Eastern Mosquitofish
Gambusia holbrooki
Green Swordtail
Xiphophorus hellerii
About
The green swordtail is a lively freshwater fish best known for the male's trailing tail spike, a favourite of the aquarium trade that has also spread far beyond its native range.
Also known as: swordtail
How to tell it apart
It is closely related to the platyfish and can even crossbreed with it, but only the male green swordtail carries the long, sword-shaped lower tail lobe that platyfish always lack.
Appearance
In the wild form the body is olive green with a red or brown stripe along the side and speckles on the dorsal fin and sometimes the tail. Males carry a long, sword-like lower lobe on the tail fin, coloured yellow and edged in black, while females grow larger than males but never develop this sword. Captive breeding has produced many colour varieties, though most still keep the dark central stripe.
Breeding
Females give birth to live young rather than laying eggs. As a pregnancy nears its end, a dark patch appears near the female's anal fin. Males can be told apart from females by a modified anal fin, called a gonopodium, used to fertilise the female. Newborn fry need plants or other cover nearby, or larger fish will eat them.
Did you know?
Escaped or released aquarium fish have built wild, self-sustaining populations on several continents, far outside this species' native Central American rivers.
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