Fish Diseases and Management

5.5.1 Cotton wool disease

Causative agent is Saprolegnia, which is the most commonly observed opportunistic pathogenic fungi affecting tropical fishes and fish eggs . Under most conditions, if the fish is well supported with clean water and good food, the fungal tufts will slough off in time without treatment. Clinical signs are greyish white, cotton-like growths on the skin, gills, eyes, or fins that may invade deeper tissues of the body. Preventive measures include removal of predisposing causes, eg, inadequate sanitation, excessive chemical treatment, or the presence of dead, infected fish and decaying organic material. If the environment is clean and skin pathogens have been eliminated, a single treatment with potassium permanganate is often adequate to control external saprolegniasis. These fungi are also susceptible to several compounds including formaldehyde, malachite green and salt.