This decoration could only be found randomly in the Animania Mystery Crate, which is no longer available for purchase. The fish in the Tide Pool move when clicked. This decoration is not functional. It has nothing to do with the Fishing aspect of the game.
It cannot be sold, although if players do not want it on their island, they can simply pick it up with the Move Tool and drop it into storage.
For info on the Tide Pools that appear along your shoreline and you can fish from see Fishing.