The ocean sunfish is found in all tropical and temperate seas of the world. Its appearance resembles a large head with an attached tail. The body of the animal is flat. When its dorsal and ventral fins are extended, the sunfish is as tall as it is long. It is the world's largest and heaviest bony fish.
They live in temperate and tropical oceanic waters around the globe.
They can be found in all oceans, where the temperature is higher than 10 °C (50 °F). Individuals migrate in hot ocean waters in the summer and may accidentally enter internal bodies of water, however, they die when water temperatures drop.
Ocean sunfish have a very peculiar appearance.
The body is tall, laterally flattened with a crescent-shaped tail that replaced the caudal fin in the course of evolution. Ocean sunfish tail is called clavus. Dorsal and anal fins are elongated and almost vertically oriented. The pectoral fins are relatively small and have a fan-like shape.
The body is covered with thick and elastic skin.
The skin is particularly thick in the abdominal region, where it can be up to 7.3 cm (2,87 in) thick. It is not covered with scales but with mucus and can be very rough, like sandpaper. An exception is a clavus, which has a smooth surface.
Typically adults measure about 1,8 m (5,9 ft) in length and 2,5 (8,2 ft) fin to fin. Weight may vary from 247 to 1000 kg (545 to 2205 lb).
Largest individuals may reach 3,3 m (10,8 ft) in length and 4,2 m (13,8 ft) vertically and weigh up to 2,300 kg (5,070 lb). Research suggests that females may be a bit larger than males.
Colors vary from brown through grey to white.
Different patterns on the skin seem to be determined by the area of occurrence. While endangered or in stress, ocean sunfish can change skin coloration to darker.
They usually live a solitary life.
Mostly they are encountered swimming alone, but pairs also have been spotted. They probably aggregate in more significant numbers during mating season as fertilization takes place in the depths of the water, not on the substrate.
They are slow swimmers.
For many years researchers thought that ocean sunfish moves only by drifting with ocean currents. With some observations, it was noticed that they propel themselves with an average speed of 3,2 km/h. Daily, sunfish can travel up to 26 km (16 mi).
While in danger, they can speed up.
When being pursued, those fish can accelerate rapidly and even jump over the water surface.
They are a predatory species, yet omnivore ones.
They eat a lot of small fish, squids, fish larvae, crustaceans, jellyfish and salps. From time to time, they vary their diet with eelgrass. As their food may lack nutrients, they need to eat a lot.
In search of food, they can dive as deep as 600 m (1 968 ft).
It is estimated that sunfish must eat 1% to 3% of their body mass a day. Foraging takes them usually about half a day. After a long presence in cold depths, ocean sunfish need to bask in the sun.
They do not have many enemies.
Those giants are hunted mostly by sea lions, killer whales and sharks. Juveniles may be also hunted by tunafish or common dolphinfish.
They are sunbathing to warm up because of their ectothermic nature.
As they do so, they straighten horizontally and float just beneath the water surface. During this process, the sunfish eagerly expose their skin to waterfowl, which helps the fish get rid of skin parasites.
The newly hatched sunfish is tiny, measuring about 2,5 mm (0,1 in).
If they are lucky enough to survive and develop into fry, they need only 15 months to achieve a size of an adult. To increase the chance of survival, juveniles swim in schools.
Females are able to produce as many as 300 million eggs.
Single egg measures 1,3 mm in diameter. Fertilization occurs in water, where released eggs are fertilized by sperm.
We still do not know how long an ocean sunfish can live.
In captivity, they may live over ten years.
They are being mistaken for sharks.
Because ocean sunfish often swim near the water's surface, their dorsal fin protrudes above the water and resembles that of sharks. Those familiar with marine animals, however, will easily distinguish them from a shark by the way they move.
Despite the fact they are quite big, they pose no threat to humans.
Ocean sunfish are docile creatures that have no interest in humans. Sometimes they can hurt people when jumping out of the water and landing on boats.
In 2005, a relatively small, 30 kg sunfish landed on a family boat, injuring a 4-year-old boy.
The accident occurred off the coast of Pembrokeshire, Wales.
They are considered a delicacy, especially in Asia.
Sunfish are very popular in Japan and Taiwan. All parts of the fish are used in cooking, from the fins to the entrails.
They are an endangered species.
IUCN classifies those fish as vulnerable (VU) as the population is decreasing. They are getting caught in fishnets or suffocate by consuming plastic bags that they mistakenly take for jellyfish - one of their foods.