You can shoot plenty of human enemies in Uncharted, but the fish are a no-go, as Evan explains:

We had hit reactions and even some death animations for the wildlife in the game but we chose to remove it. It was flagged as a potential issue by the ESRB and it seemed like a small concession to make in order to maintain our “Teen” rating. It may have also affected the rating in Europe.

That's kind of crazy, really. I can only assume that the next Sega Bass Fishing will now get an Adults Only rating for the gratuitous violence depicted toward the fish community. We are training our kids to be fishermen with these violent simulators and I won't stand for it!