Fish wings are spines connected by webbing. They can look like any fin seen on a fish.
Examples of characters with this trait:
BEAN-00129 | MYO-BEAN-0033
A puff of jelly clings to the hips and tentacles hang from it. The puff is soft and smooth and the tentacles are limp/unmoving but can be controlled with magic to move.
BEAN-0073 | MYO-BEAN-0058 | BEAN-0020 | MYO-BEAN-0017