Common Diseases in Aquarium Fish

Fish That Come Down with an Illness Need to be Medicated

Oct 20, 2009 Ian Shoust

The most common diseases that afflict aquarium fish are ich, velvet, and fungus infections. Untreated, these diseases can kill fish, but prompt action usually cures them.

Diseases in aquarium fish can occur when the fish is stressed, injured, malnourished, is housed in a tank with poor water quality, or from other fish. If fish become ill in an aquarium, it is always a good idea to test the water. After that, the fish will need to be treated. Here are the symptoms of the most common diseases in aquarium fish, and what can be done to treat them.

Ich (Ichthyophthirius)

Ich, or white spot disease, is the most common disease that affects aquarium fish. It is a protozoan disease, and looks like little white dots covering the fish (see picture below). The ich parasite usually attacks fish when they are stressed, such as when they are moved to a new tank, or if the water quality in their aquarium is poor. Ich is contagious, so a fish with ich should be isolated in a different tank, if possible.

One of the first signs of ich is that the fish rub themselves up against the gravel or other ornaments in the aquarium. If caught early, ich is easily eradicated with over the counter medications available at your pet store. Most of these medications require the carbon to be removed, and the temperature to be raised in the aquarium. These medications are usually effective within 3 days. After treatment, a 25% water change should be made, and new carbon should be put in the filter.

A healthy and varied diet will help aquarium fish be more resistant to ich. Adding garlic to the diet of fish also helps to ward off the ich parasite. Seachem makes a product called Garlic Guard that can be added to frozen food to help keep fish ich free.

Velvet

Like ich, velvet is a parasitic infection, caused by the protozoan Oodinium. It looks similar to ich, but the dots are smaller. The dots are also not always white, but more yellowish in color.

As with ich, the early signs of velvet are fish rubbing against the gravel or other hard surfaces in the tank. There are many treatments for velvet, and often, the same medication treats both velvet and ich. Caution should be used when using medications containing copper. If a fish is scaleless (loaches, eels), then only a half dose of the medication should be used. Many of these medications also kill invertebrates, such as snails. Read the directions of any medication carefully, to make sure it won't harm anything in your tank.

Body Fungus

Diseases described as fungus are actually bacteria, collectively described as Columnaris. Mouth fungus, or cotton mouth disease, looks like white tufts of cotton are growing out of the mouth. Body fungus looks the same, except the cotton-like tufts appear on the body. Red lesions on the fish are also common symptoms of body fungus. Fin and tail rot is when this bacteria attacks the tail and fins of aquarium fish, and causes them to slowly disintegrate (see below).

Fish fungus enters the body of aquarium fish through open wounds. It is contagious, but easily treatable. There are a variety of medications on the market that cure fungal infections in aquarium fish, as well as help them grow back scales and fins (Erythromycin, Melafix, PImafix etc). Staff at your pet store should be able to point you in the right direction. The carbon should be removed from an aquarium when treating fish with medication. Once the treatments are finished, a 25% water change should be done.

As with any disease, prevention in the key. Proper housing, good water conditions, and excellent nutrition prevent aquarium fish from falling ill the the first place.

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