2,744 kilos. That is the weight of an ocean sunfish found dead in December 2021 off the coast of Faial Island, in the Azores, and it is currently the heaviest bony fish ever weighed.
This giant was not a Mola mola, the species everyone calls ocean sunfish. It belonged to a related species, Mola alexandrini. The detail matters because many pages mix up species, records, and reproduction figures.
Here we review what has been measured, what remains an old estimate, and what you can reasonably expect if you dive in Bali or the Mediterranean.
What is the largest ocean sunfish ever weighed?
The record belongs to a Mola alexandrini weighing 2,744 kg, found floating dead near Faial, in the Azores, in December 2021. The study published in 2022 in the Journal of Fish Biology, led by José Nuno Gomes-Pereira, makes it the heaviest known bony fish. It measured about 3.25 m long and 3.6 m high.
The previous record came from Japan. According to Smithsonian Magazine, an ocean sunfish of about 2,300 kg was weighed there in 1996, also a Mola alexandrini. Researchers noted a wound with traces of red paint on the Azores specimen. A collision is possible, before or after death. The body was buried in Faial Natural Park after examination.
This is why the old version of this article was mistaken in attributing “two tons” to Mola mola without specifying the species.
But Mola mola remains a heavyweight. Large individuals exceed a ton and approach three meters high, with dorsal and anal fins spread, which is enough to make it one of the most massive fish you might encounter in recreational diving. Short and efficient, this point is worth remembering.
How many species of ocean sunfish are there?
The genus Mola includes three recognized species: Mola mola, the common ocean sunfish; Mola alexandrini, the heaviest; and Mola tecta, described only in 2017. The three look similar enough to have been confused for centuries, which explains much of the mixed figures still found today in guides and on the web.
Mola tecta was described by a team led by Marianne Nyegaard from Murdoch University in the Zoological Journal of the Linnean Society. Its name comes from the Latin tectus, meaning “hidden.” In English, it is called the hoodwinker sunfish, the ocean sunfish that fooled everyone. It is known around New Zealand, southeastern Australia, South Africa, and southern Chile. It maintains a slender silhouette even as an adult, without the frontal bump of its cousins.
Thus, when a diving photo mentions “Mola mola,” the species is not always verified.
The body plan, however, is common to all three. No true caudal fin. Instead, a rigid fold, the clavus, formed by the rays of the dorsal and anal fins, serves as a rudder while these two large fins beat in concert. The teeth are fused into a beak. The skin, thick and rough, often carries parasites, hence the cleaning sessions mentioned below.
What does the ocean sunfish eat and how deep does it go?
The ocean sunfish feeds mainly on jellyfish and other gelatinous animals, supplemented by zooplankton, small fish, crustaceans, and algae. It spends most of its time in the upper layer of the ocean, with regular descents into colder waters, then ascents to warm up.
In Bali, ocean sunfish equipped with tags spent 95% of their time within the first 250 meters, according to the study by Tierney Thys and colleagues published in 2016. They traversed waters ranging from 10 to 27.5 °C. The figure of “50 to 200 meters” from the old version therefore gave a false precision.
The gelatinous diet raises a simple question. A jellyfish contains very little energy per kilo, so the animal must swallow large quantities to maintain such a mass, which is why it is often linked to the topic of jellyfish invasions and their causes. Still, caution is advised. No study cited here shows that it alone controls jellyfish blooms. For the biology of its prey, the page on jellyfish, their life cycle, and species covers it thoroughly.
And no, it does not spend its life drifting on the surface.
It is sometimes seen lying on its side near the surface, which led to the belief that it was a sick or lazy animal. This posture partly serves to warm up after a descent into cold water. It also allows seabirds, such as gulls, to peck at its parasites. It even sometimes jumps out of the water, a behavior that National Geographic links to the need to get rid of these parasites. The previous version stated the opposite.
Does the sunfish really lay 300 million eggs?
The figure of 300 million eggs exists, but it does not describe a measured spawning. It is an old estimate of the number of eggs contained in the single ovary of a female about 1.4 m long, cited by researcher Tierney Thys. It is unknown how many eggs a female actually releases, at what rate, and where, and none of the sources consulted provide a measure of spawning in the natural environment.
