Assessment of Growth, Reproduction, Recruitment and Virtual
Population Analysis of Invasive Species, Coptodon zilllii
in Garmat Ali River, Iraq
ABDUL-RAZAK M. MOHAMED*
Department of Fisheries and Marine Resources, College of Agriculture, University of Basrah
IRAQ
SARAH M. AL-WAN
Basrah Agriculture Directorate, Ministry of Agriculture
IRAQ
Abstract: Coptodon zillii has been an invasive fish in Iraqi waters since 2007 and now well
established and dominating in different water bodies of the country. The aim of this article is
to evaluate the growth, mortality, probability of capture, recruitment pattern, reproduction,
yield-per-recruit and virtual population analysis of this species in the Garmat Ali River, Iraq
from September 2018 and August 2019. The length and weight of the species were between
7.7 cm and 23.2 cm and 50 g to 144.0 g, respectively. The results of the relationship between
them indicate positive allometric growth. The population parameters, including asymptotic
length (L∞= 27.0 cm), growth coefficient (K= 0.270), and growth performance index (Φ'=
2.294) were computed. The estimated total length at first capture (Lc) was 14.87 cm, and the
first maturity (Lm) lengths were 8.2 and 8.4 cm for males and females, respectively. The
recruitment pattern of C. zillii was continuous throughout the year with bimodal recruitment.
This study showed higher fishing mortality than natural mortality. The current exploitation
rate was lowly elevated compared to E0.1 and Emax. Virtual population analysis exhibited that
mid-lengths (14-18 cm) were exposed to the highest fishing mortality. Thus, the fishing
activities must be increased to obtain higher yields that could be considered from the species
for use as animal forage or for export by increasing the fishing activities through increasing
fishing efforts and decreasing the mesh-size nets used by the fishermen.
Key-Words: - Coptodon zillii, Growth, Reproduction, Mortality, Yield-per-recruit, Garmat Ali
River, Iraq.
Received: June 13, 2022. Revised: August 25, 2023. Accepted: September 19, 2023. Published: October 25, 2023.
1 Introduction
The Cichlidae family is one of the major
families of fish with 348 genera, 2332
available species and 1755 valid species [1].
Cichlids are a group of subtropical to tropical
freshwater fish of Cichlidae that are native to
Africa and the south-western Middle East and
inhabit a variety of fresh and less commonly
brackish water habitats, from shallow streams
and ponds through the rivers, lakes and
estuaries [2]. Cichlids have been intentionally
dispersed worldwide for the biological control
of aquatic weeds and insects, as well as
baitfish, ornamental and commercial purposes
[3], but their invasion into non-native
freshwater ecosystems may alter
phytoplankton community structure, nutrient
availability and water quality, causing the
deterioration of the ecological state of the
impacted ecosystems [4; 5; 6; 7].
The redbelly tilapia, Coptodon zillii
(Gervais, 1848) is a member of the Cichlidae
family that invaded Iraqi waters and early
International Journal of Applied Sciences & Development
DOI: 10.37394/232029.2023.2.14
Abdul-Razak M. Mohamed, Sarah M. Al-Wan
E-ISSN: 2945-0454
133
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recorded from the Euphrates River near
Musaib City, middle of Iraq [9; 10]. Later, C.
zillii was documented in the main outfall drain
in south Iraq in 2009 by Mutlak and Al-Faisal
[11] and became widely distributed in different
natural waters of the country [12; 13; 14; 15;
16]. The total landing of C. zillii within other
invaded tilapia species, Oreochromis niloticus
and O. aureus in Basrah province in 2021 was
394.9 t, about 16.7% of the total fish landings
[17].
Several studies have been conducted on the
stock assessment of C. zillii by different
authors in its distribution areas using FiSAT II
software, especially in the Egyptian waters
such as Mehanna [18] in Wadi El-Raiyan
Lakes, Mahmoud and Mazrouh [19] in Rosetta
branch, Nile River, Mahomoud et al. [20] in
Lake Timsah, Mahmoud et al. [21] in Nozha
Hydrodrome and El-Bokhty and El-Far [22] in
Nile River, Aswan, and the Cross River basin,
Nigeria [23], and Lake Volta, Ghana [24]. In
Iraq, the growth, mortality, recruitment and
yield-per-recruit of C. zillii from the Shatt Al-
Arab River have been studied by Mohamed
[25], and the current study is the second study
on the species.
