It enters the fish through scratches on the skin or through the digestive tract, destroys the fish's defense, breaks down the blood vessels allowing blood and serum to leak out into the surrounding tissues and kills the fish. Fungus Fungus will be a major activity in your aquarium. It can become a serious source of disease-related problems if not kept under control. Your entire tray of eggs can become a solid mass of fungus. If you filled your aquarium with stream or lake water you brought protozoans with it.
Protozoans are microscopic one-celled animals, most of which are harmless.
Some protozoans, however, live in or on your salmon fry. They are invisible to the naked eye. Death, reduced feeding activity, flashing, changes in tissue structure, slow growth and reduced stamina are all signs of potential protozoan disease in your fish. The infected fish try to close up their fins and rub against hard objects. The parasites show up as white, pinhead-size specks on the fins and body.