Since the line can be used continuously, it should not serve as an infinite rupee source. Unless he also found rupoors as often.
I think it'd be quite funny if, in keeping with his notable inadequacy as the Hero, our Link could only catch footwear, fishbones, waterweed, Octoroks, Like Likes, and, if used in a certain spot, the Ocarina. In the once-only event that he does find a genuine fish, he throws it back on the basis that it promised him three wishes.