We have a large koi carp (I would approximate 50cm long) that has an injury to its head — a gash which has left a triangular flap of flesh about 4cm wide. There is no sign of blood, and the inside of the gash is white. This injury occurred within the last 36 hours.

Photos are below, and if necessary, I have a video that I can attempt to upload if it provides a clearer visual.

My question is, does an injury of this type require medical attention? If so, how would one go about treating this wound?

(Consider me a complete newbie in fish care, as somebody else used to care for them.)

Fish Injury - Photo #1 Fish Injury - Photo #2 Fish Injury - Photo #3

  • Do you have other koi with it?
    – Joanne C
    Jul 3, 2015 at 10:34
  • There is one other koi in the pond — same age, size and (AFAIK) brood. Jul 3, 2015 at 16:22

1 Answer 1


Yes. It does need treatment. As with an injury to any living being, this may get infected.

You need to quarantine this fish immediately, and begin treatment. First of all, move this fish to a separate tank, such as a spare fish tank, or a tub. Use water from your original fish tank in this (do not use fresh or new tap water). Set up an air-stone in the tank. Take out some of this water in a small bowl, and add some rock salt to it. Rock salt should be added in the ratio of about 1 tea spoon per 10 gallons (of the water in the tub). Salt will prevent some infections. Add this salted water gradually, and if your fish shows signs of stress such as thrashing or gasping, stop adding salt and add some water to dilute. Be advised that Salt stings, and you koi might get stressed out a bit. Any discomfort for more than a minute is when you should stop adding salted water.

In case any secondary infections are observed, use Merck Methylene blue. You can add 5 ML for each 10 gallons.

Since adding salt and methylene blue to your original tank will cause unwanted stress to your other fish, and also since Methylene blue kills the beneficial bacteria in your filter, quarantining is a must.

  • After further research, and speaking to a couple of friends who care for fish, I feel the best course of action is leave the fish to heal, keep a close eye on it and take action if the injury appears to worsen. As the injury followed the fitting of a pond cover, which involved somebody being in the pond and a reasonably substantial change to the pond environment, I don't want to further stress the fish unless necessary. However, this is very helpful to know, if treatment is needed now or in the future, so thank you for the detailed answer. Jul 4, 2015 at 16:49

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