Tench compete for food with trout and salmon.
Fish and Game and Department of Conservation officers may drain three Christchurch ponds after the illegal release of a carnivorous sports fish.
Fish and Game regional manager for North Canterbury Ross Millichamp said tench, a fish that competes for food with trout, salmon and native fish, had been
released within Christchurch city limits three times in the past eight months.
Fish and Game and the department were considering options including draining the ponds, chemical control, netting and closing the ponds to fishing.
"We will prosecute anybody found responsible," Mr Millichamp said.
Department spokeswoman Helen McCaughan said the tench had been released without permission into ponds across Christchurch, including a new city council reserve development at Ferrymead.
She said landowners at the other two sites had asked that the restricted access locations not be made public.
Tench, which are native to Europe, were first introduced to New Zealand in 1867 as a coarse fish for sport. They fight strongly and can grow to more than 3kg.
Coloured olive, often with a gold tinge, tench have bright orange eyes and are prolific breeders, living in still or slow moving waters and preying on insect larvae, crustaceans and molluscs.
Ms McCaughan said it appeared the fish were being released intentionally. All fish found by the department and Fish and Game were about the same size.
"We have no idea who would be releasing them," she said. "Obviously someone who has an interest in tench, either because they like to fish for them or just because they think they're an attractive fish."
She said there were a number of tench populations in Christchurch where people could fish legally.
Mr Millichamp said people who wanted to move or release fish had to follow a formal Fish and Game process.
"Fish and Game or DoC are the only agencies allowed to move or release fish into the environment," he said. The agencies would welcome information from the public about people seen putting fish into waterways.
- NZPA
