Koi keepers sometimes need to examine or treat their fish for illnesses or injuries. However, restraining and maneuvering koi to provide medical care is complicated. A fish’s slime coat is incredibly hard to handle, especially if the fish resists your efforts. Immobilizing a koi while examining or treating it can prevent it from hurting itself or you from dropping it. Fortunately, using a chemical solution to sedate a koi is relatively easy and safe.
When to Inspect and Treat
Inspect your koi if you notice missing scales, bumps, blemishes, or behavioral issues. Troublesome actions can include slow movement, erratic swimming, or flashing. Many keepers also examine their koi right before and after torpor, which occurs when water temperatures consistently remain at or below 50°F. Koi are particularly vulnerable to parasitic and bacterial infections as they enter and exit this hibernating state.
If you identify an injury (particularly prevalent in the breeding season), a lesion, or a parasite, sedation allows you to intervene without risking further harm. Treatment could involve stitching, applying antiseptic or other topical treatments, or removing growths. Do not sedate koi to perform a skin scrape–the medication can make detecting parasites harder.
Options for Sedation
Two options exist that most experts consider safe for use at home. Tricaine-S is a chemical powder created specifically for aquatic sedation, and clove oil is a natural alternative that is easy to obtain.
Tricaine-S (MS222)
Tricaine is a white, water-soluble powder derived from benzocaine, a topical anesthetic that temporarily deadens nerve endings in the skin. You can purchase Tricaine from many pond and koi supply retailers. This product is licensed for use in fish but is highly acidic and can burn the gills if you use too much or expose the koi for too long. Read and follow the instructions carefully.
A solution suitable for treatment typically includes 10-50 mg of tricaine per 1 liter of water. Its acidic nature also can lower pH levels, so check water parameters before use. If the pH drops below 7, sodium bicarbonate can buffer the tricaine. Add it until the water balance reaches between 7 and 7.5. Sedation should occur within two to four minutes, and fish should recover in about 10 minutes.
Clove Oil
Clove oil is inexpensive and available over the counter. Its active ingredient is eugenol, extracted from clove plants for various uses. The oil anesthetizes fish by decreasing neurosensory functions in the cerebral cortex and should take effect within about three to seven minutes.
Clove oil’s strength and composition vary slightly among manufacturers. Therefore, it is best to start with a small amount and gradually increase it until the fish is sedated. This typically should take between five and ten drops of oil per gallon of water. You must vigorously stir or shake the mixture because oil does not naturally combine with water. Clove oil euthanizes koi in concentrations of about 20-25 drops per gallon, so be very careful not to overuse it.
Preparation
Stop feeding your koi 12-24 hours before you sedate it. You can either fast all your fish–they will be fine for a day without food–or separate the koi you are sedating and keep it in a holding tank during fasting. An empty stomach reduces the risk of regurgitation that could lodge in the gills and prevent the fish from filtering oxygen from the water. Before handling koi, ensure your hands are clean and your fingernails are short, and remove any bracelets, rings, or watches.
To minimize stress, the koi should be out of its pond for the shortest time possible. A koi’s stress levels can actually affect its response to the sedative. A highly stressed koi will resist the anesthesia, necessitating a higher dose that could increase the risk of an adverse reaction. Additionally, stressed fish have a higher risk of bleeding and may start hemorrhaging from the gills. Fish that bleed tend to have a more difficult recovery. Therefore, it is important to have the equipment you will need ready beforehand.
Equipment
Net
The net should be suitable for securing the koi and moving it from the pond to the treatment bowl. The best option is a high-quality pan net (a shallow net resembling a frying pan) that guides the koi without trapping it. Do not lift the koi out of the water. Rest the net’s rim on the edge of the transportation bowl. Tip the bowl toward the net with your free hand and gently guide the koi into it.
Hospital Tank
A hospital tank housing one koi should be at least 100 gallons–larger if you’re keeping multiple fish in it. Even though your koi will only stay in this tank briefly, the water quality is still important. Aerate the water and check its temperature and other parameters to ensure conditions are similar to those in the pond.
Treatment Bowl
You will need a bowl to place the koi in. Use a viewing or showing bowl if you have one, or create your own using a plastic or rubber tub. The appropriate size depends on the koi but should be high enough to secure the fish and wide enough for it to fit comfortably. The water level should cover the koi completely.
Treatment Cradle
If you are examining koi, you will need a treatment cradle to lay the fish while you work on it. The cradle should be soft and wet so its material does not strip the slime coat. You can purchase one or make your own with various DIY options, including layers of towels and pool covering over styrofoam.
Performing Sedation
The sedative will cause the koi to roll on its side. To test the fish for sedation, gently prod it or lift its body from the center. The koi should lay still while retaining slow gill movement. If it moves, keep it in the sedative bowl for several more seconds and try again. Do not leave the fish unattended while it’s sedated. If you suspect the fish is sedated too deeply at any point, move it to aerated water and manually assist its gill movement by moving its body back and forth, allowing water to pass over it.
Lift the koi out of the sedation bowl and onto the treatment stage. Do not attempt to treat it while it is in the bowl, as this will continue to expose the fish to the sedatives and can lead to an overdose. After examining and treating the sedated koi, place it back into its hospital tank until it thoroughly revives and resumes regular activity. At that point, it is safe to return the koi to the pond.
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