ACTA ZOOLOGICA BULGARICA
Research Article
Acta zool. bulg., Suppl. 9, 2017: 117-130
Variation in Life History and Feeding Ecology
of the Invasive Eastern Mosquitoish, Gambusia holbrooki
Girard, 1859 (Poeciliidae), in a Groundwater-dependent
Wetland in Turkey
Baran Yoğurtçuoğlu & F. Güler Ekmekçi
Hydrobiology Section, Department of Biology, Faculty of Science, Hacettepe University, 06800 Ankara, Turkey;
E-mail: yokbaran@gmail.com
Abstract:
We studied the variations in life history and feeding ecology of G. holbrooki in Acıgöl, a groundwaterdependent wetland and the only distribution area of the critically endangered Aphanius transgrediens.
Fish were sampled from three sites with diferent ecological characteristics: Site 1 with stable conditions,
small size and high ish density; Site 2 with stable conditions, large size and medium ish density; Site
3 with variable conditions, large size and low ish density. The scale readings showed two age groups in
males and three in females. The reproduction period was from April to September. More embryos and
heavier gonads were found in specimens at Site 3. The overall ratio of fertilised eggs and the absolute and
relative fecundities were the lowest at Site 1. Two diferent trophic positions, plant-based omnivory and
animal-based omnivory, were detected. The main food items at Site 2 and Site 3 were adults and larvae of
Diptera, as well as zooplankton. At the same time, mosquitoish fed predominantly on plant sources and
occasionally on the other ones at Site 1. Signiicant temporal and ontogenetic diferences in feeding were
also determined. The highest diet diversity and broadest trophic niche were found at Site 2.
Key words: Gambusia holbrooki, biodiversity, feeding strategy, Acıgöl, Aphanius transgrediens
Introduction
The way to understand the impacts of invasive species
on native fauna, in a broad sense on biodiversity, is
to understand their biology. The invasive eastern
mosquitoish, Gambusia holbrooki Girard, 1859,
has been successfully introduced into freshwater
and brackish ecosystems throughout the world as
a malaria control agent (Fernández-Delgado
1989, Pyke 2005). Since the 1990s, its reputation
as a ‘successful mosquito control agent’ has been
disreputed thanks to recent studies (Arthington
1989, Rupp 1996, Cabral & Marques 1999,
Garcia-Berthou 1999), which have disagreed on
its eiciency in mosquito control.
Gambusia holbrooki was irst introduced
in Turkey in the 1930s (Erençin 1978) for the
same purpose and now has spread throughout the
country (Ekmekçi et al. 2013). While its biology
and ecology has been well documented in its native
range (Krumholz 1948, Brown-Peterson &
Peterson 1990, Meffe 1991, Haynes & Cashner
1995, Matthews & Matthews 2011) and in Europe
(Fernández-Delgado 1989, Vargas & de Sostoa
1996, Garcia-Berthou 1999, Specziár 2004,
Scalici et al. 2007, Gkenas et al. 2012, Zarev 2012),
much fewer studies have been conducted about the
introduced populations in Turkey (Öztürk & İkiz
2002, Ergüden 2013).
In this study, we presented life history
variations of G. holbrooki among habitats with
diferent characteristics in Acıgöl, a shallow
Mediterranean lake. In addition, we elaborate its
feeding strategy with special emphasis on variations
117
Yoğurtçuoğlu B. & F. G. Ekmekçi
in spatiotemporal, ontogenetic and sexual traits.
Given the fact that Acıgöl is the only distribution area
of the critically endangered Aphanius transgrediens
(Ermin, 1946) (Freyhof 2014, Yoğurtçuoğlu
& Ekmekçi 2014), the results of the current study
may also provide insights into key elements of
conservation actions.
Materials and Methods
Study area
The study was carried out in Acıgöl, a shallow
hypersaline (mostly Na2SO4 salinity) Mediterranean
lake (N 37°48.53’; E 29°52.81’, Fig. 1). It is located
in an endorheic basin, on a tectonic depression
between two fault lines. These faults give rise to
several freshwater springs lowing into the lake
with various low rates. The area between discharge
points of the springs and the lake margin constitutes
the main wetland, where G. holbrooki and the
critically endangered A. transgrediens coexist. The
surface area of the lake together with the wetland
is approximately 80 km2 with a maximum depth of
about 2 m. However, the area of the main lake body
varies greatly throughout the year.
The emergent plant communities were
dominated by Phragmites australis, Typha sp.
and Juncus sp. with variable cover percentages
depending on the season. The other most common
species were the submerged Nasturtium oicinalis
and loating Lemna minor beside the epilithic and
ilamentous algal communities.
We examined three sites, which were spatially
close but ecologically distinct. The distinctions
between the sampling sites were due to their
variability of the physicochemical properties,
size and density of G. holbrooki (Table 1).
Physicochemical characteristics of the water (e.g.
salinity, pH, dissolved oxygen) were stable in all of
the spring outlets, except the one at the northern side
(hereafter, Site 3). This spring is connected with the
outlet channel of one of the sodium sulphate plant
ponds. Therefore, unpredictable salinity increases
occurred throughout the sampling period depending
on the pond discharge.
Data collection and statistical analysis
From September 2013 to September 2014, 934 ish
specimens were caught by a beach seine net (3 m x
1.5 m x 1.5 m, 4 mm mesh size) from the three sites.
The monthly sampling was possible only at Site 1,
because of the insuicient number of ish caught
in some months at Site 2 and Site 3. The ish were
immediately anesthetised with clove oil, then ixed
118
in 4% formaldehyde solution and transported to the
laboratory, where they were measured by a digital
calliper (total length, TL, to the nearest 0.01 mm) and
weighed by a digital precision balance (to the nearest
0.001 g). Scales were used for age determination.
The length-weight relationship was calculated,
using the equation W = a x Lb, where W is the body
weight, L the total length, a the intercept and b the
slope. The parameter estimation was established using
a linear regression analysis on log-transformed data
(Froese 2006). Analysis of covariance (ANCOVA)
was used for comparison of slopes between sites for
each sex, with the total body weight as the dependent
variable and total length as covariate.
