>>537830803
Pretty much this >>537831047, but if you want to tryhard, pick between Fresh/Saltwater and once you catch the Rare fish there, use it as the research bait so you get it more often. At max research, you can even land 5 stars thrice in a row (personal best), if not more. Higher stars seem to give slightly better exp. Clutter should be 1 exp, automatic catch 1-2, normal rarity 2-4, rare 3-5.