Iridovirus infections in farm-reared tropical ornamental fish

A systemic viral infection in both gourami Trichogaster spp. and swordtail Xiphophorus hellerii and an outbreak of lymphocystis in scalare Pterophyllum scalarae and gourami are reported to have occurred in fish reared in ornamental fish farms in Israel. The systemic infection developed in endothelial cells that became hypertrophic and their contents were modified. The presence of such cells in light-microscopically examined stained smears and sections provides an initial indication for this systemic viral infection. Infection in gourami caused hemorrhagic dropsy. Transmission electron microscopic (TEM) images of iridovirus-like particles recovered from gouramies showed them to be 138 to 201 nm from vertex to vertex (v-v); those from swordtails were 170 to 188 nm v-v. TEM images of lymphocystis virions from scalare were 312 to 342 nm v-v and from gourami 292 to 341 nm v-v. Lymphocystis cells from the gourami were joined by a solid hyaline plate, which was lacking in the infection in scalare where the intercellular spaces between the lymphocystis cells consisted of loose connective tissue.