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Diseases and Treatments for Pond Fish

When keeping fish whether it be in an aquarium or in a fish pond, the downsides has to be when one of our beloved pets contract a disease or infection which can sometimes result in a mortality if swift action is not taken. This problem may occur irrelevant of how careful we are so being pre-warned of the symptoms and which course of action to take can save a lot of our fish and give us the confidence to deal with the problems in a fast and efficient manner.

There are steps the we can take to prevent the introduction of disease and parasites, the first og which has to be keeping the water quality as high as we can in the fish pond, this will keep the fish at their healthiest and make sure that their immune system is at its highest. In the wild most fish can shake off diseases on their own, the immune system will fight of the problem in a few days but in the fish pond if the water quality is low the immune system of the fish can be weakened and the fish will start to suffer from stress, this then allows the diseases and infections to get a foothold on the fish and start to affect their overall health.

When purchasing new stock for your fish pond it does pay to quarantine the new fish for a few weeks before adding them to the fish pond, any signs of illness will show in the quarantine period and these fish can be treated separately from the main stock without any fear of the disease spreading through the whole of the fish pond. Many keepers may skip the quarantine period, maybe their budget doesn't allow for a quarantine tank, but by adding the fish directly to the fish pond, the risk of infecting the other fish is greatly increased.

Keeping a close eye on your fish can often give you a head start in spotting any kind of symptoms leading to diseases or parasitic infections. I always found it best to do this at feeding times, are any of your fish losing their appetite? Are any of your fish keeping away from the other fish or hiding in the corner of the fish pond? These two signs are classic symptoms that something is not right as is unusual wounds on the body of the fish or fungal growths that appear like tufts of cotton wool on the fishes body or fins.

This article will list the most common ailments and how to spot them, there are many treatments available and over the years some keepers may prefer one brand compared to others, usually it is a matter of personal choice as long as the treatment contains the necessary additives to treat the fish properly.

Dropsy Disease

This has to be one of the worst diseases to hit the pond fish as if spotted in the later stages it is often too late to treat the fish and the most humane action to take is to euthanase the fish to put it out of its misery. Classic symptoms are swelling of the abdomen, the scales may start to protrude sideways ( the appearance of the scales has led this disease to be known as pine cone disease for obvious reasons).

It is often a follow on the the fish having open sores or wounds, the bacteria enter the fishes body through these points and quickly affect the fishes vital organs. It is associated with two main bacteria, Aeromonas hydrophila and Mycobacteriosis . The disease seems more common in fancy goldfish, the common goldfish and Koi carp. If caught in the early stages it may be possible to treat with a suitable antibiotic medication but this can be tricky and often to no avail.


The easiest definition of an Ulcer is purely an open sore that can be caused by poor water conditions which in turn can weaken the fish immune system allowing parasites and bacterial infections to take hold. Fish are protected by a slime coat that acts as a shield against invasion, if this shield is weakened then foreign bodies can be allowed to enter the fish and cause havoc. If untreated some of these ulcers can become quite large and leave open, gaping wounds which in turn means that the fish can lose bodily fluids and in the worst scenario, mortality can occur.

Segregate the fish that possess these ulcers and treat with hydrogen peroxide directly applied with a swab, in more severe cases you should also feed the fish with medicated food that contains antibiotics.

One word of warning here, hydrogen peroxide can affect the eyes and gills on your fish so always apply carefully and avoid these areas.

If parasites are causing the ulcers then treat with a suitable parasitic medication, check the fish over carefully to see if the parasites are flukes, anchor worms or lice, there are different treatments for each one. The treatments can take up to 14 days to take effect so keep the fish segregated until fully cured or you do run the risk of spreading this problem throughout the fish pond.

Fin Rot

This has to be one of the most common and easily recognisable diseases in fish and can be treated easily if spotted at an early stage. It is caused by a bacterial infection and yet again strikes weakened fish so poor water quality is usually associated with this disease. The first signs are the fin membranes changing to a cloudy colour, these will then start to rot leaving the rays of the fins exposed, in turn the rays themselves will also begin to rot. The rotting will work its way to the bottom of the fin and then start to affect the body of the fish, if allowed to reach this stage the treatment can be harder to apply and is often less successful.

Fin rot is classed as a secondary infection, the factors that brought this about must be eradicated, test your fish pond water to make sure that the parameters are of a high enough quality to keep your fish healthy, if not make sure that your filtration system is capable of handling the ammonia and nitrite levels in the fish pond.

The fin rot itself can be treated by using a bacterial medication, treat the whole fish pond as well and also check that there are no parasites on the fish , if so treat for those with a parasitic medication.

The treatment is nearly always successful if the rot is caught in time and the fins will grow back unless they have completely rotted away, the fish should not suffer any long term effects.

To prevent this disease in the first place you should keep the water quality high, keep the fish pond clean and the bottom of the pond vacuumed so that any nasties cannot harbour in there. Many keepers will feed their fish with a medicated food in the spring as a precaution.

Fungal Infections

Fungal infections can be quite commonplace with some specimens of fish, unfortunately for us, the fungal spores can be ever present in the water column or even on décor waiting to take hold on a weak or injured fish. They can colonise lesions or open sores and appear as white filaments or even a white fluffy area resembling cotton wool. The spores feed on the external tissues of the fish and can spread over time if left untreated. Generally fungus can be easily eradicated but to prevent the problem in the first place, keep the water quality high so that the fish are strong and healthy, remove any sharp objects from the fish pond that can cause injury and perform regular fish pond maintenance to keep the fish pond clean.

The most common method of treating fungal infections is to use Malachite Green mixed with Formalin. For milder cases it is often only necessary to add some aquarium salt to the water in a quarantine vat and then place the infected fish into the vat until the fungus disappears.

White Spot (Ich)

Everyone must have heard of White Spot, even people who do not keep fish, the most obvious symptom are the white dots covering the fins and body of the fish, these are cysts that contain the protozoa Ichthyophthirius multifiliis, these feed on the tissues of the fish and can only be treated when the spores fall from the fish and are free floating in the water. The cysts will fall to the bottom of the fish pond and then release even more protozoa so after treating it is always best to perform a good vacuum to remove any remaining cysts. There are many commercial treatments available and the success rate is very high. The treatments should be applied as per instructions and the full course must be added for them to be effective, even if the fish look like they are clear, keep adding the treatment until the course is complete.

If treated correctly there should be no mortalities from this condition.

The above are the most common diseases that are found in pond fish, keeping the water quality high and the fish pond well maintained should prevent a recurrence of disease, perform regular maintenance of the fish pond and always observe the fish themselves, any sudden changes in their behaviour is usually a good indicator that something is not right!

Question left on Sat, 20 Apr 2013 05:02:44 by Amanda

I have lost a lot of fish this winter for no obvious reason - from 19 down to 5. Our pond is set into a decked area behind the house and has a pump, waterfall, filter and plants,

pH 8.5
Ammonia 0.1
Nitrite 0-0.1
Nitrate 10

The orange colour on my goldfish (which is orange with black tips on fins and tail) appears to be fading in strips along its back and side (its not an old fish) and I think possibly one of my Shubunkins is developing the same problem - any ideas? I can't see anything else wrong with any of the fish (no White Spot or Fin Rot).

Answer by staff: Hi Amanda

Goldfish can change colour at any age although it is more common as they reach adulthood and old age. Loss of sunlight and their diet can also affect their colouration but there are colour enhancing foods on the market for this problem.

How deep is your pond as we have just emerged from a very harsh winter and I an just wondering if the water was deep enough fore the fish to go down to, for goldfish I would suggest at least 36 inches in the deepest part.