Ulcerative dermatitis consistent with thraustochytrid infection in 3 captive north pacific big eye octopuses (Octopus californicus).

Ulcerative dermatitis is common in captive cephalopods and often results from trauma to their delicate epidermis with subsequent infection by opportunistic pathogens. We report 3 cases of fatal ulcerative dermatitis caused by a rare pathogen in a cohort of captive, adult, north Pacific big eye octopuses (Octopus californicus). Abundant, 5 to 8 µm diameter, roughly spherical organisms, often located in pairs or clusters, were infiltrating the ulcers in all 3 cases. Ultrastructurally, the organisms possessed multilamellated to scaley cell walls and were surrounded by empty, irregularly ovoid, 1 μm diameter, membrane-bound structures consistent with an ectoplasmic net. These features are consistent with thraustochytrid, a marine saprophyte. Previous reports of pathogenic thraustochytrid infections in cephalopods are rare, suggesting this is an uncommon albeit serious infection in captive cephalopod populations.