Ocean Sunfish or Common Mola (Mola mola), family Molidae, order Tetraodontiformes, found in temperate and tropical oceans around the world

The largest bony fish in the world, growing up to 3.3 m (10 ft 10 in) in height, up to 1.8 m (5 ft 11 in) in length, and weighing up to  2,300 kg (5,100 lb) ... 1,000 kg (545 to 2,205 lb) as a mas weight is more common.

They feed on a wide variety of invertebrates and small fish (not just jellyfish, as was once thought).

Today's fish of the day is the slender sunfish! 

The slender sunfish, known by the scientific name Ranzania laevis, is the only remaining sunfish in the Ranzania genus. Found worldwide around the tropical and subtropical areas, form a range of  71°North to 55°South. Found from a depth of 1-140 meters, these fish spend all of their time on the epipelagic zone. Despite this, these fish are considered incredibly elusive, finding ways to dodge humans as often as they can, as such most research on these fish comes from stranded fish along the Australian coast. In particular across multiple strandings along the Southern Australian coast. Of which only very few specimens are able to be returned to the ocean from. 

Unlike their close relatives, the mola sunfishes, the slender sunfish is incredibly small. Growing only 100cm in length at maximum, as opposed to their cousins, which can grow upwards of 5 meters. This however is to the slender sunfish's benefit, as they are the only fast moving marine sunfish. The other remaining 5 sunfish species are all rather slow moving, consuming only plankton and jellyfish, the slender sunfish however has chosen a far more difficult pathway. Instead consuming squid, which are known for their speed and agility. I can find no information about known predators of the slender sunfish, although their skin is far thinner than that of their relatives, and thus it's likely they're predated on by marine mammals and large sharks. 

There is little to no info about the reproduction of the slender sunfish, and no information about lifecycle or lifespan. However, if we assume that the slender sunfish breeds similarly to the common ocean sunfish (Mola mola) then we can assume that they release eggs into the water to be externally fertilized, and become plankton, floating until they mature and hatch into fry. As the slender sunfish ages, it will begin to lose the caudal tail it is born with, slowly fusing into a clavas, which helps them move faster in the water. Marine sunfish are not known for their speed, and for years it was thought that Mola's had no ability to move of their own accord, but were rather being propelled by the water. This misinformation goes hand in hand with the idea that when these sunfish bask at the surface of the water, they are stuck. However, this behavior is done to entice cleanerfish, and seabirds, such that they may remove and eat the skin parasites collected by the sunfish over time. Molas can swim with their anal and dorsal fins, using the pectoral fins as stabilizers. These fish are even able to control the angle and force it produces well swimming! Similar to how bird wings work! Sunfish may also steer themselves with strong jets of water shot from the mouth. Which is possibly why the mouth is fused open permanently by the shape of their hardened beak. 

Mola mola. The mola we all knowla. The mola we all molove. What an incredible creature, Mola mola is! Such a strange shape, so many eggs, no swim bladder... and the size. Its most prized aspect! If you know one thing about Mola mola, it’s that it is the largest bony fish, right?

...Right?

Nuh-uh-uh, Mola mola. Don’t try and sneak away. It’s very noticeable. After all, you are one of the biggest bony fish!

Let me repeat that. One of the biggest bony fish.

Mola mola, the ocean sunfish, is NOT in fact the largest known bony fish! You’d think we were talking about Mola tecta, because this sunfish has hoodwinked us!

Behold MOLA ALEXANDRINI! Known, very appropriately, as the giant sunfish. This is the true heaviest bony fish! Not Mola mola, as has so been thought, and as I have even claimed in front of all of you. I was wrong! Mola alexandrini has been recorded weighing up to 6,049 pounds, with Mola mola trailing in the measly little 2,000s range. But if Mola alexandrini can be so much bigger, how was Mola mola seen as the champion for so long?

It was a misunderstanding. A misidentification! That huge specimen was caught all the way back in 1996, but thought to be Mola mola until it was reevaluated in 2017! Members of the Mola genus are just always accidentally tricking us humans. I’m sure they would say “sooorry” in a deep and booming, yet slow and gentle voice if they knew.

So how can you #KnowYourMolas? It is easy to confuse them- even scientists do it- but generally, be sure to notice the shapes of both the face and the clavus (the funny butt fin)! If the face is relatively smooth, and especially if the clavus has a scalloped shape, that’s Mola mola. If the face is bulgy and bumpy and the clavus is smooth and round, that’s Mola alexandrini! And if the face is smooth but the clavus is too, then you have been hoodwinked by Mola tecta!

So there you have it. The truth about the Mola mola! Not the biggest after all... but that does not matter to me. Mola mola will always be my favorite! That being said, please show Mola alexandrini some love too, as despite its size, it is still a lesser known Mola!

And who knows? Maybe even alexandrini will be dethroned! Maybe we will find a bigger alexandrini, or maybe a bigger mola! Maybe even a different species altogether is the true largest bony fish! There is no way to know what the future has in store... so many secrets in the ocean!

A stimboard with ocean sunfish and space!

Despite being up to 250cm long, these beasts were hiding in plain sight until 2014, because they were mistaken for other two species of sunfish. Although environmental DNA testing of the waters around Australia indicated there was third species of sunfish around - it was just that nobody knew what it looked like.

Then one washed up near Christchurch and could be studied in detail. It was initially tought they were found in Southern Oceans, but specimens from the northern hemisphere are also turning out to be the Hoodwinker. There was also a 130-year old preserved specimen in a Dutch Museum's storage area but it was stuck behind a giraffe.

Molids (named after the Latin for millstone) have bodies that end immeadiately behind the dorsal and anal fin. They also have the fewest vertebrae of any fish - 16 in Mola mola - and a mostly cartilaginous skeleton. Despite that, sunfish are the heaviest bony fish - up to 3m long and weighing 2700kg.

The Hoodwinker eats pelagic salps and siphonophores, and like the other sunfish basks at the surface to warm up before diving back into the depths, flapping their dorsal and anal fin like wings. Basking also gives gulls and other birds a chance to pick off parasites.

Fossil sunfish are known from as far back as the Eocene.