Occurrence at the Busselton Jetty
The presence of John Dories around the observatory is now a rare occurrence. They are often referred to as the “ghost fish” where in many cases only the silhouette can be seen in the distance. Always seen solitary, the John Dory has been observed ambushing a school of yellow tail scad by swimming vertically at speed, so as to look greatly reduced in size, into the school as part of its feeding tactic.
The John Dory is a visually distinctive fish, recognised by its silvery grey oval, laterally-compressed thin body, extremely elongate dorsal fins, a large downward-angled mouth, and a white ringed, circular spot centred on the sides of its body. It has microscopic, sharp scales running around the edge of the body. John Dory occur most often in deep waters of up to 150 metres, however have been recorded at depths as low as 360 metres, living near the sea bed. They tend to be a solitary species. The species is found in temperate marine waters worldwide and occupies a wide range around the southern half of Australia from Port Hedland, WA to southern Queensland.
The John Dory is a relatively poor swimmer, yet is one of the top predators in its habitat. This species preys upon a variety of fish, especially schooling fish, where it adopts a stalking method before extending its protrusible jaw into a long suction tube to engulf prey. Occasionally they feed on squid and cuttlefish. Sexual maturity occurs around 3 to 4 years of age, and reproduction takes place by releasing sperm and eggs into the water where they settle on the substrate and become fertilised. The life span of the John Dory is approximately 12 years in the wild and they attain a maximum length of 75 centimetres.
It is a highly regarded table fish fetching high market prices, and is trawled in moderate quantities.
Other common names include St Peter’s Fish, this name refers to the “thumbprint” on the side of the fish supposedly left by St Peter when he caught the fish (biblical).