General Description: Mosquitofish (Gambusia affinis) are, small, sexually dimorphic fish with stout bodies, generally dull gray colors, a rounded tail, and a terminal, upward-pointing mouth. Females are larger than males, growing to 2.5-inches long rather than only 1.5-inches. In addition to being smaller, males have a pointed (rather than rounded) anal fin.

Taxonomy: Live Bearers (Poeciliidae)

Other Names: western mosquitofish.

Diet: Omnivorous. Feeds on invertebrates, detritus, and algae in the water column and at the surface of the water.

Favored Habitat: These fish are native to fresh US and Mexican waters that flow into the Gulf of Mexico, including all of the Mississippi River system. In these places, they prefer standing or slow-flowing water such as vegetated ponds and lakes, backwaters, and stream pools.

Where to Find: Around Las Vegas, look for Mosquitofish in man-made ponds and the Moapa River system. Mosquitofish are a problem for native fish in the Moapa National Wildlife Refuge.

Comments: These non-native fish have been widely introduced around the world to control mosquitoes. Unfortunately, they also interfere with native fish, frogs, and other species.

Mosquitofish do not lay eggs, rather they produce live baby fish, hence the family name: "live bearers." These fish are highly prolific.

At the surface of the water, the upturned, terminal mouth is clearly visible. The upturned mouth is an adaptation for feeding at the surface of the water, places where mosquito larvae tend to congregate.