Goldfish health problems. Treating fish disease.

As any responsible, loving parent will testify, it doesn’t matter how well you look out for your children’s welfare, at some time they are likely to experience an unpredictable eventuality or catch the latest bug that is ‘going around’.

These health problems are recognised as the trials of life and by no means reflect poorly on their parents. The same can be said for fish.

Goldfish are peace-loving, non-aggressive fish. They keep themselves to themselves and if provided with a healthy pond environment, will have the potential to outlive an other household pet.

However, infective ‘bugs’ would not be doing their job if they didn’t regularly try to attack a fish’s immune system, (water is a very effective transmitter of disease). Goldfish and other pond fish are also prone to accidental bumps and bruises which if left untreated could prevent fish with problems as they may well become infected later.

The vast topic of fish disease is a potentially mind blowing subject when confronted by the number of disease causing organisms and their mode of attack. However by sticking to a few simple rules of husbandry while looking out for a number of behavioural symptoms displayed by fish, a responsible pond owner can soon become skilled at identifying and treating diseases well before such problems get out of hand.

What are the signs?

A healthy goldfish should show a good appetite and actively compete for food at feeding time. If some or all of the fish deviate from ‘normal’ behaviour, then it is likely that there is a problem developing, and waiting for your diagnosis and intervention.

A change in behaviour should be interpreted as a fish showing the first signs of ‘discomfort’ in the current conditions. The likely cause of such discomfort is a decline in water quality that unless redressed, will lead to the fish’s defences being lowered. The fish’s condition will deteriorate and a full-blown disease will develop unless the cause of the stress is removed.

Which Disease?

There are many diseases, some of which can only be positively identified by taking a mucus scrape and viewing the sample under a microscope. Very rarely though will a fish only be plagued with a microscopic disease, but will more than likely show other visible symptoms. The most common diseases that can be diagnosed by the naked eye are as follows:-

1. Finrot. Caused by bacteria that erode the tail and fin tissue. Can progress to kill a fish if left untreated. Most commonly gets a foothold after poor water conditions.

2. Fungus. A white cotton-wool like growth on any part of a fish’s body. Fungus is not contagious between healthy fish but will invade existing wounds or abrasions. Treating abrasions will reduce the likelihood of fungal infection.

3. White Spot. Pin head white spots all over the fish’s body and fins. Caused by a microscopic parasite. Fish appear to be more susceptible to whitespot after extreme changes in water temperature. If left untreated, it will rapidly spread throughout the pond fish and take a heavy toll. Effective pond water treatments are available.

4. Ulcers. Usually on the flanks or belly of a fish, an ulcer is a blood-red localised depression in the skin, where scales and tissue have been eroded away by bacteria. Can be very difficult to treat and many fish are lost to Ulcers each year.

5. External Parasites. Although the majority of these are not visible to the naked eye, their presence can be apparent through fish flicking, flashing and scratching through irritation. The aquatic equivalent of animal fleas, they can be treated by dosing the pond water with medication.

6. Carp Pox. The symptoms look worse than their effect on fish. Similar to warts in humans, Carp Pox is caused by a virus and will recede when temperatures warm up, allowing the fish to fight the virus themselves. No medication is effective against Carp Pox.


Of the above goldfish ailments 1-5 can be treated effectively by pond treatments available in aquatic stores. Unlike treating any other pet, the fish themselves are not treated, but rather their environment, where pond water is dosed with medication. In this way, it costs the same to treat 1 fish as 21 fish in the same pond. With most problems, it is essential that the whole pond is treated to avoid re-infection.

Goldfish disease problems are more frequent in ponds in the spring when water temperatures start to rise after the long winter. Fish that have over-wintered may well have gone several months without eating, and their body reserves will be at their lowest.

In such circumstances, and at low temperatures, the goldfish’s immune defence system will be suppressed, leaving it vulnerable to attack. Pathogenic bacteria will multiply a lot quicker than the fish can adapt, increasing the likelihood of disease. For this reason, it can be a wise course of action to dose the pond with a broad spectrum antibacterial treatment as winter turns into spring to aid fish in their battle against disease. This is also widely practised in autumn to assist fish through their winter break.

Kill blanketweed and string algae.