As with the other Oomycetes, the Aphanomyces
hyphae can be better visualized on histopathology
sections using GMS or PAS. Unlike the
saprolegniasis, an intense granulomatous reaction
is associated with this fungus and there is
sometimes granuloma formation. Multinucleated
giant cells may not be always present, and
this appears to depend on the species of the
fish. 62'63 There is marked myofibrillar damage
and associated hemorrhage. In mature lesions,
the degenerate fungal hyphae are often within
granulomas consisting primarily of macrophages
and epithelioid cells. 47 Experimentally, lower
temperatures reduced the inflammatory process.
59