Why Do Fish Rub Their Body Against Objects?

When a fish rubs against objects, it usually has parasites irritating its skin. Protozoan parasites frequently plague aquarium fish. However, there are two major treatment options to clear up this problem. With quick intervention, you can probably save your fish if you start treatment when you see this behavior.

  1. Ich and Velvet

    • If you encounter parasites in your aquarium, they will almost certainly be velvet or ich. These are very similar infections. Both ich and velvet are protozoans, single-celled organisms with complex cells more like animal cells than bacteria. These particular protozoans have a complex life cycle, wherein they form cysts on fish during one stage. However, they also reproduce in aquarium gravel and have a more vulnerable free-swimming stage. Most treatments target the free-swimming stage, since the parasites can easily succumb to medication and salt treatment at this phase.

    Other Symptoms

    • In addition to rubbing their bodies on decorations in the aquarium, you will see other signs of these parasites. In ich, the body appears to have salt crystals sprinkled on it. These are the actual cysts, containing multiple parasites. In velvet, the cysts resemble powered sugar with a yellowish tint. Afflicted fish also act lethargic and may hide in the recesses of the aquarium or float aimlessly as the parasites weaken them.

    Salt Treatment

    • The older treatment -- but still quite effective -- for both velvet and ich is adding salt to the water. Keep in mind that some fish cannot tolerate even low levels of salt; cory catfish and elephant-nose fish are known for this. If you have these fish, stick to medications. To treat with salt, raise the aquarium temperature to between 82 and 86 degrees Fahrenheit. Measure out 3 teaspoons of salt per gallon of aquarium water. Mix this salt into aquarium water in a bucket; don't just dump it into the main tank. Thoroughly mix the salt, completely dissolving it, then dump the salted water into the tank. Ich or velvet should clear up in about a week. Regular water changes will dilute and eventually remove the salt.

    Medications

    • Most pet shops sell medication that will clear up ich and velvet. Read the labels carefully and follow the manufacturer's instructions to the letter. When treating with a medication, remove any carbon or zeolite from the filter and discard it. These materials absorb medications and may render them inert. Like salt treatment, medication typically takes about a week to clear up the infection. However, some antibiotics may harm the bacteria that break down fish waste in aquariums, so test ammonia and nitrite levels when using them.

    Other Ailments

    • While ich or velvet are the most likely culprits, a few other conditions may cause fish to rub themselves against objects. If you've recently changed the water, or didn't dechlorinate it, there could be problem with your tap water. Consult your local fish store to find out if the local water has any quirks. In some cases, you may need to resort to water purification like reverse osmosis. Additionally, bacteria and fungi can cause similiar infections. In these cases, you may see red streaks or ulcers on the body, or fuzzy or slimy patches. They tend to resist salt treatment, but antibiotics and antifungals work almost identically to anti-protozoan drugs. Just read the label and follow directions carefully.