Marine life in Bali. Oceanic Sunfish (Mola Mola).
Scuba diving with Mola Mola in Bali, the dream of every diver.
How big is Oceanic Sunfish?
The ocean sunfish or common mola (Mola mola) is the heaviest bony fish in the world with an average of 1,000 kg. weight and 1.8 m. in length, although we can find specimens that exceed 2 tons and 4 m wingspan.
Where do they live?
Sunfish (Mola mola) are pelagic animals (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.
Fun facts about Mola Mola
They belong to the Molidae family, and their closest relatives are pufferfish, triggerfish, and boxfish. Although there are indeed not many similarities in morphology, we can find it in the way it swims, but especially in the morphology of its mouth, more specifically in its teeth. The mouth is small, with strong jaws, where the maxilla and premaxilla have fused into two plates, like the beak of a bird, and therefore can not close the mouth properly. They only have 3 teeth. 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 an digest it.
All of them belong to the order of tetraodontiforms, characterised by the absence of scales. Instead, they have very thick and elastic skin covered with a gelatinous mucosa that serves as protection. Its thickness can be up to 7.6 cm.
They also don’t have a swim bladder that makes them float in the water. But its layer of subcutaneous jelly keeps them neutrally buoyant. They swim constantly (or move fins side-to-side to hover).
Despite its cataloged as osteictio, in reality, its tissues are mainly cartilaginous, higher than bone. This allows them to reach those unthinkable dimensions for other bony fish.
Why the name is mola mola?
The scientific name of this fish (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 moon fish (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.
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 behaviour.
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 behaviour 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.
More fascinating facts about mola mola
Those fish have actually no tale. With very flat bodies Mola Mola can grow as tall as they grow long, which gives them its moon shape.
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.
Although they may seem clumsy at first glance, they are able to move as quickly as oceanic sharks to feed or avoid their predators and can even jump out of the water.
Ocean sunfish has just 16 vertebrae, the fewest of any fish. Humans, in comparison, have 33. It has a reduced skeleton that is mostly cartilaginous and also lacks ribs.
Its brain is very small, even smaller than one of its two kidneys, which are located just behind the brain. An individual weighing 200 kg can have a brain weighting very few grams.
Its diet is based on different types of gelatinous zooplankton such as jellyfish. This is a nutrient-poor diet, as a result, it needs to eat large quantities to maintain its large size and develop. They also like squids, sponges, crustaceans and small fish.
They lay more eggs than any other vertebrate animal!
Female mola mola can lay over 300 million eggs at a time, more than any other vertebrate in the world. When living in the open ocean and alone, they find it difficult to find a partner and the chances of mating are very low.
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.
What colour are they?
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.
In Bali they are studying these fish
In Bali, they are being tagged to learn about them. What they want to discover is how the Molas use currents, temperatures and the open ocean to live their lives. The data collected so far shows that the Molas really do not travel much … like, at all. In Bali they live in the area between Candidasa and Nusa Penida, where depths of up to 600 meters are reached, and in the channel between Nusa Penida and Lembongan, with depths of up to 1000 meters.
Another important fact that they discovered is that they are not clumsy or lazy fish. They go up to the surface to sunbathe and clean themselves in coral reefs and then go down to the deep ocean at least 40 times per day. When the sun rises, they begin their dive. As the sun gets brighter, they go a little deeper, up to 600 meters, at very low temperatures, and that is why we see them on the surface sunbathing all the time. They go up, they get hot, and then they go back down, they go up and down, and they go up and down.
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 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.
Where can we dive with Mola Mola – Oceanic Sunfish in Bali?
Mola Mola in Bali live 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 by the strong currents they can present. Therefore diving with mola mola is only possible for experienced and skilled divers. For safety, always previous check dive is mandatory.
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 sunfish and manta ray population of the island. 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 the Mola Mola Sunfish – 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 (or 3 body lengths) from the closest
Sunfish when the animal is at a cleaning station.
- Maintain a minimum distance of 10 m [or 5 body lengths] when 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 behaviour.
- 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 which have endorsed and adhere to the Code of Conduct
- Follow the directions of your dive guide
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