The main symptom of this disease is the small salt-grain like spots which give the disease one of its common names. Fish may also be seen to rub against hard objects. Later fish may be seen to be gasping and gill damage could also be evident. However, you should have noticed Whitespot in your tank well before this stage. Not only is this disease unsightly to behold, but it causes the fish a lot of stress; which can kill a fish easier than the disease itself. This is also possibly the most common disease amongst tank fish today. When I first started keeping tropical fish in the mid 70s there were several diseases we had to be on our guard against. Since then these appear to have greatly diminished. But Whitespot is still around and just as annoying, both for the aquarist and the fish!

The disease is caused by a protozoan parasite, Ichthyophthirius multifiliis, and is very contagious. The parasites spend a portion of their life cycle embedded beneath the skin of the fish, where they feed from the body tissue. The white cyst in which they are enclosed gives the characteristic white spots. Adults emerge from these cysts and fall to the floor of the aquarium, where they multiply inside a protective capsule. Some time later, the capsule bursts, releasing hundreds of free-swimming infectious parasites which attach themselves to new hosts. Whitespot is often introduced with new fish which have not been quarantined. Outbreaks of whitespot often occur after fish have been exposed to cooler than normal temperatures. Clown loaches in particular are prone to whitespot. Introducing new fish to an established, generally protected, tank is usually the easiest way to transmit this problem.  Only buy from a reputable dealer who displays his fish in clean healthy tanks. Whitespot is one of the easiest diseases to "spot" on a fish so trust your own eyes when selecting a specimen for your tanks.

There are two main approaches to curing whitespot, and opinions can vary from "expert to rank novice" on which is the more effective. There are several effective commercially available remedies, normally based on malachite green and formalin. Note that malachite green is hard on scale less fish like catfish and loaches, and also other fish such as tetras. Some alternative medications are based on copper and formalin. The other method employed is to add salt to the tank (gradually), up to a level of 6-8 tsp per gallon. Note that fish vary in their tolerance of salt, and for more sensitive soft-water species, it may be better to use 3-4 tsp per gallon maximum. Higher salt levels may also affect plant growth. I personally found this method rather aggressive, although I did use sea salt, not table salt.

In either case, increasing the temperature should kill the parasite off more quickly, because it will speed up the life cycle of the parasite, so that the free-swimming stage is reached as quickly as possible - this is the only stage affected by medications. However, increasing the temperature means there will be less oxygen dissolved in the water (some medications can lower it too), so ensure the tank is well aerated, and do not raise the temperature beyond around 28^oC (82^oF).

Due to the life cycle of the parasite, the whole tank must be treated, in order to kill the parasites which are not attached to fish. Therefore it is not appropriate to treat only the affected fish in a separate isolation tank. But please please please, follow the instructions on the bottle or accompanying pamphlet - these are not there for nothing.

Effective commercial remedies include Protozin and Maracide. In my earlier days of fish keeping I trusted WS3 from King British. However, some obscure law in the early days of Britain's European membership decided that the original medicine was far too strong for our poor little fishes and it was effectively diluted and, at that time, lost a lot of its effectiveness. At least that's how I saw it at the time.

Mike Kemble
Webmaster