Does your fish dart about like something's chasing him? Perhaps he runs into the gravel and tank decorations with a violent twisting motion. First make sure something isn't actually chasing him! Then watch his behavior closely for other signs of trouble.


Many conditions can make your fish swim like he's got one oar out of the water. Skin and gill parasites like ich, saltwater ich, gill and skin flukes, fish lice and anchor worms are common problems and cause itchy skin or gills. Affected fish often try to rub, or "flash," the affected area on hard surfaces such as aquarium decorations.

If your fish struggles to climb or dive through the water, his swim bladder may be infected. Circling and whirling patterns often indicate nervous system disorders. Sometimes bacteria or even parasites infiltrate the brain and surrounding tissues, causing neurological damage.

Another obvious but overlooked reason behind erratic swimming is blindness or poor vision caused by cataracts or corneal damage. Heredity or nutritional deficiencies produce cataracts; trauma or bacterial infection typically brings about corneal abnormalities. Fluid retention or excess gas in the water can lead to a condition called exophthalmia (pop-eye), which can impair vision. In some fish species, tapeworms or flukes can find their way into the eye, causing it to turn white and blind. Water quality problems, which can lead to increased waste by-products in the water, may irritate your fish. They may respond by darting about uncomfortably.

What You Can Do at Home

First, test the water for common abnormalities, such as ammonia, nitrite and pH imbalances. Your local aquarium store or veterinarian can perform the tests if you don't own a kit. Check your aquarium thermometer and air pump to make sure they're working properly.

Next, perform an immediate 25 percent water change and siphon the debris from the gravel to improve the biological filtration. Make sure you dechlorinate the new water and match the water's temperature and pH. Diluting the pollutant or disease organism within the tank may buy your fish valuable time while you attempt to uncover the cause.

When to Call the Veterinarian

If water analysis doesn't yield any answers, consult a qualified fish veterinarian right away. He or she may examine your fish, recheck your water parameters and take a thorough medical history to identify the problem. The doctor also may recommend gill biopsies, impression smears of the skin, blood tests, X-rays and an ultrasound. The veterinarian may need to eliminate all possible pathogens one by one to determine the cause of your pet's distress.

If you can't find an aquatic veterinarian in your area, consult knowledgeable local pet store employees about your problems. Researching the symptoms on your own may be a last resort, but many books provide excellent information.


The prognosis for your fish's strange swimming behavior varies from good to guarded. The veterinarian can usually treat diseases such as fish lice, skin flukes and anchor worms. Ich, amyloodinium infection, gill flukes or nervous system disorders can cause irreversible damage. Blind fish rarely survive because vision loss often results in starvation.