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Various species of aquatic fungi, including Saprolegnia and Achlya. |
Grey, brown or with cotton-wool-like growths or tufts on the skin and fins
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External fungal problems are rarely reported on marine fish. It normally begins as a small patch but can develop if left untreated, quickly killing the fish in some circumstances. Fungus may also attach fish eggs.
Fungus and fungal spores are quite common in aquatic environments and are particularly abundant where there is plenty of decaying organic matter. The infectious spores of fungus may transmit the disease from fish to fish. However, the layer of mucus that covers the skin of healthy, undamaged fish is normally a very effective barrier to the spores. If, for one reason or another, this mucus layer becomes damaged-following rough handling, fighting or spawning activity, for example-this will provide an opportunity for the fungus to gain a foothold. Fungus may also invade the lesions left by other diseases, such as white spot or ulcer diseases. A sudden change of temperature, unhygienic aquarium conditions and poor water quality may all predispose fish to fungus. In the case of fish eggs, fungus attacks the dead eggs and may spread to the adjacent healthy eggs, killing the whole batch. |
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