noun
water mould; saprolegnia; cotton mould
A type of aquatic fungus-like organism, often seen as a fuzzy growth on fish or organic matter in water. Common in aquarium and fishkeeping contexts.
金魚の体に水カビが生えてしまった。
Water mould has grown on the goldfish's body.
水カビは水質が悪いと発生しやすい。
Water mould tends to appear when water quality is poor.
General term for mould or mildew; 水カビ specifically refers to aquatic moulds like Saprolegnia.
Compound of 水 (water) and カビ (mould). The exact origin is straightforward; the term is used primarily in biological and aquarium contexts.