The infection that hit kanakana in southern waterways last year appears to have returned.

Last September dead kanakana, or lamprey, were found in the Mataura River with red lesions.

The Aeromonas salmonicida bacterium was identified in samples, common in fish worldwide but never before seen in New Zealand.

In October, one trout at the Otago Fish and Game Macraes hatchery was also found to have the infection,

Affected fish develop lesions and ulcers on the skin, leading to internal bleeding in muscles and organs, and in some cases death.

Primary Industries Ministry (formerly MAF) response manager Simon McDonald said the ministry's Animal Health Laboratory was examining samples from two affected kanakana found in the Mataura River by a fisherman last month.

Work to fully identify the bacteria strain last year was put on hold when the upstream migration ended and no more specimens were available for testing, he said. “We investigated whether this condition was due to an infectious agent, like a bacterium or virus . . . and if so what its impacts might be - for example on customary fishing, on other species and on aquaculture,” Mr McDonald said.

While they found the aeromonas bacteria in the samples they were not able to determine that it was the cause of the kanakana deaths, or whether other factors such as environmental conditions were involved, he said.

A ministry team would collect samples to try to identify what was affecting the Southland kanakana this season.

Southland Fish and Game senior fish and game officer Zane Moss said they were optimistic the bacteria would not affect trout fisheries as there was no evidence it had affected trout in Southland last year.

It had not been confirmed but he believed kanakana with similar symptoms had been found in the Waikawa River a couple of weeks ago. The ministry had not received samples from the Waikawa River to date.

It was unknown which strain of the bacteria the kanakana had, with one more likely to affect farmed salmonids (trout and salmon). Wild populations were more robust, he said.

If people were worried about fish that looked unwell they should contact Fish and Game or the ministry.

People who found kanakana with unusual red skin markings were asked to note the location and how many were affected, and call the MPI on 0800 80 99 66.

- © Fairfax NZ News

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