The parameters of the von Bertalanfy growth
equation (L∞ – asymptotic length; k – growth
coeicient; t0 – hypothetical age at which length is
0) and the growth performance index (f’ = 2log (L∞)
+ log (k)) were calculated using ELEFAN I method
(Gayanilo et al. 1988).
The sex was determined by the anal in
morphology and by examining the gonad structure
(usually in individuals < 20 mm TL). The gonads were
dissected and weighed and the gonadosomatic index
(GSI = gonadal weight/ total weight) was calculated
for both sexes. Diferences in GSI throughout the
reproduction period were tested by one-way ANOVA
for Site 1. Embryonic development and fecundity
were studied over 102 females for Site 1, 20 females
for Site 2 and 18 females for Site 3. The ovarian
and embryonic developmental stages were modiied
from Haynes (1995) as follows: (1) small, granular,
white in colour and opaque; (2) opaque, yellow or
orange, yolked eggs; (3) recently fertilised ovum,
embryo appears as a small white cap on the surface
of the yolk; (4) embryo appears as a thin white streak,
covering one-half of the yolk diameter; (5) optic
vesicles begin to pigment; (6) eyes enlarged but not
full sized, pigmentation process almost completed,
yolk sac is partially absorbed; (7) eye pigmentation
process fully completed, body begins to pigment;
(8) caudal in elongated enough to cover the head,
paired ins appeared, yolk sac absorption almost
completed; (9) yolk sac absorption fully completed,
paired ins elongated, scales present, embryo
resembles small adult. The absolute (total number of
embryos) and relative (number of embryos per unit
of body weight) fecundity was estimated from the
gravid females, which possess fertilised eggs (from
stage 3 and older stages). The diference in size of
the gravid females during the reproductive period
was tested by one-way ANOVA, followed by Tukey
test. Linear regression analyses were used to describe
the relationship between fecundity and total length.
Variation in Life History and Feeding Ecology of the Invasive Eastern Mosquitoish, Gambusia holbrooki...
Fig. 1. Location of the sampling sites in Acıgöl, Turkey
Table 1. Some characteristics of the sampling sites, as measured and observed from September 2013 to September
2014. x – mean; min – minimum; max – maximum; Sd – standard deviation; D – depth; S – size; IsFD – intraspecific
Gambusia density; AVD – aquatic vegetation density; *** – high; ** – medium; * – low
Salinity (ppt)
x (min-max)
Temperature (°C)
Sd
x (min-max)
Physical Features
Sd
~D (cm)
Density
~S (m2)
IsGD
AVD
Site 1
0.87 (0.72-0.95)
0.06
19.8 (19.2-20.7)
0.5
50-200
60
***
**
Site 2
0.71 (0.60-0.79)
0.05
19.9 (19.4-21.1)
0.4
50-100
2500
**
***
Site 3
10.17 (0.54-58.56)
17.35
18.6 (10.9-26.8)
5.4
100-200
1200
*
*
The diference between the slopes of the regression
equations was tested by ANCOVA.
For analysis of the feeding ecology, 175
stomach samples were selected from coinciding
sampling months in order to compare feeding habits
among sampling sites. The entire gut was removed
and dissected, and the gut contents were identiied
and counted under a dissecting microscope for
macroscopic food items. A Sedgewick rafter chamber
was used to count and identify smaller organisms.
The volume of the gut contents and food items were
estimated using two methods. Firstly, the individual
gut contents and/or inseparable unique categories
(e.g. detritus) were squashed on a plate to a uniform
depth (here we used the Sedgewick rafter) and the
area of the squash was measured (Hellawell &
Abel 1971). Secondly, the volume of speciic food
items was estimated through calculation of a volume
of geometric shape closest to it (Sun & Liu 2003).
This procedure was carried out by a digital image
119
Yoğurtçuoğlu B. & F. G. Ekmekçi
analysis software – IMAGEJ (Schindelin et al.
2012). The identiiable parts of organisms, such as
heads, were considered as individuals.
The dietary importance of each food category
was expressed by percent number (%N), percent
volume (%V), and frequency of occurrence (%FO),
as follows: %N – number of prey i/total number of
prey x 100; %V – volume of prey i/total volume of
prey x 100; %FO – number of the guts containing
prey i/total number of the guts containing prey x 100
(Hyslop 1980). The index of relative importance
(IRI = (%N + %V) x %FO) was used to incorporate
these indices (Pinkas et al. 1971).
To test the intraspeciic (among size groups
and between sexes) and seasonal diferences in
the diet composition, permutational multivariate
analysis of variance (PERMANOVA) was applied,
using Bray-Curtis similarity resemblance matrices
of square-root transformed volume data, with 9999
permutations. Three length classes (< 30 mm, 3040 mm, and > 40 mm) were assigned to assess the
ontogenetic variation in feeding habits. Canonical
Analysis of Principal coordinates (CAP) was
performed to display a visual ordination of the
dietary pattern among sampling sites by using IRI
data. This method was preferred against traditional
ordination methods since it uncovers patterns that
are masked in an unconstrained scaling ordination
(Anderson & Willis 2003). PERMANOVA and
CAP analysis were performed by a PERMANOVA+
v1.0.1. PRIMER v6 software package (Anderson
et al. 2008).
The diet diversity was calculated using the
Shannon index (H΄):
,
(H΄)
where p is the proportion of the number of prey
item ‘i’ to the total number of prey organisms. The
niche breadth, an indication of trophic generalisation
level, was quantiied by the Levins index (B) (Krebs
1989
):
where Pi is the proportion of each food category
‘i’ in the diet and n is the total number of food
categories in the diet of G. holbrooki. The Levins
index was also standardised by the equation (B-1) /
(n-1) to represent the niche breadth on a scale from
0 (narrow niche) to 1 (broad niche). The fractional
trophic level (TROPH) values were estimated using
TrophLab (Stergiou & Karpouzi 2002).
Finally, to visualise the feeding strategy,
the Costello graphical method (Costello 1990),
modiied by Amundsen et al. (1996) was used.
