you touched on it and I want to second the point.
when cooking is further developed, and more recipes call for different fish, the value of the fish will increase, especially if the value of the dishes are increased. The same is true with alchemy. Potion recipes can call for some of the more rare fish, and if I'm not mistaken, a couple of fish already have alchemical uses in their description.
as with the implementation of various fishing equipment, nets, spears, etc. I'd like to see certain types of fish only catchable by certain types of equipment. For example, it isn't logical to be able to catch a crayfish (if crayfish are supposed to be anything like crawfish in RL) with a fishing pole. Nets or traps would be necessary. Also, in addition to poles, I'd like to see the implementation of bait and lures, each specific to catch certain types of fish.
In terms of types of fish I'd like to see added, umm, perhaps more shellfish? crabs, mussels, oysters, scallops, SHRIMP, lobster. Perhaps when the bottom levels are introduced, we can add bigger game to the fare, tuna, bass, sharks!, marlin etc. In line with the bait and lures idea, have some fish such as minnows, sardines, which could be used as bait fish to catch the bigger fish. Because, you know, big fish eat the little ones.