DAO 77:191-198 (2007)  -  DOI: https://doi.org/10.3354/dao01846

Severe mortality in wild Atlantic salmon Salmo salar due to proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae (Myxozoa)

Erik Sterud1,6, Torbjørn Forseth2, Ola Ugedal2, Trygve T. Poppe3, Anders Jørgensen1, Torkjell Bruheim4, Hans-Petter Fjeldstad5, Tor Atle Mo1,*

1National Veterinary Institute, PO Box 8156 Dep. 0033 Oslo, Norway
2Norwegian Institute for Nature Research, 7485 Trondheim, Norway
3Norwegian School of Veterinary Science, PO Box 8146 Dep. 0033 Oslo, Norway
4National Veterinary Institute, 7485 Trondheim, Norway
5Sintef, 7465 Trondheim, Norway
6Present address: Standards Norway, PO Box 242, 1326 Lysaker, Norway
*Corresponding author. Email:

ABSTRACT: Extensive mortality in Atlantic salmon fry was reported in the River Åelva from 2002 to 2004. Dead fish were collected in late summer 2006, and live fish were sampled by electrofishing in September the same year. At autopsy and in histological sections, the fish kidneys were found to be pale and considerably enlarged. Proliferative lesions with characteristic PKX cells were seen in a majority of the fish. DNA from kidney samples of diseased fish was subjected to PCR and sequencing, and the amplified sequences matched those of Tetracapsuloides bryosalmonae. We concluded that this myxozoan transmitted from bryozoans was the main cause of the observed mortality in salmon fry in 2006. Results from quantitative electrofishing in 2005 and 2006, combined with the observed fry mortality from 2002 to 2004, show that the smolt production in the river is severely reduced and that T. bryosalmonae is the most likely explanation for this decline. The present study is the first to report a considerable negative population effect in wild Atlantic salmon due to proliferative kidney disease (PKD). It also represents the northernmost PKD outbreak in wild fish. The river is regulated for hydroelectric power purposes, causing reduced water flow and elevated summer temperatures, and the present PKD outbreak may serve as an example of increased disease vulnerability of northern fish populations in a warmer climate.


KEY WORDS: Myxozoa · Proliferative kidney disease · PKD · Tetracapsuloides bryosalmonae ·Malacosporea · Salmonid


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Cite this article as: Sterud E, Forseth T, Ugedal O, Poppe TT and others (2007) Severe mortality in wild Atlantic salmon Salmo salar due to proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae (Myxozoa). Dis Aquat Org 77:191-198. https://doi.org/10.3354/dao01846

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