Sunfish find in Wonboyn Lake puzzling says Australian Museum

"This is amazing. I have only seen sunfish while fishing for marlin on the continental shelf. It had only recently died since it was very fresh," Mr Williamson said.

"No one I have spoken with has ever heard of a sunfish in Wonboyn Lake."

He also spoke with the local Fisheries Officer in Eden, Ian Merrington who agreed he had not heard of a sunfish sighting in the lake.

Not only had Mr Merrington never heard of a sunfish sighting in Wonboyn, the Australian Museum said they had never heard of a sunfish anywhere in a lake.

Mr Williamson said the sunfish weighed about 25kgs and was 800mm long and 1260mm from fin tip to fin tip, making it a relatively young specimen as sunfish can grow to several metres long.

Ocean sunfish are usually found in oceanic waters, but occasionally come inshore. Sunfishes in general are often seen at the surface where they may be mistaken for sharks, because of the large dorsal fin. Usually they are spotted by people fishing while offshore.

Amanda Hay, collection manager and ichthyology (study of fish) manager at the Australian Museum confirmed it was a 'Bumphead Sunfish' which was one of three species which could be seen along the NSW coast.

READ ALSO:

Dead whale shark washed up near Eden

Mystery of strange Eden sea creature solved

Strange remains of sea creature wash up

"You have some wonderful DPI Fisheries people down there who alerted us to the find," Ms Hay said.

Mr Williamson took a DNA sample from the dead fish with Mr Merrington ensuring it got to the Australian Museum.

"Generally we would come and pick it up but we're locked down at the moment," Ms Hay said.

"It's really unusual to see one washed up in a lake especially as they're an open ocean fish and feed off comb jellies."

The DNA sample, which is preserved in alcohol, can be used by researchers who study sunfish and will form part of the collection at the museum.

Sunfish are the largest bony fish in the world. They have attracted interest for centuries because of their unique shape and large size but are more recent additions on the evolutionary tree than rays and sharks, Ms Hay explained.

The teeth in each jaw are fused to form a plate, and the mouth is small in comparison to the body size. Sunfishes are found worldwide in the open ocean of tropical and temperate seas. They are completely without a caudal fin, instead replaced by a 'clavus', which in latin means 'rudder'.

Fisheries officer Ian Merrington also assisted the Australian Museum when a whale shark carcass was washed up near Eden.

Ms Hay said the whale shark was another puzzling case as it was a juvenile male and "generally they like warmer waters".

"Fisheries called us but it was too big and too hard for us to get there and deal with it and Taronga Zoo, who are the only ones who can do an autopsy, couldn't do it," Ms Hay said.

"However Fisheries took the fins and some muscle from the fins and got it to us so that it can be accessed for research.

"That definitely is the most southern end of where you would find them but the East Australian current would have been at its warmest at around that time," Ms Hay said.