it weighs more than 2.7 tons!

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This is a humpback sunfish (Mola alexandrini), 3.6 meters long. He was found dead, off Faial, an island in the Azores. His weight ? 2744 kilograms, which makes this specimen the heaviest bony fish in the world. The record was previously held for another fish of the same species, caught in Kamogawa in Japan in 1996; it weighed 2.3 tons for 2.7 meters long.

This mastodon was spotted floating lifeless off the island of Faial in December 2021. Members of the Portuguese association Atlantic Naturalist towed its carcass to the shore to examine and weigh this impressive specimen. The study of animals of extreme size provides new information on the physiology of species and their role in ecosystems, but very little morphological data is currently available.

Sunfish are known to be among the heaviest bony (or osteichthyan) fish. They are characterized by a skeleton composed mainly of bone tissue (as opposed to cartilaginous fish, such as sharks). There are three different species: mola mola (sea bass), Mola alexandrini (humpback sunfish, or southern sunfish) and Mola tecta (or deceptive bluegill). They are found in temperate and tropical oceans around the world.

A species identified by its morphology

This new specimen was weighed using a crane; the ventral area was dissected, and samples of skin with scales, muscle tissue and digestive tract were collected for further analysis.

Sunfish measurements Mola alexandrini recently identified. © JN Gomes-Pereira et al.

This sunfish measured 359 cm in total length, for a maximum width of 86 cm (measured at the middle of the body). specimens of the genus Mola more than two meters can be reliably identified on the basis of their morphology: “ The combination of taxonomic characters used to identify the specimen as M. alexandrini was head hump, chin hump and clavus shape [ndlr : une pseudo-queue] », Specify the authors of the article describing the specimen.

The large specimens of m.mola from the North Atlantic also have a bump on the head, but the shape of their clavus is different: it appears wavy, whereas the clavus of M. alexandrini is rounded in shape. A DNA analysis confirmed the membership of this species (thanks to a match of more than 99.8% with the reference genomic sequences from previously identified individuals).

The morphology of the scales was inspected under the microscope: the scales in the ventral area were mainly conical in shape and arranged in clusters; their general aspect was rather rough, and the upper scales possessed ramifications.

The analyzes unfortunately did not make it possible to determine the cause of death with certainty. ” Analysis of the contents of the digestive tract revealed it to be empty and inspection for marine debris also found no remains of anthropogenic debris. “, note the scientists.

A figure still far from wildlife records

Examination of the body, however, revealed a large contusion, approximately 12 centimeters deep, on the right anterior side of the “hump”. Around this depression, the thick layer of subcutaneous collagen was soft for more than 20 centimeters, suggesting that the contusion was the result of a fairly large impact. In addition, the skin around the wound showed remnants of brick red paint, such as that normally used on the keel of boats. However, the team cannot determine whether the impact took place before or after the death of the animal.

This finding shows that the species M. alexandrini can reach more than twice the maximum weight of its congener, the sunfish m.mola (whose heaviest known specimen weighs 1320 kg). But despite these 2.7 tonnes, M. alexandrini is not about to dethrone the heaviest fish in the world, which are essentially sharks.

In 1st place in the ranking: the whale shark, or Rhincodon typus, which can weigh up to 34 tons and reach 18 meters in length! The largest scientifically measured whale shark weighed 21,318.9 kilograms; it was caught off Pakistan in 1949. The 2nd place is occupied by the basking shark, or Cetorhinus maximus, some specimens of which weigh a little more than five tons, for a dozen meters long. The third place in the ranking of the heaviest fish is occupied by the giant oceanic manta ray (Mobula birostris), which can weigh up to three tons — it also holds the record for the largest wingspan in the animal kingdom, which can be up to nine meters.

And if we consider all the fauna, it is obviously on the cetacean side that the heaviest animal is found: the blue whale, which can reach 170 tons, is the largest animal in the world, followed by the whale and its approximately 70 tons.

Source: JN Gomes-Pereira et al., Journal of Fish Biology

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