Koi are known to be quite hardy however this does not exempt them from being vulnerable to infectious organisms and parasites, especially when they are constantly subjected to stress or poor water conditions.
Here are some of the most common koi diseases, their causes, symptoms, treatment and prevention:
| How to Treat Sick Koi | ||||
| Disease Condition | Cause | Symptoms | Prevention and Treatment | Remarks |
| Ich | Protozoa | Affected fish have white spots dotted all over the body | - increase salt concentration of the pond to about 0.5% for several days
- gradually increase the water temperature to about 70F while increasing aeration - Add malachite green or formalin to the tank water at a ratio of 1.5 mg of malachite green for every litter of water |
Smaller koi is most susceptible to the effects
- always wear gloves when handling malachite green or formalin |
| Dropsy (also called Pinecone) | Bacteria | - swelling or lifting of the scales
- bulging eyes |
- raise the temperature
- add salt - administer antibiotics |
Once symptoms are spotted, separate the infected fish as soon as possible |
| Ulcers, Fin Rot, Cloudy Eye, Split fins | Bacteria | Wounds, White Cotton-like Patches | - OTC antibiotic preparations
- provide aeration using a small air pump and air stone - remove the infected fish form the pond and place in a quarantine tank - make a 0.30% salt solution and put it in the quarantine tank. Make sure the salt has completely dissolved before adding fish to otherwise your koi’s gills can get burned |
- putting the infected koi in a separate tank will save you from treating the whole pond and wasting money on medication |
| Costia | Parasite (Ichthyobodo sp) | - causes damage to the gills and skin
- spider webbing - red veining |
- potassium permanganate, acriflavine, and 3% salt baths | Signs of the disease can also be manifested by prolonged exposure to ammonia in the water, shipping, or stress
- Important predisposing factors include overcrowding, poor management, poor water conditions, sick fish |
| Anchor Worm | Lernae sp (a crustacean parasite) | - the female anchor worm can be seen like a thread hanging from your koi. The head anchors or embeds into the body of the koi
- inflammation - the anchor worm may leave a hole in the koi’s protective slime coat and skin, paving the way for opportunistic bacteria to invade the koi’s systems |
- Female worms can be removed using tweezers or small pincers.
- rub a broad-spectrum antibiotic on the infected site - pond treatment |
- juvenile stages of the worm stays in the gills of koi while adult females buries into the skin and underlying tissues
- when removing the parasite, make sure to remove each completely, by dipping cotton in strong potassium permanganate solution and dabbing the worm with the solution causing it to release its grip. |
| Cotton Wool Disease (also called, Columnaris) | Flexibacter columnaris | Appearance of white threads in the mouth of the koi
- dry skin - sometimes the koi can turn dark in color and white sores appear on the koi’s skin - infected fish can also have a soggy belly with a slimy coating over its skin |
- Add potassium permanganate in the pond water
- Administer antibiotics and spot treatment |
- Infected koi must be separated from the other fish
- important predisposing factors include poor water quality, handling and shipping, inadequate diet |
About the Author:
Peter Hartono is the founder and CEO of Just Aquatic - a proud Australian company that offers top of the line aquarium supplies and gold fish tank supplies carrying top of the line brands including API, biOrb and Exo Terra.
