[unclejed]

The shrimp could be doing it if it finds where the fish is "sleeping" as it forages at night. A nip here and a nip there every night. I would add some stress zyme or stress coat to help the fishes slime coat and help it heal. The only real definitive suggestion I have for you is to catch the shrimp and if you don't have any where for it, lfs may hold it for you for a week or two. If the tail repairs and goes back to normal, you will have definite proof it was the shrimp. If so, the lfs may give you credit for the shrimp.