Poeciliids, including the livebearers, are found in fresh and brackish waters from the eastern United States south through the Caribbean to northeastern Argentina and in Africa. There are about 37 genera with about 304 species (Nelson, 2006) and one or two species of livebearer has been widely introduced around the world as a control agent for malaria and is found in Iran.

This family is characterised by an anteriorly rounded and posteriorly compressed body and a depressed head; large cycloid scales on the head and body; supraorbital pores with neuromasts in fleshy grooves; a small, terminal mouth with the lower jaw projecting; teeth incisor-like or villiform on the jaws; gill membranes free from the isthmus; 4-6 branchiostegals; no spiny fin rays; a small dorsal fin; pectoral fins set high on the side (in contrast to Cyprinodontidae anterior pelvic fins; no adipose fin; and the anal fin in males is developed into a copulatory organ with rays 3-5 modified while females have a rounded anal fin (in livebearers only, the species found in Iran, in contrast to Cyprinodontidae).

The gonopodium is used for transferring sperm packets into the female. It is moveable to the side or forward to allow copulation to occur. The sperm packets release sperm when placed in the female and some can be stored for future use. Details of gonopodium anatomy are important in identifying and classifying species. The gonopodium is composed primarily of the third, fourth and fifth anal rays with various hooks, serrae and spines. Young are born alive, a condition known as ovoviviparity where the eggs develop and hatch in the mother.

Livebearers are found in habitats from mountain streams to brackish coastal marshes and river mouths. Food is mostly encrusting algae and the associated, small invertebrates. Males tend to be smaller than females and more brightly coloured. These colours are best seen during the courtship display.

Some species are important in the aquarium business, such as the guppy and swordtail, while the mosquitofish has been used world-wide as a predator on aquatic mosquito larvae, the adult fly being a carrier of malaria. They have also been used extensively in genetics research, research on tumours and in immunology. Some livebearers are all-female species and egg development is stimulated by spermatozoa from another species, without any genetic contribution. Young are identical to the mother. This unusual form of reproduction is called gynogenesis. Others have superfetation where eggs are at different developmental stages within the mother and are born over a period of several days rather than all at once.

Genus Gambusia
Poey, 1854

This genus is characterised by large scales, short dorsal and anal fins, the anal fin in males anteriorly placed and modified into a long intromittent organ (or gonopodium), dorsal fin inserted behind the anal fin origin (in contrast to Aphanius, Cyprinodontidae), and dorsal and caudal fins are spotted.

Gambusia affinis
(Baird and Girard, 1853)

Gambusia holbrooki was considered to be a subspecies of this species. Iranian mosquitofish were G. holbrooki but it is possible that some populations consist of G. affinis although none were seen by me or by Holčík and Oláh (1992). Shakirova and Sukhanova (1994) report this species from the Atrek River in Turkmenistan, which flows into Iran, as well as Kopetdag streams on the northern border of Iran. However identification of these taxa may be confused. The source of most (? all) Middle East mosquitofish is Europe and Kottelat and Freyhof (2007) record that there is no confirmed presence of G. affinis in Europe.

Gambusia holbrooki
Girard, 1859

Common names

گامبوزيا (= gambusia).

[gambuzi, zoory, or zurri in Arabic; gambuziya in Azerbaijan; gambuziya in Russian; mosquitofish; eastern mosquitofish (for holbrooki, western mosquitofish for affinis); plague minnow, in reference to its ecological impact].

Systematics

Gambusia holbrooki was originally described from eastern Florida and South Carolina, U.S.A. Wooten et al. (1988) distinguish the eastern and western mosquitofish in the U.S.A. based on morphology, biochemistry and distribution. However, extensive hybridization occurs in the native habitat and the composition of all the introduced Iranian populations has not been studied. Introduced populations world-wide are generally referred to the taxon holbrooki.

Key characters

Males are easily recognised by the anal fin rays 3-5 being specially modified into an elongate gonopodium for intromittent fertilisation. G. holbrooki has 8 dorsal and 11 anal total fin rays while G. affinis has 7 dorsal and 10 anal total fin rays (Walters and Freeman, 2000).

