Kurzgesagt – In a Nutshell

Sources – Sunfish

Disclaimer: As some viewers correctly pointed out, we made a mistake at 7:20. We swapped the labels "Salps’" and "Ctenophores." Thanks for the hint!

Disclaimer: There is a distinction between larvae and adult sunfish. Unless otherwise specified, references to sunfish in the script generally refer to adults. When juveniles or larvae are meant, this is explicitly stated.

While we jokingly refer to the ocean sunfish as the “dumbest creature alive,” this is not a statement about its actual intelligence. Our comment is meant to reflect its peculiar appearance and behavior from a human perspective, not a measured evaluation of its mental capacity. Think of it as “dumb-looking,” not definitively dumb.

– The genus of Mola is a fish built wrong, a giant head that evolution lost interest half way through. Its body is very flat and circular without a real tail, instead it has a sort of rudder-like stump. Two fins on the top and bottom give it an, uhm, unorthodox swimming style.

#Phillips et al. The ocean sunfishes (family Molidea): Recommendations from the IUCN molidae review panel. Marine Policy. 2023.

https://www.sciencedirect.com/science/article/abs/pii/S0308597X23002932

Quote: “The ocean sunfishes (family Molidae) include the largest and heaviest bony fishes in the world and species within the family are distributed from southern Chile to the Arctic Circle. The Molidae currently contains five species within three genera: Mola mola (Linnaeus, 1758), Mola alexandrini (Ranzani, 1839), Mola tecta (Nyegaard et al., 2017), Masturus lanceolatus (Liénard, 1840) and Ranzania laevis (Pennant, 1776).”

#Mowatt-Larssen T, Thys TM, Hildering J, Caldera EJ, Biesack EE, McDowell JR and Nyegaard M (2025) Hook, line, and social media: crowd-sourced images reveal size and species patterns of ocean sunfishes (Tetraodontiformes, Molidae) from California to Alaska. Front. Mar. Sci. 11:1482873. doi: 10.3389/fmars.2024.1482873
https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1482873/full

Quote: “Ocean sunfishes (Molidae; ‘molids’) are charismatic teleost megafauna known for their unusual appearance, high fecundity and large adult size, including the record for heaviest bony fish. Currently, one small (<75 cm total length, TL) and four large species (>2.4 m TL) are recognized across three genera: slender sunfish Ranzania laevis (Pennant 1776), sharptail sunfish Masturus lanceolatus (Liénard 1840), ocean sunfish Mola mola (Linnaeus 1758), giant sunfish Mola alexandrini (Ranzani 1834) sensu Sawai et al. (2018) and Sawai and Nyegaard (2023), and the recently described hoodwinker sunfish Mola tecta Nyegaard et al., 2017.”

#Ocean Sunfish. National Geographic. Retrieved April 2025.

https://www.nationalgeographic.com/animals/fish/facts/ocean-sunfish

Quote: “Sunfish, or mola, develop their truncated, bullet-like shape because the back fin which they are born with simply never grows. Instead, it folds into itself as the enormous creature matures, creating a rounded rudder called a clavus. Mola in Latin means "millstone" and describes the ocean sunfish’s somewhat circular shape. They are a silvery color and have a rough skin texture.”

In fact, molid larvae have a caudal larval fin fold, but it never develops true fin rays or bones. Instead, the caudal fin is completely lost during development and replaced by modified dorsal and anal fin elements forming the clavus.

#Johnson GD, Britz R. Leis' conundrum: Homology of the clavus of the ocean sunfishes. 2. Ontogeny of the median fins and axial skeleton of Ranzania laevis (Teleostei, Tetraodontiformes, Molidae). J Morphol. 2005

https://onlinelibrary.wiley.com/doi/10.1002/jmor.10242

Quote: “We thus conclude that the molid clavus is unequivocally formed by modified elements of the dorsal and anal fin and that the caudal fin is lost in molids.

(...) The anterior two fin rays are serially associated with the two distal bifurcations of the first proximal-middle radial. The chorda projects straight into the caudal larval fin fold. No fin rays or supporting bones are developed in this area.”

– They propel themselves forward by flapping their fins in a goofy wobbling motion with as little grace as possible. It’s less like swimming and more like underwater flying –although when they really try, Mola can match strong swimmers like salmon or marlins.

#Davenport J, Phillips ND, Cotter E, Eagling LE, Houghton JDR. The locomotor system of the ocean sunfish Mola mola (L.): role of gelatinous exoskeleton, horizontal septum, muscles and tendons. J Anat. 2018
https://pmc.ncbi.nlm.nih.gov/articles/PMC6081505/

Quote: “Once thought to be slow‐moving surface‐dwelling fish that fed solely on gelatinous prey, sunfish are now known to be highly active fish that feed benthically on a variety of prey when young, chase fast‐moving prey in mid water, and are capable of substantial vertical (hundreds of metres) and horizontal (hundreds/thousands of km) migrations (Pope et al. 2010; Nakamura & Sato, 2014). Burst swimming speeds of 2.1 m s−1 (1 m TL fish) and 6.6 m s−1 (2 m TL fish) have been recorded (Nakamura & Sato, 2014; Thys et al. 2015), similar to values recorded for a variety of streamlined scombroid fish (Block et al. 1992). Sustained (cruising) swimming speeds are much lower (0.2–0.7 m s−1; Nakamura & Sato, 2014), but allow swimming rates of < 60 km day−1, comparable with cruising speeds of fish with axial musculature such as salmon and marlin (Pope et al. 2010).”

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “Further insights into M. mola locomotion were achieved when Watanabe and Sato (2008) used high resolution multi-channel data loggers to record the movements of three individuals in Otsuchi Bay, Japan under natural conditions. The fish undertook frequent vertical movements and swam at continuous speeds of 0.4–0.7 m s-1 (similar to records of other large fishes such as salmon, marlins and pelagic sharks). It was also confirmed that ocean sunfish stroke their dorsal and anal fins synchronously (dominant frequency 0.3–0.6 Hz) to generate a lift based thrust that was likened to the symmetrical flipper beats of penguins (Watanabe and Sato 2008). Essentially, M. mola uses its anal and dorsal fins as a pair of wings. It is worth noting that this is the only animal known to use two fins for this purpose that are not originally bilaterally symmetrical (Watanabe and Sato 2008). Watanabe and Sato (2008) argued that the symmetrical pair of dorsal and anal fins are well suited for cruising because they are mechanically more efficient (Walker and Westneat 2000) and give more thrust per stroke at high speed (Vogel 1994) compared to the drag-based swimming of other Tetraodontiform fishes (e.g. pufferfish, Gordon et al. 1996; box fish, Hove et al. 2001 and burrfish, Arreola and Westneat 1996).”

#Daniel Kemp. The Solar-Powered Fish with Jellies in Their Bellies: Molas. US Fish and Wildlife Service. 2022.

https://www.fws.gov/story/solar-powered-fish-jellies-their-bellies-molas

Quote: “In stark contrast to the way they’re often seen slowly drifting near the surface, molas are actually some seriously efficient swimmers. Tagged specimens have been recorded traveling nearly 20 miles in a single day, reaching speeds of about 20 feet per second, and making lengthy migrations from Taiwan to New Caledonia. Most surprising of all, they’ve been observed making stunning leaps out of the water, launching themselves 10 feet or more into the air.

(...)

They may look like they're just some ne'er-do-well, lying around, you know, sucking down jellies at the surface. But they are hiding quite an active agenda— they can dive to 1000 meters, up to 40 times a day.

(...)

Sunfish musculature reflects this, with most of their muscle mass being clustered around their dorsal and ventral fins rather than their rudder.”

#Mola Mola. Monterey Bay Aquarium. Retrieved April 2025.
https://www.montereybayaquarium.org/animals/animals-a-to-z/ocean-sunfish

Quote: “Scientists, impressed by its slow-motion swimming at first, guessed that the mola must drift wherever ocean currents takes it. But molas in Southern California have been tracked swimming 16 miles (26 km) in a day, at a top speed of two miles (3.2 km) per hour — which, to give them credit, is not far off the speed of a yellowfin tuna when it's just cruising.”

