I normally make my wall fish facing left. The reason for this is because I read from left to right and most of my customers read from left to right. Our eyes are trained to start at the left and move to the right and then in a clock-wise direction. And when we look at someting alive we tend to look at the eyes and face first and then take in the rest of the body. So I plan my fish so that you automatically start with the face and move down the rest of the fish. This is something to take into consideration when planning the composition of anything visual. But rules are made to be broken and every once in awhile things need to move away from the normal or comfortable zone. Like fish swimming upstream.