Dermocystidium sp. (Mesomycetozoea: Dermocystidiaceae) primary ocular infection in a koi carp (Cyprinus carpio var. koi)

Dermocystidium spp. (Mesomycetozoea: Dermocystidiaceae) comprises several species able to infect a wide range of freshwater but also marine fish.The lesions caused by Dermocystidium spp. in fish are chronic and characterized by visible cysts or nodules on skin and fins, but severe gills and systemic infections causing mortality have been described in several species. The present study described a primary ocular infection by Dermocystidium sp. in a koi carp (Cyprinus carpio var. koi). The fish presented an evident subconjunctival whitish exophytic tissue, surrounded by reddish edges, that protruded over both ocular bulbs. The fish was necropsied, and tissues (eyes, gills, heart, liver, spleen, stomach, intestine, brain) were fixed in 10% buffered formalin for histology. according to the spore size range (5.53–12.90 µm), the morphology of spores and the infected tissue, the present case appears to be consistent with an infection by Dermocystidium koi.Considering the economic value of koi carps and the possible direct transmission of the infection in optimal temperature condition, Dermocystidium spp. infection should be considered as an important disease also in ornamental species.