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The awesomest fish: the sunfish

This week I want to dedicate this post to common sunfish (Mola mola), one of the biggest bony fishes in the planet and the one with the smallest brains compared with its body. Curiously, an individual of 200 kg had a brain of just 4 grammes (like a walnut)! 

INTRODUCTION

Nowadays, there are four species of sunfishes, which are all included in the Molidae family: the Roundtailed or Common mola (Mola mola), the Southern ocean sunfish (Mola ramsayi), the Sharp-tailed mola (Masturus lanceolatus) and the Slender mola (Ranzania laevis). Today, I will talk about the Common mola (Mola mola) because it is the commonest.

Mola mola 1 Roundtailed or Common mola (Mola mola) (Foto:Per-Ola Norman, Creative Commons)
Masturus_lanceolatus2Sharp-tailed mola (Masturus lanceolatus) (Foto: NOAA/PIRO Observer Program, Creative Commons)
Ranzania_laevis2Slender mola (Ranzania laevis) (Foto: NOAA/PIRO Observer Program, Creative Commons)

COMMON MOLA (MOLA MOLA)’S DESCRIPTION

Common mola’s body have been somehow truncated leaving them little more than a large head with long fins atop and below. Not having in consideration the fins, its body is less than twice as long as it is deep. The tail is not exactly a tail; it consists on expansions of the dorsal and anal fin rays and it is rounded. Skin is gritty and is covered with mucus. Its body is typically silvery in color with slight sheen and can exhibit changeable spotty patterns.

Mola molaCommon mola (Mola mola). Picture made by Blanca Figuerola (Visit her site).

Teeth of each jaw are joined forming an only piece, with an small mouth compared with the body.

The average size for an adult is 1.8 m (from the mouth till the end of the tail) and 2.4 m from each end of the fins. The average weight is one tonne. They hold the record for the world’s heaviest bony fish: a 3.1 meter long specimen weighted in at 2,235 kg.

REPRODUCTION

Sunfishes have a high reproductive potential, as a female of 1.4 meters long can produce 300 million eggs in its single ovary, which are tiny. They have three larvae stages and in the last, the body is covered by bony rays, which are lost when they achieve the adult age.

DIET

Common mola eats a variety of foods, being the most common prey items of gelatinous zooplankton like jellyfishes, Portuguese man-o-war, ctenophores and salps. In addition, they feed on squids, sponges, serpent star bits, eel grass, crustaceans, small fishes and eel larvae.

DISTRIBUTION

They live in all tempered seas and oceans worldwide. They usually live in open sea, but sometimes they move closer the coast, from the surface to 300-400 m deep.

PARASITES AND PREDATORS

It has been detected more than 50 species of parasites in sunfishes, from very different groups, including shark larvae. Moreover, it has been found parasites in their parasites.

On the other side, due to its size, they have few predators, just killer whales and sea lions. Sea lions exhibit a behaviour related to sunfishes. They eat their fins and they abandon the body and sinks to the bottom, where are ate by starfishes.

REFERENCES

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Licencia Creative Commons
Licencia Creative Commons Atribución-NoComercial-CompartirIgual 4.0 Internacional.

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