October 2003 Mosquito Fish - Our Most Effective Larvicide Have you ever noticed the drab, greyish colored, little fish that swim along the shoreline of Florida’s lakes, ponds, or rivers? If you have then you’ve seen “mosquito fish.” Many different fish species are used throughout the world as a biological control for mosquitoes. The one used most often in Florida, the United States, and the rest of the world is Gambusia affinis. Why is Gambusia the number one choice for use in mosquito control? Almost all fish eat mosquitoes with absolute delight. In fact, I haven’t seen a fish that doesn’t like mosquito larvae. The attributes that make Gambusia an ideal biocontrol agent for mosquito control is its reproductive potential, hardiness, tenacity, and its ability to access areas where mosquito larva prefer. During the summer an adult female will give live birth to 50 to 100 young every 4 to 6 weeks, depending upon the water temperature. The young are 1/4 inch long at birth and are capable of eating mosquito larva immediately. Gambusia grow rapidly and can reproduce 4 to 6 weeks after they are born. Without predation and a bountiful food supply, mosquito fish can multiply to tremendous numbers in just 3 to 4 months. Their ability to adapt to fluctuating environmental conditions is amazing. I’ve seen them under ice, in mud puddles where the water temperature was over 100° F., they can survive in water that is saltier than ocean water and survive in highly polluted water with low oxygen levels (I’ve placed Gambusia in sewage lagoons and sewage treatment plant extended aeration tanks and they survived, even thrived). Gambusia are top minnows which means they feed primarily at the surface, where mosquito larva hang out. This characteristic and their small size (females grow to 3 inches, males to 1 ½ inches) allows them to get into very shallow water where mosquito larva hide. Gambusia are opportunistic feeders - they’ll eat just about anything from algae to themselves, if need be, but they prefer insect larvae. Adult fish can eat 50 mosquito larva in 30 minutes and well over 100 per day.
Gambusia affinis, originally established in Texas and widely distributed throughout the world, was imported from Italy in 1928. Gambusia has been used in mosquito control programs for over 60 years. Prior to using Gambusia, the common guppy was the fish used for mosquito control. The guppy has a lot of the same characteristics, it reproduces quickly, is a top minnow, small to access shallow water, and hardy - but no where near as hardy or tenacious as Gambusia. After it was found to be more effective than guppies in regard to eating mosquito larva, Gambusia is now used worldwide to help combat malaria.
The attributes that make Gambusia a great biocontrol agent for mosquitoes has also earned it a reputation as a “biological pollutant” in many areas of the world. Gambusia’s opportunistic feeding habits, high rate of reproduction, and tenacity can impact local fish populations by out-competing them for food or by eating the eggs and fry of native fish. Fortunately, in Florida, we have a mosquito fish native to the southern part of the state called Gambusia holbrooki. This fish is almost identical to Gambusia affinis except for some minor morphological differences and life history characteristics such as embryo size, maturity rate, life span, etc. - but basically the same fish...the ecological niche is here, so the use of affinis doesn’t create any significant “biological pollution”, at least not in Florida.
In South Walton we try to establish this fish wherever we can, basically in permanent or semi-permanent waterholding areas such as drainage retention areas, catch basins, animal watering troughs, abandoned swimming pools, drainage ditches, flooded wetlands, birdbaths, fountains, etc. In 2000 I placed 10 fish in the small birdbath I have and they are still surviving. I clean the birdbath periodically by removing as much debris as possible by hand, top it off with water when needed, have not fed them at all, and they’ve survived on whatever has happened to fall into the birdbath.
At our facility we raise our own Gambusia in a pond about 1 ½ feet deep, 12 feet wide and 30 feet long. The fish are free to the public and are compatible with most ornamental pond fish such as goldfish, koi and carp.
A lot of folks feel that because they have a pond or ditch on their property, they need mosquito fish, chances are, if the waterbody is natural or manmade but connected to a natural waterbody, then Gambusia are probably already there. The beauty of mosquito fish is the fact that they go wherever the water they are in goes. This tendency provides mosquito control in areas we normally can’t access. In addition to their ability to access remote areas, these fish never take breaks or vacations, don’t have to be re-applied like other larvicides (unless the water dries up), and will multiply to the carrying capacity of the waterbody they are in. When placed in manmade waterbodies such as drainage retention areas or abandoned swimming pools (areas without natural predators) they will produce large numbers and provide excellent mosquito control for as long as the water remains. In the natural environment their numbers are controlled by predators and provide an important food source for other fish and wading birds.
In summary, Gambusia affinis can become a “biological pollutant” in some areas of the world, in specific aquatic systems. Here however, in Florida and most other areas of the U.S., they’re an indispensable tool for mosquito control and are also an integral part of the natural ecosystem. |