Morphology

Dorsal fin with 5-9 rays, usually 7 (with the last two counted as one), anal fin with 7-11 rays, usually 10, and pectoral fin with 11-14 rays. Lateral scale rows number 26-33. In males, the posterior edge of the joints of the first elongate ray is serrated (smooth in affinis), the cusps of the posterior branch of the second elongate ray are short and almost straight (long and curved in affinis), and the apical hook of the posterior branch of this ray is short with 2-3 joints (very long with 4-6 joints). Vertebrae 28-34. The karyotype is 2n=48. Detailed counts on Iranian specimens were not made; examination of cleared and stained material indicates that the species in Iran and Iraq is G. holbrooki.

Sexual dimorphism

Males reach a smaller adult size than females (see below). Males have the end of the anal fin base well ahead of the beginning of the dorsal fin. Females lack a gonopodium and the end of the anal fin is under the beginning of the dorsal fin. In addition various morphometric characters differ widely (see Abdurakhmanov (1962) for details).

Colour

Males are translucent grey to light olive with a blue, green or purplish sheen on the sides and opercle. The back is olive-brown to yellowish-brown and the belly silvery or yellowish. A dark bar passes through the eye. The iris has a purple sheen. The flanks may appear spotted as pigment margins the scales to form a diamond pattern on the body. Dorsal and caudal fins are spotted and a dusky, light tan but other fins are clear. Adult females have a large, triangular, bluish-purple blotch on the lower flank behind the pectoral fin (called the gravid spot). The black peritoneum can be seen through the body wall.

Size

Reaches 63.0 mm in females and 45.4 mm in males (Tabibzadeh et al., 1970a; Vargas and de Sostoa, 1996), perhaps to 8 cm in the largest females (Reshetnikov, 2002).

Distribution

The natural distribution is from New Jersey southward to northern Mexico but it has been introduced to all continents except Antarctica. This species was first introduced to the Ghazian marshes of the Caspian littoral of Iran in 1922-1930. Some mosquitofish may have spread from the Lenkoran District of Azerbaijan, reaching the Safid Rud in 1937 (Shukolyukov, 1949). From the Ghazian stock, additional samples were collected in 1966 for introduction around the country via raising ponds to over 3000 permanent water bodies (Tabibzadeh et al., 1970a, 1970b; Spillman, 1972; Emadi, 1996c). Many of these contained fishes but some were previously fishless or at least now appear to contain only mosquitofish, e.g. springs at Kahurak and Hormak in Sistan and Baluchestan Province. Over 1.5 million fish were distributed in 1969 alone (Tabibzadeh et al., 1970b). This species is now the most widely distributed fish in Iran (Abbasi et al., 1999; Kiabi et al., 1999; Abdoli, 2000).

Zoogeography

This species is an exotic, originating in eastern and southern North America and introduced to Iran from stocks introduced to Italy and from Baku in Azerbaijan.

Habitat

Mosquitofish are normally inhabitants of clear and weedy streams and ditches, weedy margins of large rivers and lakes, marshes and brackish coastal lagoons, usually over mud or sand bottoms. They prefer more open waters with less vegetation than Aphanius dispar, for example. Males and females in aquaria swam together in a mixed school in contrast to the sexually segregated schools of Aphanius dispar (Al-Daham et al., 1977). In the Anzali Mordab, dense schools are found in surface waters of areas covered by submerged and floating vegetation while deeper water is fishless (Holčík and Oláh, 1992). In Iran, it is one of two most abundant species in Caspian wetland areas along with Carassius auratus (Iranian Fisheries Research and Training Organization Newsletter, 19:4, 1998).

Al-Daham and Bhatti (1977) found G. affinis, probably this species, to have a complete tolerance of 10.25‰ sea water and 90% of fish survived 20.5‰ for 24 hours and even as high as 58‰. This species has been reported to survive in waters up to 42°C and as low as 0.5°C. Summer air temperatures of 45°C and winter temperatures several degrees below zero are survived as long as the water is deep enough (Tabibzadeh et al., 1970a). Upper and lower thermal tolerance increases with body size (Al-Habbib and Yacoob, 1993). At temperatures below 15-18°C, mosquitofish grow but do not mature or breed. They prefer a temperature of 31°C.