120
Here, the prey-speciic abundance (%Pi) was plotted
against the frequency of occurrence (%FO). The
%Pi is the percentage of prey category i to the
total number of prey items in the stomachs, which
contained the prey category i.
Results
Life history traits
Of the total ish captured, 622 were females and
371 were males (c2=62.9, P<0.001). This ratio
difered between the sampling sites and the seasons
with a decrease in female/male ratio in spring
and summer (Table 2). Three age groups (0+, 1+
and 2+) in females and two (0+ and 1+) in males
were determined. The dominant age group was
0+ in both sexes (42.4% in females and 58.0%
in males). In fact, only two individuals of 1+
males were sampled from Site 3. The total length
ranged between 14.0 mm and 61.4 mm in females
and between 16.2 mm and 33.3 mm in males
(Table 3). The analysis of covariance ANCOVA
showed signiicant diferences in length-weight
relationships (Table 3) between the sampling sites
for each sex (females F=11.79, P=<0.001; males
F=5.64, P=0.004). The females were longer and
heavier than the males of the same age (Student
t-test for 0+ age group t=5.74, P<0.001 and for
1+ age group t=16.91, P<0.001). The seasonal
growth varied between sexes as depicted by the
mean monthly lengths of individuals (Fig. 2). The
null growth in females initiated in February and
followed by a notable secondary stage just before
the beginning of summer (March-April). The initial
growth stage in males occurred less obviously in
October. The growth performance index was higher
in females than in males, whereas the males reached
to their asymptotic length at a faster rate (Table 4).
The smallest gravid female with mature
embryos was with 28.6 mm TL, the smallest male
with fully developed gonopodium was with 20.0 mm
TL. The average GSI value started to increase from
April and reached its maximum in June for both
sexes at Site 3, where the monthly sampling was
achieved completely (Fig. 3). The highest GSI value
was recorded as 40.9% for a female captured from
Site 3 in August. When assessing the GSI together
with the frequency of gravid females (Fig. 4), the
reproductive period of G. holbrooki in Acıgöl could
be seen to commence in April and end in September.
The absolute and relative fecundity values
and fertilisation success that was estimated for the
females caught at the three sampling sites (Table
5) revealed the highest average absolute fecundity
Variation in Life History and Feeding Ecology of the Invasive Eastern Mosquitoish, Gambusia holbrooki...
Table 2. Seasonal sex ratio of Gambusia holbrooki caught in Acıgöl from September 2013 to September 2014.
Signiicant diferences from parity were tested by chi-square test
Season
Number of individuals
Location
Females
Autumn
Winter
Spring
Summer
Ratio
Females:Males
c2
P-value
Males
Site 1
109
69
1.58:1
8.55
< 0.05
Site 2
89
44
2.02:1
14.56
< 0.05
Site 3
100
44
2.27:1
21.01
< 0.05
Site 1
50
17
2.94:1
15.28
< 0.05
Site 2
0
0
–
–
–
Site 3
0
0
–
–
–
Site 1
70
46
1.52:1
4.56
< 0.05
Site 2
34
35
0.97:1
0.01
0.95
Site 3
20
12
1.67:1
1.53
0.216
Site 1
116
69
1.68:1
11.44
< 0.05
Site 2
0
0
–
–
–
Site 3
34
35
0.97:1
0.01
0.95
Table 3. Estimated length-weight relationship parameters for Gambusia holbrooki males and females in Acıgöl. F –
females; M – males; C – sexes combined; n – sample size; TL – total length; W – total body weight; a and b –
parameters of the equations (see Materials and Methods); Cl – conidence limits; r2 – coeicient of determination
TL (cm)
W (g)
Regression Parameters
Sites
Sex
n
Min
Max
Min
Max
a
b
b Cl %95
r2
Site 1
F
322
1.85
5.14
0.06
1.80
0.0064
3.48
3.44-3.53
0.988
M
186
2.01
3.33
0.07
0.38
0.0071
3.27
3.14-3.39
0.936
C
508
1.85
5.14
0.06
1.80
0.0055
3.57
3.53-3.61
0.985
Site 2
Site 3
F
128
1.40
5.09
0.03
1.80
0.0077
3.25
3.17-3.32
0.983
M
84
1.62
3.20
0.04
0.30
0.0094
2.95
2.85-3.10
0.974
C
212
1.40
5.09
0.03
1.80
0.0074
3.26
3.20-3.33
0.981
F
134
1.84
6.14
0.06
3.07
0.0071
3.33
3.24-3.42
0.976
M
80
1.76
3.23
0.05
0.36
0.0083
3.09
2.88-3.29
0.918
C
214
1.76
6.14
0.05
3.07
0.0067
3.36
3.28-3.43
0.974
Table 4. Estimated von Bertalanfy parameters and growth performance indices of Gambusia holbrooki in Acıgöl. L∞ –
asymptotic length; k – growth coeicient; t0 – hypothetical age at which length is 0 (year); f’ – growth performance index
Parameters
Site 1
Site 2
Site 3
Females
Males
Females
Males
Females
Males
L∞ (mm)
55.57
34.10
58.57
35.63
64.29
38.38
k (yr-1)
0.61
0.89
0.36
0.69
0.36
0.76
t0 (yr)
-0.29
-0.31
-0.63
-0.19
-0.37
-0.19
1.28
1.02
1.09
0.94
1.17
1.05
f’
at Site 3. However, the average relative fecundity
was the highest at Site 2. The fertilisation success
was higher at Site 3 with the highest percentage of
malformed eggs. The size of the gravid females was
signiicantly diferent during the reproductive period
(ANOVA, F=3.87, P=0.023; Site 1 = Site 2, Site 1
= Site 3 and Site 2 < Site 3, according to the Tukey
test). The equations of the relationships between the
fecundity (F) and total length (TL) of G. holbrooki at
the three sites were:
FSite1 = -36.41 + 1.51 TL (r2=22.9%; F=29.16,
P<0.001),
FSite2 = -109.4 + 3.93 TL (r2=64.3%; F=32.54,
P<0.001) and
FSite3 = -92.70 + 3.39 TL (r2=78.1%; F=57.19,
P<0.001)
121
Yoğurtçuoğlu B. & F. G. Ekmekçi
Fig. 2. Monthly growth pattern of Gambusia holbrooki at Site 1 in Acıgöl. Average total lengths with bars representing
standard deviation
Fig. 3. Variation in mean (± standard deviation) gonadosomatic indices of male and female Gambusia holbrooki,
sampled in Acıgöl, between September 2013 and September 2014
122
Variation in Life History and Feeding Ecology of the Invasive Eastern Mosquitoish, Gambusia holbrooki...
