Isolation of an Iridovirus from Farm-Raised Gouramis (Trichogaster Trichopterus) with Fatal Disease

Abstract

Gouramis (Trichogaster trichopterus) are a popular freshwater tropical fish raised extensively in Florida for the ornamental fish trade. Between June 1991 and February 1992, 2 separate groups of farm-raised gouramis experienced death rates of approximately 0.5-10%/day for approximately 2 weeks. About 30 diseased fish from each group were presented to the Veterinary Diagnostic Laboratory at Kissimmee, Florida. About 20 fish from each shipment survived transport and were placed in aerated aquaria and observed for 7 days; dead fish were discarded. Most infected individuals appeared clinically healthy and maintained good appetites. However, adults developed patches of hyperpigmentation and lethargy 24-96 hours prior to death, and about 30% of affected juveniles and adults exhibited abdominal distention. Approximately 70% of the fish died during the observation period, and the remaining moribund fish were killed. Necropsy of 5 individuals from each group revealed splenomegaly (2-fold greater diameter than normal) with reddening of the adjacent intestine. Clear amber fluid (0.5-2 ml) was present in the coelomic cavities of the fish with distended abdomens. Attempts to culture bacterial pathogens from spleens and kidneys on tryptose blood agar plates were unsuccessful. Ultrastructural examination was performed on pellets harvested from tissue homogenates and on ultrathin tissue sections. Samples included spleen, anterior kidney, liver, and intestine; 1 heart sample was processed for epoxy sections only. To obtain pellets, unfixed tissues were homogenized in deionized water (10% w/v) and then centrifuged at 4,000 x g for 10 minutes. The supernatant was centrifuged at 14,000 x g for 60 minutes. The resulting pellet was suspended in 25 µ1 deionized water, mixed with an equal volume of 1.5% phosphotungstic acid (pH 6.8), and applied to grids covered with carbon-coated polyvinyl formal film a using a micropi