I've been using this
Animal Crossing: New Horizons Fish Guide - How To Catch, Prices, Shadow Sizes, And More
Here are all the fish--and where and when you can catch them--in Animal Crossing: New Horizons for Nintendo Switch.www.gamespot.com
So this is the list of catches you need by the end of the March, it seems, for Northern Hemisphere:
Bitterling : Nov-Mar : River : All day
Football Fish : Nov-Mar : Ocean : 4 PM - 9 AM
Sea Butterfly : Dec-Mar : Ocean : All day
Stringfish : Dec-Mar : River (Clifftop) : 4 PM - 9 AM
Sturgeon : Sept - Mar : River (Mouth, where the river meets the sea) : All day
Yellow Perch : Oct - Mar : River : All day
Emperor Butterfly : Dec-Mar, June-Sept : Flying : 5 PM - 8 AM