Muddy and polluted conditions, acid to alkaline water, and dissolved oxygen less than 1 mg/l are survived by this species. pH range survived is 4.46-10.2 and dissolved oxygen levels as low as 0.2-0.4 mg/l as long as water surface access is available. They can take advantage of the oxygen rich surface layer as they position their bodies with flattened head and back immediately adjacent to t\he air-water interface (Lewis, 1970).

Their success in Iran and other waters world-wide is attributed to the following factors according to Meffe and Snelson (1989):- 1) abundant in original range, 2) polyphagous, 3) short generation time, 4) a single female can colonise since livebearer, 5) broad physiological tolerances, 6) closely associated with man, 7) high genetic variability, 8) specialized reproduction with moderate numbers of advanced young several times a year, and 9) high aggression levels.

Age and growth

Numbers of each sex in a population vary between localities, mostly females predominate over males. Males are more sensitive to temperature extremes, starving and overcrowding and this will affect such things as size and age at maturity. Males do not grow much after sexual maturity is attained but females have indeterminate growth, although growth slows as energy is put into egg production. The average condition factor for males was 1.2369 and for females 1.0906 in southern Iraq. The condition factor slowly decreases as length increases in the male and vice versa for females (Huq et al. 1977). Sexual maturity can be reached in only 2-3 months but such fish die before winter. Minimal size for maturity is 16-28 mm total length. In the laboratory under ideal conditions sexual maturity can be attained in 3 weeks. Life span seldom exceeds 15 months, although the range is 6-24+ months depending on when in the spawning season the fish was born. In Spain, maximum ages are 2+ for females and 0+ for males (Vargas and de Sostoa, 1996). Fish born late in the year may not mature until the following year.

Growth to maturity can be so rapid that a 50-fold increase in numbers can occur over a 10-week period. Densities may reach over half a million fish per hectare. Under ideal conditions it is theoretically possible for 10 pregnant females to produce 5 million fish in 6 months.

Esmaeili and Ebrahimi (2006) give a significant length-weight relationship based on 35 Iranian fish measuring 1.98-3.27 cm standard length. The a-value was 0.0190 and the b-value 3.214 (a b-value < 3 indicating a fish that becomes less rotund as length increases and a b-value >3 indicating a fish that becomes more rotund as length increases).

Food

Generally this species is regarded as an opportunistic omnivore. Swanson et al. (1996) refer to this fish as an aggressive predator and Al-Daham et al. (1970) for southern Iraqi fish considered it to be a carnivore, feeding on aquatic and terrestrial insects including spiders, ants, beetles and mites, and also filamentous algae. Females are cannibals. Food includes diatoms, algae, worms, crustaceans including zooplankton, insects, snails, other fishes and amphibian larvae. The mosquitofish is dependent on sight to detect and attack prey. Selection of zooplankton can lead to an increase in phytoplankton numbers (and thus affect water quality) and to changes in size frequencies of zooplankton populations.

Food is taken at or near the surface and by grazing on plants and rocks. Tabibzadeh et al. (1970a, 1970b) record diet as molluscs, aquatic insects and various forms of mosquito larvae. They report up to 94 pupae or 104 mosquito fourth-stage larvae eaten per day by this fish and effective clearance of springs and marshes. Large-sized mosquitofish took more than 500 second instar mosquito larvae per day and medium- and large-sized mosquitofish consumed 22-64 fourth instar larvae per day in an Iraqi study under laboratory conditions (Mohsen et al., 1989). Abdoli (2000) lists Diptera and Chironomidae as food items. Meffe and Snelson (1989) report predatory behaviour on the young of other species of fish and females attack other fishes, shredding fins and sometimes causing mortality.

