A giant sunfish discovered by two fishermen after it washed ashore was so big they thought it was fake.

The rare creature was found at the mouth of Murray River in south Australia by Steven Jones and his fishing crew on Saturday.

Mr Jones’ partner Linette Grzelak posted pictures of the fish on Facebook, saying: “A sunfish found by my partner along the Coorong a couple nights ago. I thought it was fake lol.”

The ocean sunfish is of the mola mola species, which is the best-known sunfish, however it is the rarest kind found in south Australian waters.

The South Australian Museum estimated the fish to be about 1.8m long but they can grow to 3.3m in length and 4.2m across the fins.

Fishermen find gargantuan sunfish washed up on beach Show all 4 1 /4 Fishermen find gargantuan sunfish washed up on beach Fishermen find gargantuan sunfish washed up on beach Sunfish Steven Jones and his fishing crew discovered a mola mola sunfish washed ashore at the mouth of Murray River in South Australia. Ralph Foster Fishermen find gargantuan sunfish washed up on beach Sunfish Steven Jones and his fishing crew discovered a mola mola sunfish washed ashore at the mouth of Murray River in South Australia. Ralph Foster Fishermen find gargantuan sunfish washed up on beach Sunfish Steven Jones and his fishing crew discovered a mola mola sunfish washed ashore at the mouth of Murray River in South Australia. Ralph Foster Fishermen find gargantuan sunfish washed up on beach Sunfish Steven Jones and his fishing crew discovered a mola mola sunfish washed ashore at the mouth of Murray River in South Australia. Ralph Foster

National Parks South Australia, which shared Ms Grzelak’s pictures on Facebook, said sunfish are “the world’s largest bony fish and can weigh more than a car”.

It later posted an update saying the fish was “healthy looking and without any obvious injuries”.

It also said while it was not uncommon for the fish to be seen off the Coorong, it was most likely the fish was “passing through rather than resident in the area”.

Sunfish feed primarily on jelly fish and are known to come close to shore when there are large numbers of jelly fish to feed on.

They get their name from their habit of basking in the sunshine before diving to deep depths beneath the ocean, and they can swim great lengths.

Earlier this month a rare hoodwinker sunfish, or mola tecta, washed up on a beach in California – the first time the species had been sighted in the northern hemisphere in 130 years.

It was identified in 2017 and is thought to live in the southern hemisphere.

The species was nicknamed “hoodwinker” because of how long it had taken for it to be identified.

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According to Ralph Foster, the fish collection manager at the South Australian Museum, sunfish can do a lot of damage if they collide with yachts.