Atypical bacterial gill disease: a new form of bacterial gill disease affecting intensively reared salmonids

• Published in: Journal of Fish Diseases
• Main Authors: Ostland, V. E., Byrne, P. J., Lumsden, J. S., MacPhee, D. D., Derksen, J. A., Haulena, M., Skar, K., Myhr, E., Ferguson, H. W.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1999
• Subjects: Canada; Norway; Atlantic salmon
• Online Access: http://dx.doi.org/10.1046/j.1365-2761.1999.00181.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-2761.1999.00181.x; https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2761.1999.00181.x

An unusual form of bacterial gill disease (BGD) was identified which affected five species of cultured salmonids from Canada (i.e. rainbow trout, chinook salmon and Atlantic salmon), Norway (i.e. brown trout) and Chile (i.e. coho salmon). All outbreaks occurred at low water temperatures (< 10 °C) and with clinical presentations distinct from classical BGD, which is caused by Flavobacterium branchiophilum . In contrast to classical BGD, fish did not show marked respiratory distress with flaring of the opercula, the animals did not orientate at the surface of the water column near inflow water or at the margins of the tanks, and the feed response of the fish was varied. While mortality was increased, it was not precipitous as in classical BGD. Eight outbreaks were examined in greater detail using histopathology, scanning electron microscopy, bacteriology and immunohistochemistry. Large numbers of small bacterial rods were seen adhering to the lamellar epithelium of affected gills from all outbreaks. Histologically, the lamellar epithelium appeared swollen, often with evidence of single cell degeneration and exfoliation. In more severe instances, the formation of lamellar synechiae was seen, usually associated with sequestration of bacteria between fused lamellae. By contrast with typical BGD, overt epithelial hyperplasia, lamellar fusion and filamental clubbing were not common sequelae to infection; instead, the end result was shortened and somewhat stubby lamellae covered with swollen epithelial cells. The predominant bacterium recovered from affected gills was a small, Gram‐negative, motile, fluorescent pigment‐producing rod that shared phenotypic characteristics with Pseudomonas fluorescens . Polyclonal antisera prepared against three representative isolates indicated a weak antigenic similarity among them. Immunohistochemistry corroborated this finding, in that the antisera reacted strongly with gill sections containing the homologous bacteria, but not against morphologically similar bacteria in ...