**The title, authors, background and project objectives for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**
Mycobacteriosis: A potential threat to Great Lakes fisheries
2 Department of Fisheries and Wildlife and Department of Pathobiology and Diagnostic Investigation
13 Natural Resources Bldg
Michigan State University
East Lansing, MI, 48824-1222
In the State of Michigan, there is increasing concern about the spread of Mycobacterium spp. infections in cattle and wild populations of white-tailed deer, coyotes, raccoons, red fox, black bear, and bobcat (Palmer et al., 2000; Bruning-Fann et al., 2001). Research institutions, state authorities, and federal agencies have joined forces to identify, monitor, and control this naturally occurring infection on land. Unfortunately, the possibility of a similar surge in Mycobacterium spp. infections in Michigan’s aquatic animals has been overlooked.
Mycobacterium infections have been described in over 200 species of aquarium, captive, farmed, feral, and wild fish populations in the United States and worldwide (Hedrick et al., 1987; Hatai et al. 1988; Chinabut et al., 1990; Bruno et al., 1998, Rhodes et al. 2001). Historically, most epizootics of fish mycobacteriosis have been attributed to M. marinum (Shotts and Teska, 1989; Belas et al., 1995). In the last decade, however, natural infections of fish were caused by other Mycobacterium spp such as M. fortuitum, M. chelonae, M. abscessus, M. neoaurum, M. scrofulaceum, M. simiae, and M. poriterae, (Lansdell et al., 1993; Tortoli et al., 1996, Falkinham, 1996). Until recently, emerging Mycobacterium spp., highly pathogenic to fish, continue to surface including M. shottsii and M. triplex (Decostere et al., 2004; Herbst et al., 2001; Rhodes et al., 2001).
In the summer of 2002, Michigan State University-Aquatic Animal Health
Laboratory received samples from largemouth bass (Micropterus salmoides) with
hemorrhagic skin nodules and ulcerations. The sick fish were caught from Sand Lake in
southern Michigan. Histopathological examination revealed extensive granulomatous
inflammation within the dermis and subcutaneous tissues and in the spleens. Acid-fast
rods were detected within the skin lesions and in internal organs (e.g., liver, spleen, and
kidneys). After several weeks of incubation of tissues on Lowenstein bacterial medium at room temperature, a very slowly growing acid-fast organism was isolated. Mycobacterium sp. was isolated and designated as LMBM-Cabl. This is considered the first record of mycobacterial infection in fish residing in the Great Lakes basin.
The objectives of this GLFC-funded study were to:
a) identify the LMBM-Cabl Mycobacterium sp. isolate associated with the lesions in Michigan’s largemouth bass,
b) determine its pathogenicity to susceptible largemouth bass,
c) develop enhanced molecular diagnostic for its detection, and
d) determine its prevalence in mature largemouth bass and important salmonid fish species in the Great Lakes.