– Sunfish also don’t have a swim bladder, the gas-filled organ most fish use for buoyancy. Instead they have a jelly-like layer of flesh that is 90% water to dive or surface, which is definitely not helping with agility. Most of the time Mola cruises around leisurely.

#Mola Mola. Monterey Bay Aquarium. Retrieved April 2025.
https://www.montereybayaquarium.org/animals/animals-a-to-z/ocean-sunfish

Quote: “The mola is a slower swimmer than most other large pelagic fish. An adult mola lacks a gas-filled swim bladder, the organ that gives most bony fish exquisite control over buoyancy.”

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “The study by Watanabe and Sato (2008) also examined the internal and external morphologies of 49 ocean sunfish (body mass ranging from 2 to 959 kg) collected from local fish markets. It was demonstrated that despite the missing swim-bladder, ocean sunfish are neutrally buoyant (mean body density 1,027 ± 4 kg m-3 , N = 20) in seawater (density ca. 1,026 kg m-3 ) and that a thick layer of´low-density, subcutaneous, gelatinous tissue plays a major role providing this buoyancy (Watanabe and Sato 2008). The degenerate, cartilaginous skeleton of M. mola (Cleland 1862) also likely contributes to buoyancy (Davenport and Kjørsvik 1986). Importantly, the gelatinous tissue is incompressible, enabling rapid depth changes without the changes in buoyancy that would be experienced by fish possessing swim-bladders (Yancey et al. 1989). This combination of a lift-based swimming mode and neutral buoyancy from incompressible, gelatinous tissue appears to allow M. mola to move over considerable distances, despite its unusual morphology.”

#Davenport J, Phillips ND, Cotter E, Eagling LE, Houghton JDR. The locomotor system of the ocean sunfish Mola mola (L.): role of gelatinous exoskeleton, horizontal septum, muscles and tendons. J Anat. 2018
https://pmc.ncbi.nlm.nih.gov/articles/PMC6081505/

Quote: “Ocean sunfish exhibit the most extreme known form of tetraodontiform locomotion. Although all tetraodontid fish (including pufferfish and boxfish) employ the dorsal and anal fins as propulsors, in most cases these are supplemented by the action of other fins; they are median and paired fin (MPF) swimmers. For example, Gordon et al. (1996) showed that pufferfish combine in‐phase use of the dorsal and anal fins with out‐of phase pectoral fin propulsion. During burst swimming they even recruit the caudal fin (used as a rudder at lower speeds) to provide additional propulsive force. The puffer body shape is variable and a degree of posterior body undulation occurs at high speed. In the ocean sunfish the caudal fin is absent, the body entirely rigid and the pectoral fins very small; although they are undoubtedly of use in low speed manoeuvring, they can make little contribution to cruising or burst swimming. Effectively rectilinear propulsion depends on two median fins alone.”

Quote: “Sunfish tissue water contents are displayed in Table 1 and compared with data for the lumpfish Cyclopterus lumpus (Davenport & Kjørsvik, 1986), another oceanic fish of demersal ancestry that has a thick gelatinous subcutaneous layer that aids in the attainment of neutral buoyancy and acts as an exoskeleton. These data show that the subcutaneous tissue of the capsule has similar water content (90%) to that of female lumpfish subcutaneous tissue (93%), rather lower than the 96.5% of gelatinous tissues of deep‐sea snail fish (Gerringer et al. 2017) and the 95–98% of neutrally‐buoyant gelatinous invertebrates such as medusae (Doyle et al. 2007). However, the water content is higher than that of the sunfish fin muscles (79–84%). The salt content (23% of dry mass) is low by comparison with known jellyfish prey (Doyle et al. 2007); this presumably reflects the low osmolarity of body fluids of teleosts by comparison with marine invertebrates. Most (77%) of the dry mass is made up of organic matter (Table 2).”

In contrast to past assumptions, sunfish are actually relatively active swimmers.

#Carnevale G. et al. Evolution and Fossil Record of the Ocean Sunfishes. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: “Because of their abbreviated body shape and habit of passively floating on the sea surface, the ocean sunfishes were historically regarded as slow-moving surface-dwellers that fed primarily on gelatinous zooplankton (e.g., Fraser-Brunner 1951, Hooper et al. 1973). However, recent studies have revealed that they are highly active animals undergoing considerable horizontal and vertical migrations, and that they have apparent ontogenetic dietary shifts in which young individuals feed benthically on a variety of prey, and adults are also capable of chasing fast-moving midwater prey (e.g., Nakamura and Sato 2014, Phillips et al. 2015, Nyegaard et al. 2017, Sousa et al. 2016, Sousa et al. 2020 [Chapter 8]).”

(...)

Owing to their atypical morphology and characteristic basking behavior (see Pope et al. 2010, Nakamura et al. 2015), there was a historical perception that the species drifted passively (Pope et al. 2010). However, over recent years, these views have changed radically with strong empirical data revealing high performance burst swimming and long-distance movements against major current regimes (Cartamil and Lowe 2004, Sims et al. 2009b, Sousa et al. 2016a, Chang et al. 2019).

– Their teeth are fused into a parrot-like beak that sits in a tiny gaping pout that is open most of the time. Together with two huge empty eyes, the sunfish has a perpetual derpy face, always looking stunned.

The misconception that Mola mola is physically unable to close its mouth likely stems from frequent observations of the fish swimming with its mouth open. In reality, sunfish can anatomically close their mouths. They often keep them open while swimming to actively pump water over their gills for respiration. This behavior has been misinterpreted, and the myth has been around at least since the 1950s as our expert stated.

#Mola Mola. Monterey Bay Aquarium. Retrieved April 2025.
https://www.montereybayaquarium.org/animals/animals-a-to-z/ocean-sunfish
Quote: “Inside a mola's tiny mouth are two pairs of hard teeth plates shaped with a slightly curved ridge that look kind of like a bird's beak. The mola eats mainly jellies and other gelatinous organisms, from big moon jellies to ctenophores, to tiny comb jellies.

To break its dinner into manageable pieces, the mola doesn’t chew. It sucks the jellies in and out of its mouth until they're reduced to gelatinous chunks. It is thought that the mola can enjoy this potentially painful diet because of a mucuslike lining in the digestive tract that keeps it from getting stung. A mola will occasionally eat squid, fish, algaes crustaceans and other invertebrates. A mola may migrate vertically several times a day to find deeper dwelling gelatinous organisms in the open ocean.”

#Ocean Sunfish. National Geographic. Retrieved April 2025.

https://www.nationalgeographic.com/animals/fish/facts/ocean-sunfish

Quote: “Mola are found in temperate and tropical oceans around the world. They are frequently seen basking in the sun near the surface and are often mistaken for sharks when their huge dorsal fins emerge above the water. Their teeth are fused into a beak-like structure, and they are unable to fully close their relatively small mouths.”

– Sunfish don’t have proper scales but some of the thickest skin in the ocean after whales. Up to 15 cm thick it is rough and rubbery and often covered in mucus, like an armour made from car tyres. Although most of what it is protecting is not that great in the first place.

Instead of having the common, proper overlapping scales, their skin is extremely thick and rough, covered in tiny bony structures, highly modified, plate-like dermal scales featuring a central upright spine and radial ridges. These scales interlock tightly through pronounced interdigitations.

#Katayama, E and Matsuura, K. Fine Structures of Scales of Ocean Sunfishes (Actinopterygii, Tetraodontiformes, Molidae): Another Morphological Character Supporting Phylogenetic Relationships of the Molid Genera. Bull. Natl. Mus. Nat. Sci., Ser. A, 42(2). 2016

https://www.kahaku.go.jp/research/publication/zoology/download/42_2/BNMNS_A42-2_95.pdf

#Mola Mola. Monterey Bay Aquarium. Retrieved April 2025.

https://www.montereybayaquarium.org/animals/animals-a-to-z/ocean-sunfish

Quote: “The mola is related to pufferfish, and a just-hatched mola is puffy, round and covered with spines like its relatives. Pufferfish are extremely poisonous in specific parts of their bodies, but scientific studies have so far found no trace of the toxin in the mola. In fact, strange as it may sound for a parasite-ridden fish with skin that's thick and rubbery like a car tire, the mola makes a popular meal in parts of Asia and is also used in medicine. Apart from humans, other predators include sea lions, sharks and killer whales.”

