fish

Saprolegnia (Water Mold)

A fungal-like infection causing white, cottony patches on fish. Usually secondary to injury, stress, or poor water quality. Treatment: antifungal medication and improved conditions.

Symptoms

White or gray cottony, wool-like tufts on skin, fins, gills, or eggs.
Tufts grow larger over time and stand off the skin surface.
Fish become listless; gill infections cause breathing difficulty.

Common Causes

Water mould (Saprolegnia) is opportunistic — it colonizes injured or stressed fish.
Usually secondary to injury, stress, or poor water quality (E1).
Egg masses and post-spawning fish are especially susceptible.

What to Check

Look for the wound or stressor that allowed the mould to take hold.
Check water quality and temperature — cold, poor water favours outbreaks.
Remove dead eggs or heavily affected tissue promptly.

What Not to Do

Do not treat the tufts without addressing water quality and the underlying injury — it returns (E1: treatment includes improved conditions).
Do not medicate lightly — antifungal treatment should be paired with clean water, not replace it.

This guide is informational and does not replace professional veterinary advice. If fish are severely ill, consult a veterinarian.

Saprolegnia (Water Mold)

Symptoms

Common Causes

What to Check

What Not to Do

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Saprolegnia (Water Mold)

Symptoms

Common Causes

What to Check

What Not to Do