Cryptobia iubilans infection in juvenile discus.

Four commercial producers of discus (Symphysodon aequifasciatus) were found to have fish infested with the flagellate Cryptobia iubilans. Affected fish had granulomatous gastritis, and many also had granulomatous disease of other organs. The parasite had to be differentiated from the related flagellates Spironucleus spp, which induce different lesions. Transmission electron microscopy was found to be useful in detecting and identifying the parasite. Morbidity and mortality rates in the various fish populations appeared to be linked to a number of variables, including water quality, presence of other parasites and bacteria, diet, species, size, and age of the fish, and optimization of husbandry appeared to be important in alleviating the severity of disease. Metronidazole was not effective for treatment of C iubilans, but bath treatments with dimetridazole (80 mg/L for 24 hours, repeated daily for 3 days) or 2-amino-5-nitrothiazol (10 mg/L for 24 hours, repeated daily for 3 days) may be useful in decreasing the prevalence of infestation.

Use of blood culture as a nonlethal method for isolating bacteria from fish.

Simple nonlethal blood culture methodology, an alternative to euthanasia for diagnosing systemic bacterial infections in fish, is described. Blood was extracted from the caudal vein of 20 individuals of five fish species, incubated in brain-heart infusion broth, and then plated onto enriched blood agar. Nine of these fish were subsequently euthanized and necropsied for confirmatory tissue cultures. Five species of bacteria were isolated from the blood cultures from nine fish, and the tissue culture results in euthanized, necropsied fish agreed with the blood culture results in all cases. All the fish that were not euthanized survived for 24 hr, although two heavily parasitized fish subsequently died.