#New England Coastal Wildlife Alliance. Mola mola Research & Rescue. Retrieved April 2025.

https://necwa.org/necwa-projects-mola.html

Quote: “The skin is silver in coloration and has a slight sheen overall. Although not obvious from a distance, the skin is covered with copious amounts of mucus. The skin is also very thick and has a gritty texture when touched.”

#Oceansunfish.org. Retrieved April 2024.

https://oceansunfish.org/species-and-distribution/

Quote: ”Mola mola have a rounded tail when they are juveniles which can become scalloped as they mature and become larger. Some adults in the eastern Atlantic can possess a bulbous head similar to Mola alexandrini. The scales of M. mola are multi-cusped and jagged making their skin very gritty like rough sandpaper. M. mola are covered with copious amounts of mucus and typically silvery in color with a slight opalescent sheen and can also be dappled with spots. M. mola’s clavus (the sunfish version of a “tail”) is supported by 8-9 ossicles (small, bony formations) and 10-13 rays (Nyegaard et al. 2016). M. mola can grow to be enormous: nearly 11 feet long and 2910 lbs (Heilner 1920, Kawakami et al. 2008, respectively).”

#Nyegaard et al. Hiding in broad daylight: molecular and morphological data reveal a new ocean sunfish species (Tetraodontiformes: Molidae) that has eluded recognition. Zoological Journal of the Linnean Society. 2017.
https://academic.oup.com/zoolinnean/article-abstract/182/3/631/3979130
Quote: “The body scales of the sunfishes are modified into small spines or denticles (Cleland, 1862; Tyler, 1980; Gauldie, 1992) and differ between genera in the family Molidae (Katayama & Matsuura, 2016), as well as between species in the genus Mola (Cadenat, 1959; Gauldie, 1992; Sawai et al., 2015; Sawai, 2016b).”

– Sunfish can become as big and massive as a large car but its organs are collected together in the front of their body, while most of their bulk is oddly textured, flabby, gelatinous tissue – an animal made from all the worst parts of a steak. This very mid meat is supported by a sort of weird skeleton without ribs or a tailbone and a lot of cartilage.

It’s a myth that sunfish are simply made of cartilage. They have a modified, cartilaginous skeleton, an evolutionary adaptation that aids in buoyancy control and contributes to its distinctive mode of locomotion.

Quote: “Sunfish tissue water contents are displayed in Table 1 and compared with data for the lumpfish Cyclopterus lumpus (Davenport & Kjørsvik, 1986), another oceanic fish of demersal ancestry that has a thick gelatinous subcutaneous layer that aids in the attainment of neutral buoyancy and acts as an exoskeleton. These data show that the subcutaneous tissue of the capsule has similar water content (90%) to that of female lumpfish subcutaneous tissue (93%), rather lower than the 96.5% of gelatinous tissues of deep-sea snail fish (Gerringer et al. 2017) and the 95–98% of neutrally-buoyant gelatinous invertebrates such as medusae (Doyle et al. 2007). However, the water content is higher than that of the sunfish fin muscles (79–84%). The salt content (23% of dry mass) is low by comparison with known jellyfish prey (Doyle et al. 2007); this presumably reflects the low osmolarity of body fluids of teleosts by comparison with marine invertebrates. Most (77%) of the dry mass is made up of organic matter (Table 2).”

Quote: “The degenerate, cartilaginous skeleton of M. mola (Cleland 1862) also likely contributes to buoyancy (Davenport and Kjørsvik 1986). Importantly, the gelatinous tissue is incompressible, enabling rapid depth changes without the changes in buoyancy that would be experienced by fish possessing swim-bladders (Yancey et al. 1989).“

#Carnevale G. et al. Evolution and Fossil Record of the Ocean Sunfishes. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: One of the most striking features of the molid skeleton is the considerable reduction of the bony tissue and the concomitant abundance of cartilage (Fraser-Brunner 1951). The bones are weakly ossified and characterized by a delicate fibrous or spongy texture, especially in the species of the genera Masturus and Mola (e.g., Gregory and Raven 1934, Raven 1939b).

(...)

The exoskeletal role of the hypodermis and its role in providing buoyancy both merit further exploration. Although Clelland (1862) described the ocean sunfish’s internal skeleton as largely cartilaginous, public museum specimens of large Mola mola skeletons appear lightly calcified in places.”

#Chanet B, et al. Visceral anatomy of ocean sunfish (Mola mola (L., 1758), Molidae, Tetraodontiformes) and angler (Lophius piscatorius (L., 1758), Lophiidae, Lophiiformes) investigated by non-invasive imaging techniques. C R Biol. 2012 https://pubmed.ncbi.nlm.nih.gov/23312298/

#Brown and Manzanares. Rare Occurrences of Ocean Sunfish (Mola mola) in the Bay Islands of Honduras; Notes on Distribution and Osteology. Caribbean Journal of Science. 2024.

https://www.researchgate.net/publication/385590113_Rare_Occurrences_of_Ocean_Sunfish_Mola_mola_in_the_Bay_Islands_of_Honduras_Notes_on_Distribution_and_Osteology

Quote: “The skeletal structure of the ocean sunfish, Mola mola, is as unique as its overall appearance. Unlike other bony fish, Mola mola possess a degenerate endoskeleton primarily composed of cartilage rather than bone, with reduced and fused caudal elements (Watanabe and Sato 2008; Pope et al. 2010). The vertebral column is severely reduced with no ribs (Cleland 1862). The caudal fin is absent with no axial musculature. Its clavus, dorsal, and anal fins are formed by a series of rod-like bones and fin rays, integrated with tendons and complex musculature (Davenport et al. 2018). The bones that do exist are weakly ossified, resulting in a structure that is less dense. This skeletal composition allows the sunfish to grow rapidly to its remarkable size without being hindered by the weight of a fully ossified skeleton (Pan et al. 2016). Other key adaptations include a capsule of incompressible, subcutaneous gelatinous tissue comprising up to 44% of the animal’s body mass, enabling Mola mola to navigate efficiently between depths in its pelagic environment, while maintaining structural integrity and buoyancy (Watanabe and Sato 2008).”

#Bemis KE et al. Overview of the Anatomy of Ocean Sunfishes (Molidae: Tetraodontiformes) Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

– Their weird bodies are a mobile mini ecosystem, infested and saturated with around 50 species of parasites – probably more than any other fish. Crustaceans, barnacles, various worms and protozoans live on and in their skin, muscles, gills or organs.

#Ahuir-Baraja AE. Parasites of the Ocean Sunfishes. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: “The ocean sunfishes exemplify this problem clearly, as the family Molidae includes some of the most heavily parasitized fish worldwide (Dollfus 1946, Fraser-Brunner 1951, Love and Moser 1983, Ahuir-Baraja et al. 2017, de Figueiredo et al. 2017). However, our knowledge of how these parasites affect the biology or behavior of molids is limited compared to other teleosts.

(...)

From wild individuals, a total of 73 different species of mainly metazoan parasites have been recorded in Mola mola (N = 66 species), M. alexandrini (Ranzani, 1839) (17), Masturus lanceolatus (5) and Ranzania laevis (Pennant, 1776) (3) (Table 1). To date, no references for Mola tecta Nyegaard et al. 2017 are included since no parasite faunal studies have been published for this species.”

#Cristina de Figueiredo N et al. Checklist dos parasitos do peixe Lua (Mola mola: Molidae) no mundo. PubVet. 12/3. 2018

https://www.researchgate.net/publication/323493357_Checklist_dos_parasitos_do_peixe_Lua_Mola_mola_Molidae_no_mundo

Quote: “Foram encontrados 51 trabalhos relacionados a parasitos da espécie Mola mola no mundo, no estudo foram registradas 44 espécies de parasitos e 9 espécies são sinônimos, ou seja, são parasitos conhecidos por mais de um nome”

(Translation: “The study found 51 studies on parasites of the Mola mola species in the world, 44 parasite species were recorded and 9 species are synonyms, i.e. they are

parasites known by more than one name.”)

– They are such a paradise for parasites that even their parasites have their own smaller parasites!

