Although the potential impact of the sailfin molly on the aquatic life in Wadi Al-Bahayes may seem insignificant at first glance, it is important to the fish fauna there due to the introduction of new species, predation, competition, habitat and genetic changes, and the emergence of parasites and diseases. Research is needed to obtain basic information about the population of the sailfin molly, as well as the causes of introduction of the species and its effects on local and endemic fish communities in Wadi Al-Bahayes.
There are very few studies on breeding and feeding characteristics (Al-Ghanim 2005; Alkahem et al. 2007; AI-Akel et al. 2010) and growth parameters of sailfin mollies (Klassen et al. 2004; Morris 2005; dan Hasnidar 2019) in the natural environment, and among them there is no study on their population in Oman. Such data are lacking from Oman and could be useful for management of this invasive species. The sailfin molly is a robust species that shows great plasticity in its life cycle. Due to the fact that this species is currently well established in Omani waters, an assessment of its impact and ecological role is indeed worthwhile and necessary. Therefore, the objective of our study was to investigate the growth parameters of the
The care of experimental animals was in compliance with the Animal Welfare Law issued by the Sultanate of Oman, as well as other guidelines and policies approved by the Sultan Qaboos University Animal Ethics Committee (Project name: Omani Freshwater Fish, Classification and Biology – permit reference number: SQU/AEC/2020-2021/2).
The study was carried out in Wadi Al-Bahayes (Oman; 23°40′47″N; 58°11′36″E; Fig. 1). Wadi Al-Bahayes is a densely vegetated flat brackish water body. Sampling was carried out in June and August 2020 using a hand net-fish trap and a crab net baited with bread. A total of 124 individuals were caught from Wadi Al-Bahayes (Fig. 2). The fish species
Sampling area – Wadi Al-Bahayes in Oman (photo by Dr. Saud Al Jufaili)
The distribution of females and males was determined according to age. The overall ratio of males to females was estimated using χ2 (0.05) test (Düzgüneş et al. 1995). Total length (in cm) and weight (in g) frequency distribution for all specimens was calculated. The relationship between weight and total length was determined using the exponential regression equation W = a × TLb, where W is the body weight in g, TL is the total length in cm, “a” is the intercept and “b” is the regression coefficient. The coefficient of determination (R2) was also estimated (Ricker 1975). The growth of the
The age of the fish ranged from 1 to 4 years. The dominant age groups were I and II (Table 1). Of the total fish examined, 46 (37.10%) were males and 78 (62.90%) were females. The overall ratio of males to females was 0.59:1.00 and χ2 analysis showed that it was significant (
Age and sex distribution for females (F), males (M) and all
Age | Females | Males | All | M:F | |||
---|---|---|---|---|---|---|---|
N | %N | N | %N | N | %N | ||
1 | 37 | 29.84 | 24 | 19.35 | 61 | 49.19 | 0.65:1.00 ( |
2 | 28 | 22.58 | 12 | 9.68 | 40 | 32.26 | 0.43:1.00 ( |
3 | 11 | 8.87 | 4 | 3.23 | 15 | 12.10 | 0.36:1.00 ( |
4 | 2 | 1.61 | 6 | 4.84 | 8 | 6.45 | 3.00:1.00 ( |
∑ | 78 | 62.90 | 46 | 37.10 | 124 | 100 | 0.59:1.00 ( |
