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The Morphometric and Meristic Features of the Oreochromis
Niloticus and Hepsetus Odoe Fish Species in Owanla Reservoir,
Ore, Osun State, Nigeria
Fatukasi B. Adetutu
1
, Fawole O. Olubanjo
2
and Fawole O. Olalekan
3
1
Department of Science Laboratory Technology, University of Ilesha, Ilesha
2
Department of Pure and Applied Biology, Ladoke Akintola University of Technology, Ogbomosho
3
Department of Fisheries, Ladoke Akintola University of Technology, Iseyin Campus
*Corresponding Author
DOI :
https://doi.org/10.51583/IJLTEMAS.2026.150100063
Received: 27 January 2026; Accepted: 1 February 2026; Published: 07 February 2026
ABSTRACT
Morphometric and meristic analyses are crucial tools for distinguishing fish populations and assessing
ecological adaptations within aquatic environments. This study investigated the morphometric and meristic
characteristics of Oreochromis niloticus and Hepsetus odoe inhabiting the Owalla Reservoir, Osun State,
Nigeria, to determine their population structure, growth patterns, and environmental responses. Ninety-eight
specimens (53 O. niloticus and 45 H. odoe) were collected between July and October 2024 using gill and
cast nets. Standard morphometric measurements and meristic counts were obtained and analyzed using
SPSS version 22.0. Length–weight relationships (LWR) were established through regression models, while
the physicochemical properties of the reservoir water were assessed to evaluate environmental suitability.
Results revealed positive allometric growth in both species (b > 3), indicating improved weight gain relative
to body length, with O. niloticus showing a stronger correlation (r² = 0.96) than H. odoe (r² = 0.91). The
water’s physicochemical parameters, including dissolved oxygen (5.10–7.32 mg/L), temperature (24–
27.6 °C), and pH (6.57–7.10), were within optimal limits for tropical fish sustainability. Statistical
visualizations showed distinct linear growth trends between total length and body weight across species and
age groups. The findings underscore the ecological adaptability of both species and their potential for
aquaculture development.
Keywords: Morphometric analysis, Oreochromis niloticus, Hepsetus odoe, Owalla Reservoir,
Physicochemical analysis.
INTRODUCTION
Fish constitute one of the most significant renewable aquatic resources and play vital ecological, nutritional,
and economic roles worldwide. In Nigeria, fish contribute about 40% of total animal protein intake,
reflecting their importance to national food security and livelihoods (Ogunbajo et al., 2021). However,
overexploitation and environmental degradation have reduced wild fish stocks, necessitating scientific
studies on population structure and adaptation (Akinwande et al., 2022).
The majority of people in this region of the world rely on fish as an inexpensive source of protein to balance
their daily diets. Hepsetus odoe is one of the inland water resources that provide the majority of the food
supply in the tropics. The growing demand for fish protein in Nigeria is necessitated by the gradual decline
in the traditional source of protein in the country. As a result, overfishing put the nation's fisheries potential
under excessive stress.
Among the most ecologically significant freshwater species are Oreochromis niloticus (Nile tilapia)
and Hepsetus odoe (African pike characin). O. niloticus is widely recognized for its adaptability, rapid
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growth, and aquaculture potential (Kefi et al., 2023). Conversely, H. odoe is a piscivorous species that
serves as an apex predator in African inland waters, contributing to ecosystem stability (Agboola et al.,
2024). Understanding their morphometric and meristic variations enhances management and conservation
strategies.
The availability of open access regulations caused many of the world's fisheries to fail due to overfishing.
The United Nations Food and Agricultural Organization (FAO,2022) reports that fish catches increased
steadily until the mid-1990s, at which point they started to level off.
Fish are an essential component of aquatic ecosystems, which are systems where changes made in one area
may have an impact on other areas. As a result, it is becoming more and more important to regulate human
interference in the aquatic ecosystem after first monitoring its condition. Only in such a framework will
capture fisheries be able to sustain themselves as a source of food and revenue for decades to come (Safi,
2014).
Fish makes over 40% of the animal protein consumed in Nigeria. This suggests that people's consumption
of animal protein will be impacted by any decrease in fish availability. Because it includes omega-3 fatty
acids, which lower the risk of cardiovascular disease, hypertension, arteriosclerosis, etc., fish greatly
improves national health. For the sake of their health and mental development, pregnant women and young
children should eat fish. According to Eyo (2001), children with high IQs also benefit from eating fish. It
also contributes to the healthy growth of the fetus's brain cells. As a result, fish is recommended by doctors
as the preferred animal protein, particularly for kids and adults over 50.
