These enzymes break down cells and tissues enabling the fungi to absorb nutrients such as proteins and carbohydrates. Fungal infections are called mycoses . Water moulds consist of a tangled mass of individual filaments called hyphae. As the mass grows it forms compact tufts that are collectively called a mycelium . The mass of fungi filaments or mycelium can be seen clearly without a microscope.
Moulds reproduce by releasing thousands of spores into the surrounding water.
The fungal spores are highly resistant to drying and chemical attack and thus Saprolegnia spores and molds are common in all ponds and tanks. It is believed that the fish mucus contains effective fungicides that prevent fungal growths under normal circumstances. It is worth pointing out that large amounts of decomposing organic matter within the system will encourage fungal growth. Other predisposing factors include water pollution and overcrowding. Less commonly, Saprolegnia can act as a primary pathogen infecting fish that haven't shown signs of previous damage.