Populations Structure of Mosquitofish Gambusia Affinis (Baird and Girard; 1853) in Four Different Lakes in Benghazi, Libya
Department of Zoology, University of Benghazi, Libya
Submission: July 03, 2019; Published: July 22, 2019
*Corresponding author: Houssein Elbaraasi, Department of Zoology, Faculty of Science, University of Benghazi, Benghazi, Libya
How to cite this article: Enas E, Houssein E. Populations Structure of Mosquitofish Gambusia Affinis (Baird and Girard; 1853) in Four Different Lakes in Benghazi, Libya. Int J Environ Sci Nat Res. 2019; 20(4): 556041. DOI:10.19080/IJESNR.2019.20.556041
The aim of this study was to investigate some biological aspects within the populations of mosquitofish Gambusia affinis in four different brackish water lakes which are, Althama (A), Aian Elmajdob (B), Bodizera (C) and Ard Alahlam (D) in Benghazi, Libya. Result of the sex ratio of males to females was 1.1:1 in site A, 2.5:1 in site B, 0.6:1 in site C, and 2:1 in site D. The highest mean total length and weight of female was in Aian Elmajdob lake 4.52 ± 0.34cm, 1.28 ± 0.33g, the lowest mean total length and weight of female was in Bodizera lake 3.44 ± 0.35cm, 0.49±0.01g. However, 3.19 ± 0.29cm, 0.35 ± 0.12g were the highest mean total length and weight of males in Ard Alahlam lake. The lowest mean total length and weight was in Althama lake 2.73 ± 0.28cm, 0.21 ± 0.09g.
The mosquitofish Gambusia affinis (Baird and Girard; 1853) belong to poecilidae (live bearers) family. It is a small greenish olive to brown above, grey-blue on sides, and silvery- white below in colors. It has short body with flattened head. Its mouth pointed upward for surface feeding [1,2].
The origin of Gambusia affinis is in fresh and brackish waters of the eastern and southeastern United State of America and Gulf of Mexico . It has been progressively introduced to many countries such as Spain, Eastern European countries, Italy and North Africa as malaria control . It lives in wide range of waters from flowing rivers, to vegetated ponds and lakes, also in backwaters and quiet pools of streams.
The mosquitofish is omnivorous feeds on small aquatic invertebrates including insects, their eggs and larvae, aquatic crustaceans such as cladocerans, ostracods, copepods as well as eggs and fry of small fish, small gastropods and amphibian tadpoles. Its diet may also opportunistically include terrestrial insects which fall into the water, as well as filamentous, algae and detritus [4-9].
G.affinis is short lived animal with a maximum lifespan of just two or three years . This species exhibits sexual dimorphism with females typically being larger than males [11,12].
Mosquitofish are typically occurring at temperatures between 12-29ºC . It is generally found at lower salinity . It can tolerate salinities between 0 and 25ppt . Moreover, Salinity mainly affected mosquitofish females which, despite presenting earlier maturation and higher reproductive investment hence supporting the hypothesis that salinity limits mosquitofish invasive success . The overall aim of this study was to assess the biology and population structure of G. affinis in four different brackish water lakes (Althama, Aian Elmajdob, Bodizera and Ard Alahlam) in Benghazi, Libya this assess lies in studies some biological aspects within the populations.
Populations of the mosquitofish Gambusia affinis in four lakes (sites), located in the eastern part of Benghazi city, were studied. The lakes are: Althama (site A), Aian El majdob (site B), Bodizera (site C), and Ard Alahlam (site D) (Figure 1).
A total of 658 specimens were collected by dip net from all sites, about 212 specimens from Althama, 161 specimens from Aian El majdob, 127 specimens from Bodizera and 158 specimens from Ard Alahlam. Samples were kept in 10% formalin and transferred to the Aquaculture and Fisheries lab at the Zoology Department, Faculty of Science, University of Benghazi.
Upon arriving to the lab, fish sex was determined, body
weight was taken using a digital balance and the morphological
measurements were taken by a rule.
Total length and weight and Length frequency distributions
between male and females in the sites were analysis using ANOVA.
The sex ratio is given as males: females (M: F), The chi-square (X²)
was used to verify the significant differences between the sex ratio
of the species within the populations that commonly expected 1:1
sex ratio .
The condition factor (K) was calculated by the formula :
K= 100w/ L³
Where W= Weight (g), L= Total length (cm).
