TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

Transmission of Furunculosis and Enteric Redmouth by
Means of Fluidized Sand Biofilters
G. L. Bullock, Research Microbiologist, Conservation Fund’s
Freshwater Institute, Shepherdstown, WV.
W. B. Schill, Chemist, USGS, National Fish Health Research Laboratory, Kearneysville,
WV.
Abstract
E. Burchard, Research Associate, Conservation Fund’s Freshwater Institute,
Shepherdstown, WV.
Two bacterial pathogens of salmonids, Aeromonas salmonicida cause of furunculosis, or
Yersinia ruckeri, cause of enteric redmouth, were added for five days to the pump inlet of
a recirculating culture system, without fish, in order to determine if the pathogens would
become established in the fluidized sand biofilters and infect newly added salmonids.
Before addition of the cultures, the biofilters were sampled and found free of both
pathogens. However, both pathogens could be cultured from biofilters after cultures were
added. When culture addition was completed the recycle system, except for biofilters,
was disinfected with 200 ppm chlorine for two hours. Biofilters were continuously
washed for 24 hr with springwater. Rainbow trout (Oncorhynchus mykiss) to detect Y.
ruckeri, or Arctic char (salvelinus alpinus), to detect A. salmonicida, were then added to
the recycle system. Three weeks after addition of rainbow trout, Y. ruckeri was cultured
from feces and trout began dying from enteric redmouth. Two weeks after char were
added clinical furunculosis was diagnosed and A. salmonicida was isolated from
survivors. After enteric redmouth or furunculosis had been transmitted from biofilters,
fish were removed, and the entire system was treated with 10 ppm chloramine-T in an
attempt to remove the pathogens from the biofilters. The system was then restocked with
either char or rainbow trout. After six weeks neither furunculosis nor redmouth occurred
and neither pathogen could be isolated from salmonids or bilofilters. Biofilter
transmission experiments were repeated with both pathogens, and an additional
procedure for disease transmission tested.
Introduction
Infectious diseases are a major cause of mortality in intensive aquaculture. Precautions
such as use of specific pathogen frees stocks of fish, clean water supply, proper
sanitation, and biosecurity are necessary to reduce disease outbreaks. In a recirculating
culture system another possible source of pathogens is biofilters. If a disease outbreak
occurs there is a possibility the pathogen may become established in biofilters and infect
newly stocked fish. Several reviews have described disease problems in recirculating
1