Disease In Fish


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You have set up your perfect aquarium, it has beautiful fish and a great look, but then something goes wrong, maybe your fish start dying, maybe they are showing abnormal behavior. Chances are your fish have caught a disease. But don’t panic! There are ways of treating it and making sure it is unlikely to happen again.

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How does a fish get diseased?

In the aquarium and in your fish live many bacteria, viruses and life forms known as protozoan. Many of them are ‘good’ to have as they keep the balance just right. Even the life forms that cause the illness are present, but because of this balance they don’t cause problems. However when a fish becomes stressed, either due to sudden changes or an unbalance such as a large amount of pathogens being introduced, it is at much greater risk.

How can you prevent it?

Making sure the aquarium is clean and taking precautions to monitor the levels within the aquarium is essential. Also making sure the fish can carry out their natural behavior, such as hiding, by providing the right environment will reduce stress. This also means making sure none of the fish are bullying each other or are being timid of other species in the tank. You should also be careful when introducing new members, making sure they are healthy specimens without disease. Even with such precautions, disease may still take hold from time to time.

The first signs!

It is important that you learn to spot the signs early so that you can treat it quickly and prevent it from becoming a bigger problem. The behavior of the fish may become notably different. Reluctance to feed, darting around in an alarmed state, no balance, rubbing or darting past objects, hiding more than usual, being shy, or unusual positioning in the aquarium are all early warning signs.

More physical signs include swollen or distended appearance, fins discolored, eroded or clamped to the fish. The gills may change color, look sore or move rapidly. Eyes may look swollen or cloudy and the mouth may look eroded, sore or ‘sticky’. You may notice that the fish has darkened or became paler or perhaps has spots or discolored areas. You may even notice holes, ulcers, growths or sore areas on the body of the fish.

If you have noticed any of these signs you can now use the information below to determine what it is and how to treat it effectively.

Poor water quality or water poisoning

Symptoms: Fish gape at the surface, or hang by the surface. They have rapid gill movement and may lull onto their side. There may be patches of slime on the body or near the gills. Eyes may appear clouded and the color of the fish may darken. The fish may also suddenly dart around before returning to the surface or losing balance. This may only show up in certain species depending on the cause

Causes: Poor water quality, meaning either high or low Ph levels, or high ammonia and nitrate levels. This could be caused by over stocking tanks with too many fish. It could also be due to chlorine or excess metals following a water change with untreated tap water. If certain species are showing it, it could be from excessive treatment of previous disease of which they were susceptible to an active ingredient, this applies to invertebrates especially. There also could be the possibility that a toxin has entered the water, household cleaner, sprays, room freshener and so on.

Care: Test the water for Ph and nitrate ammonia levels. Treat according to results. You should also perform a water change with pre-treated water (use a tap safe water treatment). Following that you should also try to work out the exact cause so to take precautions.

Swim Bladder

Symptoms: Unable to maintain balance, swimming upside down, on the side or being pushed to the surface. May also be unable to swim up and may hit the side of the tank and roll over. This is not accompanied by any other symptom.

A bacterial infection, or previous damage from a bacterial infection in the swim bladder. This means the fish cannot swim as normal and this in itself causes a lot of stress and if untreated, death.

Care: Treat with a preparation to treat swim bladder, be sure to follow the manufacturers advice. You can also use tonic salt in quantities of 5g per litre. This will help the fish right itself, although must be added over a few days to avoid shock.

Internal Bacterial Infection

Symptoms: Often the first sign is unexplained deaths as it has variable symptoms, which can at first indicate wrongly to other problems. These symptoms can include, fins appearing eroded or opaque, eyes becoming swollen, distended or a hollowing of the abdomen, holes or ulcers on the fish, the fish’s color becoming darkened and the fish being unable to maintain balance. However any one of these symptoms can show with any other, sometimes they don’t at all.

