The Biology and Associated Pathology of Goussia carpelli (Léger and Stankovitch) in Goldfish Carassius auratus (Linnaeus)

Chronic mortalities have been a recurrent problem in common goldfish Carassius auratus throughout the United States and a coccidian, morphologically identical to Goussia carpelli, is suspected to be the primary etiological agent. This parasite may cause severe mortalities due to enteritis in cultured carp Cyprinus carpio in Europe and the pathology and epizootiology was similar in goldfish. In our study, goldfish became infected shortly after hatching and sporulated oocysts were found in 15-day-old fish. Fish are usually harvested from ponds after six weeks and are shipped to wholesalers. At this time they stopped feeding, became lethargic, emaciated, and cumulative mortalities of 50–75% occurred over a two to three week period. Necropsies revealed a chronic enteritis with numerous sporulated oocysts surrounded by yellow bodies in the lamina propria of the intestine. Most of the oocysts were shed or degenerated as the disease progressed, but fish continued to die. Histological analyses of these fish revealed numerous yellow bodies, inflammatory and necrotic cells in the lamina propria of the gut and the intestines often had lost their villar structure. The yellow bodies, identified as lipofuscin or ceroid by electron microscopy and histochemical analysis, were also found in the spleen and kidney of severely affected fish. Experimental infection in the laboratory was accomplished using tubificid worms and grass shrimp (Palaemonetes kadiakensis) fed oocysts, but direct transmission of the parasite using fresh or cold aged occysts was unsuccessful.