Ocean sunfish hanging in cool waters of Bali Nusa Penida. They are the heaviest bony fish in our oceans, weighing between one and two metric tonnes. Photo: Paul Sorenson.
Due to their large size, the ocean sunfish must consume one to three per cent of their body weight per day to stay healthy. Photo: Paul Sorenson.
Welcome to the Marine Mili series, a regular column about all things marine! During this series I aim to inspire people to want to protect our oceans and all the marine life that call our oceans home. Hopefully after reading each column, you would have learnt something new, including what we can do to help protect and preserve our oceans. You can follow me and my journey on my Instagram page: _marine_mili.
Do you recognise this strange fish? This is the ocean sunfish, which is quite rare to spot as they live in deep water, only coming to the surface occasionally.
While I have not been lucky enough to see one, they are sometimes spotted from helicopters or planes that travel over Bass Strait. One was even recently spotted washed up in Frankston.
The ocean sunfish got their name from sunbathing to warm up. In their constant search for food, the ocean sunfish can dive up to depths of 200 metres below the surface. Deep dives will last about 10 minutes, and as the water is so deep down it becomes very cold. Therefore, the sunfish must sunbathe on the surface to “warm up” before diving back down to continue feeding. This sunbathing activity is often when they can be spotted.
The ocean sunfish is certainly a strange creature. On top of this unusual behaviour, they also have a bizarre anatomy.
Unlike a lot of other fish, the ocean sunfish doesn’t have a tail. In order to swim, they have to continuously move their two long fins (dorsal and anal fins) from side to side.
They are also the heaviest bony fish in our oceans, weighing between one and two metric tonnes. This makes them as heavy as a camel.
Due to their large size, the ocean sunfish must consume one to three per cent of their body weight per day to stay healthy, which often has them eating hundreds of jellyfish per day.
Ocean sunfish are omnivores with a diet mainly consisting of jellyfish and salps; however, they also feed on small fish, crustaceans, zooplankton and algae. Despite consuming so much food each day, these fish are not able to fully close their mouths. Instead, they must push their food in and out of their mouth until it is broken up into small pieces.
The ocean sunfish can be found worldwide, particularly in the waters from New South Wales, Victoria, down to Tasmania, and west to South Australia and even Western Australia.
So next time you are on a scenic flight or travelling our beautiful oceans, keep an eye out for these elusive fish.
