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About Fish
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Fish Under Stress
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Visitors To The Pond
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The Pond Through The Year
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Autumn & Winter
Breaking The Ice
10 Problems
Useful Facts & Figures

Allotment Articles1.
Allotment Articles 2.

Fish Diseases And Parasites

Fish, like any other animal, can catch various diseases and likewise they are also afflicted with a range of parasites. Some are relatively trivial and easily treated with a salt bath, or proprietary medicine, but others need much stronger medicine which can only be prescribed by a vet.

As with most ailments prevention is better than curing the problem after it occurs and maintaining healthy water in your pond should prevent most problems. Below are listed some of the most common problems affecting fish and their symptoms.

ANCHOR WORMS. This parasite is quite large and easily seen with the naked eye as they grow to about 2cm in length. Their very distinctive shape, as the name suggests, is recognizable as an anchor. The parasite makes a sizeable wound in its prey and grips on tightly. It can damage the fish quite severely if they are removed clumsily, but a parasite treatment should easily kill them. They are most often seen on Koi Carp.

BLACK SPOT. This is another parasite and not to be confused with the natural black markings that a lot of goldfish have when young. It is actually caused by a cyst forming in the fish around the parasite that gradually gets bigger making a black circle on the fish. It is relatively harmless, but as with any infection, should be treated with an anti parasite treatment.

CARP POX. As this is a viral infection, there is no treatment for it, but the one consolation is that it does not kill fish, it merely disfigures them. It can be likened to a Human catching a cold, as it is relatively harmless. The symptoms seem to be most prevalent at low temperatures such as during the winter in a pond. 

In the summer the symptoms often disappear as they do when the fish gets older. An infected fish will develop white lumps on its body. It is contagious, so infected fish should be isolated from other carp related species. Again this problem seems to be most common with Koi keepers. 

DROPSY. There are some new medicines on the market that claim to be able to treat this viral infection. If a fish is badly infected it should be destroyed as the disease is slightly contagious. It is thought that infected fish catch the disease by eating fish droppings. Dropsy causes infected fish to swell up, because the osmotic process that regulates the fishís body fluids, fails, resulting in the fish retaining water. This eventually makes the scales stick out like a pinecone. Dropsy is quite rare in ponds, but a fairly common problem in aquariums.

FIN ROT. This is a bacterial infection that is very common in poorly maintained aquariums and very small ponds. It is caused by bad filtration leading to polluted water. The bacteria often cause the fins to be reddened and will gradually cause the fins to slowly be eaten away leaving only the bones. However with prompt treatment the fins usually re-grow as good as new. Any bacterial treatment will cure this disease and it should never be fatal.

FUNGUS. This looks like a tuft of cotton wool growing on the fish. In very green water it may appear to be green, but is otherwise white in colour. The infection is actually secondary in its nature. That is to say that the fish must already have a problem such as an open wound before fungus develops. The problem may be caused by any number of things including pollution, so to cure it you have to find the original cause as well as treating the fungus.

GILL FLUKES. These are small parasites that embed themselves in the delicate membranes of the gills. In an infected fish the gill flaps often stick out and appear reddened making breathing difficult for the fish. Any proprietary anti parasite treatment should cure the problem quickly and effectively.

GILL ROT. This bacterial infection is particularly nasty and difficult to treat. It is often seen in Koi that have just been imported from a breeder who was not fussy about his water conditions. In a badly infected fish not only will the gill smell and be seen to be rotting, but the gill flap may well have a hole in it. In extreme cases the fish should be destroyed.

LEECHES. These are of course a parasite and as such are easy to get rid of. They can be removed physically, but it advisable to wear gloves because they can latch onto your hands and if pulled off will leave a barb in the flesh that will fester. They do not appear very often in aquariums but are quite common in ponds as they can arrive on plants as eggs.

LICE. These are a special variety specially adapted to live in water on fish. They irritate the fish causing them to rub on ornaments and the side of the pond, but donít cause any great damage. However they can spread disease and if suspected should be treated with any parasite treatment to destroy them.

