ABSTRACT: Mortality and gill lesions in Atlantic salmon Salmosalar reared in a seawater netpen in British Columbia, Canada, were associated with a dense bloom of diatoms containing predominantly Skeletonema costatum, Thalassiosiraaestivalis and T. rotula. Other diatoms, present as minor components of the bloom, included Thalassionemanitzschioides, Coscinodiscus sp. and Pseudonitzschia sp. Gills of moribund and dead fish exhibited excessive mucus production. Histological examination revealed necrosis of the gill epithelium and edema at the base of secondary lamellae. The edematous spaces contained an inflammatory infiltrate. The mechanism of gill damage was not determined, but was likely due to physical irritation by the algae. None of these diatoms have previously been reported to cause disease in fish.

KEY WORDS: Gill disease . Salmo salar . Skeletonema . Thalassiosira

Published in DAO Vol. 22, No. 1 (1995) on May 4
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1995