Gold Fish Tail missing!

[gsparsan2]

Hi guys, I have a 6000L outdoor pond with 12x Koi of various sizes, 2x large IR Sharks, 1x Pleco and 4x Goldfish, plus some wild guppies. I've had this pond for 5 years and many of the fish come from a smaller pond I had for another 5 years previously. I noticed one of the goldfish this morning with almost all its tail fin gone! It looks like it has been a few days and is healing already. I took it out for a photo and put it back in. It seems to be swimming normally and there is no mark of fin rot or anything anywhere else on him. See picture below (sorry for the dusty water in the bowl). I have never seen a koi or these IR Sharks fin nibbling or being aggressive towards the goldfish. IN fact the other 3 gold fish are perfectly fine with very long and nice fins. The 2nd picture of the same goldfish a few months ago.

Has anyone seen or experienced Koi biting off goldfish fins? Or what could be an alternative explanation?

 

[davidparker]

I've had koi and goldfish together for years, and while koi aren’t usually aggressive, they might nip at weaker or slower fish, especially during feeding frenzies. Another possibility is the IR sharks—they’re generally peaceful but can be active swimmers and might have startled or accidentally injured the goldfish. Also, fin damage can sometimes happen if the fish got caught on something in the pond, like a sharp rock or rough surface. Since it’s healing and swimming fine, just keep an eye on it for any signs of infection!

 

[gsparsan2]

Update: Tail is growing back and fish is healthy. The swimming is still a bit slow and awkward but it looks well fed.