The present work covers growth, mortality
and exploitation rates, length at first capture,
recruitment pattern, reproduction, biological
target reference points and virtual population
analysis of the C. zillii population in the
Garmat Ali River, north of Basrah, to provide
information for proper management of this
species.
2 Materials and Methods
Monthly random samples were collected from
three sites along the Garmat Ali River, north of
Basrah city. The first site is located near Al-
Najeebia Bridge opposite the Naval Academy
site, the second site is located near Garmat Ali
Bridge, and the third site is located at the
upper river before its confluence with the East
Hammar marsh (Fig. 1). The sampling was
performed with the help of local fishermen
using gill nets, cast nets and electro-fishing
from September 2018 to August 2019 [26]. At
the time of the catch, the water surface
temperature was recorded with a simple
thermometer. The samples were taken fresh
and examined in the laboratory.
Fig. 1: Map of Garmat Ali River
with locations of study sites.
The total length of the individual samples
was measured with the help of a measuring
board to the nearest 0.1 cm. The body weight
of the individual was also determined to the
nearest 0.1g. The length-weight relationship
was computed using the power equation
following Le Cren [27]: W= a x Lb, where a
the intercept and b is the slope (growth
coefficient). To test the b (slope) value against
the value of 3, the Student’s t-test was
employed to predict the type of growth,
isometric or allometric [28]. However, the
length-weight relationship was established on
Microsoft Excel version 10.
The individual fish specimen was dissected
and the gonads were removed to determine sex
and weighed to the nearest 0.001 g to calculate
the gonad-somatic index (GSI) as:
GSI= (Gonad weight/Body weight)*100 [29].
The length at first sexual maturity for both
sexes was estimated from the length at which
50% of fish were mature [30].
The length frequency data were pooled into
bimonthly periods from the three stations,
subsequently categorized into class intervals of
1.0 cm, which were used to calculate the
population characteristics using the FiSAT II
computer software package (FAO-ICLARM
Stock Assessment Tools) as explained by
Gayanilo et al., [31].
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DOI: 10.37394/232029.2023.2.14
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E-ISSN: 2945-0454
134
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The parameters of the von Bertalanffy
growth function (VBGF), asymptotic length
(L∝) and growth coefficient (K) were
estimated using the ELEFAN-I routine
incorporated in the FiSAT software. The K
scan routine was conducted to assess a reliable
estimate of the K value. The estimates of L∞
and K were then used to estimate the growth
performance index (Ǿ) using the equation log10
K + 2 log10 L∞ [32]. The potential longevity
was estimated as tmax= to + 3/K [33].
The instantaneous rate of total mortality (Z)
was estimated by the length converted catch
curve module of the FiSAT-II program, and
the natural mortality was calculated by the
same program using the mean annual water
temperature in the study area as 24.6oC. The
fishing mortality (F) was estimated by the
following equation, F= Z-M, and the present
exploitation rate (Epresent) was calculated by the
following equation, i.e., E= F/Z [34].
The Probability of capture at different
lengths was estimated from the length-
converted catch curve using L∞ and K
parameters as in the FiSAT-II package. The
estimates of the values of L25, L50 and L75
represent different lengths at which 25%, 50%
and 75% of the fish will be vulnerable to the
fishing gear [32]. The L50 represents the size at
which 50% of the catches are retained by the
gear or 50% of the recruits are under full
exploitation.
The recruitment pattern of the stock was
determined by backward projection on the
length axis of the set of available length
frequency data as described in FiSAT
software. With the length-frequency data,
asymptotic length (L∞), growth coefficient (K)
and growth performance index (Ǿ) as input
parameters to fit the recruitment pattern with
one or two normal distributions (pulses) per
year, indicating the relative strength of each
pulse.
The relative yield-per-recruit (Y'/R) and
relative biomass-per-recruit (B'/R) models
were estimated for the species using the knife-
edge analysis of Beverton and Holt [35] as
modified by Pauly and Soriano [36] and
incorporated in FiSAT software. The data of
Lc/L∞ and M/K values were used to estimate
E0.1 (maximum economic yield), E0.5 (optimum
sustainable yield) and Emax (maximum
sustainable yield). The present exploitation
rate (Epresent) and the biological target reference
points (E0.1 and Emax) were used to indicate the
stock status [37].
The length-frequency data also were used
to carry out virtual population analysis (VPA)
for the species using a routine modified from
Jones and van Zalinge [38] and incorporated in
the FiSAT package to reconstruct the
population from size-wise total catch data in
the length-frequency samples raised to the
total catch [31]. The input parameters in the
VPA analysis were L∞, K, M and F, in
addition to the constants of the length-weight
relationship (a and b), and the outputs were the
biomass (tons), the yield (tons), total and
fishing mortality and exploitation ratios.