Causes: An unbalance in the bacteria in the aquarium, as well as poor water quality. Will occur following stress by any factor and especially so if the fish has been wounded or fighting.

Care: Previously only veterinarian prescribed antibiotics have been effective, however you can now buy an internal bacteria solution to treat the water directly. You should also test the water for any unbalance and act accordingly.

Bacterial Gill Disease

Symptoms: The fish will gaps and hang at the surface of the water and you may notice rapid gill movement, the gills will also look pale and in severe cases look eroded.

Causes: A bacterial infection usually at the onset of an internal bacterial infection. However this is localized to the gills for the time. An unbalance in the water quality and stress can cause this to happen.

Care: Like an internal bacterial infection you could only previously use veterinarian prescribed antibiotics. However swift treatment with an internal bacteria solution will remove the threat directly. You should also test the water for any unbalance and act accordingly.


Symptoms: Bulges that are white or cotton wool like growths, particularly on the head and sides.

Causes: An imbalance of the fungal spores naturally found in aquaria, usually after stress or damage to gill or mucus membrane.

Care: Use an anti fungus treatment for freshwater fish. Check that the water quality is okay and that there is nothing damaging your fish.

Fin Rot

Symptoms: Fins appear eroded, opaque and may have streaks of ‘blood’ running through them.

Causes: Unbalance of naturally present bacteria, usually after the fish has been stressed.

Care: It is important to treat this promptly before it reaches the base of the fin. Treat with an anti fungus and fin rot treatment and check water quality.

Mouth Rot

Symptoms: There may be some erosion on the head but more focused around the mouth, there may also be some cotton wool like growths around the mouth area.

Causes: Unbalance of naturally present bacteria, usually after the fish has been stressed.

Care: An anti fungus and Fin rot treatment should clear it up, follow with a water test. It is important to act quickly.

Slime Disease

Patches of slime accompanied by flicking and rubbing against objects, as well as cloudy eyes. You may also see the fish gaping or hanging near the surface and the gills may appear pale although this isn’t always seen.

Causes: Stress allows parasitical infection from parasites naturally present.

Care: Use an anti-slime and velvet treatment, test the water and remove any areas of stress.


Symptoms: The fish will have an abnormal peppering of golden spots and will rub against objects in the aquarium. The fish may have pale gills and gape at the surface, but this isn’t always seen.

Causes: Unbalance of naturally present parasites, usually after the fish has been stressed.

Care: use an anti-slime and velvet treatment, testing the water and removing any stress factors.

White Spot

Symptoms: There will be lots of abnormal white spots, about the size of a grain of sugar, accompanied by flicking and rubbing against objects in the aquarium. The fish may also gasp at the surface and have pale fins.

Causes: Unbalance of naturally present parasites, usually after the fish has been stressed.

Care: Use a white spot treatment preparation and lower the temperature of the aquarium by a few degrees for a week. Remove sources of stress.

Higher Form Parasite

Symptoms: The fish may gape and hang at the surface. It will have pale gills that may sometimes appear eroded. It will rub along solid objects and plants and may try to jump out of the water but most obvious is that it will have pale discs, worm like attachments or thread like discs on the body or gill area.

Causes: There are several causes, usually from infection from wild caught or infected stock. The offenders are mainly crustacean and have different appearances. Anchor worms are up to 20mm long and bury into the skin of the fish. Fish Lice are disc shaped parasites that feed on the mucus membrane, on skin or the fins. They can cause bacterial infection. Gill maggots are found attached to the gill area, as well as in the mouth and are called such because of the maggot like egg sack that is often seen. They can all cause death, but gill maggots even more so.

Care: Use an anti crustacean parasite treatment as soon as you notice any symptoms. Read the instructions carefully as they can have some side effects on the condition of your aquarium. If possible try to identify the source of your problem and deal with it appropriately.

Source, http://www.articlecity.com/articles/pets_and_animals/article_2744.shtml