I do it this way: I'm using a Fishing Bot which is fishing in 3 areas, so i can find all three types. Krasag, Vally of 4 Winds and the Klaxxi Area.
I'm using a macro, hotkey to one, which deletes all of those fish types and is autoclicked by autoit every 25sec.
I Let the bot farm one night.
The next morning i go to battle.net and click item restoration and i restore the deleted fishes. Now i have the whole post full with fish and can loot them every day to turn them in.