Oh, if only Robert Shaw had still be around to add a bit of menace to this. Instead, we rely on Robert De Niro as the gangster fish whose son is found dead in suspicious circumstances. Local plodder - if fish can actually plod - "Oscar" happens upon the corpse and sees an opportunity to claim that he was the brave killer - codenamed "Sharkslayer", and that he is a natural ally of those opposed to the rule of "Don Lino". The enemy of my enemy being my friend sort of thing. Thing is, poor old "Oscar" really isn't cut out for life amongst the big fishes, and his new friendship with "Lenny" -…