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Open Access High Mortality in a Large-scale Zebrafish Colony (Brachydanio rerio Hamilton & Buchanan, 1822) Associated with Lecythophora mutabilis (van Beyma) W. Gams & McGinnis

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Zebrafish (Brachydanio rerio) have become an important model system for studying vertebrate embryonic development and gene function through manipulation of genotype and characterization of resultant phenotypes. An established research zebrafish colony without substantial disease problems for more than 7 years of operation began experiencing appreciable mortalities in November of 1997. Young fish (fry), from five to 24 days after hatching, spontaneously developed elongate strands of organic material protruding from the mouth, operculum, and anal pore, leading workers in the laboratory to describe the infected fish as “bearded.” Unlike typical freshwater fish fungal infections, the skin surface did not have evidence of fungal colonization. The disease was associated with progressive lethargy, reduced feeding, and subsequent mortality. From 10 to 100% of the fry in a given tank were affected. Initial examination indicated that the biofilm around the head of affected fry consisted of bundles of septate fungal hyphae, large numbers of mixed bacterial populations, and protozoans. Environmental samples of air and water in the laboratory were obtained to ascertain the source of the infective agent and to isolate and identify the fungus. A fungus identified as Lecythophora mutabilis was isolated repeatedly from infected fish and water samples from infected fish tanks, and from the main laboratory water supply tanks, but not from laboratory air. Some biofilm beards on fish were found to consist of relatively pure bacterial populations, and beards on occasional fish examined in the later part of the study consisted of hyphae and spores of the oomycete genus Aphanomyces. Lecythophora mutabilis did not invade tissues; however, elimination of the epizootic correlated with reduction in the number of L. mutabilis conidia in the water following modification of the laboratory water system by use of new filtration and sterilization systems. We conclude that the dense hyphal strands of L. mutabilis composing the predominant biofilm type, along with mixed bacteria and protozoa, contributed to the die-off in young fry by occluding the oral cavity and/or gills, leading to starvation and/or asphyxiation.

Document Type: Research Article

Affiliations: 1: Microbiology, Pathology and Parasitology Department, College of Veterinary Medicine, North Carolina State University, Raleigh, North Carolina 27606 2: Division of Comparative Medicine, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 3: Center for Applied Aquaculture, The Oceanic Institute, Waimanalo, Hawaii 96795 4: Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 5: University of Alberta Microfungus Collection and Herbarium, Devonian Botanic Garden, University of Alberta, Edmonton AB T6G 2E1, Alberta, Canada 6: Fungus Testing Laboratory, Pathology Department, University of Texas Health Science Center at San Antonio, San Antonio, Texas 78284 7: Medical Mycology Research Center, School of Medicine, The University of Texas Medical Branch at Galveston, Galveston, Texas 77555

Publication date: 2001-08-01

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  • Comparative Medicine (CM), an international journal of comparative and experimental medicine, is the leading English-language publication in the field and is ranked by the Science Citation Index in the upper third of all scientific journals. The mission of CM is to disseminate high-quality, peer-reviewed information that expands biomedical knowledge and promotes human and animal health through the study of laboratory animal disease, animal models of disease, and basic biologic mechanisms related to disease in people and animals.

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