Folia Parasitologica 46[3] 179-184 (1999)

Transmission of the monogenean Gyrodactylus salaris

Arnulf Soleng¹, Peder A. Jansen², Tor A. Bakke¹

¹ Zoological Museum, University of Oslo, Sars gate 1, N-0562 Oslo, Norway

² Department of Zoology, Norwegian University of Science and Technology, N-7034 Trondheim, Norway

The present study is focusing on the transmission of the monogenean ectoparasite Gyrodactylus salaris Malmberg, 1957, a major pathogen on natural populations of Norwegian Atlantic salmon, Salmo salar L. In laboratory experiments the transmission rate of G. salaris after direct host to host contact was positively correlated with water temperature (1.2, 4.7 and 12.2°C). The transmission of detached G. salaris in the planktonic drift was studied in field experiments where salmon parr were individually isolated for 24 hours in small wire mesh cages suspended in the water column. Ten out of 157 salmon parr (prevalence 6.4%, mean intensity 1.0) contracted G. salaris infections after this exposure. Furthermore, 200 uninfected marked salmon parr were released into the same area of the river. After 24 and 48 hours, respectively 18 and 19 marked parr were caught by electro-fishing. The prevalence of G. salaris was 44.4% (mean intensity 1.9) after 24 hours, rising to 57.9% (mean intensity 2.3) after 48 hours. Gyrodactylids have no specific transmission stage or swimming ability, but detached G. salaris drifting in the water column were found to infect salmon parr. However, the transmission rate was markedly higher to free-living fish, suggesting that transmission routes such as indirect transmission from the substrate or direct contact transmission from infected live and/or dead fish, are relatively more important than transmission by drifting detached parasites.

Keywords: Gyrodactylus salaris, Monogenea, temperature, transmission, Salmo salar

Received: December 1, 1998; Accepted: March 23, 1999; Published: September 1, 1999  Show citation