Aphanomyces species associated with red spot disease: an ulcerative disease of estuarine fish from eastern Australia

Abstract

Broad, non-septate, fungal hyphae are a eonstant finding in the neerotising dermatitis lesions and dermal ulcers eharaeteristie of red spot disease. During a one-year period, fungi with hyphae morphologically consistent with those seen in histologieal sections of lesions were recovered from 27 out of 28 lesions on sea mullet, Mugil cephalus L., yellowfin bream, Acanthopagrus australis (Owen), and sand whiting, Sillago ciliata Cuvier, collected from three widely separated river systems in eastern Australia. Cultural and morphological characteristics, including spore formation, of 24 of these isolates were examined. In addition, toleranees to different salinities, growth on different media and growth at different temperatures were studied for three representative isolates, one from eaeh species of fish. These studies suggest that all isolates belonged to a single speeies within the genus Aphanomyces. Their role in the pathogenesis of red spot disease, and their relationship with other Aphanomyces spp. affeeting fish, is diseussed.

Histopathology of Aphanomyces Infection in Dwarf Gourami(Colisa lalia).

“…The absence of multinuclear giant cells in the present lesions was similar to MG in snake head, Channa argus, and sea mullet (Miyazaki and Egusa, 1973c) and RSD in sea mullet (Callinan et al, 1989). In addition, fungi belonging to the genus Aphanomyces were isolated from almost all previous cases (Hatai et al, 1977;Dykstra et al, 1986;Fraser et al, 1992;Roberts et al, 1993) and all of the authors concluded that isolated fungi might act as important etiological agents in the pathogenesis of the cases. Therefore, the present case should be classified into a category of mycotic granulomatous diseases resembling MG, UM, RSD and EUS.…”

Epizootic Ulcerative Syndrome: Information up to 1997.

“…that is normally isolated from the muscle area near the lesions (Egusa, 1992, Fraser et al, 1992Hatai et al, 1994;Roberts et al, 1993). Recently, it has been shown that all Aphanomyces spp.…”

“…This specific pathogenic fungus showed the ability to invade the skin lesions of EUS-infected fish. Isolation of this particular fungus is difficult as it is a slow growing strain and most of the hyphae in the muscle are dead except for the tips that are penetrating deeper into the muscle tissue (Roberts et al, 1993) Pathogenicity of the fungus After success in isolating the slow growing fungus, A. invadans, from EUS-infected fish in various coun tries (Egusa, 1992;Fraser et al, 1992;, pathogenicity studies were conducted. The intramuscular injection of spore suspensions into some susceptible fish species (snakehead, barbs) demonstrated a severe necrotising myogranulomatous condition at the injected site similar to the pathological feature of fish naturally infected with EUS.…”

Molecular Assays for DetectingAphanomyces invadansin Ulcerative Mycotic Fish Lesions

“…This species occurs worldwide and infects both wild and cultured fish, often leading to mass fish mortality (4,9,27,40). It was originally documented as the cause of mycotic granulomatosis of ayu (Plecoglossus altivelis altivelis) in Japan (18) and more recently as the cause of epizootic ulcerative syndrome or red spot of striped snakehead (Channa striata) and striped mullet (Mugil cephalus) from southern Asia and Australia (9,15,21,30,40). These skin diseases (mycotic granulomatosis, epizootic ulcerative syndrome, red spot, and UM) are clinically identical and occur in either freshwater or estuarine fish.…”