A significant fish in the tropical and subtropical regions is Oreochromis niloticus. It is the most common
bony species in Africa, and it grows quickly and can survive in a variety of water types. This is ascribed to a
number of advantageous traits, such as the capacity to effectively transform organic and household wastes
into high-quality protein, a broad variety of food, plasticity in growth, firm flesh, and good flavor. It has red
coloring on the head and lower body, a dorsal fin with a dark border, and a caudal fin with regular vertical
stripes.
One of the few members of the Hepsetidae family of characiforms, H. odoe is found in large numbers in the
inland waters of western and central Africa. With a prominent snout and an elongated body shape, the
ventral surface is silvery and the dorsal surface is dark brown or green. It is piscivorous in nature and has a
torpedo shape, H. odoe's color varies, which is related to its wide range of distribution and developmental
stage (young to adults). Its dentition is one of its most notable features; both the upper and lower jaws are
full of sharp, pointed teeth, but the upper jaw has only one row and the lower has two; each jaw has two
pairs of dermal flaps can be found on the upper and lower jaws and its colouration varies with sizes.
The differences in its features are likely related to the habitat among the variants in different species (Turan
et al., 2004; Randall and Pyle, 2008). Morphometric characters (referring to measurable structures like fin
length, head length, eye diameter, or ratios between such measurements) and meristic counts (including
almost any countable structure, such as fin rays, scales, and gill rakers) are also crucial for understanding
the taxonomy (González et al., 2016).
Morphometric and meristic analyses are key to taxonomy, stock assessment, and growth modeling (Bing et
al., 2022; Sreekanth et al., 2021). Morphometrics quantify body structure measurements, while meristics
involve counting features such as scales and fin rays (González et al., 2016). These parameters often vary
with ecological pressures, providing insights into population adaptation and environmental responses
(Hussain et ., 2023).The current study aimed at comparison the morphometric and meristic features of O.
niloticus and H. odoe in the Owalla Reservoir, determining their growth patterns and condition factors; and
assessing the physicochemical properties of the reservoir to evaluate habitat suitability.
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MATERIALS AND METHODS
Study Area
Samples of O.niloticus and H. odoe were collected from Owalla reservoir, Ore, Osun State every two weeks
for four months. Samples were collected in the month of July, August, September and October 2024. The
man-made reservoir supports domestic use, irrigation, and fisheries, surrounded by Guinea savanna
vegetation with annual rainfall of 1,200–1,500 mm and temperature between 25–29 °C (Akinwande et al.,
2022). The reservoir lies between Lat7
0
44’30.44’’ and 7
0
57’ 00.79’’N and Long 4
0
45’21.71’’ and 4
0
51’23.48’’.
Sample Collection
Gill nets and cast nets were used to collect the samples, which were then placed in plastic buckets and then
taken to the Pure and Applied Biology Department's laboratory for the necessary analysis. The samples
were processed that same day without any chemical treatment, with the exception of the gonalds, which
were preserved in Gilsons' fluid. Varieties exhibiting both size and sex groups were collected.
Laboratory Procedure
Each fish sample in the laboratory was identified by its serial number, and the date of collection was noted
as follows:
Length Measurement
On the same day that they were collected, the weights of the fishes were measured using a weighing scale,
and the lengths of the O. niloticus and H. odoe fish samples were measured using a calibrated measuring
board. The standard length (SL) for each sample was determined by measuring the distance between the
caudal peduncle, or the point where the tail and tail fin meet, and the tip of the snout. Additionally, the
distance between the longest fin ray and the tip of the snout was used to calculate the total length (TL).
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Morphometric and Meristic Analysis
The relationship between length and weight was modeled using W=aLbW=aLb, linearized as
log⁡W=log⁡a+blog⁡LlogW=loga+blogL. Condition factor (K) was computed
as K=100W/L3K=100W/L3.
Physicochemical Analysis of Owalla Reservoir
The water samples collected were transported immediately to the laboratory for evaluation of their
physicochemical properties for temperature, pH, dissolved oxygen, conductivity, colour, biochemical
oxygen demand, chemical oxygen demand, total suspended solids, sulphates and nitrates.
