ScienceDaily (Apr. 24, 2009) reports on a European study of proliferative kidney disease (PKD), a cause of major stock losses on fish farms in England. The study was funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

PKD has devastated the UK’s fish farming industry. Fish were observed to carry and spread PKD in the new study. The new discovery will give researchers the key to develop better ways to deal with PKD. The research was conducted by Professor Sandra Adams and Dr David Morris at the University of Stirling’s Institute of Aquaculture and is reported in the latest edition of BBSRC Business magazine.

PKD devastates fish, causing inflammation of the kidneys resulting in death of newly introduced fish on infected farms – the estimated annual cost to the UK trout industry alone is £2.5M. Little has been understood about how PKD spread occurs until now. According to the report in Science Daily:

Researchers had previously discovered the parasite in freshwater bryozoa, which are colony-forming animals that feed on microscopic algae. Some species of the bryozoa resemble plants and can fragment to form new colonies that could spread the disease.

Prof Adams and Dr Morris have now shown for the first time that native fish can also spread PKD, rather than being simply dead-end hosts.

Prof Adams said: "We were able to show that the parasite that causes deadly PKD in fish could cycle between brown trout and bryozoa indefinitely".

Now scientists have a working model of the life cycle of the parasite, making it possible to develop ways to control PKD. For instance farmed rainbow trout have a "severe immune response" to PKD, which can kill the fish, but brown trout do not.

But, as Prof Adams explains:

"In their native environment in the USA, rainbow trout are more resilient to PKD. This suggests that there are at least two strains of this particular parasite: one adapted to North American species and one adapted to European species. Therefore, rainbow trout introduced to European waters are likely to be infected with the wrong strain of the parasite, which explains the severe immune response and subsequent disease".

There have been recent reports of PKD affecting wild salmon in Europe and North America, indicating that it is an emerging threat to these ecologically and economically important fisheries.

Prof Janet Allen, Director of Research at BBSRC, said:

"Farmed fish are a crucial part of the food chain, providing nutritious and affordable food for many people. They are also economically important in many areas. When a disease such as this threatens fish farming it is vital that we provide the science to understand the problem and its source and deliver the research to tackle it."

Hawaii is involved in some fish farming but the incidence of PKD has not been reported. However a great deal of fish farmed elsewhere is sold here.