#Ahuir-Baraja AE. Parasites of the Ocean Sunfishes. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: “Other studies have reported on epibionts like the pelagic gooseneck barnacle, Lepas (Anatifa) anatifera (Linnaeus, 1758), (Crustacea, Lepadidae), which live harmlessly on mola skin (Barreiros and Teves 2005). Also occuring on the skin is the spider crab Acanthonyx petiverii H. Milne Edwards, 1834 (Crustacea, Epialtidae) (cited as A. scutiformis (Dana, 1851) in the checklist from de Figueiredo et al. 2017). Commensals, such as remoras, Echeneis naucrates Linnaeus, 1758 (Perciformes, Echeneidae), have also been reported within the gill chamber of both M. mola and Masturus lanceolatus (Liénard, 1840) (Schwartz and Lindquist 1987). Some epibionts use other parasites as attachment substrata, e.g., goose barnacles, Conchoderma virgatum Spengler, 1789 (Crustacea, Lepadidae), attached to parasitic copepods in M. mola (Balakrishnan 1969, Cooper et al. 1982).”

– Some Mola are also followed by an entourage of other fish that seek protection, food scraps or feed on their inhabitants.

#Mola Mola. Monterey Bay Aquarium. Retrieved April 2025.
https://www.montereybayaquarium.org/animals/animals-a-to-z/ocean-sunfish
Quote: “While cruising along, a mola often has plenty of company. Nearly 40 different kinds of parasites have been observed in or on molas, including a few gooseneck barnacles that were discovered living in a mola's throat. (Some of the parasites that live on the mola even carry their own parasites.)”

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “Another possible explanation for the basking behaviour of ocean sunfish may relate to the substantial infestations of parasites observed in some individuals (Fraser-Brunner 1951; Konow et al. 2006). A report by the National Marine Fisheries Service (National Oceanic and Atmospheric Administration) lists 54 species of parasitic organisms found on M. mola (Love and Moser 1983). More than half of these species are members of Platyhelminthes, with cestodes (7 species), monogeans (8 species) and especially digeneans (16 species) found in the intestines, liver, gills, muscle connective tissue and skin (Love and Moser 1983). Crustaceans, especially copepods (14 species) but also isopods, cirripedes and branchiurans have been found on the skin, gills, buccal cavity and operculum (Love and Moser 1983). Other parasites are nematodes, protozoans and members of Acanthodephala (Love and Moser 1983). There is growing evidence to support the long-held view that M. mola may reside at the surface to solicit cleaning by seabirds or fish (Thys 1994; Konow, et al. 2006). This is supported by the association of M. mola with kelp beds that has been linked with parasite elimination through the action of cleaner fish (Cartamil and Lowe 2004; Hixon 1979). An Indonesian study observed ocean sunfish being cleaned by five different species of fish and also witnessed breaching events that were suggested as a possible means of decreasing parasite load (Konow et al. 2006).”

#Schwartz and Lindquist. Observations on mola basking behavior, parasites, echeneidid associations, and body-organ weight relationships. The Journal of the Elisha Mitchell Scientific Society, 103(1), 1987
https://dc.lib.unc.edu/cgi-bin/showfile.exe?CISOROOT=/jncas&CISOPTR=3236
Quote: “Although the literature is replete with observations of remoras on molids or in their oral chambers, few remoras were found near the gills.”

– This awkward situation may be the root of their most bizarre behavior: Mola frequently swim to the surface to float on their side like a pancake. They are sunbathing to warm up again from deep cold dives – which is where they got their name from. But they also do it to present their body to seabirds like albatrosses. The birds start picking the parasites from the Sunfish body – while smaller fish that live near the surface take care of the bottom half – cleaning them in exchange for a snack.

#Ocean Sunfish. National Geographic. Retrieved April 2025. https://www.nationalgeographic.com/animals/fish/facts/ocean-sunfish
Quote: “Ocean sunfish can become so infested with skin parasites, they will often invite small fish or even birds to feast on the pesky critters. They will even breach the surface up to 10 feet in the air and land with a splash in an attempt to shake the parasites.”

#Abe et al. Observations on a school of ocean sunfish and evidence for a symbiotic cleaning association with albatrosses. Mar Biol. 2012.

https://link.springer.com/article/10.1007/s00227-011-1873-6
Quote: “Ocean sunfish typically inhabit the water column, but are often found on the sea surface (Pope et al. 2010). It has been hypothesized that ocean sunfish might spend their

time at the sea surface to “re-warm” their body after diving into the cold deep waters of the ocean (Cartamil and Lowe 2004; Dewar et al. 2010). Another hypothesis on this “sunbathing” behavior is that ocean sunfish may take advantage of other vertebrates inclined to engage in parasite cleaning behavior at or near the sea surface (Hixon 1979; Thys 1994; Konow et al. 2006). Hixon (1979) and Konow et al. (2006) observed “cleaner” fishes picking parasites from an ocean sunfish, and Thys (1994) stated that seabirds also engage in

the same behavior.
[...]
Parasite removal from the host, so-called “cleaning behavior,” is a well-known symbiotic relationship between fishes (Grutter 1999), birds and mammals (Ruggiero 1996; Bradshaw and White 2006). This type of symbiosis may be applied to our observed association between the albatrosses and the basking ocean sunfish. Thys (1994) stated that seabirds feed on copepod parasites from the body surface of basking ocean sunfish, although her direct evidence for this is unclear. Our observations represent the first direct, photo-documented evidence of symbiotic cleaning behavior by albatross species on ocean sunfish in pelagic waters. The association of ocean sunfish with small cleaner fishes has been reported in coastal, nearshore waters (Hixon 1979; Thys 1994; Konow et al. 2006). These Weld observations strongly suggest that, at least, one of the reasons ocean sunfish bask at the sea surface may be to engage in ecto-parasite removal through symbiotic cleaning behavior with a variety of other vertebrates."

#Daniel Kemp. The Solar-Powered Fish with Jellies in Their Bellies: Molas. US Fish and Wildlife Service. 2022.
https://www.fws.gov/story/solar-powered-fish-jellies-their-bellies-molas

Quote: ““Birds are not the best masseuse. They're not the hygienist you would opt for. And if given the opportunity, they will poke the Mola's eyes out in a second, in a heartbeat. So, the molas have this muscle where they can pull their eyes deep into their sockets and protect their eyes. And the seagulls…they're in it just to get that tasty morsel. And if they take a bit of the poor sunfish's skin with it, doesn't matter.”

– While this is a great adaptation to their parasite infection it sadly often leads to dead sunfish when they collide with boats. Since they are still cold and slow from the deep when they float on the surface, they can't react to anything coming at them.

https://australian.museum/learn/animals/fishes/ocean-sunfish-mola-mola/
Quote: “These Sunfish often meet their end by being struck by a ship. On 18 September 1908, the Steamer Fiona, was 65 km from Sydney when it suffered a ‘violent concussion’. A boat was lowered over the side and the men onboard saw a Sunfish jammed in the framework of the port propeller. The fish was the largest known at the time, measuring ’10 feet, 2 inches’ (3.1 m) in length and ’13 feet, 4 inches’ (4.1 m) in height.”

#Sousa LL et al. Movements and Foraging Behavior of Ocean Sunfish. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: “Being an ectothermic species, the body temperature of sunfish can be expected to be affected by ambient water temperature. Ectotherms regulate their body temperature by moving between different temperature environments (e.g., Dubois et al. 2009, Kiefer et al. 2007). Acoustic tracking of sunfish by Cartamil and Lowe (2004) suggested behavioral thermoregulation by showing a significant relationship between the maximum dive depth and the post-dive period spent in the surface mixed layer. Behavioral thermoregulation is commonly seen in many species of fishes, both endothermic (e.g., Pacific Bluefin tuna Thunnus orientalis, Kitagawa et al. 2001) and ectothermic (e.g., blue shark Prionace glauca; Carey and Scharold 1990), with all of these species alternating between deep excursions into cold water and ‘rewarming’ periods in the surface mixed layer. Moreover, ocean sunfish are often observed lying motionless at the sea surface, which has been interpreted as a ‘basking’ behavior (Pope et al. 2010). Although parasite removal by seabirds has been suggested to be the reason for this surfacing behavior (Abe et al. 2012), the permanence at the surface after every excursion to deep, cold water further supports the thermoregulatory hypothesis (Cartamil and Lowe 2004, Dewar et al. 2010).”

