What Are Mosquito Fish?

The mosquito fish or gambusia (Gambusia affinis) is a small and unspectacular fish that is widely used to control mosquito populations across the world. It is now one of the most widespread freshwater fish species in the world. Their fast reproductive rate, hardiness and voracious appetite mean that mosquito fish will consume all the mosquito larvae in a body of water. In many places where they have been introduced, mosquito fish have out-competed local fish and amphibian species and caused great ecological damage. There are a number of other closely related species from the southern and eastern United States that are also sometimes referred to as mosquito fish, such as the eastern mosquito fish (G. holbrooki).

  1. Description

    • Females reach 2.5 inches in length while the males are much smaller at 1.5 inches. Both sexes are a dull gray color with visible if tiny scales and a pale, rounded belly and curved, convex tail. The males have a pointed anal fin behind the belly while in the females this fin is a mirror of the dorsal fin on the back. The eye is large in proportion to the head and the mouth slightly under-slung.

    Range

    • Mosquito fish are found in lakes and rivers around the Gulf of Mexico from southern Indiana and Illinois and as far south as Florida and Mexico. On the Atlantic coast of the United States they can be found as far north as New Jersey. Introductions have meant that the species is present in almost every state and in most countries of the world where still water does not freeze in the winter. They are regarded as an invasive pest species in Australia and New Zealand.

    Habitat

    • Mosquito fish thrive in brackish and fresh water at temperatures between 33 and 95 degrees F. They are found in lakes, rivers, canals, ponds and ditches as well as in man-made reservoirs. They are able to survive in warm stagnant water that is too low in oxygen for most other fish species.

    Behavior

    • An adult can consume up to 200 mosquito larvae a day and will eat almost anything else it can fit into its mouth, even its own young. There is growing evidence that mosquito fish will consume other prey in preference to mosquito larvae if they are available. Adults are aggressive towards other fish species and will even eat injured or sick adults of their own species.

    Reproduction

    • Males use their pointed anal fin to deliver sperm to the females. Females are able to retain sperm for up to two months after mating. Mosquito fish give birth to live young and a large female can produce up to 50 young every eight weeks. The fry live among weeds until they have grown too large to be eaten by adult mosquito fish.