Ocean Sunfish Facts “Mola Mola”

ocean sunfish

Last updated on August 10th, 2022 at 12:29 am

The ocean sunfish is the largest of all bony fish and can grow to be as long as 10 feet. For many years, it was thought that ocean sunfish was just a myth, but in 1835 they were first discovered. They are mostly found near coral reefs at depths of 1,000 feet or more.

The ocean sunfish has an interesting lifestyle – rather than hiding away from predators as most other fish do, ocean sunfish will often swim towards them head-on!

They are generally very docile fish and will spend much of their time resting on the sand or in caves, however, they do need to be watched closely as if startled, they may accidentally injure themselves. They can move incredibly quickly for such a large fish but only do so when propelling themselves through the water using their fins or tail flapping.

The ocean sunfish, or Mola mola, is the heaviest known bony fish in the world. These amazing creatures can grow to be up to 10 feet long and weigh up to 5,000 pounds! This blog post will take a look at some interesting facts about ocean sunfish. Read on for more information!

Origin and descriptions

ocean sunfish

The ocean sunfish is native to tropical and temperate waters around the world. They are found in oceans, but most often near areas where there is little wave action or turbulence, such as on top of sand flats, mudflats, or reefs.

The ocean sunfish has a very unique and interesting appearance, with an oval-shaped body that can be as long as three meters. It’s often described to look like it is wearing the world’s largest unibrow, because of its large head that looks similar to a cloud or mountain peak. The dorsal fin on top is small and triangular.

The ocean sunfish has a very large mouth, with the lower jaw being slightly longer than its upper jaw and extending past the eyes by at least half of its width. As one would expect from their appearance, they have rough skin that is often covered in parasites or scars from collisions with objects such as boats or jellyfish tentacles. They lack a caudal (tail) fin, and instead propel themselves by using their large, round pectoral fins.

Species profile

ocean sunfish

The ocean sunfish, or Mola mola as it is known in the scientific community, belongs to a family of bony fish called Tetraodontiformes. It has an average length between 0.25m and 0.95 meters and weighs between 150 kg (330 lbs) and >1000 kilograms (>2200 lbs). They are found in temperate waters all around the world. The ocean sunfish is hard to miss due to its size, unusual shape, jelly-bean-like eyes with tiny pectoral fins which hardly move at all.

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Ocean sunfish scientific name

The scientific name of the ocean sunfish is Mola mola

Color and appearance

The ocean sunfish is mostly brown with a silvery-grey tinge. They have an odd flattened shape that resembles a disc and has large fins on either side of their body, one being much larger than the other. The dorsal fin runs from just ahead of the eyes to well past the tail while their pectoral fins are tiny in comparison.

It has a small mouth which is located at the very front of its face and it eats using suction feeding to draw in jellyfish, larval fish, eggs, and mollusks from the water column.

Their skin is relatively thick with temperature control being their primary method for regulating body heat. They use this system due to their lack of a swim bladder which is typically used to maintain buoyancy in fish.

Their eyes are large and round, almost brain-like with dark brown spots that look like pupils giving them an odd “wandering” appearance. In addition to this, they have photophores around their eyes which produce light for attracting prey but also help the ocean sunfish to blend in with its environment.

Their fins are also unique; the dorsal fin is deeply notched and looks like a comb while their anal fin runs all along their underbelly (underside). Their tail or caudal fin is small compared to their body size but unlike most fish, they lack any ribs, pelvic bones, or a swim bladder.

Their mouth is a small opening at the very front of their face which they use to ooze out mucus for catching jellyfish and eat them by expanding their mouths allowing prey into their throat cavity, this process takes around 30 minutes per fish.

Range and habitat

The ocean sunfish is found throughout the world in temperate and tropical waters. They tend to be mostly solitary creatures but can gather together at certain times of the year when they migrate towards the poles for winter, with some traveling as far north as Norway during this time.

They generally prefer temperate and tropical waters, oceans or seas that is warmer than 12°C (54°F) and in some places such as the Galapagos Islands, they prefer water which is around 24°C (75°F).

They can be found at depths of up to 200 meters (660 ft) but usually only dive down to 100m (330ft), spending much of their time near the surface. They tend to swim with their dorsal fin, protruding from the water which is why they are also known as “flying fish” along with their ability to glide through the air.

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Ocean sunfish size

The ocean sunfish has a very unusual body shape with an average length of around three meters (ten feet) and weighing up to two tonnes, making them one of the largest bony fish in existence.

Ocean sunfish are the heaviest and most massive of all bony fish in the world.  They can weigh anything between 150 kg (330 lbs) to >1000 kilograms (>2200 lbs), reaching lengths of up to three meters long (ten feet). The average size for an ocean sunfish is around 400 kg (~880 lbs).

Tank size

Ocean sunfish are very difficult to care for and ill-suited to home aquariums. If you do wish to keep one as a pet then at least 400 gallons (1800 L) is required along with open space that mimics their natural environment. They need good water quality, lots of oxygen, and places such as rocks or other objects to rest on.

