While I doubt the "owner" of that jug would appreciate anyone taking the fish and/or trashing his jug .... since the jug did not have any means of identification labeled on it, it may have been in violation of the MO regs, in which case it may have been prudent to release the fish & trash the jug. IF MO has no regs on having any ID on the jugs, I think I'd have just let it go on its merry way. That's probably what I would have done, in either case, since that way you're not "involved" in any part of an "ethics" conundrum.
Had a similar incident happen to me on Watts Bar Lake, many years ago. Jug came bobbing along, no name/ID labeling ... it got close enough to the boat that we didn't have to chase it down, so we grabbed the jug just to see what was on the line. It had about a 8-10lb Cat on it ... we dropped the jug back & let it go on its way. Last we saw of it, it was on its way towards the dam end of the lake. Rofl
... cp