Experimental Production of Bacterial Gill Disease in Trout by Horizontal Transmission and by Bath Challenge

Abstract

Bacterial gill disease was horizontally transmitted both within and between salmonid species by using good-quality water common to both sick and healthy fish, and by using young and mature animals. Clinical disease was produced within 24 h, and mortality resulted often within 48 h, even in 2-or 3-year-old rainbow trout Oncorhynchus mykiss. Clinical disease was correlated with the appearance of filamentous bacteria on the gill surface. These bacteria were isolated and determined to be morphologically, biochemically, and antigenically related to Flavobacterium branchiophila. Subsequently, they were used to produce bacterial gill disease in fingerling rainbow trout by adding a pure culture of 10 5 organisms/mL of tank water, once again, good water quality conditions were maintained. Attachment of large numbers of bacteria to the gill surface was seen immediately postexposure, followed by clinical disease within 20 h and death by 24 h.

Influence of feeding on the development of bacterial gill disease in rainbow trout Oncorhynchus mykiss

“…Colonization of the gill by filamentous bacteria was thought to be a nonspecific mixed infection secondary to environmental stressors, and not the primary mediator of the disease (Bullock 1972, Snieszko 1981. However, it is now established that a yellow pigmented filamentous bacterium, Flavobacterium branchiophilum (von Graevenitz 1990), is the etiologic agent of BGD (Wakabayashi et al 1980, Farkas 1985, Ferguson et al 1991, Ostland et al 1994, and that the disease can be produced even under good water quality conditions (Ferguson et al 1991). Nevertheless, the inevitable role of environmental factors in the development of the disease remains to be elucidated.…”

“…Isolation of the etiologic agent of BGD (Ferguson et al 1991, Ostland et al 1994) has permitted experimental reproduction of the disease. In this laboratory BGD has been repeatedly and consistently reproduced by 1 h bath exposure of rainbow trout Oncorhynchus mykiss to Flavobacterium branchiophilum (LAB 4a).…”

Development of an enzyme-linked immunosorbent assay (ELISA) to estimate the quantity of Flavobacterium branchiophilum on the gills of rainbow trout Oncorhynchus mykiss

“…F. branchiophilum (LAB 4a) was used for production of antisera, bath exposure of rainbow trout, and for the preparation of samples of known bacterial concentration. The LAB 4a strain of F branchlophilum orlginated in a naturally occurring outbreak of BGD in brook trout Salvelinus fontinalis (Ferguson et al 1991). and was subsequently identified on the basis of morphological, physiological, bioche.mica1 and antigenic properties (Ostland et al 1994).…”

“…Bacterial gill disease (BGD), one of the most common diseases of cultured salmonids in Ontario, Canada (Daoust & Ferguson 1983, Speare & Ferguson 1989, is caused by the Gram-negative filamentous organism Flavobacterium branchiophilum (Kimura et al 1978, Wakabayashi et al 1980, Farkas 1985, Heo et al 1990, Ferguson et al 1991, Ostland et al 1994.…”

“…Recently, BGD was successfully reproduced in healthy rainbow trout Oncorhynchus mykiss fingerlings by bath exposure to Flavobacterium branchiophilum (Ferguson et al 1991). The ability to reliably 'Present address: Maple Leaf Foods, Inc., Shur Gain Division, PO Box 279.…”