3 Results
3.1 Growth
In the present study, 702 specimens of C. zillii
were collected, with the length and weight
being 7.7 to 23.2 cm and 5.0 to 144.0 g,
respectively. The relationship between length
and weight was estimated as W=0.009*L3.237,
r2= 0.954. The t-test revealed that the
regression slope (b) was significantly different
from value 3 (t= 8.798, P>0.05), which
indicates positive allometric growth.
The initial extreme length (Lmax) value
was used in ELEFAN-I, incorporated in the
FiSAT package producing the optimum
growth curve. The best value of VBGF growth
constant (K) was estimated as 0.270 by
ELEFAN-I (Fig. 2). The response surface (Rn)
was calculated as 0.192 which selected the
best combination of growth parameters L∞=
27.0 cm and K= 0.270. The optimized growth
curve was superimposed on the restructured
length-frequency histograms (Fig. 3). The to
was estimated as -1.148 years, and the
calculated value for the growth performance
index (Ǿ) was 2.294, while longevity (tmax)
was 9.96.
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Fig. 2: K-scan routines of C. zillii.
Fig. 3: Restructured length-frequency
distribution with growth curves
superimposed using ELEFAN-1 for C.
zillii.
3.2 Mortality and exploitation rates
The total mortality rate (Z), the natural
mortality (M) and the fishing mortality (F)
were estimated using a length-converted catch
curve (Fig. 4). The darkened quadrilaterals
represent the points used in calculating Z
through least squares lines regression. The
blank circles represent points either not fully
recruited or nearing L∞ and hence discarded
from the calculation. A good fit to the
descending right-hand limits of the catch curve
was considered. The values of Z, M and F
obtained were found to be 1.86, 0.74 and 1.13,
respectively. The present exploitation rate
(Epresent) was estimated at 0.60.
Fig. 4: Length converted catch curves of
C. zillii.
3.3 Length at first capture (Lc50)
Figure 5 illustrates the probability of capture
of each size class of C. zillii for L25, L50 and
L75 based on the length-converted catch curve.
The length at first capture (the length at which
50% of the fish are vulnerable to capture) was
estimated as Lc50= 14.87 cm and the values of
L25 and L75 were found to be 14.07 and 15.75
cm.
Fig. 5: Probability of capture for C. zillii.
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3.4 Recruitment
The recruitment pattern of C. zillii is presented
in Figure 6. There are two modes, i.e. bimodal
recruitment of unequal pulse strengths in a
year. The first mode occur in March with a
percentage of recruitment at 8.36% and the
other occurs in July with a percentage of
recruitment at 16.73%.
Fig. 6: Recruitment pattern of C. zillii.
3.5 Reproduction
From a total number of 545 fish sampled, 201
males and 316 females were detected. A total
of 545 fish were analyzed, 302 (55.4%) were
males and 243 (44.6%) were females. The
overall sex ratio between males and females
was found to be 1:0.81 showing the
domination of males in the samples and
significantly different from the expected ratio
of 1:1 (χ2= 6.39, p= 0.05). The lengths at first
maturity (Lm50) for males and females were 8.2
and 8.4 cm, respectively caught during
February.
The gonad-somatic index (GSI) for both
sexes followed nearly the same trend and the
GSI values of females were higher than those
of males (Fig. 7). However, the highest value
of GSI for females (5.35) occurred in April
and then gradually dropped to the lowest value
(0.04) in July, while the highest value for
males occurred in July (1.89) and the lower
value (0.02) in August.
Fig. 7: Monthly variations in the gonad-
somatic index of C. zillii.
3.6 Biological target reference points
The relative yield-per-recruit (Y’/R) and
biomass-per-recruit (B’/R) models displayed
that their values were 0.017 and 0.227,
respectively. The results of this analysis
produced the following estimated values of
E0.1, E0.5 and Emax 0.753, 0.374 and 0.939,
respectively (Fig. 8). The present exploitation
rate
Fig. 8: The biological target reference
points of C. zillii.
(Epresent) was (0.60) below the biological target
reference points (E0.1 and Emax) indicating the
0,0
1,0
2,0
3,0
4,0
5,0
6,0
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
♀
♂
Gonadosomatic index
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stock of C. zillii was under an exploitation
state.
