Koi Diseases

Early detection is the key to keeping your kois disease-free. By making it a habit to regularly scrutinize your kois when they surface to feed, you can spot unusual behaviors or physical changes that can alert you to stress or illness.

Common koi diseases come from four quarters: parasitic, bacterial, viral and fungal organisms. Parasites afflict kois when you don't take the time to quarantine a new fish before putting it into the pond. They can latch on to the gills, skin, mouths, and fins which are the preferred breeding grounds for pathogens.

Observe for changes in the skin and fins first as these areas are more vulnerable to infections. The fins are used for movement, balance, and direction; take a closer look for possible infestations if they're moving jerkily or not at all. The mucous layer that surrounds that skin is also the koi's first line of defense against pathogens. Thickened skin around the head or body is usually indicative of parasites.

Be concerned when there are reddened or abraded areas around the fins, the mouth or the underbelly. Foggy patches on the skin, sores, white cottony growths, and rotten tails usually point to bacterial, viral or fungal infections such as ulcers, and tail/fin rot, as well as mouth fungus, flexibacter, cotton wool/mouth, columnaris, and koi herpes virus diseases.

The worst that could happen to your koi is when they get dropsy (or pine cone disease). The koi’s belly is unnaturally swollen and its scales are raised, not unlike pinecones in appearance. It may mean heart or kidney failure, or an internal bacterial infection. When that happens, your koi will be beyond help as dropsy usually leads to death.

You also need to watch out for these behaviors as they often mean an unwell or stressed fish:

1. Doesn't feed. Kois are discriminating eaters so it might be just a dislike for the food you've given them. If the lack of appetite persists, your koi may have a bacterial infection like cloudy eye, or cotton wool disease (indicating the white cottony growths around the mouth).

2. Stays at the bottom of the pond for long periods. Your koi may be infected with skin flukes or costia, especially if they have clamped fins. If the lethargy is coupled with uncoordinated movements, bulging eyes, skin hemorrhages, and a bloated appearance, then your fish may be afflicted with spring viremia of carp, a viral infection.

3. Labored or uneven breathing. The kois may have gill rot, a fungal infection, or be infested with chilodonella or gill flukes, especially if you also see them rubbing their bodies against rocks and pond surfaces or are swimming jerkily.

4. Rubs body against rocks and sides of pond. When your kois start scratching their bodies against surfaces in your pond, chances are, they've trying to scratch off parasites like the anchor worm, chilodonella, costia, fish lice, leeches, skin flukes, trichodina, or the "Ich." Their skins could get abraded, which would leave them defenseless against pathogens.

There are several ways to nurse sick fish back to health and keep the rest hale and hearty, but improving pond water quality, testing for elementary imbalances, and continuous water changes still remain to be the best defense against disease-causing pathogens. If you suspect a more severe illness, quarantine the sick fish so you can prevent a pandemic in your pond.