Eastern Mosquitofish

Appearance

The eastern mosquitofish is a small, light-colored fish with semitransparent fins. The females usually have a black stripe near their eye area and light spots can be seen on the caudal and dorsal fins of both sexes. Due to its similar size, shape, and reproductive habits, it can easily be mistaken for a guppy. Generally, males reach 1.5 in and females 2.5 in. These fish are a livebearer species, and as such, the females are larger and more rounded than the males. Pregnant females are also easily recognizable by their gravid spot; a darker area on their bellies where they hold the fry.

Mosquitofish may have a melanistic color pattern with black spots, resembling a dalmatian. This could result in its being misidentified as another species.

Distribution

Eastern mosquitofish are native to the southeastern United States. They have been introduced worldwide and have become an invasive species in many places including Australia and Europe.

Habitat

Eastern mosquitofish are found in shallow, standing to slow-flowing water, mostly in vegetated ponds, lakes, and sloughs. This species thrives in water between 31 °C and 35 °C, and seems to be able to acclimate to temperatures above and below this. "G. holbrooki" has been shown to survive in water with pH and chemical levels known to kill other fish species, and prefers to live in areas where the water flows at a slow pace, is clear and without free-floating plant life, and seeks shelter in rooted plants. No decrease in this species due to human activities has been noted. The Eastern mosquitofish is easily maintained and has never been considered an endangered or threatened species due to its ability to thrive in its native habitat. Due to releases in new areas, "G. holbrooki" has actually increased its range. It tolerates chemical and thermal changes quite easily.

Reproduction

Temperature has been shown to change the length of time it takes them to reach reproductive maturity and body size. This species is also known to give birth to live young instead of laying a clutch of eggs. The breeding season is between midspring and midautumn, with the peak breeding time being around summer. Females can have up to nine broods per mating season, with the average size ranging from five to 100. The variability of the average brood size is due to many variables, including temperature, age, and available nutrients. Higher temperatures have been shown to increase the fecundity of this species. The gestation period for this species is between 22 and 25 days. Predation stress is also known to affect their reproduction. Predator-exposed females were found to give birth to higher number of stillborn offspring compared to unexposed females.

Food

"G. holbrooki" is considered a planktivorous species which consumes algae and detritus. Feeding habits seem to change based on maturity and mating season. "Gambusia holbrooki" will, if need arises, switch food sources to survive. With an increase of competition, this species will switch from a diet rich in phytoplankton, algae, and detritus to one consisting of zooplankton, invertebrates, the larvae of many other fish and amphibian species, and plant-associated animals. The main source of competition for "G. holbrooki" seems to be an increase of its own species and other planktivorous species. The main problem with this is, as mentioned before, it will change its diet; this is common even among the juveniles and both sexes of its own species. The females tend to not specialize on one prey, and consume all evenly, whereas the males and juveniles specialize on one prey type. However. males, females, and juveniles all consume detritus at the same rate.

Predators

Little research has been done to determine all "G. holbrooki" predators, due to its own predatory nature in the areas where it has been introduced. In the introduced areas, it has been known to cause top-down trophic effects due to its eating the larvae of some top predators, which include frogs and other fish. Visual exposure to its predator, largemouth bass is known to affect its reproduction.