What saltwater ich is
Saltwater ich, also called marine white spot disease, is caused by a parasitic protozoan called Cryptocaryon irritans. It attaches to the skin and gills of fish and is one of the most common diseases in marine aquariums. Wild fish are exposed to it too, but in the wild the parasite is spread over a large volume of water. In a home tank, the concentrated fish and small water volume let numbers build up quickly, especially if the fish are stressed. If your tank is freshwater, see how to treat ich in fish instead.
Symptoms and what it can be confused with
Common signs include:
- Small white spots on the body, fins or gills, often described as pinhead-sized
- Scratching or rubbing against rocks or sand (“flashing”)
- Rapid or heavy breathing, which can signal gill involvement
- Clamped fins, lethargy and loss of appetite
The spots can come and go, and a fish may look fine for a day and then look worse. Marine velvet (Amyloodinium) can look similar but produces finer, dust-like spots and can progress very quickly. Because the treatments for different diseases vary, be careful to identify the problem. If you are unsure, consider consulting an experienced aquatic veterinarian or an experienced hobbyist.
Can saltwater fish survive ich?
Many fish can survive, particularly if the infection is caught early and the fish is otherwise healthy and well fed. Severe infections can be fatal, especially when the gills are heavily affected, and the parasite can kill several fish in a tank. The outcome depends on the fish’s species, condition and stress level, and on how quickly you act.
Can fish recover from ich on their own?
Some fish with strong immune systems can fight off a light infection, and wild fish often do. In an aquarium, though, the parasite can keep re-infecting fish, so relying on recovery without action is risky. It is generally better to treat promptly and reduce stress.
Why the parasite is hard to remove
The parasite has a multi-stage life cycle. In simple terms, the feeding stage sits on the fish, then drops off, forms a cyst on surfaces in the tank, and eventually releases free-swimming young that look for new fish. Many treatments only affect the free-swimming stage, which is why a short course often fails. Timelines also vary with temperature, and some strains seem to take longer than others.
Treatment overview
Common approaches used by hobbyists include:
- Copper in a hospital tank. Often used for marine ich. It must never go in a reef display. See copper treatment for marine fish.
- Other medications or methods. Some hobbyists use chloroquine phosphate, hyposalinity, or a tank-transfer method. Each has trade-offs and some are not suitable for every species or for tanks with invertebrates. Research carefully and follow product instructions.
- Supportive care. Good water quality, a varied diet and low stress help fish cope.
Treatment generally takes place in a separate tank so the display can remain free of medication. Move fish carefully and with minimal stress.
Fallow display tank
Because the parasite needs fish to survive, a commonly cited approach is to leave the display tank without fish for a set time so the parasite cannot complete its cycle. Many experienced hobbyists cite 76 days as a conservative length. Corals and many invertebrates do not host the parasite, so they can usually stay in the display. Be careful about cross-contamination from nets, buckets and hands, and keep treated fish separate from the display.
Does ich ever go away?
It can, but it is difficult to prove that it is gone from a tank that still has fish in it. If you treat all fish and leave the display fallow for an adequate time, you may eliminate it. Otherwise, the parasite can persist at low levels and flare up when fish are stressed. Some keepers manage rather than eradicate it, but this carries risk.
Can humans catch ich from fish?
Marine ich is a parasite of fish and is not known to infect people. It is still wise to wash your hands and equipment well after working in any aquarium and to avoid sharing nets between tanks, because other fish diseases and some bacteria can affect people.
Prevention
- Quarantine every new fish for several weeks before adding it to the display. See saltwater fish care.
- Keep water quality stable and avoid overcrowding.
- Provide a varied diet.
- Reduce aggression by choosing compatible species. See compatible reef fish.
- Keep equipment and nets for quarantine and display separate.