Reproduction

Na'ama and Al-Hassan (1989) report G. affinis (presumably G. holbrooki) to have a brood size up to 48 from Baghdad specimens and 51 from the Basrah area, Iraq. The smallest reproductive female was 1.7 cm total length. Weight is the most accurate predictor of brood size. In Iran, Tabibzadeh et al. (1970a) found that females mature and reproduce within 2 months at temperatures above 15°C. In less favourable conditions this may take 8-10 months. A minimum photoperiod of 12.5-13 hours is necessary to stimulate reproduction although year-round temperatures above 20°C can offset this light requirement. About 17 days after fertilisation, the female gives birth to as many as 428 live fish over a period of about 1 month after 3-8 weeks gestation. Each fertilisation can give 2-3 broods and each female can produce up to 9 broods during her life, although 2-5 is more usual.

The breeding season extends from April to November in favourable conditions, May to September in more temperate conditions. Several months pass between successive spawnings. Eggs are up to 1.8 mm in diameter when mature and embryos are about 6-8 mm at birth. The young are protected within the female and are independent when born, with resulting low mortality. Environmental breeding requirements are simple and with low mortality results in the successful spread of this exotic.

The small male approaches the female from behind and with a rapid motion inserts his gonopodium tip into the female. The gravid spot is a releasing stimulus. It indicates a receptive female and also is a target for the male gonopodium. Sperm are transferred in a spermatophore. During mating the gonopodium is angled forward at 140-150°.

Most males copulate without courtship. When courtship occurs it involves the male assuming an s-shaped position with its body and vibrating in front of, or at the side of, the female. Males are aggressive and dominate smaller males to restrict access to females. Females may be inseminated by several males and sperm can be stored to be used up to 10 months later. A single transplanted female can populate a new habitat.

Parasites and predators

None reported from Iran.

Economic importance

Introduced widely to combat malaria by consuming the aquatic larvae and pupae of the carrier mosquito. However to be effective, this fish must have aquatic plants cleared from its habitat. The mosquitofish is also a predator on the eggs and young of other, native fishes and a competitor for food, and it alters ecosystems by greatly reducing rotifer, crustacean and insect populations allowing phytoplankton to increase dramatically (Myers, 1965; Hurlbert et al., 1972; Tabibzadeh et al., 1970a; Edrissian, 2006; Chandra et al., 2008). Native species might well be more effective predators on mosquito larvae (see account of Aphanius dispar and Ahmed et al. (1988) and Beidas and White (1982)). Muhaisen et al. (1985) studied control of this species in Iraq as larvae on fish farms and found potassium permanganate, copper sulphate, acriflavine and malachite green to be effective.

Haas and Pal (1984) point out that Gambusia may favour schistosomiasis, a human parasite, by altering the ecology of freshwaters, perhaps by reducing the numbers of natural predators on vectors of this parasite. They also note that it is considered a pest by fish farmers.

Tabibzadeh et al. (1970a, 1970b), Motabar (1978) and Swanson et al. (1996) give methods for raising and distributing mosquitofish. Also used as a research species and sometimes seen in aquaria. Al-Nasiri and Sharma (1978) used this species in Iraq to study the toxicity of the agricultural insecticide Ekatin 25 to fish and Mohsen et al. (1989) studied the predatory efficiency and tolerance to mosquito larvicides.

Conservation

The most widespread fish in Iran and, as an exotic, not in need of any protection. However this distribution undoubtedly affects the conservation status of native species since mosquitofish have a strong impact in small and non-diverse habitats such as the small springs found throughout Iran. Muus and Dahlstrøm (1999) mention that it tends to oust native toothcarps.

Further work

The effects of this species in competition with native fishes should be investigated although it is so widespread that it could never be eradicated.

Sources

Meffe and Snelson (1989) give the ecology and evolution of the family and Rauchenberger (1989) the systematics of the genus. Swanson et al. (1996) and Pyke (2005, 2008) review biology, culture and mosquito control and are a source for general information above.

