Summary

The speckled mosquito fish, Phalloceros caudimaculatus (also known as the ‘one-spot livebearer’), is a native fish in South America. In March 2002, an introduced population of speckled mosquito fish was discovered at Collaroy, in the Sydney metropolitan area, the first record of this species in eastern Australia. Electrofishing and light-trap surveys were conducted at the site, and dip-netting and visual surveys were conducted in surrounding ponds and streams. The pest fish were found to be widespread and abundant at the Collaroy site, but they were not found elsewhere.

Rotenone (familiar to many as Derris Dust) has been used as a fish poison in Australia for over 40 years. It has often been used in small quantities by scientists to sample structurally complex habitats and areas where other sampling techniques aren’t efficient. It has also been used by fisheries managers to control pest fish, often in an effort to protect endangered species or restore recreational fisheries. Unfortunately, little of this use has been formally documented in the scientific literature.

The process for registering poisons such as rotenone in Australia and gaining approval for their use in controlling pest fish is cumbersome. This is discussed in the context of an attempt to eradicate the speckled mosquito fish at Collaroy, NSW. Rotenone was applied by hand, by spraying and from a small boat. Many pest fish were killed, but complete eradication was not achieved. Rotenone appears to have limited application for the eradication of small fish from deep pools that have dense aquatic vegetation around their edges, unless the pools are drained completely and pest aquatic plant species are removed prior to treatment.