Marine Creature of the Month October

In a blog slot later than usual, it is time for Marine Creature of the Month! This one was inspired by an episode from the O series of Qi, Ocean, where I honestly would have scored all the points. One of the questions was about this particular creature and I knew the answer (if you ignore the fact I refered to it by its Pokémon counterpart!). Naturally, I wanted to learn more about this weird and wonderful creature, so without further waffle, here we are!

Sunfish, Mola Mola

Photo from Apex Predators

Kingdom: Animalia

Class: Actinopterygii

Conservation Status: VU (Vulnerable)

Found: Across the globe

Diet: Jellyfish, small fish, larvae, squid

Weight: Between 247 - 1,000kg (545 - 2,205lbs)

Size: Up to 3.2m (10.5ft)

Habitat: Tropical, temperate waters; pelagic water.

Can I just start by saying, isn't nature wonderful?! Look at that shape! This fish does not look like it could possibly exist, let alone function and survive, yet here it is. One of three ocean species too - the common ocean sunfish, mola mola; the hoodwinker sunfish, mola trecta; and mola ramsayi. It is a massive fish whose nature and lifecycle is still largely a mystery. In captivity, they live for around ten years, but no one knows how long they live in the wild.

So let's start with its shape. It looks like it's been flattened with a steam roller! The lateral flattening of its disproportionally short body coupled with its extended dorsal and ventral fins makes it look like it is on sideways. They have fewer vertebrae of any other fish, which explains the stunted appearance. This is exacerbated by the truncated shape of its tail. Most fish have caudal fins for a tail whereas the mola mola has a rounded clavus, which is more of a pseudo tail. Other than creating their distinctive shape, it alters the way they swim. Originally it was thought that they just drifted on currents as their shape do not allow for the side to side motion most fish use for swimming. However, it has been observed that they swim with a sculling motion for which their dorsal and ventral fins are perfectly designed. They use them as rudders.

Sunfish are found across the globe and garnered their name from the appearance of them sunbathing on the ocean's surface. They are grey or white, with some regional variance. Their skin is amazing, in that it can change to darker colours when under attack. I would presume this would help to camouflage them but the reason was unclear. Their skin is also incredibly thick, up to 7.3cm (2.9in) in places, and made up of denticles and mucus rather than scales. This makes their hide incredibly tough, as denticles are actually little teeth. (Sharks have them!) They can, however, have up to 40 species of parasites living upon them at any one point. Like land mammals, they use smaller fish and seabirds within their ecosystem to pick their skin clean for them. Alternatively, they breach the surface up to 3m (10ft) in an attempt to dislodge the parasites. These parasites could be one of the reasons why they sun bathe at the surface, to give the seabirds chance to feast.

Another reason believed to be why they bask is to warm themselves. Recent findings show that they spend much more time in deep water than previously thought. Dietary evidence suggests they feed at a variety of depth levels, hunting in pelagic waters rather than at the surface. It was thought they ate jellyfish, exclusively, in vast quantities to develop and sustain their massive bulk despite the lack of nutritional value they possess. There is now evidence they eat small fish, larvae, and squid, which are found in the deeper waters. They have fused, beak-like teeth at the front of their mouth and pharyngeal teeth in their throat, equipping them to deal with whatever critter they hunt. After hunting, they return to the surface to warm themselves up!

They clearly eat enough, for these sunfish can grow up to 3.2m (10.5ft) and weigh up to 1,000kg (2,205lbs). I am a 1.6m (5'6ft) woman and weigh roughly 77kg (169lbs); so this fish is three times my height but is twelve times my weight! To help support and enable this size, mola mola have cartilagenous tissue which is much lighter than bone. Without it, they would not be able to survive their own massive size.

But sunfish do not start out massive. Sunfish fry start off at 2.5cm (1in) long and weigh less than a gram. This means they grow millions of times bigger over the course of their life. They are visually quite different too. Sunfish fry look more like pufferfish than their adult selves due to the spines which cover their body. They loose these as they grow and mature. Little is known about their spawning. It is believed there are spawning sites across the globe in a number of oceans and that they externally fertilise. As young fish, they school together for safety but as they grow bigger they become more solitary creatures. Some have been spotted living in pairs.

Being so big, they can live in solitude for they have very few predators. Sharks, orcas (killer whales), and sea lions will eat them but I can imagine they'd go for easier prey first. The smaller, younger sunfish are, naturally, more vulnerable to predation. Sadly, the mola mola's biggest predators are humans and pollution. They are considered a delicacy in parts of Asia, though from what I have seen the whole fish is used rather than just one part. I think if an animal is going to give its life for food then the whole thing should be used - otherwise it is wasteful and a mockery of its death. However, they do fall victim to ghost fishing, in gillnets particularly, and some fishermen are known to fin them as revenge for the mola mola eating their bait. Much like with sharks, they have their fins cut off them alive before being thrown back into the sea - slowly dying and unable to move.

Other human-related threats to the mola mola is the mere existence of boats. Sometimes they crash - damaging both themselves and the boat. But the biggest human threat to them is our pollution. Like turtles, mola mola eat jellyfish. Plastic bags look an awful lot like jellyfish under the water. Sunfish eat them by mistake and starve to death while feeling full. This madness must stop! Nature is wonderful enough to create lives such as the sunfish. Man creates plastic death. (Ok, I'm feeling a little dramatic about Monday's news, but shouldn't we all?!)

From PADI

Fun Facts!

• Mola mola are the heaviest bony fish alive today.
• Females produce the most amount of eggs of any vertebrate - they produce up to 300 million each time they spawn. 300 million!!
• They belong to the same biological order as pufferfish.
• Most of its names allude to their flat shape. The latin mola means millstone, which could also be a refernce to its colour.
• Its English name sunfish refers to its habit of sun bathing.
• Its French name, however, takes the opposite inspiration. It is called pesca luna which means moon fish! This is due to its shape, not because it howls at the moon or anything.

Check out the #MCotM October board!