To answer your question with wc fish I have bought from Central America..... I have found two approaches.
One ..... It's the more risky one by also the fastest..... I withhold food from the fish until they are hungry enough to eat anything
Two..... I give them krill or blood worms ( frozen that I thaw) while also giving them a pellet or two ...... To teach the fish that pellets are good too...
Monsters of fishing for fish and bringing them home, you could jump in on the cold water group buy. There are a lot of fish on that list that you could find in the pac northwest