The condition factor (K) were analysed using ANOVA followed
by Tukey’s Multiple Comparison test. All the statistical analysis
and calculations were done by Graph software and Microsoft
A total of 658 specimens were collected from four different
brackish-water lakes located in Benghazi, Libya. Site A. Althama
(n=212), Site B. Ain Elmajdob (n=161), Site C. Bodizera (n=127),
and Site D. Ard Alahlam (n=158). It was determined (Table 1) that
46% of the samples were females (n=97), 54% males (n=115) in
site A; 28% females (n= 45), 72% males (n=116) in site B; 60%
females (n=77), 40% males (n=50) in site C; 32% females (n=50),
68% males (n=108) in site D. The sex ratio of males to females was
1.1:1 in site A, 2.5:1 in site B, 0.6:1 in site C, and 2:1 in site D (Table
1) and the analysis showed that in sites A and B the ratio of males
and females differ significantly (P=0.42 and P=1.08, respectively),
While in site C and D the differences was statistically insignificant
The data on sex ratio in relation to size group is given in Table
2 in details. However, it suggests that in site A, females less than
males in all the size groups except in 3.6-4.0cm group (74) and
4.1-4.5cm group (20). In site B, males were more than females in
all size group except in 4.1-4.5cm group (22) and 4.6-5.0cm group
(20). In site C, males were more than females in 2.1-2.5 (7) and
2.6-3.0cm (25) size groups. While females were more than males
in all the rest of size groups (Table 2). Lastly, in site D, males were more than females in 2.1-2.5cm (2), 2.6-3.0cm (32), and 3.1-3.5cm
(64) size groups, whereas, females were more than males in 3.6-
4.0cm (13), 4.1-4.5cm (27), 4.6-5.0cm (8) and 5.1-6.0cm (1) size
groups. Probability from chi-square test showed that P values
were found to be significant differences in all size groups of all
P: probability from χ2-test showed P>0.05 in all sites.
Female mosquitofish collected during this study ranged
from 3.0cm to 4.6cm in total length in site A, 3.0 to 5.3 in site
B, 2.4 to 4.2 in site C, and ranged from 3.5 to 5.3 in site D. Male
mosquitofish collected during this study ranged from 2.2cm to
4.0cm in total length in site A, 2.1 to 5.0 in site B, 2.5 to 3.8 in site
C, and ranged from 2.4 to 4.2 in site D. Accordingly, total length
frequency distribution within the sites showed that female fish
size (TL) ranging between 3.6 and 4.0 was the highest in site A
(74 fish) (Figure 2), in site B the highest number was between
4.1-4.5 (22 fish) (Figure 3), in site C was between 3.1 and 3.5 is
the highest (43 fish) (Figure 4), and 27 fish in site D between 4.1
and 4.5 (Figure 5). However, there was a significant difference
(P>0.05) according to t-test between the sites A, B and C. While
site D did not differ significantly with site B.
Total length frequency distribution within the sites showed
that male fish size (TL) ranging between 2.6 and 3.0 was the
highest in site A (75 fish) (Figure 6), in site B the highest number
was between 3.1-3.5 (53 fish) (Figure 7), in site C was between
2.6 and 3.0 is the highest (25 fish) (Figure 8), and 64 fish in site D
between 3.1 and 3.5 (Figure 9). However, there was no significant
difference, (P<0.05) according to t-test, between the sites.
Mean total length of female mosquitofish in site A was 3.95 ±
0.2cm (mean ± SD), in site B was 4.52 ± 0.3cm, in site C was 3.44
± 0.3cm and in site D was 4.21±0.3cm. While mean total length of
male mosquitofish in site A was 2.73 ± 0.2cm (mean ± SD), in site
B was 3.14 ± 0.3cm, in site C was 2.94 ± 0.28cm and in site D was
3.19 ± 0.3cm. The statistical analysis, however, showed that there
was a significant difference in the total length of females between
all the sites (P>0.05). While there were no significant differences
only between sites B and D in the total length of male’s fish.
Female mosquitofish weight ranged from 0.53g to 1.44g in
site A, 0.1g to 2.1g in site B, 0.1g to 0.8g in site C and 0.3g to 1.6g
in site D. Males mosquitofish weight ranged from 0.1g to 0.9g in
site A, 0.1 to 2.0g in site B, 0.1 to 0.3 in site C and 0.1g to 1.0g in
site D. Moreover, mean female fish weight in site A was 0.86 ± 0.1,
in site B was 1.28 ± 0.3, in site C was 0.50 ± 0.1 and in site D was 1.02 ± 0.27. While, mean male fish weight in site A was 0.21± 0.1,
in site B was 0.33 ± 0.2, in site C was 0.26 ± 0.06 and in site D was
0.35 ± 0.1. The statistical analysis showed that was a significant
differences (P>0.05) in all female weight in all sites, while there
was no significant differences in male weight between site A and
C, site B and D. Lastly, Mean female length and weight were larger
than mean male length and weight in all sites.
The variation of condition factor (K) in females and males
of G. affinis within the sites is shown in Figure 10 and Figure 11.