(...)

“Beyond fisheries and bycatch, additional negative human interactions with sunfish involve ship strikes. Notable collisions include a strike with the warship HMS Leander off the Japanese coast in 1886 (Cole 2011). On September 18th 1908, 65 km from Sydney Harbour, Australia, the steamship M/V Fiona ran into a 3.1 m TL, 1996 kg (4400 lb) ocean sunfish (Fig. 9), which jammed the ship’s propeller (Gudger 1928). More recently on 13th October 1998, another large sunfish, 2.5 m TL weighing 1400 kg became stuck on the bow of the cement carrier M/V Goliath in Jervis Bay, New South Wales, Australia (Nyegaard and Sawai 2018). This fish caused the ship to slow down from 14 to 11 knots and its rough skin wore the ship’s paint to bare metal. In the case of yacht racers, ocean sunfishes pose a regular hazard with numerous reports of collisions happening during competitions such as during the annual Rolex Sydney Hobart Yacht race (e.g., The Daily Telegraph 2019, Kothe 2012). Competitors are wary of encountering a “malevolent sunfish lurking in the Bass Strait” which could bring their boats to a grinding halt and ruin their chances for a win (Clarey 2014, Montgomery 2015). In any ship collision, the softer-bodied sunfish will of course bear the brunt of the damage and, if not killed outright, carry scars as evidenced by the presence of multiple propeller gashes found regularly (e.g., see Fig. 9 in Nyegaard et al. 2020 [Chapter 12]).“

– Once Mola reach a certain size most predatory fish seem to avoid them, probably wrongfully assuming their size means that they could fight back – and because their outsides are too tough. Orcas, sharks and sea lions sometimes attack and take a bite – usually only to say: “No thank you, I prefer starving to death”.

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “There are several documented accounts of predation on M. mola by sealions (T. Thys, unpublished observations), orcas (Gladstone 1988) and large sharks (Fergusson et al. 2000). For example, ocean sunfish have repeatedly been found in the stomachs of blue sharks (N. Queiroz, unpublished observation; Fig. 6) and a white shark, Carcharodon carcharias measuring over 5 m (TL) that was harpooned near the Italian port of Messina in Sicily was found to include the fresh remains of a large adult M. mola (Fergusson et al. 2000). The fish had been bitten into three sections that when combined indicated a TL of around 2 m (Fergusson et al. 2000). It should be noted, however, that the accuracy of this account by Fergusson et al. (2000) has been contested (Celona et al. 2001). Californian sea lions, Zalophus californianus, have been observed biting the fins off ocean sunfish during the autumn months in Monterey, California and beating the dismembered bodies against the sea surface, presumably to tear through M. mola’s tough skin (T. Thys, unpublished observations).”

#Fergusson IK et al. Predation by white sharks Carcharodon carcharias (Chondrichthyes: Lamnidae) upon chelonians, with new records from the Mediterranean Sea and a first record of the ocean sunfish Mola mola (Osteichthyes: Molidae) as stomach contents. Environmental Biology of Fishes 58. 2000

https://link.springer.com/article/10.1023/A:1007639324360

Quote: “The white shark may be the chief marine predator of adult chelonians in the Mediterranean Sea, albeit the impact of this predation upon turtle populations is nominal compared to other sources of mortality. Further, we give an account describing an adult ocean sunfish, Mola mola, in the stomach of a white shark taken in Italian waters.”

#Nyegaard M et al. Tiger shark predation on large ocean sunfishes (Family Molidae) – two Australian observations. Environ Biol Fish 102. 2019

https://link.springer.com/article/10.1007/s10641-019-00926-y

Quote: “Sharks are commonly listed as predators of the large ocean sunfishes (genera Mola and Masturus), yet documented shark predation events on adult sunfish are exceedingly infrequent in the literature. Here we recount two Australian observations of tiger shark (Galeocerdo cuvier) predation on sunfish of ca. 1.3 and 2 m total length, respectively. The attacks demonstrate that tiger sharks are both able and willing to predate on large sunfish; however, based on a paucity of sunfish remains in tiger shark stomach analyses, and a lack of reports of the common sunfish parasite Molicola horridus in tiger sharks, these observations likely represent opportunistic predation events. The seemingly limited interactions may reflect differing habitat use by sunfish and tiger sharks within their overlapping distribution ranges, alternatively, large sunfish may comprise low quality or undesired prey for tiger sharks. Further, despite indications of prey debilitation during both accounts, the attacks likely represent indiscriminate tiger shark feeding events with no particular prey handling strategy.”

#Ahuir-Baraja AE. Parasites of the Ocean Sunfishes. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press

https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: “Larger molids (up to 3.1 m length) (Carwardine 1995, Roach 2003) are known prey for orcas, Orcinus orca (Linnaeus, 1758), white sharks, Carcharodon carcharias (Linnaeus, 1758), sea lions, Zalophus californianus (Lesson, 1828), and tiger sharks, Galeocerdo cuvier (Péron and Lesueur, 1822) (Gladstone 1988, Fergusson et al. 2000, Ryan and Holmes 2012, Nyegaard et al. 2019).”

– Because for big predators sunfish are watery, not very nutritious, cartilage filled, parasite-ridden jelly donuts. They simply prefer to eat almost anything else. Leaving Mola swimming around with big chunks missing, looking even more ridiculous.

#Hebridean Whale and Dolphin Trust. Sunfish. Retrieved April 2025.

https://www.hwdt.org/sunfish

Quote: “Sunfish may be predated upon by sharks, sealions and killer whales. Sunfish meat is considered a delicacy in some Asian countries but it is generally not thought to be good to eat, and its sale in the European Union is banned. They are at greater risk of being caught as bycatch, and they may also become entangled in fishing gear. It is likely that sunfish commonly encounter plastic bags in the ocean and they may swallow them if mistaken for their jellyfish prey. Collisions with boats may also be common with sunfish, causing injuries and possibly death.”

https://scienceworld.scholastic.com/issues/2023-24/040824/chomped.html?language=english#:~:text=Nyegaard%E2%80%99s%20recent%20research,getting%20chomped

Quote: “Nyegaard’s recent research hints that sunfish may rely on their rumps to survive attacks from predators. She studied videos of sunfish being hunted by orcas. These large ocean predators are also known as killer whales. Nyegaard observed sunfish quickly flipping upside down as an orca came near. “It looked as if they were trying to keep their back ends toward the orca so it wouldn’t bite where their organs are,” says Nyegaard. Sticking out its rear might be an adaptation to help the sunfish survive getting chomped.”

– Sea lions have been observed to skip the whole sunfish and only eat its organs, play with its body like with a frisbee and then leave the rest for scavengers.

#Keartes, S. In photos: Sea lion burrows chest-deep in a Mola mola meal. Earth Touch News Network. 2016

https://www.earthtouchnews.com/natural-world/predator-vs-prey/in-photos-sea-lion-burrows-chest-deep-in-a-mola-mola-meal/

#Daniel Kemp. The Solar-Powered Fish with Jellies in Their Bellies: Molas. US Fish and Wildlife Service. 2022.
https://www.fws.gov/story/solar-powered-fish-jellies-their-bellies-molas

Quote: “As if molas sitting at the surface weren’t being inconvenienced enough, their large size and distinct lack of stealth make them an extremely tempting target for any large predators in their vicinity. While their extremely thick skin offers them some protection, Dr. Thys’ comparison of them to a tough-to-crack coconut is quite apt. Orca, various sharks, and sea lions are all known to regularly attack sunfish, though sea lions can often have a harder time getting through their skin. However, Dr. Thys speaks of a macabre form of play that’s been observed in sea lion herds preying upon molas:

“They play ultimate frisbee with them. They rip off the dorsal and anal fins, fashion them into these little round disks and toss them in between each other…they can get into the hide, they'll eat the sunfish, but if they get tired with it, then they'll just kind of toss it around like a Frisbee.”

While molas have little in the way of counterattacking tactics when facing predators, the sight of free-swimming molas with noticeable shark bite scars may suggest that they can be agile enough to escape sometimes.”

– Sunfish have one of the lowest brain to body ratios in the animal kingdom. A car-sized mola has a walnut-sized brain and only a tiny spine. So its mind runs an early alpha version of intelligence with updates disabled. If you look a sunfish deep into its eyes, you will mostly see your reflection.