Fig. 4. Changes in the percentage of female Gambusia holbrooki bearing eggs/ embryos in each developmental stage
as deined in Materials and Methods with the egg diameter change during the reproductive period. np – non-pregnant
Table 5. Absolute and relative fecundity and fertilisation success of Gambusia holbrooki in Acıgöl. AF – absolute
fecundity; RF – relative fecundity; Nf – non-fertilised eggs; M – malformed eggs; n – number of females examined
for fecundity; n’ – number of eggs examined for fertilisation success
Fecundity
Fertilisation success
Sites
n
AF
(Mean±sd)
Min-max
RF
(Mean±sd)
Min-max
n’
Nf (%)
M (%)
Site 1
102
26.3±15.2
1-76
27.1±14.5
1.4-85.5
2689
5.60
0.80
Site 2
20
43.1±32.2
10-125
54.2±21.7
32.1-127.7
862
3.55
0.78
Site 3
18
57.7±41.3
6-130
38.9±13.3
7.1-68.7
1039
1.93
2.48
The diference in the slopes of the regression
equations was statistically signiicant (ANCOVA,
F=29.01, P<0.001), due to the signiicance of
diference between Site 1 and the other two sites
(Tukey test).
P<0.001). The most important food component was
the adult nematocerans in spring (Fig. 5). The diet
shifted towards the plant sources and detritus in
summer, followed by the dominance of nematoceran
larvae in autumn.
Overall diet description and seasonal variation
None of the 175 stomach samples examined was
completely empty. The dietary spectrum was
summarised under 26 food categories (Table 6).
Regarding the occurrence in the diet and the percent
volume, the most common food items were plant
materials (especially ilamentous algae) and detritus at
Site 1 and insect groups at Site 2 (mostly nematoceran
Diptera) and Site 3 (mostly brachyceran Diptera).
The most important contribution to the overall food
components in terms of the percent number was made
by invertebrate eggs at Site 1 and by zooplankton at
Site 2.
The demonstration of the full seasonal variation
in feeding was possible only for Site 1. IRI was
signiicantly diferent between the seasons at this
sampling site (PERMANOVA, pseudo-F = 4.17,
Feeding ecology
Two diferent trophic positions were represented by
G. holbrooki in Acıgöl: omnivory with a preference
for plants at Site 1 and omnivory with a preference
for animals at Sites 2 and 3. The main food items
explaining the variation among dietary composition
of the individuals are displayed in Fig. 6, after
performing PERMANOVA to detect signiicant
diferences in the diet between the sites (pseudo-F
= 11.56, P<0.001). Despite the spring feeding
pattern seen at Site 1 (Fig. 5), most of the variation
was contributed by ilamentous algae, detritus and
diatoms.
The diet composition was dominated by
Hydracinidae, Cladocera and Copepoda in small
individuals, whereas shifted towards diferent taxa,
e.g., insects (at Site 2 and Site 3) and ilamentous
123
Yoğurtçuoğlu B. & F. G. Ekmekçi
Table 6. Overall diet composition of Gambusia holbrooki in Acıgöl: frequency of occurrence, % number and %
volume of the main food categories. Estimated S-W diversity index and niche breadth with conidence intervals and
trophic level ± standard error
Prey Categories
Site 1
Site 2
Site 3
% FO
%N
%V
% FO
%N
%V
% FO
%N
%V
54.22
27.06
36.72
78.13
32.43
88.94
94.23
84.89
89.71
Coleoptera
2.41
0.66
3.55
12.50
3.75
46.05
19.23
6.58
8.80
Hemiptera
1.21
0.17
1.14
3.13
0.27
1.60
7.69
2.19
17.41
Homoptera
1.21
0.17
0.09
0.00
0.00
0.00
1.92
0.44
0.44
Brachycera
8.43
2.31
10.17
6.25
0.80
10.27
40.39
19.30
49.01
Nematocera (adult)
31.36
9.74
13.03
71.88
13.94
16.98
53.85
33.77
6.50
Nematocera (larvae)
18.07
3.47
7.02
46.88
10.99
6.68
5.77
2.87
0.67
Insecta
Trichoptera (larvae)
3.61
0.83
0.96
0.00
0.00
0.00
0.00
0.00
0.00
Ephemeroptera (larvae)
0.00
0.00
0.00
9.38
1.88
6.79
1.92
1.32
5.47
Other (unidentiied)
8.43
9.74
0.77
6.25
0.80
0.57
11.54
18.42
1.41
Zooplankton
18.07
8.09
0.03
53.13
41.56
2.23
9.62
7.02
0.10
Cladocera
14.46
6.77
0.03
37.50
25.74
0.75
5.77
3.51
0.01
Copepoda
0.00
0.00
0.00
31.25
15.55
1.42
7.70
2.63
0.08
Ostracoda
0.00
0.00
0.00
3.13
0.27
0.07
1.92
0.44
0.02
3.61
1.32
<0.00
0.00
0.00
0.00
1.92
0.44
<0.00
13.25
59.08
0.17
31.25
21.72
2.58
23.08
6.14
7.90
Rotifera
Other Invertebrates
Amphipoda
0.00
0.00
0.00
6.25
0.54
1.13
7.69
2.63
7.84
Gastropoda
1.21
0.17
0.07
6.25
0.54
1.10
0.00
0.00
0.00
Hydrachnidia
0.00
0.00
0.00
15.63
1.34
0.07
13.46
3.51
0.06
Invertebrate eggs
8.43
54.95
0.02
6.25
18.50
0.03
0.00
0.00
0.00
Other (unidentiied)
Vertebrata
Aphanius scales
1.21
3.96
0.08
3.13
0.80
0.25
0.00
0.00
0.00
6.02
0.99
0.69
18.75
3.79
0.05
1.92
0.44
<0.00
3.61
0.66
0.01
12.50
3.22
0.04
1.92
0.44
<0.00
Aphanius adult
1.21
0.17
0.68
0.00
0.00
