SBI has had a severe economic impact on the fish industry in central Europe, but the present study is the first to describe an outbreak of SBI in Koi in Taiwan, even in Asia. A group of 7-month-old koi (Cyprinus carpio koi) showed abnormal swimming behavior and abdominal distension with a fatality rate of 40%. Smear examination of swim bladders showed numerous identical basophilic spherical organisms. Gross examination revealed severe adhesion of abdominal organs and erosion, enlarged of the swim bladder. Severe inflammation of the submucosal layer of the swim bladder and large numbers of pansporocysts and zygospores were noted microscopically with Hematoxylin and Eosin stain, Giemsa and modified Grocott's methenamine silver (GMS) stain. The nucleotide sequence of the pathogens isolated from the fish samples had a 99% homology with Sphaerospora dykovae, the pathogenic agent in swim bladder inflammation (SBI).

Key words: Cyprinus carpio koi, Sphaerospora dykovae, Swim bladder inflammation, Taiwan