Life cycle

Ocean sunfish are believed to live for around ten years, although there have been reports of some living for twenty-five years. They reach sexual maturity at the age of three and their reproduction is very interesting as it can involve broadcast spawning where they release sperm and eggs into open water, however, this has never actually been seen in ocean sunfish, so most likely they just release sperm and eggs into the water when near to a female.

The fertilized egg develops very quickly and within thirty-six hours it has developed from a single cell to something that resembles an adult fish, at around day four or five, they develop their first pigment and start swimming freely. They are independent soon after but usually get sucked up by other fish and remain in the plankton until they are around three to six centimeters long, at this point they start feeding.

Their babies look almost identical to their parents but obviously much smaller. They also have a unique shape as it is believed that when the sunfish were evolving from shallow water ancestors into deep-sea dwellers, several of them were trapped by receding glaciers which forced them to adapt their bodies into the flattened shape they are today.

Although ocean sunfish have been recorded mating with other fish such as pufferfish, it is not known whether this is intentional or just a mistake, so far there has never been any evidence of juveniles resulting from these pairings either.

They are believed to be hermaphrodites which means that they have both male and female sex organs, however, this has never been confirmed.

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Are they aggressive or peaceful?

Ocean sunfish are generally very peaceful fish and will not bother anything unless threatened. They have no teeth, so cannot really hurt other animals but they do have long heavy fins which can deliver a nasty sting if touched or stood on, this is why it’s best to avoid going near the ocean sunfish when you see one as they may mistake swimmers or divers for predators.

As they don’t really have any natural enemies, ocean sunfish are not aggressive towards humans either and will usually swim away if approached, however, it is still advised to stay at least fifteen meters (fifty feet) away from them as their tails can swipe out quickly causing serious injury.

Ocean sunfish care

ocean sunfish

Ocean sunfish are very difficult to care for and ill-suited to home aquariums. If you do wish to keep one as a pet then at least 400 gallons (1800 L) is required along with open space that mimics their natural environment. They need good water quality, lots of oxygen, and places such as rocks or other objects to rest on.

Due to their massive size and unusual shape, it is very difficult for them to stay upright, so they need somewhere such as a sandy area where they can bury themselves when feeling threatened or stressed, without this, the ocean sunfish will spend most of their time lying on one side which eventually makes it vulnerable to infections that may prove deadly.

Ocean sunfish diet

An ocean sunfish consumes around ten percent of its body weight in food each day. The diet consists primarily of jellies, but also includes tunicates and other invertebrates such as crabs, squid, octopus, and sponges. They are often seen feeding near the surface during daytime hours, where they move their massive bodies using their fins to power through the water.

Tank mates

Due to their size, ocean sunfish are best kept in a species-only aquarium. They can be very aggressive and any other tank mates that they see as food will be attacked relentlessly until eaten or forced away.

Any fish large enough to fit inside the mouth of an ocean sunfish is at risk. Even invertebrates such as crabs may be crushed by the beak-like mouth if they try to climb out over it.

Water conditions

Ocean sunfish are very sensitive to changes in their water conditions and need stable temperatures of around 25°C (77°F) with a pH between eight and twelve. They also prefer low nitrate levels as this can lead to bacterial infections that may prove fatal.

The ocean sunfish is classified as vulnerable on the IUCN Red List of Threatened Species. Due to fishing practices, pollution, and habitat loss, the population numbers are decreasing in many areas of the world which is having a detrimental effect on other species that depend upon them for survival.

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ocean sunfish

Ocean sunfish are generally difficult to breed in captivity. Even if the tank conditions are suitable, they often fail to release their gametes, so fertilization does not occur.

Once released, the egg will become spherical and transparent which is when it can be easily spotted by researchers. It then becomes a larval fish that feeds on plankton for several months before developing into an adult.

The ocean sunfish is also known as the Mola mola, although this name can be confused with other species that are sometimes referred to by the same common names. Other aliases include the king of herrings, due to their enormous size and appearance which makes them resemble a school of fish when seen from above.


The maximum lifespan of an ocean sunfish is around thirty years, although most do not reach this age.

Parasites and diseases

Ocean sunfish are susceptible to parasitic infections. One of the most widespread is caused by a copepod known as Lernaea cyprinacea which causes swim bladder disease in fish that it infests.

Ocean sunfish predators

The ocean sunfish has few predators due to its size but will be attacked if approached closely enough by other large marine animals such as sharks, orcas, and large fish.

In some parts of the world, ocean sunfish are caught by commercial fishing companies as a source of food and oil. They have little flesh on their bodies, however, which makes them less valuable than other species with similar amounts of meat per weight.

Does it make good pets?

No, the ocean sunfish is not a good candidate for being kept as a pet. They have very particular water conditions and diet requirements that are difficult to meet in captivity which means they often do not live long when held captive by humans.

Any fish large enough to fit inside the mouth of an ocean sunfish is at risk. Even invertebrates such as crabs may be crushed by the beak-like mouth if they try to climb out over it.


The ocean sunfish is a fascinating fish that is well-known for its incredible size and appearance. They are often seen feeding near the surface during daytime hours where they move their massive bodies using their fins to power through the water.

They are interesting creatures but unfortunately, their massive size makes them incredibly difficult to care for in an aquarium or garden pond, so it is best not to try as you may find yourself in a situation where you are unable to care for them longer.