i think this will be very easy to add, and make rivers/ocean have different spices of fish depending on the river size
I also thought about it. Is interesting that there are different species of fish.
There could be different methods, fishing rod and basket with bait inside. The rod could be used in the hand or nailed in the ground. If it is nailed the fish can be stolen (with the rod, optional). The basket with fish inside could also be stolen (or only the fish leaving the basket).
I suggest that there is a fishing limit, if it is passed the number of fish decreases until don´t catch anything and have to wait for they are repopulated.