Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon, Salmo salar L.

M. M. Songe, A. Willems, J. Wiik-Nielsen, E. Thoen, O. Evensen, P. van West, I. Skaar

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Here, we address the morphological changes of eyed eggs of Atlantic salmon, Salmo salar L. infected with Saprolegnia from a commercial hatchery and after experimental infection. Eyed eggs infected with Saprolegnia spp. from 10 Atlantic salmon females were obtained. Egg pathology was investigated by light and scanning electron microscopy. Eggs from six of ten females were infected with S. parasitica, and two females had infections with S. diclina clade IIIA; two Saprolegnia isolates remained unidentified. Light microscopy showed S. diclina infection resulted in the chorion in some areas being completely destroyed, whereas eggs infected with S. parasitica had an apparently intact chorion with hyphae growing within or beneath the chorion. The same contrasting pathology was found in experimentally infected eggs. Scanning electron microscopy revealed that S. parasitica grew on the egg surface and hyphae were found penetrating the chorion of the egg, and re-emerging on the surface away from the infection site. The two Saprolegnia species employ different infection strategies when colonizing salmon eggs. Saprolegnia diclina infection results in chorion destruction, while S. parasitica penetrates intact chorion. We discuss the possibility these infection mechanisms representing a necrotrophic (S. diclina) vs. a facultative biotrophic strategy (S. parasitica).
Original languageEnglish
Pages (from-to)343-352
Number of pages10
JournalJournal of Fish Diseases
Issue number3
Early online date7 Apr 2015
Publication statusPublished - Mar 2016

Bibliographical note


The work has been funded by the European Commission through the EU Marie Curie ITN project SAPRO (238550) (MMS, AW). We would also like to acknowledge support from the BBSRC and the University of Aberdeen (PvW) and Landcatch and AquaGen for providing salmon eggs. Elin Rolen's assistance with sequencing of the strains is highly appreciated.


  • chorion disruption
  • egg infection
  • infection strategies
  • saprolegnia


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