Size and age composition for females (F) and males (M) of
Age class | I | II | III | IV | Total | ||||
---|---|---|---|---|---|---|---|---|---|
Total length (cm) | ♀ | ♂ | ♀ | ♂ | ♀ | ♂ | ♀ | ♂ | |
3.70–4.20 | 9 | 8 | 17 | ||||||
4.21–4.70 | 26 | 11 | 37 | ||||||
4.71–5.20 | 2 | 5 | 21 | 5 | 33 | ||||
5.21–5.70 | 7 | 7 | 1 | 15 | |||||
5.71–6.20 | 10 | 4 | 1 | 1 | 16 | ||||
6.21–6.70 | 1 | 3 | 4 | ||||||
6.71–7.20 | 1 | 1 | |||||||
7.21–7.70 | 1 | 1 | |||||||
∑ | 37 | 24 | 28 | 12 | 11 | 4 | 2 | 6 | 124 |
TL ± sd (min.–max) | |||||||||
♀ | 4.44 ± 0,04 (3.70–4.78) | 5.13 ± 0.03 (4.83–5.56) | 5.81 ± 0.02 (5.61–5.99) | 6.41 ± 0.17 (6.16–6.66) | 4.93 ± 0.06 (3.70–6.66) | ||||
♂ | 4.34 ± 0.07 (3.70–4.79) | 5.20 ± 0.04 (4.99–5.45) | 5.93 ± 0.02 (5.85–5.99) | 6.61 ± 0.19 (6.15–7.50) | 5.00 ± 0.12 (3.70–7.50) |
Total length and weight in frequency distributions for
The following von Bertalaffy growth equations were obtained for males Lt = 11.46 [1 − e −0.127 (t + 2.71)] and females Lt = 14.51 [1 − e −0.072 (t + 3.98)] (Fig. 4). The differences between the observed and expected total lengths were statistically not significant in all age groups (t test,
L∞ value according to the von Bertalanffy growth equation (a – males, b – females)
Measured and calculated average total length values for each age in the von Bertalanffy growth equation
Age (Year) | Observed average length (cm) | Expected average length (cm) | t test |
---|---|---|---|
1 | 4.34 ♂ |
4.30 ♂ |
|
2 | 5.20 ♂ |
5.15 ♂ |
|
3 | 5.93 ♂ |
5.91 ♂ |
|
4 | 6.61 ♂ |
6.57 ♂ |
Total length–weight relationships were calculated for females, males and all
Total length–weight relationships (females, males and all specimens) of
Research conducted on
Comparison of the growth parameters of
Species | Status | Locality | Ref. | N | TL (range) | W (range) | M:F | L∞ | k | t0 | Ø ' | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
native | South Pacific, Mexico | 1 | 1868 | 1.5–6.1 | - | - | - | - | - | - | 0.023 | 3.27 | 0.968 | |
native | Gulf of California, Mexico | 2 | 44 | 1.75–5.54 | 0.18–5.54 | - | - | - | - | - | 0.0026 | 3.13 | 0.99 | |
native | Chocó region, Ecuador | 3 | 601 | 1.36–5.21 | 0.06–4.52 | - | - | - | - | - | 0.0233 | 3.16 | 0.969 | |
native | Jalpan River, Mexico | 4 | 762 | 0.8–5.0 | 1.7–3.6 | 1.00:1.00 | - | - | - | - | 0.22 | 7.41 | 0.84 | |
native | Grijalva River Basin, Mexico | 5 | 158 | 3.3–7.1 | - | - | - | - | - | - | 0.0038 | 2.782 | 0.941 | |
native | Santa Marta, Colombia | 6 | 231 | - | - | 0.69:1.00 | 39.8 | 0.21 | −0.91 | 2.52 | 0.008 | 3.045 | - | |
native | Bodoquena Plateau, Brazil | 7 | 49 | 1.50–3.29 | 0.083–1.03 | 0.0219 | 3.09 | 0.965 | ||||||
native | Mundaú River Basin, Brazil | 8 | 204 | 1.0–2.6 | 0.01–0.17 | - | - | - | - | - | 0.009 | 2.982 | 0.807 | |
native | Humid forest enclaves, Brazil | 9 | 840 | 0.63–4.13 | 0.004–1.85 | - | - | - | - | - | 0.0216 | 3.107 | 0.966 | |
native | South Pacific, Mexico | 1 | 1604 | 1.8–7.1 | - | - | - | - | - | - | 0.034 | 3.00 | 0.978 | |
native | Grijalva River Basin, Mexico | 5 | 58 | 3.0–7.5 | - | - | - | - | - | - | 0.0028 | 2.970 | 0.979 | |
native | Yucatan, Mexico | 10 | 89 | 1.4–5.2 | 0.10–6.40 | - | - | - | - | - | 0.022 | 3.302 | 0.972 | |
alien | Songkhla, Thailand | 11 | 6.033 | 0.7–6.9 | - | 1.00:1.80 | 73.58 | 0.82 | 0.99 | - | 0.000013 ♂ |
3.237 ♂ |
0.986 ♂ |
|
