Fish, Tanks and Ponds


Fish, Tanks and Ponds
A comprehensive guide to fish

White spot and its treatment

Fresh water fish with white spot
Fresh water fish with white spot

Ichthyophthirius multifiliis- Fresh water white spot

This is a fresh water only parasitic protozoa. It has quite a complicated life cycle involving many stages and it can apparently appear from nowhere under certain conditions.

The life cycle of fresh water white spot is as follows:

Theronts - the free swimming stage.

This is the only part of the life cycle where the parasite is vulnerable to medication. Theronts must find a host within a set time (temperature dependant) or they will die;

Trophont - parasitic stage.

This is the stage where the parasites can be seen on the fish: medication is ineffective against trophonts;

Tomont - cell division stage.

When the cyst falls from the fish it sinks to the bottom of the tank where the cells divide within the cyst. Eventually up to 2,000 new Theronts emerge from each cyst to look for a new host. In the confines of a fish tank new hosts are easy to find and so the infection gradually worsens until the fish weakens so much that it could die if untreated.

Medication sold for this condition will only affect the theront stage of the life cycle so it might look initially as though the treatment is being ineffective.

There are a lot of myths about this disease and how it appears and then spreads. White spot often appears from nowhere when the fish are stressed. What actually happens is that the parasite can live in the background in the form of a low grade infection which goes unnoticed and has little or no effect on healthy fish. But, when the fish become stressed - as for example happens under new tank syndrome conditions - the fishes immunity is compromised and the background infection is allowed to establish and multiply into a full-scale infection. This only needs to affect a single fish which then acts as a host and allows the number of theronts to increase dramatically and overwhelm the defences of even the healthiest of fish. If there is no low grade infection present to begin with then this scenario will not happen, however stressed the fish are.

Introducing a fish with white spot will also cause an outbreak in a similar way where it will act as a host and again, the increase in theronts will overwhelm the other previously healthy fish.

Treatment

There are a few options available and each is suited to different circumstances.

Medication: See Treatment finder

The best option in most cases is to use a white spot medication, a good brand will not affect the nitrifying bacteria, is perfectly safe for the vast majority of fish and is extremely effective. There is no need to stress the fish with a rise in temp when using a chemical remedy in a tropical tank. Medications like this work very effectively at normal tropical temperatures: trying to make it work 10% faster at the expense of stressing the fish simply isn't worth doing; Don't forget to remove carbon or other similar chemical filtration media from the filter during treatment.

Temperature method

Some fish don't tolerate medication and are as likely to die through its use as they are from the effects of the disease. In this case there is another treatment which is quite effective (but not 100% effective) against all strains of white spot. It is also quite stressful to some fish. This treatment involves raising the temperature to OVER 30C i.e 32C and this needs to be done accurately because if the real temp is only 29.8C then the white spot will worsen dramatically.

Once the temperature hits 30C most strains of white spot parasites cannot multiply and so the disease slowly dies out. Once the fish have been clear of all white spot for a few days this treatment can be stopped.

It is important that this method is used properly to make it fully effective. Most of us know that we shouldn't make sudden changes to our fishes' environment and so the common sense approach would be to slowly raise the temperature until the desired level is reached - WRONG.

If you do this the parasite will increase dramatically as the temp starts to rise and a mild infection will turn into a very dense and life threatening infection. The temp must be raised quickly, as quickly as the heater will raise it in fact. Doing this will prevent a rapid increase in theront numbers and once the desired temp is reached they will begin to decline in number.

Very warm water holds less free oxygen than cooler water, so make sure that adequate aeration is added to the tank when using this method. I have also heard that adding salt when using this method will be helpful.

Well yes and no, salt is certainly effective against the parasite but it will also further reduce the level of free oxygen in the water and could put us in the situation where the treatment works but the patient dies!!!

Once the fish are free of white spot and have been free of it for a few days you can return the temp to a more normal level. BUT, unlike raising it the temp drop must be done slowly. If the fish have acclimatised to a high temp their metabolism will have speeded up, if this is suddenly reduced their metabolism will slow down and they may go on hunger strike as a result. By reducing the temp slowly their bodies will have time to adjust and problems can be avoided.

Cold water fish:

Are a problem since neither of the methods mentioned so far are really suitable. Chemical treatments break down and become ineffective after a relatively short time in water but the white spot parasite has a long life cycle in cooler conditions which in winter in a pond could last for weeks, making medication fairly ineffective. The temperature method can't be used because it would be too stressful for the majority of cold water fish to be kept at the temp required, and some would die as a result of the temp alone. Fortunately salt is effective against the parasite and it won't degrade in the water over time.

To treat with salt use a dosage of 3gms/l and remember to use the same level of salt with any water replaced during water changes.

About White Spot

There are two conditions referred to as white spot and a third - far more deadly - condition, which looks very similar and is often mistaken for white spot. The two conditions which are actually white spot are Ichthyophthirius multifiliis (which lives in fresh water) and Cryptocaryon irritans (which lives in salt water). The third condition where the initial symptoms appear like white spot and which is impossible to tell apart just by looking is called Tetrahymena pyriformis: all three conditions have to be treated in a different way. This article will concentrate on the fresh water side of things only.