Eastern Mosquito Fish

Description This is an alien species that belongs to Poecilidae family. It is an aggressive live-bearing fish that originates from the southern United States. It has been introduced worldwide for mosquito-control. It is greenish olive to brown on the back, the sides are grey with a bluish sheen with a silvery-white belly. Females have a distinct black patch surrounded by a golden patch occurring just above the vent. Males have a highly modified anal fin, the third, fourth and fifth rays of which are elongated and thickened to form a ‘gonopodium’ which is used to inseminate the female. Females are also larger than males with maximum standard lengths of 60 mm and 35 mm respectively.   Biology It lives immediately under the surface, catching pray at or under the surface. The breeding season is between mid-spring and mid-autumn (April-October), with the peak breeding time around summer. Females can have up to nine broods per mating season, with the average number ranging from 5 to 100. Although it can tolerate a broad range of environmental conditions, they tend to avoid rapid currents, naturally variable creeks and rivers and areas of dense surface vegetation, that can obstruct access to feeding on the surface.   Distribution Gambusia holbrooki prefer warm, slow flowing or still waters, and occur amongst aquatic vegetation at the edge of water bodies in water depths of 10 cm or less. It can be found in estuarine habitats, lakes, ruderal/disturbed water courses and wetlands. It is native to southeastern United States, and can be found in many of the lakes within that area, which icludes lakes east of the Mississippi River. It was introduced worldwide in tropical and sub-tropical countries. It is established throughout southern Europe. In the Prespa Lakes it was introduced in the first half of the 20th century.   Fishing significance No.   Impacts This species has been implicated in damage to native fish, amphibians and invertebrate populations.   Measures Since 1982 the World Health Organisation has no longer recommended the use of Gambusia for malaria control purposes and indicates it should not be introduced into new areas. Ameliorative fishing.