Mola Mola

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Scuba diving with Mola Mola in Bali, the dream of every diver.

Mola mola. Fun facts

1. Mola mola is the heaviest  bony fish in the world

It weighs an average of 1,000 kg measures 1.8 m. in length, although we can find specimens that exceed 2 tons and 4 meters wingspan.

Diving with Mola Mola in Candidasa, Bali
Video by Ludovic Amevor

2. Sunfish are pelagic animals

They live on the open ocean and swim at depths to 600 meters. In fact, that’s where they spend most of their adult lives, between 200 and 600 meters.

3. Their closest relatives are pufferfish, triggerfish,  and boxfish

They belong to the Molidae family. Although there are indeed not many similarities in morphology, we can find it in the way it swims, especially in its mouth’s morphology, more specifically in its teeth.

4. They only have 3 teeth

Diving with Oceanic Sunfish in Candidasa, Bali
Video by Ludovic Amevor

They have two in the mouth and one in the throat. Sunfish doesn’t chew its food. When they eat jellyfish, they suck it in and out of their small mouths until it’s small enough to swallow and digest it.

The mouth is small, with strong jaws, where the maxilla and premaxilla have fused into two plates. Therefore mola mola cannot close the mouth properly.

5. Sunfish don’t have scales

Instead, they have very thick and elastic skin covered with a gelatinous mucosa that serves as protection.

The skin thickness can be up to 7.6 cm.  

6. They also don’t have a swim bladder

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But its layer of subcutaneous jelly keeps them neutrally buoyant. For this reason, they swim constantly or move fins side-to-side to hover.

7. The name Mola mola comes from its resemblance to the stone used in the mills to grind the grain, the “millstone”

Curiously, the sunfish is called in Spanish and French as moonfish (Pez luna and Poisson lune). In Spain, there is a legend that tells us that when fishermen went fishing at night and found some of these fish swimming near the surface, they confused it with the reflection of the moon in the water and since then this fish has been known as moonfish.

8. They like sunbathing!

The name in English “ocean sunfish” comes from this fish’s habit of sunbathing on the surface. There are several theories to explain this behavior.

One of them says that it is a way to get rid of their parasites.

Mola Mola can host up to more than 40 different parasite species on the skin. In the reefs, the cleaner wrasse and small fish do their job helping the sunfish to get rid of them. By basking on their sides at the surface, ocean sunfish allow seabirds to feed on their skin parasites.

In addition to the help of seabirds and cleaner wrasse,  a mola mola may leap up to 3 m in the air and then splash down hard to try to shake off the parasites.

Another theory to explain this sunbathing behavior may play an important role in thermal body regulation between deep dives.

The ocean gets a little colder than normal at depths 600 m, which is how deep an ocean sunfish can dive.  Prolonged periods spent in the water at temperatures of 12 °C or lower can lead to disorientation and eventual death. Because of these chilly temperatures, mola mola may swim on their side, presenting their largest profile to the sun, that they can bring their body temperatures up again and aid digestion, following dives into deeper, colder water in order to feed. 

9. The dorsal and ventral fins are very elongated and, when extended, it is as long as it is high

In the course of evolution, the caudal fin disappeared and has been replaced by a rounded structure that takes the name of “calves”, which is a kind of fan-shaped pseudo-tail

Due to the lack of a true tail to propel itself forward and the small size of its pectoral fins, the sunfish uses its thin and long dorsal and ventral fins to move.

It is pushed forward by moving both fins from one side to the other at the same time and in the same direction.

10. Its brain is very small

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An individual weighing 200 kg can have a brain weighting very few grams.

11. Its diet is based on different types of gelatinous zooplankton

This is a nutrient-poor diet, as a result, it needs to eat large quantities to maintain its large size and develop.

They like to eat jellyfish and also squids, sponges, crustaceans and small fish.

12. Female mola mola can lay over 300 million eggs at a time, more than any other vertebrate in the world

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Diving with mola mola at Gili Tepekong, Candidasa, Bali

When living in the open ocean and alone, they find it difficult to find a partner, and the chances of mating are very low.

