Perch plague put'n'take ponds

Sun perch released illegally into Danish put'n'take lakes could mean the downfall of indigenous trout

A discovery of several thousand sun perch in a lake near the Jutland town of Silkeborg is shedding light on lake eco-systems. Scientists had believed for a long time that Danish lakes were too cold for the North American freshwater fish to breed.

A number of perch has been released into the private put'n'take trout lake years ago, and a recent swipe of a net caught several generations of the fish, proving that the breed can indeed survive and spawn in local lakes.

'I known of selected lakes where sun fish are released and have been able to spawn,' said Mogens Lange of the Aquacentre in Silkeborg. 'It's a catastrophe for trout stocks because perch live on the fry and eggs of the other fish. Every time a perch eats an egg, it squeezes out the Danish fish, and we're worried that it will supersede indigenous fish.'

Put'n'take lake owners have been importing the fish for decades. They were brought in to eat carp lice, a parasitic crustacean which has taken to lake trout.

'The lice survive on the blood and flesh of the trout. When they attach themselves to the fish, the fish lose the desire to bite, meaning they are never caught in the put'n'take lakes, and owners lose money,' said Lange. 'By releasing the sun perch into the lakes, the problem is avoided.'

Lange said it is only now that people have discovered the sun perch can breed and are still unsure of what the consequences will be. He pointed to the catastrophic result of releasing killing snails and hogweed into the environment without strict monitoring. The species quickly wiped out indigenous varieties.

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