0.00
0.00
0.00
0.00
Gambusia scales
1.21
0.17
<0.00
3.13
0.57
0.10
0.00
0.00
0.00
Plant-Detritus
89.16
4.79
62.40
18.75
0.54
6.21
19.23
1.51
2.28
Detritus
39.76
–
11.96
9.38
–
1.07
5.77
–
0.07
Filamentous Algae
75.90
–
47.88
12.50
–
3.83
17.31
–
0.16
Diatoms
53.01
–
2.03
6.25
–
1.31
1.92
–
<0.00
Macrophytes
6.02
3.96
0.52
3.13
0.27
0.01
1.92
1.51
2.06
Pollen
2.41
0.83
<0.00
0.00
0.00
0.00
0.00
–
0.00
Shannon-Wiener (H’)
2.14 (2.01-2.24)
2.59 (2.51-2.66)
2.18 (2.07-2.28)
Levin’s Niche Breadth (B)
6.39 (5.42-7.24)
10.65 (9.43-11.67)
6.53 (5.57-7.45)
Std. Niche Breadth (BA)
0.23 (0.19-0.27)
0.42 (0.37-0.46)
0.24 (0.20-0.28)
2.42±0.25
3.04±0.39
3.09±0.41
Trophic Level ± SE
algae (at Site 1) in larger individuals. This ontogenetic
pattern was evident between the >40mm and <30mm
individuals, but not between these length classes and
the 30-40 mm length class. Indeed, the factorial test
with the length and sex as ixed factors indicated a
signiicant efect of length rather than of sex or length
x sex interaction on the overall diet of the species
(Table 7).
124
The feeding strategy diagrams show similar
feeding strategy patterns at all examined sites
(Fig. 7). At all sites, a mixed-feeding strategy,
with alternating levels of specialisation and
generalisation on diferent prey types was presented.
The percent of individual predators specialised on
diferent types of prey, which indicates a broad
niche, was relatively higher at Site 2. This pattern
Variation in Life History and Feeding Ecology of the Invasive Eastern Mosquitoish, Gambusia holbrooki...
Fig. 5. Seasonal change in the percent relative importance index of Gambusia holbrooki at Site 1 in Acıgöl. IRI
– index of relative importance; Zoo=zooplankton; NDl=Nematorecan Diptera (larvae); UI=unidentiied Insecta;
NDa=Nematorecan Diptera (adults); Op=other plant material; Fa=ilamentous algae; Det=detritus
Fig. 6. Two-dimensional ordination plots resulting from the diet composition data of Gambusia holbrooki at all sites
in Acıgöl. Amp=Amphipoda; BD=Brachyceran Diptera; Cla=Cladocera; Cop=Copepoda; Det=detritus; Dia=diatoms;
Epl=Ephemeroptera (larvae); Fa=ilamentous algae; Hyd=Hydracinidia; NDl=Nematorecan Diptera (larvae);
NDa=Nematorecan Diptera (adults)
was also evident in the Shannon diversity function
and Levins niche breadth estimations (Table 6).
The trophic levels of the food items that dominated
the population were diferent between the sites
(ilamentous algae and diatoms at Site 1 and Diptera
groups at Sites 2 and 3).
Discussion
The most prominent contrasting factors between the
studied sites were the water salinity and temperature,
which greatly luctuated at Site 3, and were highly
stable throughout the year at Sites 1 and 2 (Table 1).
125
Yoğurtçuoğlu B. & F. G. Ekmekçi
Fig. 7. Graphical analysis of Gambusia holbrooki feeding strategy in Acıgöl, using the modiied Costello method.
%Pi – prey-speciic abundance; %FO – frequency of occurrence; Amp=Amphipoda; Ata=A. transgrediens (adult);
Ats=A. transgrediens (scale); BD=Brachyceran Diptera; Cla=Cladocera; Col=Coleoptera; Cop=Copepoda;
Det=detritus; Dia=diatoms; Epl=Ephemeroptera (larvae); Fa=ilamentous algae; Gas=Gastropoda; Ghs=G. holbrooki
(scale); Hem=Hemiptera; Hy=Hydracinidia; Inp=insect part; Mac=macrophytes; NDl=Nematorecan Diptera (larvae);
NDa=Nematorecan Diptera (adults); Os=Ostracoda; Tri=Trichoptera (larvae)
126
Variation in Life History and Feeding Ecology of the Invasive Eastern Mosquitoish, Gambusia holbrooki...
Table 7. The factorial PERMANOVA test with length and
sex of Gambusia holbrooki as ixed factors. df – degrees
of freedom; MS – mean square; Pseudo-F – permutational
F-statistics; p(perm) – permutational p value
Source
df
MS
Pseudo-F
P(perm)
Total length
2
9990
2.8083
0.0008
Sex
1
4853.2
1.3643
0.1868
1
6349.2
1.7848
0.0714
139
3557.3
Total length x Sex
Residuals
Therefore, the individuals of G. holbrooki at Site 3
were exposed to a higher degree of environmental
stress than those at the other sites. The lack of
individuals at this site in most of the season was
related to these conditions – mostly to the extreme
salinity luctuations.
Considering the overall sampling in the
Acıgöl Lake, the females of G. holbrooki markedly
dominated the sample with lower proportion in
spring and summer. The sex ratio of Gambusia
spp., as it is known, is 1:1 at birth (Krumholz
1948). The later stage imparity can often be
linked to selective mortality, sampling bias and
diferent habitat preferences of males and females
(Fernández-Delgado 1989, Vargas & de Sostoa
1996, Fernández-Delgado & Rossomanno 1997).