The data showed different trends in both sexes. Furthermore, in
males the minimum K value was reported in site A (0.80) and
the maximum in site B (0.90). The mean K values of female’s fish
of site A was 1.40 ± 0.2, site B was 1.51 ± 0.9, site C was 1.20 ±
0.2, and site D was 1.27 ± 0.1. Moreover, the statistical analysis
showed that Sites A and C, B and C differ significantly (P>0.05)
while the other sites do not differ significantly. However, in males,
K values was not significantly different (P<0.05) between the sites
according to Tukey’s Multiple Comparison test.
Sex ratio calculation is very important to understanding the
relationship between fishes, their environment and population
status . However, it may vary from species to species, or
even in the same population at different times, because it may be
influenced by several factors such as reproductive behavior, food
availability and environmental conditions and genetic factors like
sex chromosomes .
Environmental conditions are expected to be quite variable
in the four studied lakes regarding to genetic variation and its
influences on sex ratios could have effect on the equilibrium states
in the populations, as has been found in some fishes where the
influence of genetics and temperature on sex ratios differs along
a latitudinal gradient [19,20]. Therefore, studying the sex ratio
between population variations might be of great help to further
increase our knowledge of the evolution of sex-determining
Furthermore, sex ratio indicates the proportion of male and
female in the population and is expected to be 1:1 in nature, any
differences from this ratio may indicate the dominance of one sex
over the other . The sex ratio of males to females was 1.1:1
in site A, 2.5:1 in site B, 0.6:1 in site C, and 2:1 in site D (Table 1)
and the analysis showed that in sites A and B the ratio of males
and females differ significantly (P=0.42 and P=1.08, respectively),
While in site C and D the differences was statistically insignificant
(P<0.05). However, in sites B and C males were dominance over
females. There was not much studies on sex ratio of mosquitofish,
therefore results were compared with other fish species such as
major Carp where a ratio of 1:1.4 was reported, which did not
deviate significantly from the its hypothetical distribution .
The highest number of males of the total length was between
2.7-3.2cm in all lakes, and the lowest number of males of the total
length was between 4.5-5.0cm in site B. while, the highest total
length of females was 4.5-5.0cm, the lowest of total length was
2.7-3.2cm and 5.1-5.6 cm. Gkenas et al. , found G. holbrooki
females live longer and reach larger size than males where the
smallest male was 1.6cm and the largest male was 3.4cm, while the
smallest female was 2cm and the largest female was 4.3. However,
In this the study observed the highest mean total length of females
was 4.50 ± 0.34 in site B, and the lowest mean total length was 3.42
± 0.35 in site C. while the highest mean total length of males was
3.19 ± 0.29 in site D, and 2.73 ± 0.28 in site A was the lowest mean
of males. however, the highest mean weight of females was 1.28 ±
0.33 in site B and 0.49 ± 0.01 in site C, the lowest mean of males
was 0.35 ± 0.12 in site D, 0.21 ± 0.09 in site A. Mean total length
and weight of females were higher than mean total length and
weight of males because females need longer time to mature and
continue growing throughout their life . Males stop growing
or exhibit a decelerating growth rate after the gonopodium
has been completely formed and they do not live as long after
reaching maturity . After the completion of the reproductive
period the largest individuals (mostly females) become rare due
to the high mortality which follows the reproduction [24,26,27].
In other study in turkey, females ware greater in size and weight
than males in population studied, furthermore, the total length
and weight of males were from 1.0 to 3.3cm (average, 2.34 ±
0.14cm) and from 0.01 to 0.49g respectively, while females from
1.3 to 5.7cm (average, 3.35 ± 0.35cm) and from 0.01 to 1.90g .
The condition of fishes is influences by the gonadal
development, feeding activity and several other factors .
In the present investigation, comparing K within different
populations of mosquitofish collected from different lakes. The
results suggest that feeding intensity may be the main but not the
only factor responsible for the variation in K in mosquitofish. It
seems that there is an interrelation between feeding intensity and
reproduction and these two factors are the most important that
influence the condition factor . These findings corroborate
observations by Qasim  in Centronotus gunnellus and Das 
in Mugil cephalus.
The populations structure of the mosquitofish Gambusia affinis
collected from the four different lakes in Benghazi, Libya exhibited
significant differences between the lakes. The differences could
be mainly attributed to degradation in water quality, and lakes
productivity. However, more studies need to be done regarding
to the water quality parameters as well as genotype differences
between the species within the populations in the lakes.
Arthington AH, Loloyd LN (1989) Introduced poeciliidae in Australia and New Zealand. In: Meffe GK, Snelson FF (Eds.), Evolation and Ecology of Livebearing Fishes (poeciliidae), prentice-Hall, New york, USA, pp. 33-348.