13. Newly hatched sunfish larvae are only 2.5 mm long and weigh a fraction of a gram

They grow to become fry and those who survive have the potential to grow more than 60 million times their birth size, gaining almost 0.9 kg every day until they grow completely.

It is possibly the most extreme growth size of any vertebrate animal.

The sunfish fry, with large pectoral fins, a caudal fin, and unusual body spines in the adult sunfish, resemble the miniature pufferfish, its close relatives.

Youngsters swim together in banks to protect themselves, but this behaviour is abandoned as they grow up, and as adults, they spend most of their time alone.

14. Mola mola can change color

The color of the sunfish can vary from brown to grey, silver, black, or even almost white. They may also have spots

Molas are capable of color changes particularly when stressed or under attack from a sea lion or other predator. They can turn from light to dark within a matter of moments.

15. Molas really don’t like traveling

The data collected so far shows that the molas really do not travel much like, at all. Even so, they are not clumsy or lazy fish.

They go up to the surface to sunbathe, get cleaned by cleaner fish, and go down to the deep ocean at least 40 times per day.

Although they may seem clumsy at first glance, they can move as quickly as oceanic sharks to feed or avoid their predators and can even jump out of the water.

16. Threats

Ocean sunfish may live up to ten years in captivity,  but the longevity of molas in the wild is still a mystery.

Adults are vulnerable to few natural predators, although it is prey to sea lions, killer whales and sharks.

Speaking of sharks, sunfish are commonly confused with them since they are often found swimming at shallow depth with their large dorsal fin hovering on the surface. But despite their size, oceanic mola-mola is harmless to humans.

Sometimes these fish usually appear trapped in fishing nets.

Another major threat to molas is plastic bags discarded in the water. A floating plastic bag looks like a jellyfish. A mola can absorb it and drown immediately. Or it can clog its interior and starve the fish slowly.

Unfortunately, they are classified as endangered, on the same level as polar bears, cheetahs, and giant pandas.

17. Scuba diving in Bali with Mola

Mola mola in Bali lives in the deep waters between Candidasa and Nusa Penida. They visit cleaning stations when the ocean becomes colder, usually from June to November. Occasionally Oceanic Sunfish has been spotted in other areas of Bali and out of the season. 

These dive sites are known for the strong currents they can present. Therefore diving with mola is only possible for experienced and skilled divers. For safety, always previous check dive is mandatory. 

18. Be a responsible diver

In Bali, guidelines have been designed to provide a satisfactory and safe diving experience while ensuring the lowest sustainable impact on the island’s sunfish and manta ray population. The aim of developing the Code of Conduct for Sunfish and Manta Ray interactions is to ensure Sunfish and Manta Ray can settle onto cleaning stations without being disturbed. Once settled, the Sunfish and Manta Ray can remain on station for longer periods, offering better quality interactions for divers.

Diving with Mola mola – Code of Conduct
Always approach sunfish very slowly within its field of view
Stay close to the reef and do not surround the Sunfish
If the fish are just entering the cleaning station, do not approach until the cleaning has begun and the fish have been stationary for at least 1 minute
Maintain a minimum distance of 3 m from the closest Sunfish when the animal is at a cleaning station
Maintain a minimum distance of 10 m when the animal is unsettled (not in cleaning) and considering an approach to the reef
Do not swim behind the Sunfish as this can startle the animal nor under the fish as your bubbles will disturb cleaning behavior
Wherever possible, do not block the Sunfish’s escape route to the reef or pathway onto a cleaning station
Do Not Touch and Do Not Feed the sunfish
If a Sunfish approaches you, remain still and do not touch It. If you touch it you will remove the layer of mucus that protects it against infection
Do not use flash photography as this often disturbs the fish
Never touch coral and take any marine life
Only dive with companies that have endorsed and adhere to the Code of Conduct
Follow the directions of your dive guide
Southern Dreams Diving Club

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