December 2013

Angel fish with white spots

 Five fish from a new shipment of freshwater aquarium fish received by the Tulsa Zoo and Museum died while in quarantine.  The fish had white spots on the skin.  Multifocal erosive epidermitis with intralesional bacteria and associated protozoa were observed.  Sepsis secondary to epidermal damage from the protozoan was believed to be the cause of death in the fish. A sample of a white spot from one of the fish was swabbed onto a slide, fixed, and Romanowsky stained.

What is your diagnosis?

Case and photo provided by Dr. Eileen Johnson, Oklahoma State University.

Answer

The morphological appearance of the protozoan appears very similar to that of Oodinium sp., which is a dinoflagellate that can cause velvety whitish or gold patches on the bodies, fins, and gills of freshwater aquarium fish. Over time, affected fish will have the appearance of being coated in a velvet-like film ("Velvet Disease"). Another protozoan that can commonly cause white spots on freshwater aquarium fish is the ciliate Icthyophthirius multifiliis, or "ich." White spots caused by Ichthyophthirius, however, differ than those caused by Oodiniumin that they are described to look like white grains of salt or sugar on the bodies, fins, and gills of fish. Also, Icthyophthirius sp. has a characteristic horseshoe shaped macronucleus.