Adult Sunfish can weigh up to 2300 kg, while their brains are roughly the size of a walnut, thus weighing only a few grams. Assuming a brain weight of 10 g and a body weight of 1000 kg, the Brain–body mass ratio of a Sunfish would be 1:100,000, which is among the lowest of all animals. For reference, the brain-body ratio in humans is roughly 1:50.

#Sawai E, Nyegaard M. A review of giants: Examining the species identities of the world's heaviest extant bony fishes (ocean sunfishes, family Molidae). J Fish Biol. 2022

https://pubmed.ncbi.nlm.nih.gov/35289924/

Quote: “Finally, we confirm that the world's heaviest extant bony fish specimen actually weighed was a female M. alexandrini (2300 kg, 272 cm total length) captured from Kamogawa, Chiba Prefecture, Japan, on August 16, 1996.”

#Herberstein ME, McLean DJ et al. AnimalTraits - a curated animal trait database for body mass, metabolic rate and brain size. Sci Data. 2022

https://pubmed.ncbi.nlm.nih.gov/35654905/

The Mola sits here at the intersection of 10-2 (brain size) and 103 (body size). Meaning it has a tiny brain for its body size, way less than expected ("expected" values sit close to the diagonal line running through all data points; the mola sits below the diagonal). In contrast, humans have a huge brain compared to their body size (the data point sits above the diagonal).

“Fig.1 [...] Overview of the ranges of trait values in the database at time of publication. Each point represents a single observation of [...] (b) body mass and brain size. To orient the reader, some taxa with outstanding trait values are labelled in the graph. The differing allometries of endotherms and ectotherms are apparent for both metabolic rate and brain size. Axes are log-scaled.”

#Heldstab SA et al. The economics of brain size evolution in vertebrates. Curr Biol. 2022

https://pubmed.ncbi.nlm.nih.gov/35728555/

Quote: “For instance, the brain of an adult human at rest is responsible for about 20–25% of the body’s total daily energy expenditure but makes up only 2% of the body’s weight36,37.”

#Chanet Bet al.. Visceral anatomy of ocean sunfish (Mola mola (L., 1758), Molidae, Tetraodontiformes) and angler (Lophius piscatorius (L., 1758), Lophiidae, Lophiiformes) investigated by non-invasive imaging techniques. C R Biol. 2012

https://pubmed.ncbi.nlm.nih.gov/23312298/

Quote: “In ocean sunfish, the brain occupies a small part of the cranial cavity (Fig. 5); it is surrounded by an abundant tissue (appearing in white in T2 weighting) (Fig. 5). [...] The present examinations show that both species lack a swimbladder, have an asymmetry in the hepatic lobes, possess a bile duct that terminates close to the stomach, have independent kidneys and a very reduced brain (Table 1).”

“Fig. 5. Sagittal image (MRI) of ocean sunfish. T2-weighted image. a: atrium; ba: bulbus arteriosus; br: brain; cc: cranial cavity; e: esophagus; g: gills; in: intestine; li: liver; pc: pericardiac cavity; sk: skull; st: stomach; th: thyroid; v: ventricle; va: ventral aorta. Scale bar indicates 7 cm.”

#Uehara M et al. The shortened spinal cord in tetraodontiform fishes. J Morphol. 2015

https://pubmed.ncbi.nlm.nih.gov/25388857/

Quote: “In teleosts, the spinal cord generally extends along the entire vertebral canal. The Tetraodontiformes, in which the spinal cord is greatly reduced in length with a distinct long filum terminale and cauda equina, have been regarded as an aberration. [...] In the Ostraciidae and Molidae, the spinal cord tapers abruptly at the cranium or first vertebra forming a cord-like filum terminale.”

#Chanet, Bruno et al.. Evidence for a close phylogenetic relationship between the teleost orders Tetraodontiformes and Lophiiformes based on an analysis of soft anatomy. Cybium: international journal of ichthyology. 2013

https://www.researchgate.net/publication/236211871_Evidence_for_a_close_phylogenetic_relationship_between_the_teleost_orders_Tetraodontiformes_and_Lophiiformes_based_on_an_analysis_of_soft_anatomy

Quote: “In the ocean sunfish, Mola mola (Molidae), a reduced spinal cord was described numerous times (Serres, 1824; Vignal, 1881; Gregory and Raven, 1934; Kuhlenbeck, 1975: 110, fig. 61; Chanet et al., 2012), it is a short tube-shaped organ which ends posteriorly in a cauda equina of fine nerves.”

– Despite or maybe because of their daftness they are pretty gentle fish that show no aggression towards other larger animals and are friendly to humans. Sometimes they even approach divers or boats to check out what they are and to stare at them derpily. Even if sunfish could get angry, they kind of lack the tools or temperament to hurt a human.

#Ocean Sunfish. National Geographic. Retrieved April 2025.
https://www.nationalgeographic.com/animals/fish/facts/ocean-sunfish

Quote: “They are harmless to people, but can be very curious and will often approach divers.”

– Adult sunfish are loners that spend most of their lives drifting and wobbling through the ocean solo, although sometimes they come together to make babies. Spotting two sunfish making love is extremely difficult because they rendezvous in the deep ocean. But we know their strategy is for 99.999% of their offspring to die.

#Griffin, B. 2011. "Mola mola" (On-line), Animal Diversity Web. Accessed April 17, 2025
https://animaldiversity.org/accounts/Mola_mola/
Quote: “Little is known about the mating systems of ocean fish, although they are thought to have paired courtship (Muus,1964; Hutchins, 2004). Some individuals are thought to spawn in the Sargasso Sea. (Hutchins, 2004; Muus, 1964)
[...]
Ocean sunfish are generally solitary, although they are found in groups when being cleaned by other fish (Hutchins, 2004; Konow et al., 2006).”

#National Marine Sanctuary Foundation. Creature Feature: Ocean Sunfish (Mola mola). 2019.
https://marinesanctuary.org/blog/creature-feature-ocean-sunfish-mola-mola
Quote: “While there is limited knowledge on the reproductive methods, mola are known to reproduce through broadcast spawning. Females release their eggs into the water simultaneously as males release their sperm near the released eggs.”

– Female Mola carry far more eggs than any other vertebrate on Earth – hundreds of millions of eggs in a single mating party! Sunfish eggs are tiny and float in the plankton, where millions where millions are eaten, starve or don't even hatch. The larvae that do hatch are adorable rice grain sized weirdos covered in little star shaped spines with the derpy facial expression of adult sunfish. All kinds of predators gobble up these tiny Mola by the millions, so to have any chance they need to become large quickly.

#Thys, TM et al. Ocean Sunfish Larvae: Detections, Identification and Predation. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press
https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays
Quote: “The natural history of molid larvae is poorly known despite the molids holding the vertebrate record for having the most ova in a given individual: 300 million in a 1.5 m TL female (Schmidt 1921a) and more recently, 847 million in a 2.2 m TL female (Forsgren et al. 2020 [Chapter 6]). Spawning is equally mysterious and has never been witnessed in the wild for any of the five currently recognized species: Mola mola (Linnaeus 1758), M. alexandrini (Ranzani 1839), Mola tecta Nyegaard et al. 2017, Masturus lanceolatus (Liénard 1840) and Ranzania laevis (Pennant 1776). Since molid larvae appear rarely in global plankton surveys, scant data exist on the size and timing of egg releases, larval development, dispersal patterns and survival rates through metamorphosis and into adulthood.”

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “M. mola is famously the most fecund of all vertebrates (Carwardine 1995) with a 137 cm female containing an estimated 300 million eggs (Schmidt 1921). By necessity, these eggs are very small (mean diameter 0.13 cm; Gudger 1936) and so M. mola growth is staggering. For the 0.25 cm larva to grow to a 3 m adult requires an increase in mass of 60 million times (Gudger 1936). An individual in captivity at the Monterey Bay Aquarium gained 373 kg in just 15 months (454 days, 0.82 kg day-1 ; Powell 2001) although more typical captive growth rates have been found to be between 0.02 and 0.49 kg day-1 in weight (M. Howard, personal communications. Monterey Bay aquarium, 800 Cannery Row, Monterey CA 93490; T. Nakatsubo, personal communications. International Marine Biological Institute, Kamogawa Sea World, Kamogawa, Chiba 296-0041, Japan) and on average 0.1 cm day-1 TL (Nakatsubo and Hirose 2007). These rates are also highly dependent on the starting TL of the captive animal (Nakatsubo and Hirose 2007).”