3.7 Virtual population analysis The outputs of the length-structured virtual
population analysis of C. zillii are given in
Table 1. Most harvests of the species occurred
in mid-lengths of 14-18 cm and attained a
maximum value of steady-state biomass (t) of
0.01 t at a total length range of 9-18 cm. The
recruitment of the species to the fishery was
assessed as 3957 then after the population
decrease with increased length groups. The
fishing mortality rate increased steadily during
the mid-lengths (13-20 cm) for the species,
with a maximum fishing mortality rate
(1.764/y) at 20 cm. The average value of
fishing mortality of the species was 0.576,
which was lower than the value estimated by
the catch-curve (1.13/y).
Table 1. The outputs from the virtual population analysis of C. zillii.
Mid-Length
Catch
(in numbers)
Fishing
mortality (F)
Steady-state
Biomass (tons)
7
1
0.0015
0
8
9
0.0144
0
9
25
0.0442
0.01
10
34
0.0672
0.01
11
32
0.0713
0.01
12
26
0.0659
0.01
13
48
0.1409
0.01
14
76
0.2684
0.01
15
129
0.5945
0.01
16
114
0.759
0.01
17
90
0.9542
0.01
18
66
1.2939
0.01
19
33
1.4261
0
20
15
1.7637
0
21
2
0.6222
0
22
2
1.13
0
Average
0.576
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Figure 9 illustrates the yields of the virtual
population analysis (VPA) of C. zillii in the
present study about natural losses,
survivability and fishing mortality. The natural
losses and survivability of the individuals in
the stock exhibited declining trends with rising
fishing pressure on the species. While, the
fishing mortality value of the species increased
steadily to the maximum value of 1.764 within
the length range of 20 cm, after which there
was a decline at lengths 21 and 22 cm.
Fig. 9: Length-structured virtual
population analysis of C. zillii.
4 Discussion
In the present study, the growth of C. zillii
demonstrated a positive allometric growth
according to the value of the growth
coefficient (b) of the length-weight
relationship of the species. Riedel et al. [39]
stated when b value is approximately 3, the
fish will follow an isometric growth pattern,
when b value is significantly different from 3,
the fish will follow allometric growth, but if
b>3, the fish will follow the positive
allometric, and the fish will often become
shorter and fatter and if b<3, fish will follow
the negative allometric growth, and will
become elongated during the growth process.
Our results are in agreement with the growth
of the species in the Umhfein Lake, Libya [40]
and in the Gbedikere Lake, Nigeria [41]. A
negative allometric growth pattern has been
reported in C. zillii the Lake Zwai, Ethiopia by
Negassa and Getahun [42] and in some
Egyptian waters [43; 44; 20]. On the other
hand, other studies about this species reported
isometric growth in other Egyptian waters [18;
19]. Sex, gonad maturity, the health of the fish,
degree of stomach fullness, environment,
season and number and sizes of specimens
examined were the main factors that can be
affected by the length-weight relationship in
fish [45; 46; 47].
The stock assessment information on
growth and mortality estimates for C. zilli in
the current study with those reported by the
various authors in different regions are
illustrated in Table 2. The asymptotic length
(L∞) for C. zillii in the current study was lower
than those recorded for the species in some
Egyptian waters, for instance, Wadi EL-
Raiyan Lakes and Nozha Hydrodrome [18; 21]
and in Lake Volta, Ghana [24], whereas
compared favorably with estimates from other
waters. The growth rate (K) for the species
estimated for the study was lower than
estimates from other studies, except that in the
Nozha Hydrodrome, Egypt [21]. Moreover,
the growth performance index (ø) from the
study (i.e., 2.29) was lower than those
recorded for the species in Wadi EL-Raiyan
Lakes, Egypt [18] and in Lake Volta, Ghana
[24], whereas compared favorably with
assessments from other waters. The length of
the species at first capture (Lc) in the present
study was relatively higher than estimates
from other studies. Factors such as variations
in the ecological parameters of the
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Table 2. Stock assessment information on growth and mortality estimates for C. zillii in different
ecosystems
habitats, the metabolic activity, availability of
feed items, reproductive activity, the genetic
constitution of the individuals, fishing pressure
and sample size retrieved for analysis [48; 49;
50; 51] could be the reason for the variation in
growth parameters in different geographic
locations.
