Dermocystidium is a genus of cyst-forming, eukaryotic fish parasites,^[2] the causative agents of dermocystidiosis.

The genus Dermocystidium was described in 1907. It was previously thought to be a genus of fungal parasites, related to the Thraustochytrida and Labyrinthulida (both those groups are now considered to be stramenopiles rather than fungi). Other biologists considered it to be a sporozoan protist.

It was subsequently identified as one of a group of fish parasites (the "DRIP clade") of previously uncertain affiliation, which were later identified as nonanimal, nonfungal opisthokonts,^[3] and renamed as Ichthyosporea, and after expansion as Mesomycetozoa. Parasites of crustacea (Dermocystidium daphniae) and molluscs (Dermocystidium marinum) placed in this genus have been found to be likely a bacterium and an alveolate, respectively: Sayre, Gherna and Wergin (1983) concluded that Dermocystidium daphniae was likely identical to Pasteuria ramosa Metchnikoff, 1888,^[4] while D. marinum has been reclassified as Perkinsus marinus.^[5]

The frog parasite Dermocystidium ranae has recently been segregated as Amphibiocystidium ranae.^[6]

• Dermocystidium aegyptiacus El-Mansy 2008
• Dermocystidium anguillae Spangenberg 1975— a gill parasite of eels
• Dermocystidium branchialis Léger 1914^[7] — a gill parasite of salmonids
• Dermocystidium cochliopodii Valkanov 1967^[7]
• Dermocystidium cyprini Červinka & Lom 1974^[7] — a gill parasite of carp^[8]
• Dermocystidium erschowii Garkavi, Denisov & Afanas'ev 1980— a skin parasite of carp
• Dermocystidium fennicum Pekkarinen et al. 2003— a skin parasite of perch ^[9]
• Dermocystidium gasterostei Elkan 1962^[7] — a parasite of sticklebacks^[10]
• Dermocystidium granulosum Sterba & Naumann 1970^[7]
• Dermocystidium guyenotii Thélin 1955^[7]
• Dermocystidium koi Hoshina & Sahara 1950^[7] — a skin parasite of carp
• Dermocystidium kwangtungensis ^[11]
• Dermocystidium macrophagi van de Moer, Manier & Bouix 1988
• Dermocystidium nemachili ^[7]
• Dermocystidium penneri (Jay & Pohley 1981) Borteiro et al. 2018
• Dermocystidium percae Reichenbach-Klinke 1950^[7] — a skin parasite of perch ^[9]
• Dermocystidium pusulum (Pérez 1907) Pérez 1908^[7]
• Dermocystidium salmonis ^[7] — a gill parasite of salmon
• Dermocystidium sinensis ^[11]
• Dermocystidium sinipercae^[12] — a parasite of Chinese perch
• Dermocystidium vejdovskyi Jírovec 1939^[7] — a parasite of pike