If we cant get fish as a material for cooking or potion making a different use would be that player homes could have an aquarium and you could sell the fish you catch to players so they can fill them. You could make it so that each fish you put in the aquarium acts as another actual fish. so you could put 5 carp and 1 clam and it would actually show. HQ fish would be bigger and you could even get different size tanks that could hold more or bigger fish.