Diagnosis_Genus: Piscinoodinium Lom 1981. Ectoparasitic on gills and skin of freshwater fishes; rarely subcutis. Trophont: From the attachment disc with a very short peduncle radiate numerous rod-like organelles, rhizocysts, which penetrate into and are firmly embedded in the epithelial cells of the host. there is no stomopode. There are well developped chloroplasts and starch grains. Theca without plates. Cytoplasm contains rhizocysts, laminar inclusions; there are digestive vacuoles. Subthecally, there are mucocysts. nucleus with large condensed chromosomes. Division of the tomont stage; without common envelope; produces up to 256 dinospores, without stigma.
Diagnosis_Species: Piscinoodinium pillulare Schläperclaus 1954. This parasite of freshwater fish is responsible for the disease commonly known as 'rust disease' or 'velvet disease' due to the appearance of the fish caused by the attached trophont. Found attached to the skin, gills, fins, epithelium of the oesophagus, and intestine of several species of fish from tropical and temperate regions. On the gills, the Piscinoodinium infection was commonly associated with epithelial hypertrophy, focal and diffuse hyperplasia, oedema of the respiratory epithelium and lamellar fusion (Ferraz and Sommerville). Fish show increased mucous production on body surface and gills, while ecchymosis in the caudal peduncle and operculum are often present (Martins et al. 2001). The attached trophont is pyriform or sac-like, fixed in the basal region by an attachment disc.
Levy et al. (2007) described a variant without functional chloroplast (may be another species).

Body_trophont_length: 20-74 µm (Shaharom-Harrison et al. 1990)
Body_trophont_wide: 14-49.6 µm (Shaharom-Harrison et al. 1990)