Iranian material: The following is a sub-sample of Iranian material as this species is very common and material extensive (see map for distributional information): CMNFI 1970-0515, 2, 20.6-30.2 mm standard length, Gilan, Shafa River near estuary (37º35'N, 49º09'E); CMNFI 1970-0519, 5, 14.1-19.5 mm standard length, Gilan, Chelvand River (ca. 38º18'N, ca. 48º52'E); CMNFI 1970-0590, 3, 25.1-29.2 mm standard length, Mazandaran, Shesh Deh River near Babol Sar (ca. 36º43'N, ca. 52º39'E); CMNFI 1971-0343, 1, 26.0 mm standard length, Gilan, Langarud at Chemkhaleh (37º13'N, 50º16'E); CMNFI 1979-0019, 26, 15.4-29.0 mm standard length, Fars, Pol-e Fasa (29º29'N, 52º38'30"E); CMNFI 1979-0025, 2, 28.7-33.8 mm standard length, Fars, Kor River at Marv Dasht (29º51'N, 52º46'30"E); CMNFI 1979-0026, 1, 21.6 mm standard length, Fars, Shapur River at Shapur (29º47'N, 51º35'E); CMNFI 1979-0126, 53, 14.9-33.1 mm standard length, Fars, Dasht-e Arjan springs (29º37'N, 51º58'E); CMNFI 1979-0173, 13, 24.7-39.6 mm standard length, Hormozgan, qanat at Hajjiabad (28º19'N, 55º54'E); CMNFI 1979-0192, 2, 24.9-26.4 mm standard length, Fars, qanat 2 km east of Rostaq (28º26'30"N, 55º04'E); CMNFI 1979-0226, 65, 23.1-39.2 mm standard length, Sistan, 3 km east of Kuh-e Khajeh (30º57'N, 61º17'E); CMNFI 1979-0230, 36, 7.2-44.4 mm standard length, Sistan, Jehil-e Puzak (ca. 31º15'N, ca. 61º42'E); CMNFI 1979-0283, 1, 35.9 mm standard length, Kermanshahan, Qareh Su basin (34º21'N, 47º07'E); CMNFI 1979-0288, 7, 26.8-29.4 mm standard length, Ilam and Poshtkuh, Gangir River (33º50'N, 46º18'E); CMNFI 1979-0309, 5, 15.4-32.8 mm standard length, Kerman, Fahraj River (28º57'N, 58º42'E); CMNFI 1979-0328, 2, 24.3-24.8 mm standard length, Baluchestan, jube near Bampur (27º10'30"N, 60º21'E); CMNFI 1979-0360, 13, 17.8-25.9 mm standard length, Khuzestan, Karkheh River canal (31º40'N, 48º35'E); CMNFI 1979-0478, 2, 17.8-28.2 mm standard length, Mazandaran, ditch 29 km from Eimar (37º09'N, 54º36'E); CMNFI 1979-0498, 2, 22.1-35.8 mm standard length, Fars, spring on road to Dariush Dam (30º05'N, 52º27'E); CMNFI 1980-0122, 25, 14.3-26.8 mm standard length, Mazandaran, Nerissi River (36º38'N, 52º16'E); CMNFI 1980-0128, 7, 23.6-35.6 mm standard length, Mazandaran, Qareh Su (36º49'30"N, 54º03'30"E). CMNFI 1980-0132, 5, 18.4-30.2 mm standard length, Gilan, Safid River at Kisom (37º12'N, 49º54'E); CMNFI 1980-0145, 75, 32.6-40.4 mm standard length, Gilan, Bandar-e Anzali (37º28'N, 49º27'E).

Comparative material: BM(NH) 1974.5.2:38-40, 3, 17.3-25.1 mm standard length, Iraq, Baghdad (33º21'N, 44º25'E); BM(NH) no catalogue number, 6, 10.7-37.5 mm standard length, Iraq, Baghdad Liwa (no other locality data); BM(NH) no catalogue number, 4, 28.3-38.8 mm standard length, Iraq, Baghdad Liwa (no other locality data); BM(NH) no catalogue number, 8, 16.8-32.5 mm standard length, Iraq, Kut Liwa (no other locality data); BM(NH) no catalogue number, 2, 20.3-21.9 mm standard length, Iraq, Hilla Liwa (no other locality data).

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