Gambusia (Gambusia affinis)

In their native waters surrounding the Gulf of Mexico, gambusia are renowned for their ability to eat large numbers of mosquito larvae and are also commonly called mosquitofish. This ability led to their introduction into many countries where mosquitoes were perceived to be a problem, resulting in gambusia possibly being the most widespread fish in the world today. Their arrival in New Zealand is not well documented, but probably occurred in the 1930s.

Compared to some of the other Poeciliidae, gambusia are rather drab, although the darker margins on their scales give them an attractive crosshatch pattern. They can be distinguished from other fish in New Zealand by the rounded caudal fin and single dorsal fin. However, it is difficult to distinguish gambusia from small sailfin molly and guppy. In gambusia, the dorsal fin is high and rounded, whereas on sailfin molly the base of the dorsal fin is quite long. Gambusia can be distinguished from guppies by the position of the dorsal fin in relation to the anal fin. In gambusia, the dorsal fin begins behind the anal fin, whereas on guppies the dorsal fin is opposite the anal fin.

Gambusia are small fish: females may reach 60 mm in length, but males are usually less than 40 mm. They make up for their size by being an extremely aggressive species and attacks on some native species have been well documented. Gambusia are now widespread in the northern part of the North Island, and they are spreading to parts of the lower North Island as well. Recently, several populations were discovered near Nelson - but hopefully all of these have now been eradicated. Gambusia are most definitely not a desirable addition to the fauna and their spread should be prevented.

[This page last modified September 2005]