First part: Video of microscopic examination of a skin mucus biopsy sample from a koi. Numerous trophonts and theronts of Ichthyophthirius can be seen. Unstained wet mount; magnification, 40×, 100×, and 400×. Second part: Video of microscopic examination of a gill biopsy of the same fish. Ich trophonts can be seen encysted below the epithelium. Unstained wet mount; magnification, 100×.