The following is a larva from another species called Mola alexandrini, Bumpy-head Sunfish. But they would look similar. In fact, researchers didn't have the same visual cues to differentiate between the adult species, like the shape of the clavus, in larval specimens. So they turned to genomic analysis, which ended up making the following larval Bumpy-head Sunfish first one to be ever identified genomically in the world.

#One of the World’s largest fish develops from a tiny larval Mola Sunfish. Australian Museum. Retrieved April 2025. https://australian.museum/blog/amri-news/who-am-i-the-larval-sunfish-mystery/
Quote: “The fact is that we know very little about the early life history of these fishes, as larvae are rarely seen. However, during 2017 the Australian marine research vessel the RV Investigator (operated by CSIRO) collected several of these larval Mola specimens off the New South Wales coast, and in late 2019 these little babies came to the attention of sunfish expert, Dr Marianne Nyegaard. Marianne, who is currently a Research Fellow at the Auckland War Memorial Museum, was extremely interested to know what species these larval specimens are. Unfortunately, none of the features used to describe the adults are relevant or visible in larval specimens, so how do we know which one of the three species it will grow up to be?”

– Luckily sunfish have the most rapid and extreme growth of any animal – A larvae can increase its weight 60 million times from hatching to adult. This is the equivalent of a human baby growing to the weight of an aircraft carrier.

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “M. mola is famously the most fecund of all vertebrates (Carwardine 1995) with a 137 cm female containing an estimated 300 million eggs (Schmidt 1921). By necessity, these eggs are very small (mean diameter 0.13 cm; Gudger 1936) and so M. mola growth is staggering. For the 0.25 cm larva to grow to a 3 m adult requires an increase in mass of 60 million times (Gudger 1936). An individual in captivity at the Monterey Bay Aquarium gained 373 kg in just 15 months (454 days, 0.82 kg day-1 ; Powell 2001) although more typical captive growth rates have been found to be between 0.02 and 0.49 kg day-1 in weight (M. Howard, personal communications. Monterey Bay aquarium, 800 Cannery Row, Monterey CA 93490; T. Nakatsubo, personal communications. International Marine Biological Institute, Kamogawa Sea World, Kamogawa, Chiba 296-0041, Japan) and on average 0.1 cm day-1 TL (Nakatsubo and Hirose 2007). These rates are also highly dependent on the starting TL of the captive animal (Nakatsubo and Hirose 2007).”

#Marielle Descalsota. Take a look at 10 of the world's largest aircraft carriers, from the USS Gerald R. Ford to China's Fujian. Business Insider. 2022.
https://www.businessinsider.com/largest-aircraft-carriers-world-fujian-china-gerald-ford-navy-2022-8#2-nimitz-class-us-10
Quote: “There are 10 aircraft carriers that belong to the Nimitz-class. All were built by Newport News Shipbuilding. The first aircraft carrier in the class, USS Nimitz, was commissioned in 1975 but is due to be decommissioned in 2025. The nuclear-powered warships measure 1,092 feet in length and have a displacement of 100,000 tons. It has a capacity of 6,000 crew.”

– The sunfish found a truly remarkable ecological niche: If your prey is so pathetic that other predators don’t want to bother with it, you have it all for yourself. Mola are generalized predators with a focus on small and soft stuff.

#Phillips ND et al. The Diet and Trophic Role of Ocean Sunfishes. Thys, TM, Hays, GC, Houghton, JDR. The Ocean Sunfishes. Evolution Biology and Conservation. CRC Press
https://www.taylorfrancis.com/books/edit/10.1201/9780429343360/ocean-sunfishes-tierney-thys-jonathan-houghton-graeme-hays

Quote: “More specifically, it appears that smaller sunfish (approx. < 1 m TL) adopt a mixed diet of benthic and pelagic prey (Syväranta et al. 2012, Nakamura and Sato 2014, Sousa et al. 2016, Phillips et al. 2020; Fig. 3). These smaller individuals often school seasonally in large numbers in shallow, coastal regions feeding widely within inshore food webs (e.g., Fraser-Brunner 1951, Syväranta et al. 2012, Harrod et al. 2013, Nakamura and Sato 2014, Sousa et al. 2016), with a substantial proportion of their diet comprised of benthic prey (see Fig. 2). However, as ocean sunfish (Mola spp.) grow larger, individuals appear to become more solitary,and are more commonly encountered offshore where their diet appears to shift towards primarily gelatinous zooplankton (e.g., Fraser-Brunner 1951, MacGinitie and MacGinitie 1968, Hooper et al. 1973, Nakamura and Sato 2014; Fig. 3). This apparent ontogenetic shift from a mixed, high-energy diet to predominantly low-energy density, gelatinous prey (Doyle et al. 2007, Phillips et al. 2020) initially posed an ecological conundrum for scientists as typically (although not in all cases), when body size increases, an animal’s mouth gape and prey handling capabilities also increase which enables the capture and consumption of larger and more valuable prey (Werner and Gillian 1984). Although it is well known that mass specific metabolic rates decline with body size (e.g., Peters 1983, Freedman and Noakes 2002), the largest sunfishes’ reliance on gelatinous prey appeared an unusual choice to meet the energetic demands of such a large fish. When we consider the mass-specific metabolic cost however, it appears that larger sunfishes may become more energetically efficient (Phillips et al. unpublished data) which may explain some of the sunfishes’ apparent shift towards an increasingly gelatinous diet. However, new research also suggests that many marine species, including birds, marine reptiles and many groups of fishes, incorporate gelatinous taxa in their diets and it appears that the nutritional value of gelatinous zooplankton has been significantly underestimated (e.g., Drazen and Sutton 2016, Briz et al. 2017, Phillips et al. 2017, Hays et al. 2018).”

– Their huge eyes can see incredibly well, especially in dim water, and their slow cruising speed is enough to sneak up on small prey or to sift through drifting zooplankton. Mostly fish larvae, squids, shrimps, mollusks, starfish, small crustaceans – really any soft critter they gets to.

#Kino et al. Retinal topography of ganglion cells in immature ocean sunfish, Mola mola. Environmental Biology of Fishes. 2009.
https://www.researchgate.net/publication/225945183_Retinal_topography_of_ganglion_cells_in_immature_ocean_sunfish_Mola_mola
Quote: “The SRP of immature ocean sunfish is comparable to that measured (calculated using the peak ganglion cell densities) in several adult sharks (3.7, Scyliorhinus canicula; 3.8, Galeus melastomus; and 2.8 cycles per degree, Etmopterus spinax: Bozzano and Collin 2000), and slightly higher than adult cetaceans (3.3, Pseudorca crassidens; 2.7, Lagenorhynchus obliquidens; 2.6 cycles per degree, Delphinapterus leucas: Murayama and Somiya 1998), but much lower than the adult marlin (8.5 cycles per degree, Makaira nigricans: Fritsches et al. 2003). However, it is well known that the visual acuity of fish increases with growth in size (Hariston et al. 1982; Miyazaki et al. 2000; Shand et al. 2000). The largest ocean sunfish specimen recorded to date measured in excess of 3 m (Nelson 2006). Therefore, the visual acuity we report may change as the animal grows.”

#Sousa, L. L. et al. DNA barcoding identifies a cosmopolitan diet in the ocean sunfish. Sci. Rep. (2016).
https://www.nature.com/articles/srep28762
Quote: “The ocean sunfish (Mola mola) is the world’s heaviest bony fish reaching a body mass of up to 2.3 tonnes. However, the prey M. mola consumes to fuel this prodigious growth remains poorly known. Sunfish were thought to be obligate gelatinous plankton feeders, but recent studies suggest a more generalist diet. In this study, through molecular barcoding and for the first time, the diet of sunfish in the north-east Atlantic Ocean was characterised. Overall, DNA from the diet content of 57 individuals was successfully amplified, identifying 41 different prey items. Sunfish fed mainly on crustaceans and teleosts, with cnidarians comprising only 16% of the consumed prey. Although no adult fishes were sampled, we found evidence for an ontogenetic shift in the diet, with smaller individuals feeding mainly on small crustaceans and teleost fish, whereas the diet of larger fish included more cnidarian species. Our results confirm that smaller sunfish feed predominantly on benthic and on coastal pelagic species, whereas larger fish depend on pelagic prey. Therefore, sunfish is a generalist predator with a greater diversity of links in coastal food webs than previously realised. Its removal as fisheries’ bycatch may have wider reaching ecological consequences, potentially disrupting coastal trophic interactions.”

