This does not not refer to a fish, but the yin-yang symbol. Walking with the whole body forming the yin-yang symbol allows this balance to permeate your body. Circle-walking in the yin-yang fish way prepares the body for coiling techniques. It appears simple, but needs a high level of deep skill to perform it correctly. On the external level it develops the coiling of the body through the arms.
Yin-yang fish circle-walking
Curve the arms to form the shape of the yin-yang curves, the outer arm high and the inner arm low, palms out. You do not need to turn the body fully into the centre of the circle.