"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

September 28, 2010

September 28 - Aphanomyces invadans

Aphanomyces invadans is a highly pathogenic oomycete fungi which infects the Atlantic menhaden Brevoortia tyrannus and many other species of fish from around the world. This water mould has been implicated in massive fish kills in North Carolina, resulting in hundreds of thousands of dead fish. On average, an infection resulting from less than 10 zoospores (the infective stage of this fungi) is enough to kill a fish, and even infection by just a single zoospore can result in ulcerous lesions that can lead to mortality. Fish infected with the fungi develops ulcerous lesions which ultimately lead to extensive tissue necrosis. This fungus develops extremely quicky, doubling its hyphal mass every ten days, and it is also highly invasive, extending its hyphae into various tissues including the liver, kidneys and spinal cord of the fish host. Interestingly, A. invadans outbreaks are associated with high rainfall. This is likely due to the fact that this water mould has a low salinity tolerance and will not grow in higher salinity waters.

Kiryu et al. (2003) Infectivity and pathogenicity of the oomycete Aphanomyces invadans in Atlantic menhaden Brevoortia tryannus. Diseases of Aquatic Organisms 54: 135-146.

(Photo from this paper.)

Contributed by Tommy Leung.


  1. I just discovered this blog, and I'm working my way through it sequentially. This is great, because I don't have to wait for the next entry. I'm having loads of fun.
    I do want to point out that oomycetes are not fungi, not even sort of. I think this point was made in the entry for _Phytophthora_, so I'm a little surprised by the repeated references to _Aphanomyces_ as a fungus. The Oomycota are as different from Fungi as are Apicomplexan or Dinoflagellates, 2 other clades well represented on this blog.

    Thanks for the entertainment!

  2. You're absolutely right, John. That one slipped by. I'll leave this here so folks can see the discussion, but yes, as was pointed out in the Phytophthora post, the oomycetes used to be grouped with fungi, but we now know they're on a completely different branch of the tree!