Water mold (cotton on fish)
Saprolegnia spp. · Aquatic life
In the water · Photo: Olivier Ruiz / CC BY-SA 4.0 (Wikimedia Commons)
Also called Oomycete, Fish fungus, Saprolegnia, Cotton mold
How to identify Water mold (cotton on fish)
- White to gray cottony tufts on fish skin, fins, gills or eggs
- Tufts may turn brown or green as they trap silt and algae
- Often grows on wounds, spawning sores or dead eggs
- Also grows as fuzzy halos on dead fish, insects or bait in the water
Similar species
Columnaris disease (a bacterium) causes yellowish or white patches and saddle shaped lesions, usually in warm water. Fish lice and anchor worms are small parasites visible on the skin.
Profile
| Season | Most outbreaks in cool water in spring and fall, and after winter when fish are stressed. |
|---|---|
| Starts | Most aggressive in cool water, roughly 40 to 60 F |
| Depth | On fish and organic matter at any depth |
| How it spreads or reproduces | Swimming spores in the water infect injured or stressed fish |
| Habitat | Present in nearly all fresh water and sediments; problems mostly in ponds, hatcheries and aquariums. |
Why it matters in a lake
Usually a secondary infection, so it signals that fish are injured, crowded, handled roughly or stressed by poor water quality. Reducing stress and handling and improving water quality is the main prevention.
Where it is found
- Idaho: Occasional
- Oregon: Occasional
- Wyoming: Occasional
Classification
| Kingdom | Chromista |
|---|---|
| Phylum | Oomycota |
| Class | Oomycetes |
| Order | Saprolegniales |
| Family | Saprolegniaceae |
| Scientific name | Saprolegnia spp. |
Iron bacteria
American bullfrog
Purple sulfur bacteria
Daphnia (water flea)
Midge larvae (bloodworms)Need a hand?
Found it in your lake?
Send us a photo and we will identify it and tell you what it means for your lake.
Idaho / Wyoming (208) 501-4531Oregon (541) 280-0596