Green Swordtail
Xiphophorus hellerii
Eastern Mosquitofish
Gambusia holbrooki
About
The eastern mosquitofish is a small, pale freshwater fish best known for eating mosquito larvae, which is how it got its name. It lives in slow or still water and has spread far beyond its original home.
Also known as: eastern gambusia, top minnow, gambies, bore-drain fish, starling's perch, plague minnow
How to tell it apart
In parts of Australia it can be confused with the young or female Pacific blue-eye, but that fish has a forked tail fin while the mosquitofish does not.
Appearance
This is a small, light-coloured fish with fins that are almost see-through. Females have a dark stripe near the eye, and both sexes carry light spots on the tail and back fin. Pregnant females show a dark patch on the belly, called a gravid spot, where the young develop.
Habitat
It lives in shallow, still or slow-moving water, favouring ponds, lakes, and quiet channels with rooted plants for shelter. It is native to the southeastern United States but has been introduced widely, including in Australia and Europe.
Behaviour
Where it has been introduced, this fish preys on the young of frogs and other fish, which can hurt native populations. Males can be aggressive toward females while mating, so females often gather in groups to reduce the harassment.
Diet
It mostly eats algae, detritus, and tiny drifting animals such as zooplankton, picking off very small prey near plants. When food is scarce, it switches to eating the larvae of other fish and amphibians instead.
Breeding
Females give birth to live young rather than laying eggs, breeding mainly from spring through autumn with a peak in summer. Warmer water speeds up growth and can lead to more young per brood.
Did you know?
Some individuals develop a black-spotted, dalmatian-like pattern instead of their usual plain colouring, which can make them look like an entirely different fish.
Log it in Into the Blue
Describe what you saw and we name it, then keep every species you find in your Oceandex.
