28th ANNUAL EASTERN FISH HEALTH WORKSHOP
April 21-25, 2003
An
Experimental Infection Model Of Fungal Disease In Rainbow Trout, Oncorhorhyncus
mykiss.
Charles
Gieseker1, Stanley Serfling1, Jeffery
Rach2, Thresea Schreier2, Renate Reimschuessel1
1U.S. Food and
Drug Administration Center for Veterinary Medicine,
Office of Research, 8401 Muirkirk
Road, Laurel, MD 20708;
Environmental
Sciences Center, U. S. Geological Survey, 2630 Fanta Reed Road, La Crosse,
Wisconsin 54603
The
Food and Drug Administration (FDA), in collaboration with the United States
Geological Survey, has been developing a model to facilitate controlled studies
that define the efficacy of formalin to treat fungal infections on fish. Abrasion and temperature stress in
combination with bath exposure were used to induce dermal fungal disease in
rainbow trout (Oncorhynchus mykiss). A published abrasion method, that floundered
the fish on sandpaper, was compared to a focal manual abrasion to induce an
infection by the water mold, Saprolegnia
parasitica (ATCC 22284), a common fungal pathogen of fish. The floundering abrasion technique resulted
in inconsistencies in the extent and severity of disease, while the manual
abrasion provided lesions of consistent severity. The fish were exposed to the fungus via a bath immersion from
four to 15 hours. Temperature stress
was performed concomitantly with the fungal exposure by simply moving the trout
from an acclimation tank (15±2șC) to an exposure tank (22±2șC). The effect of holding fish at different
temperatures following the bath treatment was evaluated. A 100% infection rate was found for all
exposure times 24 hours post-exposure with considerably better survival with
the short exposures. This infection
model is currently being used in cooperation with the U.S. Geological Survey to
provide efficacy data for a public master file (PMF 5693) to support the
enhancement of the approval of formalin to control mortality associated with
fungal infections in all fish species.
