Fish are of limited intelligence. If you (or the lfs that had the fish) train them with one food, they may ignore other suitable foods. Having said that, of course, some fish won't eat some things ever.
However, assuming they will ordinarily eat the food, you may need to train them in some way by raising temps, not feeding them for a while, perhaps adding flavor enhancements (garlic), tricking them by shoving the food inside another food they like (e.g., pellets inside shrimp), etc. It can be done, but it may take a little work.
Or use other foods is certainly okay if the other foods are the cost and nutritional value that works.