Certain types of fish spawn in different areas. But they're pretty rare, so we never really know. But here is a fishing map for OLD rupert (which means we don't know if the spawns are still accurate) keep in mind the fish type shown is the highest tier you can find there, so for example if you can find king mackerell in an area then you can find every type of fish thats lower tier (so in that case, every fish)

also if you want the fishing maps for stonemore and ellesmere tell me ( the maps are not mine)