Gastric Cryptosporidiosis in Juvenile Red Drum

Pond-reared fingerling red drum Sciaenops ocellatus experiencing low mortality were found to be in poor physical condition. Histopathology revealed numerous 2–5-μm spherical organisms lining the gastric microvillus border and clusters of 4–7-μm organisms within epithelial cell cytoplasmic vacuoles suggestive of cryptosporidiosis. The diagnosis was confirmed by electron microscopy, with which life cycle stages were observed to be compatible with criteria established for Cryptosporidium spp. inother fish. Although few pathologic changes have been attributed to cryptosporidial infections in fish, a moderate inflammatory response in these red drum was elicited by the parasite in association with disruption of the normal tissue architecture, epithelial necrosis, and glandular loss. Ancillary diagnostic tests, including bacteriology and parasitology, were negative. The possible contribution of this organism to mortalities seen in these fish is discussed.