The key element in this picture is scale. We can immediately see how small the fish is because of the proximity of Richard’s hand and head. So we have a direct comparison of relative size. In this case, scale provides some humor to the picture.
There are some other elements at work here too. Follow a line from the elbow to the upper right corner of the frame. The line of the upper edge of the arm, continuing with the fishing line form a diagonal line.
Notice also the subtle reflections of other fishermen in the background of the picture.
This is a posed picture but is a common situation after a fisherman hauls in a catch. Find anyone with a camera and pose.
See other pictures using scale as a composition technique.