The comparison of the rates of total
mortality (Z), natural mortality (E), fishing
mortality (F) and present exploitation rate
(Epresent) of C. zillii obtained in this study with
those stated by the various authors in different
regions are shown in Table 2. The values of Z,
M, F and Ecur of the species obtained in the
present study were within the ranges of these
parameters detected in different geographic
locations of the species. Mahmoud et al. [21]
documented the lowest value of Z (0.83) for
the species in Nozha Hydrodrome, Egypt,
while the highest value (5.60) was found in
Aswan, Nile River, Egypt [22]. The natural
mortality (M) extended from 0.20 in Wadi EL-
Raiyan Lakes, Egypt [18] to 2.38 in Aswan,
Nile River, Egypt [22], while the fishing
mortality rate for the species ranged from 0.30
in Nozha Hydrodrome, Egypt [21] to 3.65 in
Lake Volta, Ghana [24]. Moreover, the
exploitation rate (E) of the species varied from
0.37 for Nozha Hydrodrome, Egypt [21] to
0.83 for the males of the species from Lake
Timsah, Egypt [20].
The results revealed that the estimated
length at first capture (Lc) for C. zillii in the
present
study was 14.9 cm and was higher than those
stated for the species in other geographic
locations. Mahmoud and Mazrouh [19]
documented the lowest value of Lc (7.5 cm) for
the species in the Rosetta branch, Nile River,
Egypt. Moreover, the lengths at first maturity
(Lm50) for males and females of the species in
the current study were 8.2 and 8.4 cm,
respectively. El-Sayed and Moharram [52]
stated that Lm50 for females and males of C.
zillii in Abu Qir Bay, Egypt was attained at the
length of 8.7 cm and 9.7 cm, respectively.
Mahomoud et al. [20] found that the smallest
mature male in Lake Timsah, Egypt was 8.4
cm and the female was 7.5 cm. The length at
first sexual maturity was 9.8 cm for males and
11.0 cm for females of the species in Cross
River, Nigeria [53]. These differences may be
attributed to differences in genetic and
environmental conditions such as food supply,
population density and changes in temperature
and salinity [20]. Ghazwan [54] pointed out
Author
E
F
M
Z
c
L
ø
o
t
K
L∞
Location
[18]
0.82
0.90
0.20
1.10
11.5
2.74
-0.15
0.49
33.5
Wadi EL-Raiyan
Lakes, Egypt
[19]
0.55
1.32
1.09
2.41
7.5
2.13
-0.15
0.50
16.5
Rosetta branch,
Nile River, Egypt
[20]
0.83
2.19
0.46
2.66
-
2.19
-1.41
0.32
22.1
♂
Lake Timsah,
Egypt
0.78
1.50
0.38
1.88
-
2.34
-0.30
0.68
17.8
♀
[21]
0.37
0.30
0.53
0.83
13.0
2.36
-0.35
0.20
33.4
Nozha
Hydrodrome,
Egypt
[23]
0.64
2.02
1.14
3.16
11.9
-
-
0.46
27.8
Cross River
Basin, Nigeria
[22]
0.57
3.22
2.38
5.60
13.4
-
-
1.4
19.4
Aswan, Nile
River, Egypt
[25]
0.45
0.68
0.84
1.51
13.0
2.32
-0.79
0.32
25.5
Shatt Al-Arab
River
[24]
0.81
3.65
0.89
4.58
2.73
0.38
0.57
30.4
Lake Volta,
Ghana
This
study
0.60
1.13
0.74
1.86
14.9
2.29
-1.15
0.27
27.0
Garmat Ali river
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that the phenomenon of early sexual maturity
of C. zillii might be influenced by such factors
during the early stages of its life and it
acquires different levels of masculine or
feminine hormones such as androgen and
estrogen that affect the genes and genetic
control in bodies of this species. Therefore, it
can be concluded that the estimated length at
first capture (Lc) in this study was higher than
the length at first maturity (Lm50), which means
that the species catch did not meet the criteria
for good management (Lc50< Lm50), i.e. they
may be vulnerable to capture by the available
fishing gear before they mature so that every
individual would get at least one chance to
breed in their lifetime, which would help
renew the stock over the long term [55; 51].
The recruitment pattern of C. zillii in the
present study reveals that the significant pulse
occurs in July and the minor one in March.
The two unequal recruitment pulses were also
obtained by Kwarfo-Apegyah and Ofori-
Danson [56] in the Bontanga Reservoir,
Ghana, Abdul and Omoniyi [57] in the Ogun
estuary, Nigeria and Uneke and Nwani [23] in
the mid-Cross River basin, Nigeria. However,
Mohamed and Abood [58] found one seasonal
pulse for C. zillii in the Shatt Al-Arab River,
Iraq, extended from February to May, which
accounts for 63.9% of the recruits. The
recruitment pattern is associated with the
spawning time [59]. Monthly variations in the
gonad-somatic index (GSI) for both sexes of
C. zillii revealed that the spawning season in
the study river extended from April to June.