Approaching the 1:1 ratio in summer and spring in
this study can be attributed to a combination of one
or more factors: (i) mating aggregation; (ii) acting
of selective mortality by predators at the expense
of females due to pregnancy (Vargas & de Sostoa
1996, Cabral & Marques 1999); and (iii) the new
generation represented in the sample (Haynes &
Cashner 1995).
Many studies on Gambusia spp. have shown
that females have higher survival rate and larger
longevity than males (Pérez-Bote & López 2005,
Patimar et al. 2011, Ruiz-Navarro et al. 2011).
While females survived after the reproduction
period in Acıgöl, a great proportion of males from
the parental cohort did not survive the winter,
especially those sampled at Site 3. The somatic costs
of reproduction against unpredictable conditions,
which can be related to high adult mortality, may
explain this situation, considering that only two
individuals of 1+ males have been caught.
Making a comprehensive comparison on the
seasonal growth between the sampling sites was
impossible, since we could not ind ish in some
months, except at Site 1. However, according to
the estimated von Bertalanfy parameters, diferent
asymptotic length values were estimated among the
sampling sites, being the highest at Site 3, where
the water temperature reached 10°C. The efect of
temperature was more apparent on the asymptotic
length than on the growth coeicient (k) and
L∞ tended to be greater as temperature declined
(Basoline et al. 2004). The seasonal growth pattern
illustrated for Site 1 is similar to other Mediterranean
populations (Cabral & Marques 1999, Pérez-Bote
& López 2005).
It has been suggested that the timing of the
reproductive cycling in Gambusia spp. is mainly
related to photoperiod rather than temperature
(Hubbs 1971, Milton & Arthington 1983, Cech
et al. 1992). This was also proven for Acıgöl, as
the gravidity pattern and GSI were similar between
the sites even though the temperature was stable
throughout the year at Site 1 and Site 2, but not at Site
3. The reproductive season started at the beginning
of April and ended at the end of September as
observed in many other populations (Vargas & de
Sostoa 1996, Specziár 2004, Pérez-Bote & López
2005, Zarev 2012). Given that the pregnancy period
suggested for mosquitoish is about four weeks
(Krumholz 1948, Milton & Arthington 1983,
Meffe 1990), it means that G. holbrooki females
could release up to six broods in Acıgöl between
April and September.
Like many other ish species, the fecundity
has been known to be positively correlated with
female length in Gambusia spp. (Krumholz 1948).
The strongest correlation in the fecundity-length
relationship was estimated at Site 3, with larger
females and more embryos. Many studies have
shown that the reproductive investment increases
(e.g. more embryos, heavier gonads) with salinity
(Brown-Peterson & Peterson 1990, Vargas &
de Sostoa, 1996, Alcaraz et al. 2008, Swenton
& Kodric-Brown 2012). Therefore, the highest
absolute fecundity and the maximum number of
embryos found in a female were obtained at Site 3,
with the cost of the highest percent of malformed
eggs.
Although G. holbrooki is known to prefer
animal prey (Arthington 1989, Arthington
& Marshall 1999, Garcia-Berthou 1999), a
few studies suggest that the species feeds more on
plant material (Gophen et al. 1998, Arthington
& Marshall 1999, Specziár, 2004). Prey shifting
in response to availability of sources is common
in the mosquitoish (Pyke 2005). Most likely the
plant-weighed feeding habit demonstrated at Site 1,
but not at other sites, was associated with the high
intraspeciic density.
It is diicult to characterise the feeding of G.
holbrooki. Even though some studies reveal that its
127
Yoğurtçuoğlu B. & F. G. Ekmekçi
feeding is based mainly on zooplankton (Bence &
Murdoch 1986, Kramer et al. 1987, Singh & Gupta
2010), or on larvae of Diptera (Hoy et al. 1972, Peck &
Walton 2008), it has a highly lexible diet depending
on the available sources (Pyke 2005). Similarly, in
Acıgöl, three distinct compositions for three spatially
close sampling sites were identiied (Table 6).
The ontogenetic shift in diet has been reported
in previous studies (Miura et al. 1979, Farley
1980, Garcia-Berthou 1999). In Acıgöl, the diet
composition of the small individuals was dominated by
Hydracinidae, Cladocera and Copepoda, and shifted
towards larger taxa speciic to each sampling site.
Although there was remarkable sexual dimorphism
in terms of body size, the efect of the length on the
overall diet variation was more signiicant than that
of the sex. This may support the indings of Crivelli
& Boy (1987) who hypothesised that the ontogenetic
resource partitioning could involve diferent
microhabitat use of diferent size classes.
The modiied Costello method outlined a
mixed-feeding strategy for G. holbrooki in Acıgöl,
which could be unclear in the summary table of
dietary composition. Relatively broader trophic
niches with higher rate of specialised individuals
were illustrated for Site 2, which was also evident
from the diversity indices. This was not surprising,
when considering the mild environmental conditions
with a larger habitat size at Site 2.
Several studies have demonstrated the
ability of G. holbrooki to outcompete native ishes
(Pyke 2005, Alcaraz & Garcia-Berthou 2007,
Alcaraz et al. 2008). Even though there is evidence
that G. holbrooki and the critically endangered A.
transgrediens (the only native ish in the lake) do
not compete notably for food in Acıgöl (unpublished
data), Aphanius scales were observed in the stomach
of G. holbrooki, which indicates its aggressive
pressure on A. transgrediens. This behaviour seems
to be species-speciic having in mind the lower
occurrence of Gambusia scales in the examined
stomachs.
Acknowledgement: This study is part of a PhD thesis of the
irst author and was supported by the Ruford Small Grants
(Projects 16079-2 and 12983-1).
References
Alcaraz C & García-Berthou E. 2007. Life history variation
of invasive mosquitoish (Gambusia holbrooki) along a
salinity gradient. Biological Conservation 139: 83-92.
Alcaraz C., Bisazza A. & Garcia-Berthou E. 2008. Salinity
mediates the competitive interactions between invasive
mosquitoish and an endangered ish. Oecologia 155:
205-213.
