Check lungs, feet, armpits, anus, condition score.
Oh, and if he's been ringed, perhaps also check that the ring has been correctly applied, and hasn't caught a testicle mid-testis, or trapped a bit of tubing. (Not easy to tell, the latter - maybe look for tenderness, bruising?)
If all seem fine, but he's a bit listless, I'd give a shot of Combivit. Magical stuff.