'tis a mullet:
"The grandly named Promontory Gate Hotel, better known throughout the world as the Fishy Pub. It was built in 1939 to replace a former timber building destroyed when Victoria was ablaze with bushfires. History tells us that it is the fourth hotel on that present site since 1893. The seven metre long mullet that reclines on the hotel roof is the work of Venus Bay artist Colin Suggett. Colin saw his fish as a stunned mullet, something that had been valued but discarded and left to die, abandoned. The mullet is built on a steel frame with aluminium, iron and fibre scales. It was created on site at a Mount Gambier quarry in 1990 and transported to Fish Creek where it has found a home on the roof."
Picture from a better angle here.