Amundsen P. A., Gabler H. M. & Staldvik F. J. 1996. A new
approach to graphical analysis of feeding strategy from
stomach contents data – modiication of the Costello
(1990) method. Journal of Fish Biology 48: 607-614.
Anderson M. J. & Willis T. J. 2003. Canonical analysis of
principal coordinates: a useful method of constrained
ordination for ecology. Ecology 84: 511-525.
Anderson M.J., Gorley R. N. & Clarke K. R. 2008.
PERMANOVA+ for PRIMER: Guide to software and
statistical methods. Plymouth, UK: PRIMER-E Ltd., 214 p.
Arthington A. H. 1989. Diet of Gambusia ainis holbrooki,
Xiphophorus helleri, X. maculatus, and Poecilia
reticulata (Pisces: Poeciliidae) in streams of southeastern
Queensland, Australia. Asian Fisheries Science 2: 193-212.
Arthington A. H. & Marshall C. J. 1999. Diet of the exotic
mosquitoish Gambusia holbrooki in an Australian lake
and potential for competition with indigenous ish species.
Asian Fisheries Science 12: 1-16.
Basoline G., Guisande C., Patti B., Mazzola S., Cuttitta
A., Bonanno A. & Kallianiotis A. 2004. Linking habitat
conditions and growth in European anchovy (Engraulis
encrasicolus). Fisheries Research 68: 9-19.
Bence J. R. & Murdoch W. W. 1986. Prey size selection by
the mosquitoish: relation to optimal diet theory. Ecology
67 (2): 324-336.
128
Brown-Peterson N. & Peterson M. S. 1990. Comparative
life history of female mosquitoish Gambusia ainis in
tidal freshwater and oligohaline habitats. Environmental
Biology of Fishes 27: 33-41.
Cabral J. A. & Marques J. C. 1999. Life history, population
dynamics and production of eastern mosquitofish,
Gambusia holbrooki (Pisces, Poeciliidae), in rice ields
of the Lower Mondego River Valley, West Portugal. Acta
Oecologica 20: 607-620.
Cech J. J. Jr., Schwab R. G., Coles W. C. & Bridges B. B.
1992. Mosquitoish reproduction: efects of photoperiod
and nutrition. Aquaculture 101: 361-369.
Costello M. J. 1990. Predator feeding strategy and prey
importance: a new graphical analysis. Journal of Fish
Biology 36: 261-263.
Crivelli A. J. & Boy V. 1987. The diet of the mosquitoish
(Gambusia affinis (Baird and Girard) Poeciliidae) in
Mediterranean France. Annual Review of Ecology and
Systematics 42: 421-435.
Ekmekçi F. G., Kirankaya Ş. G., Gençoğlu L. & Yoğurtçuoğlu
B. 2013. Present status of invasive ishes in inland waters
of Turkey and assessment of the effects of invasion.
Istanbul University Journal of Fisheries & Aquatic
Sciences 28: 105-140.
Erençin Z. 1978. Opinions on malaria (mosquitoes) control
and the ish farming activities. Journal of the Faculty of
Veterinary Medicine, Ankara University 25: 760-766. (in
Turkish)
Ergüden S. A. 2013. Age, growth, sex ratio and diet of eastern
mosquitoish Gambusia holbrooki Girard, 1859 in Seyhan
Dam Lake (Adana/Turkey). Iranian Journal of Fisheries
Sciences 12 (1): 204-218.
Variation in Life History and Feeding Ecology of the Invasive Eastern Mosquitoish, Gambusia holbrooki...
Farley D. G. 1980. Prey selection by the mosquitoish, Gambusia
ainis (Baird and Girard) on selected non-target organisms
in Fresno County rice ields. Proceedings of the California
Mosquito and Vector Control Association 48: 51-54.
Fernández-Delgado C. 1989. Life-history patterns of the
mosquitofish, Gambusia afinis, in the estuary of the
Guadalquivir river of south-west Spain. Freshwater
Biology 22 (3): 395-404.
Fernández-Delgado C. & Rossomanno S. 1997. Reproductive
biology of the mosquitofish in a permanent natural lagoon
in south-west Spain: two tactics for one species. Journal
of Fish Biology 51: 80-92.
Freyhof J. 2014. Aphanius transgrediens. The IUCN Red List
of Threatened Species. http://dx.doi.org/10.2305/IUCN.
UK.2014-1.RLTS.T19384476A19848952.en
Froese R. 2006. Cube law, condition factor and weight-length
relationships: history, meta-analysis and recommendations.
Journal of Applied Ichthyology 22: 241-253.
Garcia-Berthou E. 1999. Food of introduced mosquitoish:
ontogenetic diet shift and prey selection. Journal of Fish
Biology 55: 135-147.
Gayanilo F. C., Jr., Soriano M. & Pauly D. 1988. A draft guide
to the Compleat ELEFAN. ICLARM Software 2. Manila,
Philippines: International Center for Living Aquatic
Resources Management, 65 p.
Gkenas C., Oikonomou A., Economou A., Kiosse F. &
Leonardos I. 2012. Life history pattern and feeding habits
of the invasive mosquitoish, Gambusia holbrooki, in Lake
Pamvotis (NW Greece). Journal of Biological ResearchThessaloniki 17: 121-136.
Gophen M., Yehuda Y., Malinkov A. & Degani G. 1998.
Food composition of the ish community in Lake Agmon.
Hydrobiologia 380: 49-57.
Haynes J. L. 1995. Standardized classification of Poeciliid
development for life history studies. Copeia 1995: 147154.
Haynes J. L. & Cashner R. C. 1995. Life history and population
dynamics of the western mosquitoish: a comparison
of natural and introduced populations. Journal of Fish
Biology 46: 1026-1041.
Hellawell J. M. & Abel R. 1971. A rapid volumetric method
for the analysis of the food of ishes. Journal of Fish
Biology 3: 29-37.
Hoy J. B., Kaufmann E. E. & O’Berg A. G. 1972. A large-scale
ield test of Gambusia ainis and chlorpyrifos for mosquito
control. Mosquito News 32: 161-171.
