I know my fish is a lot smaller than yours, but my dalmation molly (about 3 inches) got her tail stuck in the filter and I had to pull her out. Her tail was all ripped up and her whole body was bent! She didn't swim too well for awhile and stayed at the top. She kind of just floated. I was really worried about her so I watched her the whole night. In the next few days, her body was fine just like before and after a week or so her tail grew all the way back (without any meds!) I am proud to say she is doing fine and even had 7 babies! Maybe he is just injured from the accident from the filter? I'd keep an eye on him for about a week to see if he recovers at all.