I'm a little worried he has a Jx hand with clubs that backdoored the flush... He's played it so passively to the river that it feels like he didn't have us crushed or anything. I don't see myself ever folding this spot getting a million to one, but I'm also struggling to see hands we beat. Never ever 3bet this spot - it's too hard to know we are ahead here, so trying to chuck more money in seems bad. Call or fold imo.
As for his range, you didn't give stats or anything other than "fish," so I'm not really sure what kinds of hands he's defending with. But if he can "slowplay" rando Jx and then minraise the river for "value," then obviously I'm calling. But I expect to get shown 67, 65, and like QJcc a lot.