State of gonad maturation and gonad-somatic
index (GSI) values showed that C. zillii in
Lake Zwai breeds all year round with peak
activities between April and September [42].
Mahomoud et al. [20] found that the period
from January to August represented the
spawning period of C. zillii in Lake Timsah,
Egypt. Uneke and Nwani [53] point out that
GSI of C. zillii in Cross River, Nigeria showed
higher values during the period from May to
September with a peak in June, while the
lower ones occurred during the period from
October to February. Variations in the timing
of spawning may be linked to age, size,
condition and other factors such as geographic
distribution, climatic conditions, and
nutritional status of fish [60; 61].
The biological reference points are the
performance indicator of the fish stock, it often
takes various stock dynamics parameters, such
as growth, recruitment and mortality, and
reflects them to a single index [62; 63]. The
present exploitation rate (Epresent) was below
the biological target reference points (E0.1 and
Emax) indicating the stock of C. zillii was under
exploitation state [36]. This agrees with the
findings of other authors on C. zillii stock in
some waters, such as in the Rosetta branch of
the Nile River, Egypt [19], in Ogun estuary,
Nigeria [57], in Nozha Hydrodrome,
Alexandria, Egypt [21], in the River Nile,
Aswan region, Egypt [22], in the mid-Cross
River basin, Nigeria [23]. Conversely, other
studies found that the species was
overexploited, such as in Wadi El-Raiyan
Lakes, Egypt [18], in Lake Timsah, Egypt [20]
and Lake Volta, Ghana [24]. Also, the
estimated length at first capture (Lc) in this
study was higher than the length at first
maturity (Lm50). Moreover, the outputs of the
virtual population analysis (VPA) revealed that
most harvests of the species occurred in mid-
lengths of 14-18 cm, with a maximum fishing
mortality rate at a length of 20 cm.
King [63] stated that the overall purpose of
fisheries science is to provide decision-makers
with advice on the relative merits of alternative
management, and this advice may include
predictions of the reaction of stock and fishers
to varying levels of fishing effort and
conventionally, including an estimate of the
level of fishing effort required to obtain the
maximum yield that may be taken from stock
on a sustainable basis. Simoes Vitule et al. []
(2009) indicated that invasive freshwater
species are often the culprits driving
biodiversity loss, either directly through
biotic interactions or indirectly by
affecting the availability of essential
resources, facilitating the spread of
infectious disease, or through
hybridization with native taxa. The impacts
of cichlids introduced on native fish and their
habitats were well documented [3]. Tabasian et
al. [8] stated that C. zillii may compete for
food and space with the native fish species and
remove macrophytes and phytoplankton,
which leads to ecosystem-level changes in the
wetland. Also, the cichlids are little desired
International Journal of Applied Sciences & Development
DOI: 10.37394/232029.2023.2.14
Abdul-Razak M. Mohamed, Sarah M. Al-Wan
E-ISSN: 2945-0454
141
Volume 2, 2023
by the Iraqis compared to exotic and
indigenous cyprinids. Therefore, for
management purposes, the study suggests
that more harvests can be obtained by
increasing the fishing activities of this
invaded species, such as increasing the
number of fishing boats (fishing efforts)
and decreasing the mesh size for use as
animal forage or for export and therefore
decline its abundance in the long term.
5 Conclusions
The results of this study revealed that C. zillii
mature early, the length at the first capture was
much greater than the length at the first
maturity, most catches of the species happened
in mid-lengths of 14-18 cm, and the stock was
under exploitation. So, more harvest could be
obtained by a reasonable decrease in the size
of the first capture and increase the fishing
activities through increasing the fishing efforts
by the fishermen to decline its abundance in
the long term.
Acknowledgement
The author would like to acknowledge the staff of
the Department of Fisheries and Marine Resources,
College of Agriculture, the University of Basrah for
their support of the research.
Conflict of Interest
The author has declared that no competing
interests exist.
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The author would like to acknowledge the staff of
the Department of Fisheries and Marine Resources,
College of Agriculture, the University of Basrah for
their support of the research.
Conflict of Interest
The author has declared that no competing
interests exist.
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DOI: 10.37394/232029.2023.2.14
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146
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