What is known about the early stages remains limited. The larvae, tiny, are covered with spines and do not resemble the adult at all. They then grow very quickly. The vast majority do not survive, which is the rule among fish with high fecundity. The maximum age at sea remains poorly known.
Yet, millions of eggs do not protect a species.
Mola mola is classified as Vulnerable on the IUCN Red List (2011 assessment), with a population considered to be in decline. The main threat comes from bycatch: the sunfish gets caught in drifting gillnets and longlines targeting other species. Plastic bags, easily mistaken for jellyfish, add to the list.
On the culinary side, the European Union prohibits the marketing of fish from the Molidae family. Regulation 853/2004 classifies them among venomous fish families, along with pufferfish. Nothing to do with parasites, contrary to what the previous version claimed. Elsewhere, it is sometimes consumed. If you are interested in the survival strategies of marine animals, the file on extraordinary defense mechanisms in marine animals broadens the subject.
Where to observe a sunfish while diving?
The most documented site is Nusa Penida, in Bali, where sunfish come up to the reefs to be cleaned by cleaner fish. Elsewhere, including in the Mediterranean, encounters remain occasional. No site guarantees an observation, and the season gives a probability, not an appointment.
Bali and Nusa Penida
According to the team from Murdoch University who studied these fish in 2016, the observation period roughly runs from July to October. The fish studied were then named Mola ramsayi. This name has been linked since 2018 to Mola alexandrini, so the fish that divers see in Bali is not necessarily the Mola mola from tourist brochures.
The local code of conduct, developed by the Coral Triangle Center with Indonesian authorities and the diving association Gahawisri, sets clear rules. Keep at least 3 meters, or three body lengths, when the fish is at the cleaning station. Approach slowly, in its field of vision, never from behind or below. No flash. No contact, which removes the protective mucus from the skin. The text also limits groups to five divers per instructor.
For what level? At Nusa Penida, currents and cold water upwellings weigh more in the decision than the animal itself.
Clear water says nothing about the strength of the current or the exit plan provided by the club.
The required level varies according to operators and sites (impossible to decide from here). Have the briefing specify the expected current, the temperature at the bottom, and the conduct to follow if the group separates.
In the Mediterranean
Mola mola frequents the Mediterranean, where it is mostly seen near the surface, sometimes from a boat. Public data do not allow for drawing a reliable season for a specific site. However, the basic rule remains the same as in Bali: distance, slow approach, and no contact.
It is said bluntly: going on a trip for a sunfish means accepting to come back without having seen it. And touching it would bring you nothing. The page why you should never touch marine life explains what contact does to animals. Its truncated head earns it a place in the top 10 ugliest fish. The real cost of a stay focused on this animal is a week of dives and a plane ticket paid for an encounter that remains just a probability.
FAQ
Is the sunfish dangerous for divers?
No, it does not attack humans and mainly feeds on jellyfish. The risk comes more from a collision with a very large individual or site conditions, such as currents. Keep your distance, for your sake and theirs.
What is the record weight of a sunfish?
The record is 2,744 kg for a Mola alexandrini found dead in the Azores in December 2021. The study was published in 2022 in the Journal of Fish Biology. It is the heaviest known bony fish.
Can you eat sunfish in France?
No. European regulation 853/2004 prohibits the marketing of fish from the Molidae family, classified among venomous fish. Therefore, sale is forbidden in France as in the rest of the European Union.
When to see sunfish in Nusa Penida?
Researchers from Murdoch University placed the season roughly from July to October in 2016. An observation is never guaranteed. Check with the club about recent sightings and the expected current.
Sources
- This 6,000-Pound Sunfish Is the Largest Bony Fish on Record (Smithsonian Magazine, Sarah Kuta, 2022)
- Tracking a Marine Ecotourism Star: Movements of the Short Ocean Sunfish Mola ramsayi in Nusa Penida, Bali, Indonesia (Thys et al., Journal of Marine Sciences, 2016)
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