native | Coastal Lagoons, Brazil | 12 | 318 | 1.0–6.0 | 0.01–3.27 | - | - | - | - | - | 0.008 | 3.368 | 0.96 | |
native | Guaratiba Mangrove, Brazil | 13 | 555 | 1.8–7.8 | 0.07–6.48 | - | - | - | - | - | 0.0078 | 3.28 | 0.97 | |
native | Atlantic coastal drainage, Brazil | 14 | 24 | 2.06–4.07 | 0.11–0.95 | - | - | - | - | - | 0.00795 | 3.49 | 0.961 | |
native | Everglades, USA | 15 | 1671 | 0.6–5.4 | - | 0.31:1.00 | - | - | - | - | 0.0267 | 2.880 | 0.930 | |
native | Gulf of Mexico, USA | 16 | 14 | 2.6–.5.0 | - | - | - | - | - | - | 0.6674 | 2.90 | 0.94 | |
alien | Indonesia | 17 | 1062 | 2.6–7.6 | - | 0.53:1.00 | - | - | - | - | 0.00003 | 3.02 | 0.85 | |
alien | Wadi Al-Bahayes, Oman | This study | 124 | 3.7–7.5 | 0.77–4.81 | 0.59:1.00 | 11.46 ♂ |
−0.127 ♂ |
−2.71♂ |
1.22 ♂ |
0.0272 ♂ |
2.5907 ♂ |
0.9579 ♂ |
References; 1: Velázquez-Velázquez et al. 2009; 2: Moreno Sa′nchez et al. 2012; 3: Jiménez-Prado et al. 2018; 4: Bermúdez-González et al. 2020; 5: Velázquez-Velázquez et al. 2015; 6: Garcia et al. 2008; 7: Severo-Neto et al. 2018; 8: Terra et al. 2017; 9: Gurgel-Lourenço et al. 2017; 10: Vega-Cendejas et al. 2017; 11: Sa-nguansil 2009; 12: Franco et al. 2014; 13: da Costa et al. 2014;; 14: Gasparini et al. 2016; 15: Klassen et al. 2004; 16: Morris 2005; 17: dan Hasnidar 2019
In this study, the age of
The sex ratio of females to males of
Differences in the growth parameters may be due to ecological differences between the study areas, water temperature, water quality and the amount of nutrients in the environment (Atar & Mete 2009). Differences between the observed and expected total lengths were statistically not significant (t test,
Length–weight relationship parameters are important parameters for management and proper exploitation of fish populations (Dutta et al. 2012). The exponent b in the length–weight relationship in the present study varies between 2 and 4, but often reaches a value close to 3; a value of 3 indicates isometric growth and values other than 3 indicate allometric growth (Tesch 1971). According to Le Cren (1951), the b value in the length–weight relationship also varies with season, depending on the development of gonads in fish. The exponent of the total length–weight relationship is b = 2.7889 for all specimens of
Among the methods of introducing alien species is the aquarium trade, which turns out to be the main route of introduction (Nunes et al. 2015). In Wadi Al-Bahayes, where the fish specimens were collected, there are aquarium shops that trade in any freshwater fish species. There are two possibilities for the presence of sailfin mollies in the inland waters of Oman. The first high-probability possibility is that molly fish may have been released in the area by an ornamental fish hobbyist. The second low-probability possibility is that they may have come from samples of mixed fish from neighboring countries to control malaria-carrying mosquitoes.
In general, poeciliids are affected by salinity (Meffe & Snelson 1989; Martin et al. 2009). Sailfin molly populations in the brackish water system of Wadi Al-Bahayes adapted well to changes in salinity in the environment. Due to the brackish aquatic environment, lentic conditions and the ground covered with muddy vegetation, Wadi Al-Bahayes provides a very suitable habitat for the sailfin molly to establish a population.