This clinical presentation is consistent with Ich (or “white spot disease,” caused by Ichthyophthirius multifiliis).I. multifiliis is an obligatory parasite and is highly contagious between fish. It invades epithelial tissue, leaving white spots where it encysts.Dx - light microscopic visualization of the parasite at 40X or 100X. As seen here, it is large (0.5–1 mm), round, covered in cilia, with a characteristic horseshoe-shaped macronucleus. It classically constantly rotates or moves in an ameboid-like manner.Rx - formalin or copper sulfate in the water every 2–3 days for at least 3 weeks. An over-the-counter formulation of formalin and malachite green is effective but cannot be dispensed by vets due to regulatory concerns.Amyloodinium spp. are dino-flagellates that cause serious health problems in marine fish and lead to high mortality.It is called “velvet” or “coral disease” because it gives the fish a gold-brown color.Tx is copper sulfate (in food animals) or chloroquine (in ornamental fish).Whirling disease is a parasitic neurologic disease of wild and aquacultured fish.Epitheliosis is a bacterial skin disease of aquacultured fish.Refs: The Merck Veterinary Manual online. Image courtesy of D. Herdemerten.