So you've noticed that your koi are acting funny. Just yesterday, they were healthy and active. But now you notice a change. Time to diagnose and treat the problem as quickly as possible. While koi are vulnerable to a few different health issues, Columnaris is one of the most likely culprits.
What is it?
Columnaris is NOT some exotic new koi disease. However, it can show up occasionally. And when it does, it can cause a lot of damage to your fish in a short amount of time. Unfortunately, it is quite often misdiagnosed.
Columnaris is a bacterial infection caused by the bacteria Flavobacterium Columnare. It has been around since man started culturing fish, and it's not going anywhere anytime soon. It is present in practically all aquatic systems, and in the fish in those systems. From a home aquarium to a 500 acre catfish farm. No one is immune.
As with most pathogens, it causes no problems to fish in the absence of stress. However, environmental stressors such as over-crowding, poor water quality or sudden environmental changes can compromise the fish's immune system, leading to a Columnaris outbreak. Koi are especially vulnerable to Columnaris after the inherent stress involved in shipping. So take care and be extra vigilant for a few days after receiving new fish into your facility.
Microscopically, these bacteria appear as long, thin rods, usually clumped together to form dome-shaped masses with a "hay stack" appearance.
Fish will develop a white film over their body, with disintegrating fins and tails. Advanced infections will cause the fish to become emaciated, with sunken eyes and necrotic gills.
Anytime you see these symptoms combined with rapid mortality, particularly in warmer water, you should suspect Columnaris. Left untreated, it can kill 50% of a population in just 2 or 3 days.
Fin rot and sunken eyes on an infected fish.
Despite the white film that grows on an infected fish, Columnaris is not a fungus. The marketing of "fungus medications" for koi and goldfish is rampant. However, true fungus infections that cause mortality in koi and goldfish are exceedingly rare. Fungus medications will have no effect on Columnaris, and the condition will continue to worsen. Additionally, medications used to treat anchor worms, ich and other parasites will be equally ineffective. Melafix, formalin, malachite, praziquantel and salt won't work either.
So what can you use? Look for medications with antibiotics in them. Nitrofurazone, Furazolidone, Tetracycline and Oxolinic Acid have been known to be effective. We have found that Nitrofurazone seems to work the best. Whatever you choose, be sure to follow the recommended dosage and instructions carefully. Overdosing a pond or aquarium can result in complete losses.
While Columnaris is not something you will see very often, particularly if your fish supplier properly acclimates and quarantines your fish before shipping, it can show up occasionally. Due to the swift nature of the infection, all fish retailers should have medicine on hand in case of an outbreak.
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