It looks to me like your Shubunkin (not a Koi) has been attacked by your crawdad. Put the crawdad in it own tank. Melafix is an excellent medication for injured
goldfish. Test your water for Ammonia, Nitrites, and Nitrates. Do all your "Koi" look like this one in coloring? If so, then they are more than likely all Shubunkins, not Koi. If you could post pictures, it would help with the identification. What kind of plecos do you have in with them? Goldfish and plecos are both high waste-producing fish. Shubunkins are also very strong swimmers and need lots of swimming room. Also, the Shubunkins can grow to 12-14 inches in length. A 60 gallon really isn't going to be a good fit for 5 shubunkins. Add in the 3 Plecos, and your tank is very overstocked. With that many Shubunkins, you may want to look into a pond. They really should be in a larger area to provide enough swimming room as well as the increased volume of water to handle the ammonia. Please do get a liquid
test kit and test your water as soon as you can. As long as there isn't too much internal damage, there is every chance that your injured Shubunkin will recover completely. The main things to do are to remove the crawdad, keep the water as clean as possible, and (if you can) treat with Melafix to prevent infection. The Melafix will not bother the other fish so you don't really need to worry about setting up a quarantine tank as long as the other fish are leaving the injured one alone. It could be more stressful for the injured fish to move it at this point. In my opinion, Crawdads and Fish do not generally make good tank mates. Crawdads will catch and eat fish - even ones that are much larger than they are.
