Rank fish by aquarium impact, not by copied hype
The safest fish tier list still works at the family and session-value level: monster fish and stronger mutated late-session catches deserve the top slots, while filler fish should rotate out once your aquarium and rod upgrades improve.
If you only need the short answer, keep the hardest-to-replace late-session catches and demote early filler fish first. That matches the official catch-family surface and the aquarium economy loop better than forcing fake numerical rankings.
Treat mutations, fish level, and index progress as rank modifiers. A merely rarer catch is not automatically better if it loses more aquarium value than a leveled or mutated keeper already in your slots.