MOUTH FUNGUS. This is not actually a fungal infection but is caused by a bacterium. In an infected fish a small wisp of fungus may be seen to emerge from the fishes mouth and gradually part of the mouth will be eaten away. If the infection is not to severe it may be treated with a good medicine, but in bad cases the fish will have to be destroyed. It does not seem to be contagious. 

PROTOZOAN INFECTION. Protozoa are tiny organisms that are bigger than a bacterium, but smaller than a parasite. They invade the victim by entering its bloodstream and then devastate the immune system. It is a particularly nasty problem as some fish are naturally immune and can act as carriers that then infect other fish. Hence, two apparently healthy batches of fish mixed together can result in one batch dying. Infected fish die quickly, but the organisms can also exist free swimming in the water. It is best eradicated by carrying out a water change before treating with an anti protozoan treatment. However, treatment is difficult and heavy casualties can be expected from any infestation.

S.V.C. This is short for Spring Viraemea of Carp and is a notifiable viral infection that only affects carp related species. Any dealer who gets infected with this disease has to cease trading and advise The Ministry Of Agriculture and Fisheries immediately, so it is very unlikely that you will have any fish with this disease. It is a devastating disease that sometimes breaks out in the Spring, but there have only been a handful of cases in recent years.

ULCERS. These often occur after minor damage to a fish, such as happens in the breeding season, or from a parasite infection. The minor wound may not heal properly and infection can then set in. In lesser cases it may be treated, but with severe damage it may be very difficult to affect a cure and may be best to kill the fish. 

WHIRLING DISEASE. This is not actually a disease, but is a parasite infection. It sometimes appears on newly imported fish that have been reared in dirty and overcrowded conditions.
The parasite bores its way into the brain of the fish and affects the way it swims causing it to spiral through the water. Any infected fish should be destroyed, as there is no cure for this condition.

WHITE SPOT. This problem should not be confused with fungus as it is very different. Firstly it is caused by a tiny parasite that becomes active when the fish has had a chill. This usually happens with newly bought fish that have not been acclimatized properly to their new pond. That is to say they have been taken out of relatively warm water and placed in a cold pond. Any infected fish will exhibit tiny white spots the size of a pinhead all over their bodies. The problem spreads rapidly from fish to fish and if left untreated, will, in a few weeks, kill all the fish in the pond. However it is relatively easy to treat and treatment works best at higher temperatures. In fact some cures claim to work within 24 hours.

Swim Bladder Disorder seems to affect Fancy Goldfish such as Black Moors and Fan Tails more than other varieties of fish. This could be due to the fact that it is caused by air being trapped in the swim bladder.

In fancy varieties of goldfish the fish is ball shaped unlike the streamlined shape of most normal fish. This compresses the stomach and intestines into a tight tangle instead of being stretched out. Indigestion is therefore quite common and can cause air to sometimes get trapped in the stomach that is then forced into the swim bladder, which is connected to the stomach.

A non-functioning swim bladder means that a fish loses its buoyancy control. This results in the affected fish swimming at odd angles in the water, upside down or even causes it to remain at the surface unable to sink. This problem can be very difficult to cure, but there are several treatments that may be tried. The first is to raise the temperature of the water. If, the afflicted fish is in a tank, this can safely be done in a tank by adding a thermostatically controlled aquarium heater to the tank. If this does not work the next best treatment is to feed foods with a laxative quality. For larger fish washed, chopped earthworms, or maggots are very good. For smaller fish any of the live foods commonly available for aquariums such as bloodworms are ideal. Even dried insect foods have some laxative qualities, but they are not as good as fresh, live food. 

Another perhaps more palatable food, for the squeamish to give their fish with swim bladder problems, is Elodea or oxygenating plant. Not only is it very nutritious for fish, but it has laxative properties as well. Even well tried and tested remedies such as these are not always effective and there are no proprietary medicines as yet on the market for swim bladder problems. If the fish is still feeding then it might as well be left alone because sometimes this problem will cure itself naturally.

On the other hand in extreme cases where the fish canít feed any more it may be more humane to simply kill it in the approved method. It is worth remembering that dried foods are often to blame for swim bladder problems and indeed a fish that swims normally most of the time will often exhibit symptoms shortly after being fed dried food. To prevent this occurring an occasional treat of some diced fresh earthworms is advisable.