Proliferative kidney disease caused by the myxozoan parasite Tetracapsuloides bryosalmonae is reported for the first time in Iceland. Infections were confirmed in both arctic charr and brown trout but only arctic charr showed clinical signs. The last two decades, populations of arctic charr in several lakes in Iceland have greatly declined. Possible relation of this decline with increasing water temperature has been speculated. It is hypothesized that PKD may play a significant role in this decline. Studies on the distribution of PKD and its effect on wild populations of arctic charr and brown trout in Iceland are presently in progress.

For decades, Proliferative kidney disease (PKD) has been considered one of the most serious diseases of farmed salmonids in Europe and North America, causing mortality up to 90%(Clifton-Hadley et al., 1984; Hedrick et al., 1993). The impact on wild fish populations is however poorly known. The causative agent is a myxozoan species Tetracapsuloides bryosalmonae whose life cycle involves different species of freshwater