattern. The

positive allometric growth implies that the fish

becomes relatively broader and fatter as its length

increases (Riedel et al., 2007). Based on the

findings of this study, the growth pattern of B.

docmak in Lake Chamo became relatively stouter

and deep-bodied as they increase in length.

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; Froese, 2006; Yilmaz et

al., 2012 and 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). However,

TW = 0.0063TL

3.0998

R² = 0.9152

n = 469

Tw = Total weight

TL = Total length

0

2000

4000

6000

8000

10000

12000

0 20 40 60 80 100 120

Weight (g)

Length (cm)

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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 74

these factors were not specifically considered in the

present study, it was not possible to clarify which

factors among those described above influenced

these study results. It should also be noted that the

growth process can differ in the same fish species

on the basis of dwelling in diverse locations

influenced by numerous biotic and abiotic factors.

3.2. Fulton’s condition factor (K)

The analysis showed that there was no significant

difference between the mean condition factor of

males and females B. docmak (P > 0.05; Table 3).

But the mean condition factor by month’s

interaction in Lake Chamo was significantly

different (P < 0.05; Table 4). The seasonal

variation in the mean monthly condition factor was

highly significant in the months' interaction (t-test,

P = 0.000).

The monthly mean Fulton’s condition factor ranged

from 0.92 to 1.2 for females, 0.8 to 1.1 for males,

and 0.88 to 1.15 for combined sexes (Table 5). The

average K value for females, males, and combined

sexes was 1.01, 0.97, and 0.99, respectively. The

lowest condition factor for females (0.92) was

recorded in January, and the highest (1.2) was in

November. For males, the lowest value (0.8) was

recorded in March and the highest value (1.1) was

in August. For combined sexes, the lowest value

(0.88) was recorded in March and the highest

(1.15) in November.

According to Anja et al. (2009), the condition

factor of B. docmak in Lake Chamo ranged from

0.436 to 0.489 for males and from 0.449 to 0.489

for females. The condition factor (K) of the fish

species in this study was not in agreement with the

condition factors of the same fish species as

reported by Ikongbeh et al. (2012); 1.61, 1.62, and

1.62 for male, female and combined sexes,

respectively, in Lake Akata. Variations in condition

factors are influenced by many biotic and abiotic

factors such as phytoplankton abundance,

predation, water temperature, and dissolved oxygen

concentrations (Ahmed et al., 2011). The condition

factor of fish can vary on the basis of 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). When the

condition factor K value is equal to or greater than

one, it means the fish have attained a better

condition (LeCren, 1951). Ayoade (2011) also

suggests that a condition factor higher than one is a

good fish health condition.

Fisheries of Lake Chamo are under heavy fishing

pressure related to recruitment and growth

overfishing with increased effort and reduced mesh

size. There are also different agricultural practices

taking place around the lake which might disturb

and break the chain of food availability for the fish

(Shishitu, 2020). In the present study, the average

condition factor of B. docmak in Lake Chamo did

not lie in the range of a good health condition.

Even if, factors affecting the wellbeing of B.

docmak in Lake Chamo were not specifically

considered, it might be due to heavy fishing

pressure, changes in the environmental conditions

of the lake, and thereby changes in the nutritional

status of the fish.

Table 3: One-way ANOVA of Fulton’s condition factor by sex

Source of variation

SS

df

MS

F

P-value

F-critical

Between groups

0.012

1

0.012

1.667

0.210

4.301

Within groups

0.160

22

0.007

Total

0.172

23

Table 4: One-way ANOVA of Fulton’s condition factor by months

Source of variation

SS

df

MS

F

F-critical

Sig.

Between groups

0.136

11

0.012

4.077

2.717

0.011

Within groups

0036

12

0.003

Total

0.172

23

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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 75

Table 5: The mean monthly condition factor of females, males and combined sexes of B. docmak in Lake Chamo

Moths

Females

Males

Combined sexes

January

0.92

0.89

0.91

February

0.96

0.94

0.95

March

0.94

0.8

0.88

April

0.99

0.95

May

0.97

0.88

0.94

June

0.93

0.92

0.91

July

0.99

0.97

August

1.01

1.1

1.04

September

1.03

0.95

1

October

1.11

1.07

1.1

November

1.2

1.04

1.15

December

1.07

1.05

1.06

Average

1.01

0.97

0.99

3.3. Sex ratio

About 469 samples of B. docmak were collected.

Among these samples 268 (57.14%) were females

and 201 (42.86%) were males (Table 6). The

monthly sex ratio (M:F) was statistically

insignificant between males and females except for

April and May. But the total sex ratio (M:F) was

1:1.33 and statistically highly significant (χ

2

=

4.79; P<0.05). The finding indicates that there was

a deviation from the expected sex ratio of one male

to one female and reveals that females were more

numerous than males in Lake Chamo. The sex

disparity could be a result of the differential

survival to certain environmental conditions and is

described as a mechanism for regulation in fishes.

Contrarily to the present study, the sex ratio of

males to females of B. docmak was not

significantly different Anja et al., (2009) sex ratio

(1.0:1.07), Ikongbeh et al., (2012) sex ratio

(1.0:1.08) and Edwin and Simon, (2021) sex ratio

(1.0:1.26) in Lake Chamo, Lake Akata (Nigeria)

and Lake Victoria (Kenya), respectively. In the

present study, females were more numerous than

males in Lake Chamo. The general bias towards

females might be due to a potential mechanism to

produce more offspring in situations wherein the

populations are under some stress and as a result,

allocations of resources to increase biomass.

Table 6: Sex ratio of B. docmak from Lake Chamo

Months

Female

Male

Total

Expected frequency

Sex ratio (M:F)

Chi-square (χ

2

)

P-value

January

21

11

32

16

1:1.91

1.56

0.08

February

12

17

29

14.5

1:0.70

0.43

0.35

March

25

16

41

20.5

1:1.56

0.99

0.16

April

28

14

42

21

1:2

2.33

0.03*

May

20

9

29

14.5

1:2.22

2.09

0.04*

June

21

24

45

22.5

1:0.88

0.10

0.65

July

25

22

47

23.5

1:1.14

0.10

0.66

August

21

25

46

23

1:0.84

0.17

0.56

September

27

18

45

22.5

1:1.5

0.90

0.18

October

26

17

43

21.5

1:1.53

0.94

0.17

November

18

8

26

13

1:2.25

1.92

0.05

December

24

20

44

22

1:1.2

0.18

0.55

Total

268

201

469

234.5

1:1.33

4.79

0.00*

*Significant value

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Publication of College of Agriculture and Environmental Sciences, Bahir Dar University 76

4. Conclusion and Recommendations

The length-weight relationship of B. docmak in

Lake Chamo followed a positive allometric growth

pattern. The body condition of B. docmak showed

seasonal variability in the monthly condition factor

and its health condition was not as such good. The

sex ratio of B. docmak deviated from the expected

sex ratio of one male to one female where females

were more numerous than males in Lake Chamo.

Further study on water quality parameters and

biological aspects of B. docmak and other fish

species are recommended for better management of

the fish species in the lake.

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 allowing access to

the necessary facilities.

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