Hubbs C. 1971. Competition and isolation mechanisms in the
Gambusia ainis x G. heterochir hybrid swarm. Texas
Memorial Museum Bulletin 19: 1-47.
Hyslop E. J. 1980. Stomach content analysis: a review of
methods and their applications. Journal of Fish Biology
17 (4): 411-429.
Kramer V. L., Garcia R. & Colwell A. E. 1987. An evaluation
of the mosquitoish, Gambusia ainis, and the inland
silverside, Menidia beryllina, as mosquito control agents
in California wild rice ields. Journal of the American
Mosquito Control Association 3: 626-32.
Krebs C. J. 1989. Ecological Methodology. New York, USA:
Harper & Row, 634 p.
Krumholz L. A. 1948. Reproduction in the western mosquitoish
Gambusia ainis ainis (Baird & Girard) and its use in
mosquito control. Ecological Monograph 18: 1-43.
Matthews W. J. & Matthews E. M. 2011. An invasive ish
species within its native range: community efects and
population dynamics of Gambusia ainis in the central
United States. Freshwater Biology 56: 2609-2619.
Meffe G. K. 1990. Offspring size variation in eastern
mosquitoish (Gambusia holbrooki: Poeciliidae) from
contrasting thermal environments. Copeia 1990 (1): 10-18.
Meffe G. K. 1991. Life history changes in eastern mosquitoish
(Gambusia holbrooki) induced by thermal elevation.
Canadian Journal of Fisheries and Aquatic Sciences 48:
60-66.
Milton D. A. & Arthington A. H. 1983. Reproductive
biology of Gambusia ainisholbrooki (Baird and Girard),
Xiphophorus helleri (Günther) and X. maculatus (Heckel)
(Pisces; Poeciliidae) in Queensland, Australia. Journal of
Fish Biology 23: 23-41.
Miura T., Takahashi R. M. & Stewart R. J. 1979. Habitat and
food selection by the mosquitoish, Gambusia ainis.
Proceedings of the California Mosquito and Vector Control
Association 47: 46-50.
Öztürk S. & İkiz R. 2002. Some biological properties of
mosquitoish populations (Gambusia ainis) living in
inland waters of the Western Mediterranean region of
Turkey. Turkish Journal of Veterinary and Animal Science
28: 355-361.
Patimar R., Ghorbani M., Gol-Mohammadi A. & Azimi
Glugahi H. 2011. Life history pattern of mosquitoish
Gambusia holbrooki (Girard, 1859) in the Tajan River
(Southern Caspian Sea to Iran). Chinese Journal of
Oceanology and Limnology 29 (1): 167-173.
Peck G. W. & Walton W. E. 2008. Efect of mosquitoish
(Gambusia ainis) and sestonic food abundance on the
invertebrate community within a constructed treatment
wetland. Freshwater Biology 53 (11): 2220-2233.
Pérez-Bote J. L. & López M. T. 2005. Life-history pattern of
the introduced eastern mosquitoish, Gambusia holbrooki
(Baird & Girard, 1854), in a Mediterranean-type river: The
River Guadiana (SW Iberian Peninsula). Italian Journal of
Zoology 72 (3): 241-248.
Pinkas L., Oliphant M. S. & Iverson I. L. K. 1971. Food habits
of albacore, bluein tuna, and bonito in California waters.
State of California the Resources Agency Department of
Fish and Game, Fish Bulletin 152, 105 p.
Pyke G. H. 2005. A review of the biology of Gambusia ainis
and G. holbrooki. Reviews in Fish Biology and Fisheries
15: 339-365.
Ruiz-Navarro A., Moreno-Valcárcel R., Torralva M. &
Oliva-Paterna F. J. 2011. Life-history traits of the invasive
ish Gambusia holbrooki in saline streams (SE Iberian
Peninsula): does salinity limit its invasive success? Aquatic
Biology 13: 149-161.
Rupp H. R. 1996. Adverse assessments of Gambusia ainis:
an alternate view for mosquito control practitioners.
Journal of the American Mosquito Control Association
12: 155-166.
Scalici M., Avetrani P. & Gibertini G. 2007. Mosquitoish life
history in a Mediterranean wetland. Journal of Natural
History 41: 887-900.
Schindelin J., Arganda-Carreras I. & Frise E. 2012. Fiji: an
open-source platform for biological-image analysis. Nature
methods 9 (7): 676-682.
Singh N. & Gupta P. K. 2010. Food and feeding habits of an
129
Yoğurtçuoğlu B. & F. G. Ekmekçi
introduced mosquitoish, Gambusia holbrooki (Girard)
(Poeciliidae) in a subtropical lake, Lake Nainital, India.
Asian Fisheries Science 23 (3): 355-366.
Specziár A. 2004. Life history pattern and feeding ecology of
the introduced eastern mosquitoish, Gambusia holbrooki,
in a thermal spa under temperate climate, of Lake Hévíz,
Hungary. Hydrobiologia 522: 249-260.
Stergiou Κ. Ι. & Karpouzi V. S. 2002. Feeding habits and
trophic levels of Mediterranean ish. Reviews in Fish
Biology and Fisheries 11: 217-254.
Sun J. & Liu D. 2003. Geometric models for calculating cell
biovolume and surface area for phytoplankton. Journal
of Plankton Research 25 (11): 1331-1346.
130
Swenton D. M. & Kodric-Brown A. 2012. Habitat and life
history diferences between two species of Gambusia.
Environmental Biology of Fishes 94 (4): 669-680.
Vargas M. J. & De Sostoa A. 1996. Life history of Gambusia
holbrooki (Pisces, Poeciliidae) in the Ebro delta (NE
Iberian Peninsula). Hydrobiologia 341: 215-224.
Yoğurtçuoğlu B. & Ekmekçi F. G. 2014. Threatened ishes
of the world: Aphanius transgrediens Ermin, 1946
(Cyprinodontidae). Croatian Journal of Fisheries 72 (4):
186-187.
Zarev V. Y. 2012. Some life-history traits of Gambusia holbrooki
(Pisces: Poeciliidae) from Bulgaria. Acta Zoologica
Bulgarica 64 (3): 263-272.