Jellyfish back with a vengeance

The jellyfish menace, which killed more than three million salmon and trout in Norway last winter, has returned in force, the Norwegian Food Safety Authority warned yesterday.

The Authority says there have been a number of attacks during the last few days and it is asking salmon companies to be on the alert and keep a record of any attacks. Sightings are higher than this time last year.

The news hit salmon company share prices in Oslo yesterday as investors took fright.

The most dangerous variety is the perles normanets, otherwise known as string jellyfish. These travel in large groups several metres long and then split up into small units, making it easier for them to get into the cages. They usually make an appearance when winter approaches.

They proved to be a costly menace for most Norwegian and some Scottish fish farms earlier this year. SalMar was forced to lower its harvest forecast by 5,000 tonnes because of such attacks. In fact almost every company suffered to a greater or lesser degree ten months ago.

The jellyfish attack with poison, leaving the salmon and trout with burns on their skin. They also make the fish stressed and cause other diseases to worsen, says the food safety authority.

This week the Authority has asked companies to strengthen their defences by putting in preventative measures as soon as they can.

It says they should ensure that regular, systematic monitoring of fish welfare in affected cages is important to be able to assess the extent and development of damage.

It also says the capacity for recording and handling dead and damaged fish must be adapted to the size and number of fish in the facility. Fish with a poor prognosis for wound healing must be taken out of the cage and euthanised in a responsible manner to end their suffering.