He's gonna catch lampreys in the northeast, and probably some big stripped bass or salmons while he is up there. He is going to catch wels cats in the chernobyl cooling ponds, as the beast have gotten up to 14 feet due to lack of human fishing for them. While he is there I am sure he will catch some salmon or fish lake bikal. He will also visit lake lochness for the season finale. Don't know what kind of fish he plans on catching there.
I don't think he will ever showcase Golden Dorado. They are increasingly rare, and it would be hard to catch a monster sized one.
He ought to try to catch an asian paddlefish. Those things are rare af though, but they are true monsters.
I don't think he actually fished the sultan sea, but they do have a couple species of drum that gets pretty big, and sharks.