Fungal infections in Nigerian catfish — primarily caused by Saprolegnia and Achlya species — appear as white, fluffy cotton-wool growths on the skin, fins, and eggs. They are secondary opportunists that attack injured or immunocompromised fish.
Saprolegnia species are water moulds — not true fungi but Oomycetes. They are present in virtually all Nigerian pond water and cause no harm to healthy fish. They become pathogenic when fish are stressed, injured, or have a compromised immune system due to poor water quality or nutritional deficiency.
In Nigeria, Saprolegnia outbreaks peak during the harmattan season (November–February) when water temperatures drop and fish immunity is reduced. Newly hatched fry and recently netted fish are highest risk.
Salt disrupts the osmotic environment of Saprolegnia hyphae. Apply iodine-free salt at 2–3g/L and maintain for 5–7 days. This is effective for mild to moderate infections and has no risk of fish toxicity at this dose.
Malachite green is the most effective antifungal treatment for Saprolegnia. Apply at 0.1mg/L as a pond treatment. A single treatment is often sufficient for mild outbreaks. Repeat after 72 hours for severe infections. Available from aquaculture chemical suppliers in Lagos and Ibadan.
An alternative to malachite green. Apply at 2mg/L as a pond treatment. Effective against Saprolegnia but less potent than malachite green — use for mild infections or when malachite green is unavailable.
Fungal infections almost always have a trigger. Identify and fix it: improve aeration, reduce stocking density, do a water change, check feed quality for mould, and treat any visible wounds with antiseptic before return to pond.
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