The pages do not tell you all the locations of each type of fish, is that by design? I thought it should tell you all the possible locations of each fish type.
For example, take a look at eels. Fantastic Fish says they are only found in rivers, in the correct locations, but I could not find any in the rivers, but in a lake, in Grantebrishire. Only the fishmonger, or your bag, but only when you have caught one, tells you this. This is also true for other types of fish in part one.
Here is what the fishmonger tells you about Eels. The same problem goes for the other types of fish for part one.