Infectivity and pathogenicity of the oomycete Aphanomyces invadans in Atlantic menhaden Brevoortia tyrannus

Diseases of Aquatic Organisms

Vicki S. Blazer¹  Howard Kator¹  Yasunari Kiryu¹  Jeffrey D. Shields¹  Wolfgang K. Vogelbein¹ 

关键词: Dose response;    Epizootic ulcerative syndrome;    LD50;    Lesions;    Mortality;    Secondary zoospores;    Tissue repair;    Ulcerative mycosis;   

DOI  :  10.3354/dao054135

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: Atlantic menhaden Brevoortia tyrannus develop characteristic skin ulcers in response to infection by the oomycete Aphanomyces invadans. To investigate pathogenicity, we conducted a dose response study. Juvenilemenhaden were inoculated subcutaneously with 0, 1, 5, 10, 100, and 500 secondary zoospores per fish and monitored for 37 d post-injection (p.i.). Survival rates declined with increasing zoospore dose, with significantly different survivorship curves forthe different doses. Moribund and dead fish exhibited characteristic ulcerous lesions at the injection site starting at 13 d p.i. None of the sham-injected control fish (0 zoospore treatment) died. The LD₅₀ (lethal dose killing 50% of exposedmenhaden) for inoculated fish was estimated at 9.7 zoospores; however, some fish receiving an estimated single zoospore developed infections that resulted in death. Menhaden were also challenged by aqueous exposure and confirmed that A. invadanswas highly pathogenic by this more environmentally realistic route. Fish that were acclimated to culture conditions for 30 d, and presumably free of skin damage, then aqueously exposed to 100 zoospores ml^-1, exhibited 14% lesion prevalence with11% mortality. Net-handled fish that were similarly infected had a significantly higher lesion prevalence (64%) and mortality (64%). Control fish developed no lesions and did not die. Scanning electron microscopy of fish skin indicated that zoosporesadhered to intact epidermis, germinated and penetrated the epithelium with a germ tube. Our results indicate that A. invadans is a primary pathogen of menhaden and is able to cause disease at very low zoospore concentrations.

【 授权许可】

Unknown