Despite the Department of Conservation (Doc) approving the release of grass carp in North Otago, the Otago Conservation Board opposed the decision and still has reservations.
The issued was raised at a meeting at Cromwell on Friday.
Board member Dr John Williams, of Dunedin, said a fish biologist at the University of Otago had told him the carp were susceptible to a fungus that grows on the skin and was particularly severe in juveniles.
He was concerned because ''it is a fungus that has never ever been tested on galaxids''.
The North Otago Irrigation Company received approval from Doc last week to introduce the fish into its Otago and Canterbury canals to control the growth of aquatic weeds.
Company chief executive Robyn Wells told the Otago Daily Times last week that according to the National Institute of Water and Atmospheric Research, establishment of a wild population of the fish was extremely unlikely due to specific spawning and rearing requirements.
Board member Francie Diver said the problem was that once the fish were introduced, people would take them elsewhere.
''Once they're in, they're in and you can't just say `whoops, we made a mistake'.''
Southland Conservation Board member Helen McPhail was also at the meeting and said her board was cautious and would also have opposed the decision.
