Farming contributes to spread of invasive mosquitofish, Auckland researchers find

Friday, 17 February 2017

Mosquitofish are native to parts of the United States, but were introduced to New Zealand to control mosquito populations.

Farming is contributing to the spread of a pest fish in North Island waterways, a new study shows.

Scientists at the University of Auckland's School of Environment looked at mosquitofish populations, alongside agricultural land use, in 31 streams.

The research found high numbers of mosquitofish - which are aggressive, predatory fish that have been responsible for the decline of native fish and frog species in some countries - when conditions usually associated with farming were also present.

Those included low water flow, higher nutrient levels and higher water temperature.

* Farmer greed is not the cause of water woes

* Sustainable farming systems will lead to cleaner rivers

* Researcher probes deep secrets to boost fish stocks**

Abundant mosquitofish populations were also found where higher levels of aquatic plants called macrophytes, which are associated with more intensive land use, were present in the water.

Mosquitofish are between 4-7cm long and feed on mosquito larvae, as well as beetles and mites.

They were widely introduced into waterways in the early 20th Century as they were thought to be an effective mosquito control agent. However, they have not proved to be effective in limiting the insects.

'Overall our findings suggest that in addition to reducing water quality, agricultural land use may be improving conditions for these invasive fish by altering the streams to suit them,' Finn Lee, the lead author of the study, said.

'Habitat conditions we commonly associate with agricultural land use make it easier for mosquito fish to invade waterways and thrive, so water degradation is a key factor in helping mosquitofish spread.'

Associate Professor Kevin Simon said the research would help scientists to investigate farming techniques that could better control the numbers and spread of mosquitofish.

'Now that we are getting a better idea of how agricultural land use and mosquitofish populations might be linked, we can look at land management techniques that will improve water and habitat quality to better control mosquitofish populations.'