Ich Disease

Ichthyophthirius multifiliis, also known as Ich Disease, or White Spot Disease, is one of the most common diseases found in freshwater fish. Because the infected fish usually has small white spots that develop on its skin, most people call it White Spot Disease.

Ich Disease is a highly contagious parasite. It lives under the skin of the fish. The points where the parasite is under the skin of the fish are what turn white.

The parasite has a life cycle of a few days up to months, depending on the temperature of the water. The warmer the water in the aquarium the faster the life cycle is for the parasite.

Ich Disease seems to be much more common in aquarium fish, and this might partly be because of how close the fish are together. It also appears that stressed fish are much more likely to be affected by this than non stressed fish, at least at the start of the aquarium’s infection.

white spot disease
ich disease

Life Cycle Stages of Ich Disease

The life cycle of this parasite can be from days to weeks depending on the temperature. If the parasite does not have a host, and the aquarium’s water is heated to 86F the life cycle will be as fast as two days. If the water is much colder, closer to freezing it can be as long as 8 weeks!

Trophont Stage

In the initial stage of the infection the trophont embeds itself in a host fish just under the skin. This is the point where you will be able to see the white spots on the fish. It will feed on the tissue of its host. Depending on the temperature of the water this stage will vary in length. The warmer the water the faster the parasite must feed to be able to reproduce before its life cycle is completed.

Tomont Stage

Once the trophont has grown large enough in size, it will burst from the fish’s skin and be called a tomont. The tomont will look for a surface it can attach itself to. Once it attaches itself to a surface it will grow a thick cyst wall.

Tomocyst Stage

Once it has grown its thick cyst wall protecting it from the outside it is now called the tomocyst. It is at this stage where the parasite multiplies itself. Depending on the water temperature up to 1000 trophonts may be released from a tomocyst. Each one of these will be looking for a fish to infect and feed on to repeat the cycle again.

Symptoms of Ich Disease

  • White spots that look like salt grains
  • Abnormal swimming behavior
  • Fish swimming against decoration or substrate
  • Scratches on the fish from rubbing
  • Loss of appetite

In the initial symptoms of Ich Disease white spots will usually be visible all over the fish’s body. In other cases these may only appear near the gills. When these are first seen is the time to take action to prevent the rest of your aquarium from becoming infected.

The fish that initially become sick from this usually have some underlying condition that makes them more vulnerable. If left untreated in your tank it will quickly spread to the other more healthy fish.

ich disease

Treatment of Ich Disease

You may read that it is possible to treat your fish with Copper sulfate. In the past this was one of the recommended treatments, however it is a known carcinogen and many aquarium owners would add too much and kill many of the fish they were trying to save. Even if you are able to find this now, we still recommend other treatment options which will be more friendly to your fish’s long term health.

ich disease


If you are an observant pet owner you may be able to catch this disease early when it has only infected a small number of fish. If you are able to catch this early and you have a quarantine tank available, move the infected fish to a quarantine tank.

Water Change

You will want to clean the tank and do a water change of about 50% as soon as possible. Remember that the parasite likes to attach itself to a surface to multiply. Clean the tank as well as you can so that if there are any tomocysts you are able to loosen them.  Then the 50% water change will help to clear out and reduce the number of parasites that may be in the water. Do this every few days while you have infected fish to minimize the spread to any healthy fish.

Treat the Water

The reason why people eat saltwater fish for sushi and not freshwater is because parasites hate salt. This is why saltwater fish have far fewer parasites. Adding 4-5g of water per liter will make it much harder for any parasites in the water to survive.

The 1-2 punch with the salt is raising the water temperature. The best temperature to raise your water to is 86 degrees. Keep in mind that not many fish can handle water this warm, so check the maximum temperature your fish can handle before raising the temperature at all. Then raise the temperature to the highest you can without harming your fish. This will greatly speed up the life cycle of the parasite.

If it’s possible, move all of your fish to a second tank and raise the water in the main tank to 86 degrees for 4 days.  The parasite should not be able to survive without fish for 2 days at this temperature, and the extra two days is to make sure none of them survived.


There are many products commercially available that use a chemical called formalin. This can be used to treat the water to help kill the parasites and treat infected fish. Because each product is slightly different you’ll need to follow the directions for the specific product you choose.

If you use a chemical like formalin you will want to stop using any activated charcoal filters. Activated charcoal has been known to reduce the effectiveness of medication.

Prevention of Ich Disease

A little bit of prevention can save you a lot of money, and keep your families fish tank much healthier.

Be Smart while Buying!

When you are buying new fish, look at how the health of the fish are in the tank. If there are any that look sick, or you see a dead fish in the tank, don’t buy anything from that tank.

white spot disease
ich disease


Whenever possible any new fish for your aquarium should be placed into a quarantine take for 5 to 7 days. This is to make sure you do not introduce any illnesses that the fish might have brought with it from the pet shop to your healthy tank. This also applies to new plants!

Mechanical Filter

Another great option for making it much harder for Ich to develop in your aquarium at all is to use a mechanical filter with a mesh of 80 microns or less. This is something you are going to find in a more expensive filter like the canister filters.

This will let your filter move a lot of the tomont parasites as they are leaving the fish, but before they can become a tomocyst and attach to something in your tank. The more of these that you can completely remove from your tank, the much lower the chance you’ll ever have an outbreak of Ich.


Know what your fish like and what they don’t like. If they need plants to feel safe, make sure you have plants for them to hide. If you know this fish you are considering is more aggressive, or that you don’t have room in your tank for more, don’t buy fish that can stress the ones you have. This is one of the easiest things you can do to keep your fish healthy.

Water Quality

Water quality is one of the main factors that impacts the overall health of fish in your aquarium. By keeping the toxic chemicals down with regular water changes, and keeping the temperature in the happy zone for your fish you will have much more healthy fish. A clean tank is a happy and healthy tank.

Related Questions

Can fish become re-infected with Ich Disease?

While it does not appear that a fish once infected with Ich will be 100% immune, it does appear that they may have increased resistance to a reinfection. It is better however to prevent them from having to go through this again and follow the preventative measures we list in this article to keep your fish healthy.

How does Ich Disease Kill a Fish?

Fish are thought to die from an inability to get enough oxygen. When the fish’s body is reacting to the infection the top layer of gills thicken and reduces the amount of oxygen that can be taken from the water. 

This is further complicated by a large number of the Ich parasites attaching themselves to the gills of the fish. This is thought to make it much more difficult for them to pull oxygen from the water, resulting in abnormal swimming, or lack of swimming, and death.

Freshwater Fish Known to be Susceptible to Ich Disease:

Neon Tetra     Guppies     Oscar     Betta Fish     Mollies     Zebra Danios     Goldfish     Angelfish     Platies     Cherry Barb

Swordtails     Rainbowfish     Discus     Plecostomus     Corydoras Catfish

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