Bacterial gill disease of salmonids; relationship between the severity of gill lesions and bacterial recovery

Abstract

Thirteen naturally occurring outbreaks of bacterial gill disease (BGD) affecting commercially reared salmonids in Ontario (mainly rainbow trout, Oncorhynchus mykiss ) were examined histologically and bacteriologically. Bacteria recovered from healthy and diseased gills were enumerated, and the severity of the lesions from each outbreak was graded based on the histopathological changes. A positive correlation was found between the presence of gill lesions and the number of bacteria recovered from disease gills. The mean of the total yellow pigmented bacteria (YPB) recovered from healthy gills was 0.73 x 10 super(3) CFU/g with the YPB accounting for roughly 15% of the total recovered. The mean of the total YPB recovered from gills from 13 outbreaks was 12.71 x 10 super(5) CFU/g; the YPB accounted for approximately equals 35% of the total bacteria recovered.