October 31, 2006

Fish farms in Norway may spread disease as industry expands

Fish farms in Norway are increasingly being pressed for space as more of such farms proliferate, increasing the danger of disease spreading amongst the fish species, scientists from the Norwegian Institute of Fisheries and Aquaculture Ltd (Fiskeriforskning) said.

In collaboration with the Norwegian College of Fishery Science, Fiskeriforskning has conducted studies on the possibility of the disease spreading amongst salmon, cod and halibut.

While it is not yet known what kind of diseases the new farmed species are susceptible to, scientists know several bacteria and viruses can infect many different fish species, said Senior Scientist Vera Lund.

A tank system especially designed for these studies has been built at Tromso Aquaculture Research Station. Scientist introduced a bacterial or viral disease on one type of fish in a central tank. Infected waste water from the tank was transferred to tanks containing other species to see whether they would be infected.

The system has been tested by transmitting classical vibriosis from salmon to cod Forty to sixty percent mortality was registered in the tanks with cod.

Tests showed that waste water from a tank with halibut with atypical furunculosis transmitted the disease to cod in neighbouring tanks.

The cod also had a more chronic form of the disease than normal.

Since neither cod nor halibut are vaccinated against atypical furunculosis, it is also possible that cod can infect halibut in a nearby farm.

The scientist concluded their studies by sounding off a warning about the urgent need to develop vaccines for new farmed species before the problem reaches serious proportions.