FISH DISEASES – WHITE SPOT   

   For the first of this series on fish diseases we will look at perhaps the most famous fish ailment, white spot or “Ich”. White spot can affect all species of freshwater fish and is one of the more common diseases that can occur in aquariums and ponds. Although it is often treated as an ectoparasite (i.e. one that lives on the surface of the fish), it does in fact embed itself under the skin and is therefore an endoparasite.  
CAUSE

White spot is caused by a single-celled parasite, or “protozoan”, Ichthyophthirius multifiliis. Although there is a marine white spot disease, it is caused by a different parasite, Cryptocaryon irritans.

EFFECT

White spot causes damage to fish in a number of ways. Upon entering and exiting the skin it leaves a hole, which can then make it harder for the fish to maintain it’s internal salt balance, and which can become infected with secondary bacterial infections. The more parasites there are on the fish, the greater this effect is. If the parasite starts to affect the gills it can also cause the fish severe respiratory problems.

SYMPTOMS

Infected fish typically develop small white spots, up to 1mm in size, on the body and fins. Each spot contains a single parasite, and in severe infestations there may be thousands on a single fish. As well as the typical white spots, which generally take a few days to develop after the initial infection, the fish may also scratch and “flick” it’s body against objects in the tank.
In heavy infections, particularly if the gills are affected, the fish may show signs of severe respiratory distress (hanging near the surface, gasping etc.). Coupled with this it may appear lethargic, have pale skin, torn and ragged fins, areas of skin that are sloughing off, and be showing general signs of irritation (rapid movements, darting, twitching etc.). Once the disease reaches this stage though, treatment is difficult.

SOURCES OF INFECTION

There are a number of potential sources from which a white spot outbreak might develop. The most likely sources are newly introduced fish, new plants that have been taken from an infected aquarium, water from an infected aquarium, or certain live foods such as Daphnia or Tubifex that have come from infected sources. Fish that have previously been exposed to white spot can develop a temporary partial immunity to the disease. This means that if they have come from an aquarium that contains the disease they may not show any symptoms when introduced to the aquarium. However, if the fish in the aquarium have not been exposed to it they will subsequently “catch” white spot from these new fish. Sometimes the reverse can happen, if new fish are introduced to an aquarium where white spot has previously been a problem they may become infected, whilst the older residents are untouched.

PREVENTING INFECTION

There are a number of steps that can be taken to minimise the likelihood of suffering a white spot outbreak. If you are using live foods then these must be from a safe source, alternatively use fresh foods that are guaranteed to be safe, such as Tetra FreshDelica. If you buy a lot of fish then it may be worth setting up a small quarantine tank or pond in which to hold them for a few weeks, prior to exposing them to the rest of your fish. This will allow you to identify any potential problems and treat them as necessary. Alternatively, if you suspect that the new fish might be carrying something, you could treat the main tank or pond with a white spot remedy for a couple of weeks, after adding them. As with any new fish purchase, keep an eye on water quality and the behaviour of your fish for a couple of weeks after introducing them. As the infective stage of the parasite cannot survive for long without a fish host, new plants can be left in a fish free tank or container for a week (perhaps a few weeks if the temperature is low) in order to make them safe.  

LIFECYCLE   

   The lifecycle of white spot is important as it affects how the parasite is treated. This is because there are only certain times in it’s life when treatment is effective.   

The stages mark “treatable” are the only times when white spot can be affected by conventional remedies. The speed at which the parasite completes it’s lifecycle depends upon water temperature. At 10°C it can take up to 5 weeks for it to fully complete, whereas at over 21°C it is shortened to 3 – 4 days. At tropical temperatures the parasite can therefore be effectively eradicated within a week or two, whereas in a colder outdoor pond it may take much longer.   

TREATMENT

If your fish do start to display the symptoms of a white spot infection you should take the following steps:

Test the water, or pay a local retailer to test it, for ammonia, nitrite, nitrate and pH. Also ensure that the substrate, or base of the pond, is clean and that your filters are working correctly. Also check that there is plenty of aeration. Doing this will eliminate poor conditions, as these are often responsible for stressing fish and bringing on latent white spot infections.

Perform a 25-50% water change, using water conditioned with TetraPond WaterSafe or Tetra AquaSafe. This will dilute numbers of the water-bornestages of the parasite. Clean the base of the tank or pond, as this will reduce the numbers of reproductive cysts.

Add a whitespot treatment to the tank or pond. Some treatments can be harmful to certain species of fish, so unless you are sure it is best to use a safe onesuch as TetraPond MediFin or Tetra ContraSpot. Do not overdose the treatment and always make sure there is plenty of aeration, whilst the fish are being treated (this applies to the treatment of any disease).

If you have an aquarium then increasing the temperature by a few degrees can help, as it enhances the fish’s immune response, speeds up the parasite’s lifecycle, and directly affects the heat-sensitive white spot theronts. Do this slowly over a period of a day or two, and keep an eye on the fish, ensuring that there is sufficient aeration at all times.

In ponds, and in tanks that contain salt tolerant fish, adding salt can help to eradicate white spot and also aid the fish in it’s recovery. Always use aquarium or pond salt and not kitchen salt. Ponds can be dosed at 3grams per litre, and aquariums at 2grams per litre.

Perform a weekly water change of at least 25%, topping up with water that has been conditioned and, if you are using it, dosed with the correct concentration of salt. Most treatments require re-dosing at weekly intervals, but always follow the instructions provided.

Continue treating until the white spot has been completely eradicated. This will prevent the parasite re-infecting the fish at a later date. Whilst the treatment may only need to be added for 2-3 weeks in a tropical tank, in a coldwater aquarium or pond it is wise to keep it going for longer.

Following these steps will provide your fish with their best chance of recovery. If the disease is caught reasonably early on then treatment is not difficult, provided that any environmental problems that might have led to the outbreak are resolved quickly. Always monitor water quality closely during and after treating for any fish disease.

 

 

A fin covered in white spot.
Each spot contains a single parasite