Chilodonella spp are a ciliated protozoan parasite (which has a marine counterpart, Brooklynella spp) are found on both freshwater and marine fish.
Fish with chilodonelliasis typically lose condition, and copious mucous secretions may be noticed in areas where infestation is most severe. If gills are heavily infested, the fish may show signs of respiratory distress, including rapid breathing and coughing. The gills may be visibly swollen and mucoid. If the skin is heavily infested, it may have a cloudy appearance, associated with excessive mucus, and the fish may be irritated as evidenced by flashing (scratching) and decreased appetite.
Chilodonella can be easily identified from fresh biopsies of infected tissues. They are 0.5-0.7 mm, are somewhat heart-shaped with parallel bands of cilia, and move in a characteristic slow spiral.