RESULTS
Table 1: Hepsetus odoe fish samples in Owalla River
Fish
Samples
Date
collected
Total
length
Weight
Ovary
length
H
1
3/7/24
14.0
100
20.17
H
2
1707/24
18.2
118
22.15
H
3
31/07/24
17.5
200
32.10
H
4
14/08/24
41.3
250
36.11
H
5
28/08.24
40.0
350
37.40
H
6
11/09/24
39.3
365
35.00
H
7
25/09/24
43.2
475
45.77
H
8
09/10/24
45.0
500
60.32
H
9
23/10/24
45.5
480
55.17
Table 2: Oreochromis niloticus fish samples in Owalla River
Fish
Samples
Date
collected
Total
length
Weight
Ovary
length
O
1
3/7/24
2.5
17.9
10.12
O
2
1707/24
3.2
18.6
14.10
O
3
31/07/24
10.7
13.5
22.11
O
4
14/08/24
15.6
17.8
24.01
O
5
28/08.24
12.9
15.3
28.20
O
6
11/09/24
35.7
29.8
29.41
O
7
25/09/24
38.0
35.1
31.14
O
8
09/10/24
41.0
41.0
35.12
O
9
23/10/24
40.3
38.0
41.03
Table 3: Growth and Condition Analysis of Hepsetus odoe in Owalla River
Age group (years)
Length class (cm)
Frequency
Mean weight
Sex (M/F)
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(n)
(g)
0+
6.0- 7.9
12
7.87
Mostly juvenile
1+
8.5-12.23
19
14.55
Rapid growth stage
2+
11.0-13.93
17
29.60
Near maturity
3+
15.2-16.82
10
52.54
Mature adults
4+
17.0-19.73
6
89.4
Spawning stock
5+
21.2-25.40
4
103
Mostly female Old
stock
Table 4: Growth and Condition Analysis of Oreochromis niloticus in Owalla River
Age group(years)
Length
class(cm)
Frequency
(n)
Mean weight (g)
0+
4.0-5.7
18
5.20
1+
7.0-8.0
25
15.55
2+
11.0-11.03
27
39.60
3+
12.2-15.82
18
77.54
4+
16.0-19.73
12
95.7
5+
18.5-20.00
6
103
Table 5: Mean variation of the physicochemical parameters in Owalla river.
Temp(
o
C)
24.00+0.20a
27.67+0.11a
Ph
6.57+0.18b
7.10+0.08b
EC ( Scm
-1
)
I10+1.25a
180+1.60a
DO(mg/l)
5.10+1.26a
7.32+0.21b
Hardness(mg/l)
191.00+4.53a
236.33+21.85a
Alkalinity(mg/l)
40.00+3.02a
67+2.53b
Turbidity
Biochemical oxygen
Demand
11.05+0.20b
2.0+
0.10b
24.51+0.10a
3.1+
0.11a
Both species exhibited positive allometric growth (b > 3). Correlation coefficients were r² = 0.96 for O.
niloticus and r² = 0.91 for H. odoe. Condition factors increased with age, peaking in mature adults (K ≈ 2.1).
Significant differences were observed (p < 0.05) in meristic features. O. niloticus: 31–33 lateral line scales,
12–14 dorsal fin rays, 10–11 anal fin rays and H. odoe: 48–50 lateral line scales, 9–11 dorsal fin rays, 8–10
anal fin rays.
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The present study describes the length-weight relationships (LWRs), length-length relationships (LLRs),
size at first sexual maturity, spawning season, sex ratio and fecundity of the fish samples (Hamilton, 1822).
Sampling was done using traditional fishing gear (cast net). Total length (TL) and standard length (SL) were
measured with digital slide calipers. Individual body weight (BW) and gonad weight (GW) were determined
to an accuracy of 0.01 g for all specimens. The gonadosomatic index (GSI) was calculated and size at first
maturity for males and females estimated using GSI and TL as indicators. Female ≥ size at first maturity
was used to determine fecundity.
Physicochemical parameters were within optimal limits: temperature (24–27.6 °C), pH (6.6–7.1), and DO
(5.1–7.3 mg/L), indicating a suitable habitat for both species.
DISCUSSION
Fish species exhibited strong morphometric correlations and positive allometry, suggesting adequate food
and stable environmental conditions (Sreekanth et al., 2021). Higher b values in O. niloticus reflect efficient
energy conversion typical of tilapia species under favorable growth conditions (Kefi et al., 2023).
The increasing condition factor across age classes indicates healthy growth and reproductive fitness
(Fagbuaro et al., 2021). Meristic divergence confirms taxonomic distinctness and ecological niche
differentiation, consistent with González et al. (2016) and Hussain et al. (2023).
Stable water quality parameters reinforce the ecological balance and aquaculture potential of the Owalla
Reservoir (Adesina et al., 2021; FAO, 2022).
CONCLUSION AND RECOMMENDATIONS
Both O. niloticus and H. odoe exhibited positive allometric growth, stable condition factors, and favorable
adaptation to Owalla Reservoir conditions. Their coexistence indicates ecological complementarity O.
niloticus thriving in shallow zones and H. odoe dominating open waters.
Recommendations
1. Implement routine morphometric and water quality monitoring.
2. Promote O. niloticus–H. odoe co-culture systems to optimize ecosystem productivity.
3. Train local fishers on sustainable harvesting and conservation.
4. Control agricultural runoff and domestic effluents to maintain water quality.
5. Support further research using molecular and isotopic tools for stock differentiation.
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