The mosquitofish (Gambusia affinis) is small live-bearer fish that is only rarely seen in the aquarium hobby. There are actually two species of mosquitofish, with the western mosquitofish more commonly available for sale, and the eastern mosquitofish (G. Holbooki) almost never being found in fish stores.
The mosquitofish is one of the few commercially available fish that are native to North America and they were originally found in the Mississippi River and in the streams and rivers of Illinois and Indiana. They have now spread throughout the globe, largely due to their near legendary hardiness. They are now considered a major invasive threat in several countries, and have severely impacted the ecosystems of Australia.
The mosquitofish remains small in the home aquarium, with the females reaching about 3 inches in length and the male 1.5 inches. The males and females are easy to differentiate, with the males developing a bright red tail upon sexual maturity and the females developing a gravid spot (a dark spot near the rear of their abdomen.)
The mosquitofish is incredibly easy to care for, and can survive extremes in temperature and salinity. It will also thrive in low oxygen environments with poor water quality, making this fish difficult to kill even by novice fish keepers.
While most mosquitofish are kept in ponds to control – you guessed it, mosquitos, they will also do well in small aquariums. They can be housed quite easily in a 10 gallon aquarium and will thrive if you provide them with anything larger.
Something important to remember, is that mosquitofish are known as fin nippers and can be aggressive at times. While most small minnows will be perfectly compatible with mosquitofish, you should stay away from any long finned fish, or any slow moving, docile fish like fancy goldfish.
When choosing a filter, you should remember that these are live bearing fish, and a hang-on-back filter is a death sentence to any fry if you don’t cover the intake. The best choice for any liver-bearer tank is a sponge filter, but a hang-on-back filter does provide better filtration if you are able to remove the fry from the tank, or as previously stated, cover the filter intake to prevent the fry being sucked up to rather unpleasant deaths.
I would strongly recommend choosing an Aquaclear Power Filter for a mosquitofish tank. This filter combines excellent filtration with a durable design, and it will keep your tank sparkling clear for years to come. You can also read the Aquarium Tidings Aquaclear Filter Review here.
In the wild, mosquitofish primarily eat small insects, larvae and small amounts of plant material and algae. They will also consume massive amounts of mosquito larvae, and the females have been known to consume more than their body weight in a single day.
In the home aquarium they should be fed a high quality flake food, along with live or frozen foods. I personally use Hikari Micro Wafers, which I consider to be one of the best prepared foods on the market. Their favorite frozen foods are bloodworms, daphnia and brine shrimp and they will also greedily eat any live foods that are offered.
Their preferred live food is obviously mosquito larvae, but that can be hard to come by and there can be certain legal ramifications relating to breeding mosquitos. Most areas prohibit the breeding of mosquitos, and you should check with your local authorities before attempting to breed them. If you are able to breed mosquito larvae, then be sure to harvest it completely so that no larvae are able to mature into adult mosquitos.
Mosquitofish are actually one of the more difficult to breed live-bearer fish. Once you have sexed the fish, it’s always best to have a ratio of about one male for every three females. This ensures that the males won’t harass one female all the time, which can result in illness or even death from the stress.
The problem with the breeding of mosquitofish arises after the female has been impregnated. They are able to delay delivering the fry if there are threats nearby, and they consider male mosquito fish to be threats. If you want the female to deliver her fry, then you either need to relocate her to another tank once she’s showing as pregnant, or place her in a breeder box in the tank, so that she’s separated from the males.
Once she has been separated, she will normally give birth to numerous fry in a short period of time. To prevent any unpleasant cannibalism, the mother should be removed as soon as possible, though most females tend to ignore their young.
The newborn fry can be feed baby brine shrimp, mircoworms or finely ground up flake food. They can also be fed any of the now numerous fry foods commercially available.