Where to dive with ocean sunfish (mola mola)

What they are

The ocean sunfish (Mola mola) is described by DAN's Alert Diver magazine as the heaviest bony fish in the world, with some individuals reaching nearly 5,000 pounds. FishBase gives a maximum length of 333 cm. Adults eat fishes, molluscs, zooplankton, jellyfish, crustaceans and brittle stars.^1,3

A related species, the bump-head or giant sunfish (Mola alexandrini), grows to about 3.3 metres and has bumps on the head and chin that become more obvious with age. In Bali, bump-head sunfish often gather at cleaning stations to have parasites removed by reef fish.⁴

Where and when divers see them

Molas live in tropical and temperate waters around the world and visit cleaning stations, where reef fish remove their parasites. Around Bali, a 2023 study found that giant sunfish occur from the surface to well below the 40-metre recreational diving limit, and generally overlap with divers only when they come onto reefs shallower than 40 metres to be cleaned.^1,2

Around Bali, a 2023 study found that giant sunfish appear seasonally to be cleaned by reef fish, possibly linked to seasonal cold-water upwelling along the southern coast of Bali and neighbouring islands; divers most often encounter them between about July or August and November or December. The study also notes that sunfish in the Nusa Penida marine protected area are often surrounded by large numbers of divers.^1,2

Conservation status

Mola mola is listed as Vulnerable on the IUCN Red List. FishBase, which reproduces the Red List entry, gives the assessment date as June 2011. We did not find a stated global category for Mola alexandrini.³

How to behave around them

DAN's Alert Diver notes that molas leave if they perceive signs of aggression, so a slow, calm approach is key. Drawing on its work in the Nusa Penida marine protected area, the Coral Triangle Center has recommended a minimum distance of 5 metres for watching megafauna such as sunfish, with divers able to move to 3 metres depending on water turbidity and under dive-operator supervision. A separate voluntary code of conduct for mola diving at Nusa Lembongan and Nusa Penida, published by a Bali dive operator and drafted with researchers, local marine managers and guides, sets a minimum of 3 metres from a sunfish at a cleaning station and 10 metres from one that is unsettled. Other points of that Bali code:^1,5,6

• Approach slowly within the fish's field of view; do not swim behind or under it.⁶
• Do not touch or feed sunfish; touching removes the protective mucus on their skin.⁶
• Do not use flash photography.⁶
• Do not block a sunfish's path off the reef or onto a cleaning station.⁶
• Limit your interaction time to 5 minutes when other groups are present.⁶