Very unusual... I have to admit I don't have a lot of experience owning knife fish since they are a very large fish. I believe I used to have 2-3 in a small pond outside in my old house, (I moved) but either I gave them away, or the people who got the house agreed to feed them in take care of them. I was a while ago, (Few years) and I can't really remember much about them. I am guessing that it might be some kind of an infection.
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