Fish extenders (abbreviated FE) are items, usually made of cloth, that contain multiple pouches and are hung ouside the front doors of staterooms. The name is derived from the fact that they are hung on a decorative metal "fish" that sits on the wall next to each stateroom door.
Cruisers use fish extenders to exchange messages and small gifts with each other. They are more common with cruisers affiliated with a group (i.e. online forum group).