Oscar Disease in Aquarium Fish

Oscar disease is a common name for one of a few ailments that Oscar fish frequently succumb to. The most common of these is hole in the head disease, or HITH. HITH is frequently associated with Oscars because of the popularity of the fish and the frequency with which they are kept in substandard conditions (as is the case with many other large, easily obtainable fish). HITH can progress rapidly if left untreated, and is often fatal if it reaches its late stages without action.

  1. Symptoms

    • HITH is characterized early on by small, round lesions across the affected fish's face, gills and mouth. As the disease advances, the lesions become larger and more pitted, eventually developing into gaping holes on the fish's head and lateral lines. The fish may also become lethargic and go off its food.

    Causes

    • Oscar disease is almost always caused by substandard water conditions or food quality. Some studies suggest it is akin to scurvy in humans, a condition that develops after prolonged vitamin deficiency, but it is likely a combination of these factors which causes the onset of illness. Fish fed on a diet primarily based on feeder fish are often afflicted at some point, as are fish which are overcrowded into a tank (which in turn leads to low water quality and high stress).

    Treatment

    • Treatment of HITH should begin with 30 percent water changes done every three days, in combination with improved food quality, such as the introduction of a balanced cichlid pellet. If the disease has progressed into advanced stages, metronidazole can be dosed into the aquarium water to help treat secondary infection. (Remember to remove the carbon from the filter to prevent it from absorbing the medication.)

    Prevention

    • HITH is easily prevented by maintaining good water quality and offering a well-balanced diet comprised of both pellet or flake food and frozen or live snacks. Test water parameters often to make sure that ammonia, nitrate and nitrite all stay at 0 ppm. Give your fish plenty of room to swim and lots of hiding places to break the line of sight between fish in the tank.

    Other Conditions

    • The Oscar disease name is also sometimes applied to other conditions that may appear in Oscars, such as fungal infections. If fungus is suspected, treat in the same manner as for HITH, but dose Malachite Green in addition to the metronidazole. Fish with suspected fungal infections should be quickly quarantined to avoid the spread of illness between fish.