1644 Scientific Reports: Clinical Report JAVMA, Vol 224, No. 10, May 15, 2004 AQUATIC MEDICINE I n spring 1998, a Florida tropical fish producer (farm A) reported that approximately 20% to 40% of the 2- to 5-week-old discus (Symphysodon aequifasciatus) at the farm had become sick and died, along with approximately 5% of the 2- to 3-month- old juveniles. The facility had recently undergone restructuring, which had included adding a separate grow-out recirculating system and modifying the existing breeder system. The recirculating system tanks used for the grow-out phase each contained established sponge filters for biological filtration that were derived from the breeder system tanks. Water quality parameters had been unstable for several weeks with high total ammonia nitrogen (TAN) and nitrite concentrations. The target pH for raising the juvenile discus was 5.8 to 6.2, but the measured pH was 5.2 to 5.7. Because acidic pH and resulting low alkalinity greatly reduce the growth and metabolic efficiency of nitrifying bacteria, it was thought that the acidic pH was having a negative effect on the biofilters. Therefore, the water was changed weekly in an attempt to increase the pH and decrease the TAN and nitrite concentrations. The producer had also added some other South American cichlids to 1 of the breeder systems in the facility during the win- ter and spring of 1998. Three moribund discus (23 to 26 mm total length [TL; the length of a fish measured from the front of the jaw that is most anterior to the end of the longest caudal ray]) were submitted to the University of Florida’s Tropical Aquaculture Labora- tory in Ruskin for necropsy and microbiologic eval- uation. Major findings were intestinal parasites (hexamitid flagellates, presumably Spironucleus spp) and a moderate number of granulomas in stomach tissue from the fish. Microbiologic culture of brain and kidney specimens on tryptic soy agar (TSA) with 5% sheep’s blood at 30 o C did not yield any bac- terial growth after 48 hours. The problems at the farm were attributed to poor water quality and Spironucleus infection. Two months later, discus were still becoming sick and dying even though water quality had stabi- lized, and 3 to 4 weeks after that, the producer began to notice even higher morbidity and mortality rates. At this time, most life stages were affected, including fry (2 to 4 weeks old), juveniles (1 to 6 months old), and breeders (1 to 3 years old). The morbidity rate was highest among the 2- to 4-week- old fish, with clinical signs including darkening, lat- eral recumbency, lethargy, and hanging and moving slowly in the water column; mortality rate was 70% to 90%. Fish that were > 2 months old, including breeders, had high morbidity rates but low mortali- ty rates (2% to 5%). These fish became dark, had increased mucus production and respiratory rates, and became laterally recumbent for 1 or more weeks before recovering. At this time, an additional 6 moribund 2- to 4- week-old discus (12 to 17 mm TL) from the same affected systems at farm A were submitted to the Tropical Aquaculture Laboratory for evaluation. Gross abnormalities included a larger-than-normal amount of mucus on the gills, skin, and fins. Fin ero- sions were also evident, and low numbers of monoge- neans (family Dactylogyridae) were seen in gill sam- ples. Hexamitid flagellates, presumably Spironucleus spp on the basis of morphology, movement, and loca- tion, and low numbers of nematodes (Camallanus spp) were seen in the lumen of the intestine. In the lumen and within the mucosa and submucosa of the stomach and intestines from most of the fish were Cryptobia iubilans infection in juvenile discus Roy P. E. Yanong, VMD; Eric Curtis, BS; Riccardo Russo, MS; Ruth Francis-Floyd, DVM, MS, DACZM; RuthEllen Klinger, MS; Ilze Berzins, PhD, DVM; Karen Kelley, MS; Sarah L. Poynton, PhD ' The flagellate Cryptobia iubilans is an important parasite of discus and many other cichlids that typ- ically induces granulomatous disease, primarily involving the stomach. ' The clinical importance of C iubilans infestation may be overlooked because of an absence of live parasites after the acute phase of infestation and occurrence of related enteric protozoa. ' Morbidity and mortality rates in a population of fish infested with C iubilans appear to be linked to a number of environmental and biological variables. ' Bath treatments with dimetridazole or 2-amino-5- nitrothiazol may help decrease the prevalence of infestation, but further study is required. From the Tropical Aquaculture Laboratory, Department of Fisheries and Aquatic Sciences, Institute of Food and Agricultural Sciences, University of Florida, Ruskin, FL 33570 (Yanong, Curtis, Russo); the Departments of Fisheries and Aquatic Sciences, Institute of Food and Agricultural Sciences (Francis-Floyd, Berzins) and Large Animal Clinical Sciences, College of Veterinary Medicine (Francis- Floyd, Klinger), University of Florida, Gainesville, FL 32653; the Florida Aquarium, 701 Channelside Dr, Tampa, FL 33602 (Berzins); the Electron Microscopy Core Laboratory, Interdisciplinary Center for Biotechnology Research, University of Florida, Gainesville, FL 32611 (Kelley); and the Division of Comparative Medicine, School of Medicine, Johns Hopkins University, Baltimore, MD 21205 (Poynton). Mr. Curtis’ present address is the John G. Shedd Aquarium, 1200 S Lake Shore Dr, Chicago, IL 60605. Presented in part at the 30th Annual Conference of the International Association for Aquatic Animal Medicine, Boston, May 1999. The authors thank Marty Greenwell, Pam Dennis, Hans Roese, Dieter Steinhagen, Eva Nohynkova, Jan Landsberg, Jeff Hill, Jorge Hernandez, and Ken Portier for technical assistance and Deborah Britt Pouder for assistance with figures. Supported by a grant from the Florida Tropical Fish Farms Association. Address correspondence to Dr. Yanong.