Epizootic ulcerative syndrome caused by Aphanomyces invadans in captive bullseye snakehead Channa marulius collected from south Florida, USA

Abstract

Epizootic ulcerative syndrome (EUS) caused by the oomycete Aphanomyces invadans is an invasive, opportunistic disease of both freshwater and estuarine fishes. Originally documented as the cause of mycotic granulomatosis of ornamental fishes in Japan and as the cause of EUS of fishes in southeast Asia and Australia, this pathogen is also present in estuaries and freshwater bodies of the Atlantic and gulf coasts of the USA. We describe a mass mortality event of 343 captive juvenile bullseye snakehead Channa marulius collected from freshwater canals in Miami-Dade County, Florida. Clinical signs appeared within the first 2 d of captivity and included petechiae, ulceration, erratic swimming, and inappetence. Histological examination revealed hyphae invading from the skin lesions deep into the musculature and internal organs. Species identification was confirmed using a species-specific PCR assay. Despite therapeutic attempts, 100% mortality occurred. This represents the first documented case of EUS in bullseye snakehead fish collected from waters in the USA. Future investigation of the distribution and prevalence of A. invadans within the bullseye snakehead range in south Florida may give insight into this pathogen-host system. KEY WORDS: Epizootic ulcerative syndrome · Mycotic dermatitis · Mycotic myositis · Non-native fish species · Oomycete · Water mold Resale or republication not permitted without written consent of the publisherDis Aquat Org 88: [169][170][171][172][173][174][175] 2010 are almost exclusively reported from wild-caught fishes (Dykstra et al. 1989, Noga et al. 1991, Blazer et al. 1999. In 1984, the first confirmed cases of EUS in the USA were documented in Atlantic menhaden Brevoortia tyrannus from estuaries of North Carolina (Dykstra et al. 1986). Since 1984, fish exhibiting ulcerative lesions typical of A. invadans infection have been documented in estuaries and rivers of the Atlantic coast from Long Island to Florida (Blazer et al. 2002, Hawke et al. 2003. Most recently, Sosa et al. (2007b) documented A. invadans infection of 21 species of fish collected from estuarine and freshwater systems throughout Florida.Aphanomyces invadans is an opportunistic pathogen that can be highly invasive, gaining entry through surface wounds or an otherwise compromised mucus barrier. In challenge studies, mortality associated with EUS is high and may approach 100% (Kiryu et al. 2003, Johnson et al. 2004, Sosa et al. 2007a). Cases of EUS in snakeheads (Family: Channidae) have previously been documented in southeast Asia (Lilley et al. 1998). Treatment is only applicable to captive animals and often has limited success because some antifungal agents (e.g. malachite green and formalin) are toxic to the fish or do not penetrate the body deeply enough to reach the pathogen, which invades deep into the muscle tissue and internal organs (Campbell et al. 2001).Snakeheads are a group of freshwater, air-breathing fish, consisting of approximately 30 species in 2 genera, Channa and Parachanna. The former is ...

Field observations of fish species susceptible to epizootic ulcerative syndrome in the Zambezi River basin in Sesheke District of Zambia

“…The samples preserved in formalin were then processed and analyzed by histological processing, i.e., dehydration through ascending alcohol grades, clearing in xylene, impregnation with wax, cutting at about 5 μm, mounting on a glass slide, complete de-waxing, and staining in haematoxylin and eosin (Oidtmann et al 2008;Saylor et al 2010). The tissue sections were then examined under a light microscope.…”

“…The disease is caused by Aphanomyces invadans (Saprolegniaceae), a peronosporomycete fungus, and often affects stressed and injured fish in the wild (Oidtmann et al 2008). It is characterized by body lesions, skin ulcerations, and bloody patches on the body, followed by heavy mortalities (Saylor et al 2010). This disease scenario was observed in Sesheke District of Zambia on the river banks of the fourth largest river in Africa.…”

Scientific Opinion on Epizootic Ulcerative Syndrome

“…A variety of factors leading to skin damage appear to predispose fish to infection, including physical trauma (Kiryu et al, 2003), exposure to water of low pH (Bondad-Reantaso et al, 1992;Callinan et al, 1996;Fairweather, 1999;Choongo et al, 2009), skin lesions as a result of intra-species aggression (biting) (Fairweather, 1999;Saylor et al, 2010), or infections of fish with dinoflagellates (Dykstra and Kane, 2000). Challenge experiments with strains of A. invadans from Southeast Asia have suggested that zoospores attach to the dermis and not the epidermis before invasion .…”

Emergence of the Epizootic Ulcerative Syndrome in Pond Reared Carp Fish (Cyprinids) and It's Control Measure in Chitwan, Central Nepal

“…EUS has been reported in more than 94 fish species spread across 26 countries (Lilley et al, 1998;Andrew et al 2008;Saylor et al 2010;Boys et al 2012;Huchzermeyer et al 2012;Oidtmann, 2012). EUS was spread across Asia from Japan and Australia to Pakistan in 1996 and to southern Africa in 2006 (Baldock et al, 2005).…”