Mosquito Fish -- Gambusia affinis  

History:  Mosquito fish are a member of the Poecilidae Family, more commonly known as minnows.  They were introduced into Oregon from the mid-west (Southern Illinois south to Alabama and Mexico). It is thought that the mosquito fish enjoy a wider distribution throughout the world than any other freshwater fish, due to introductions of this species to control mosquitoes.

Physiology:  Mosquito fish are small, ranging from 1-2.5".  They are grayish-olive above and silvery below; pigmentation changes to match the environment. Life expectancy of mosquito fish is up to three years.

Mosquito fish are opportunistic feeders--they eat plant organisms including algae and phytoplankton (desmids/diatoms) and animal organisms including mosquito larvae, nematodes, copepods, chironmid larvae and zooplankton.  Their mouth is located on the upper part of the head, thus they are uniquely adapted for eating mosquito larvae. Most fish have been observed to eat 50 mosquito larvae in 30 minutes. Larger mosquito fish are cannibalistic and will prey on newborn mosquito fish, as well as other smaller fish.

At temperatures below 41-degress F, mosquito fish move to deeper water or to the mud-water interface and become inactive. There is poor over-winter survival in water less than 18 in depth.

Mosquito fish have a wide range of temperature tolerance (32.9-degress F to 107.6-degress F) and high salinity tolerance (15 ppt).

Habitat:  Mosquito fish prefer warm, sluggish streams, drainage ditches or standing water with abundant vegetation.  Mosquito larvae can be reduced by 58-95% in ponds.  However, mosquito fish are less effective in areas with heavy aquatic vegetation where they are unsuccessful in getting to pockets of larvae.

Reproduction:  Like others in the minnow family, Mosquito fish produce live young throughout the summer months and thus are quite prolific.  Males are smaller than the females (1.5-2") and have a specialized anal fin known as a gonopodium.  Females are larger (up to 2.5") and have a small, rounded anal fin.



Other Information: Mosquito fish have earned a reputation as the number one biological control for use with mosquitoes. Situations where control has proved to be inadequate are those which are too cold, too plant-infested, too polluted, too extensive or too temporary for the fish to achieve mosquito controlling densities.

Stocking of Mosquito fish: Mosquito fish do not adequately distribute themselves when introduced into a pond. Ideally, fish to be stocked should be divided into 3-4 equally spaced areas.

Sticklebacks (a small fish with spines along the dorsal fin) will prey on young mosquito fish.