– But maybe their favorite meals are from the jelly kind of sea life, like jellyfish, ctenophores and salps – which really is something since these are almost entirely water and have almost no calories. So to get any meaningful amount of nutrition sunfish can mow through swarms of jellyfish, sometimes devouring thousands in a single day.

#Hays et al. A Paradigm Shift in the Trophic Importance of Jellyfish? Trends in Ecology & Evolution. 2018.

https://doi.org/10.1016/j.tree.2018.09.001

Quote: “While it is well known that jellyfish can be voracious predators and so play important roles as consumers, they have historically often been viewed as trophic dead ends [6]. Underpinning this view is the generally low nutritional content of jellyfish (or at least the gelatinous ‘bell’), meaning that large volumes need to be consumed for a predator to meet metabolic demands. For example, comparative energy densities have been reported of 0.10–0.18 kJ per g wet mass1 for scyphozoan jellyfish and 2.4–5.8 kJ per g wet mass1 for various fish species, respectively [7]. Put simply, in this case a predator would need to eat about 25–30 times as much gelatinous tissue compared with fish to ingest the same energy content. A more recent review reiterates the low energy density of jellyfish on a wet weight basis [8].
Given the low energy density of jellyfish, it has classically been argued that a diet of jellyfish would necessitate a predator carrying around a large ‘belly-full-of-jelly’ which would lead to

lower streamlining and reduced maneuverability, hence leading to higher susceptibility of that jelly-feeder to predation itself [6]. It is for this reason there is a long-standing suggestion for why two of the most well-known consumers of jellyfish, the ocean sunfish (Mola mola) and the leatherback turtle (Dermochelys coriacea), are both massive. Both species weigh many hundreds of kilograms as adults, with their large size thought to confer protection against predation, even if these mega-vertebrates are slow swimming following a bout of feeding [6].

Observations of feeding and energy balance equations illustrate how these predators likely consume vast amounts of jellyfish to maintain energy balance. For example, by attaching a video camera system to the carapace of leatherback turtles it was estimated that adults,

weighing around 450 kg, foraging in summer off Nova Scotia consume an average of 330-kg

jellyfish wet mass per day, equivalent to 73% of their body mass per day [9]. Aside from these specialist feeders of jellyfish it has been known for many decades that a range of species may occasionally consume jellyfish [10–13], but their contribution to the energy budget of ocean predators has been equivocal and has tended to be ignored [14].”

– Without a swim bladder, Mola can dive very deep and surface quickly and freely, giving them a huge range, able to travel dozens of kilometers a day to graze on the seafloor or reefs, hunt for jelly in the deep or consume plankton and algae near the surface. Mola are the cows of the ocean. Huge and slow, constantly floating around slurping in high volumes of low nutrient food.

#Dewar et al. Satellite tracking the world's largest jelly predator, the ocean sunfish, Mola mola, in the Western Pacific. Journal of Experimental Marine Biology and Ecology. 2010.

https://www.sciencedirect.com/science/article/abs/pii/S0022098110002285?via%3Dihub

Quote: “Molas forage near the base of the food web like most of the largest whales, sharks, and rays. They may consume krill and other crustaceans (Aﬂalo, 1904), but their primary food source appears to be a mixed assemblage of gelatinous zooplankton, referred to here as jellies (Fraser-Brunner, 1951). One of the few large pelagic organisms that share this unique trophic niche is the leatherback sea turtle, the largest of the extant marine turtles.”

#Hebridean Whale and Dolphin Trust. Sunfish. Retrieved April 2025.

https://www.hwdt.org/sunfish

Quote: “Sunfish are present in all oceans of the world, but seem restricted to waters warmer than about 10°C. Contrary to popular belief, they spend most of their time submerged at depths of 200 to 600 metres.”

#J. Syvaranta et al. Stable isotopes challenge the perception of ocean sunfish Mola mola as obligate jellyfish predators. Journal of Fish Biology. 2011.

https://oceansunfish.org/Syvaranta2011sunfishSIAJFB.pdf

Quote: “Mola mola are typically considered obligate or primary consumers of gelatinous zooplankton (Fraser-Brunner, 1951) and whilst this view has pervaded the literature, it has

little empirical support. Indeed, field guides and reference books provide tantalizing

insights that the diet of M. mola might extend beyond gelatinous zooplankton by

listing various stomach contents including algae, crustaceans, ophiuroids, molluscs,

hydroids and fishes (Norman & Fraser, 1949; Clemens & Wilby, 1961; Hart, 1973),

although how these observations were obtained is rarely specified (Pope et al., 2010).
[...]

Using stable isotope analysis (SIA), the general hypothesis that aggregations of small M. mola may be better integrated into classical marine food webs than previously thought was examined. Analyses of carbon (δ13C) and nitrogen (δ15N) stable isotope ratios of consumers and their putative prey provide time-integrated information about energy sources, food web structure and consumer trophic positions within ecosystems (Peterson & Fry, 1987). Generally, δ15N values increase by 2–4‰ per trophic level and can be used to define trophic levels of consumers, whereas δ13C values change only little in trophic transfer (McCutchan et al., 2003). In marine systems, benthic and pelagic sources of C differ in terms of 13C enrichment, with pelagic-derived C being depleted in 13C relative to C derived from benthic or inshore primary producers (France, 1995; Mallela & Harrod, 2008).”

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9
Quote: “Ocean sunfish occupy a broad range of depths and move extensively throughout the water column (Sims et al. 2009a; Hays et al. 2009). Cartamil and Lowe (2004) observed a diel pattern in depth utilisation, with fish residing in the warmer mixed layer above or

within the thermocline at night and repeatedly diving beneath the thermocline into cooler water during the day (Californian waters, July–September 2001). Sims et al. (2009a) tracked sunfish in the North-East Atlantic in late winter to early spring and late summer to early autumn and observed all three study animals occupying significantly (P\0.003) greater depths during the day (mean diurnal depths of 250.7, 112.1 and 50.7 m versus mean nocturnal depths of 104.7, 63.18 and 29.9 m for each fish, respectively). This behaviour matches the strategy of normal diel vertical migration (DVM) and has been attributed to a strategy of near continual feeding on vertically migrating prey (Sims et al. 2009a; Hays et al. 2009) although concurrent data on the distribution of potential prey have not yet been analysed. Hays et al. (2009) again saw DVM with sunfish in South African waters, although this was not an invariant behaviour with individuals sometimes not displaying vertical movements.”

– Since they don’t really chew with their beak, sunfish have found another absurd way to eat: Long, claw-like teeth in their throat. Mola suck in their prey, pull it through their throat teeth that prevent it from escaping and maybe to move it around to rip it apart like a slow motion wood chipper.

How these teeth work is not yet entirely clear. It has been assumed that the animals move the prey back and forth over the teeth to crush it. In the meantime, however, there is a tendency to believe that they are used to hold back gelatinous prey.

#Hebridean Whale and Dolphin Trust. Sunfish. Retrieved April 2025.

https://www.hwdt.org/sunfish

Quote: “Jellyfish make up a large part of the sunfish diet, and they will also feed on small fish, squid, crustaceans, zooplankton and eelgrass. Water is sucked in and pushed out of the mouth rapidly to break up soft-bodied prey. The beak can break up harder bodied prey, whilst teeth in the throat further grind food before it is swallowed. The range of prey taken indicates that sunfish forage at various depths, from the surface to the seafloor.”

#Flaum et al. Functional morphology of the pharyngeal teeth of the ocean sunfish, Mola mola. The Anatomical Record. 2024.

https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25531

Quote: “Many fish use a set of pharyngeal jaws in their throat to aid in prey capture and processing, particularly of large or complex prey. In this study—combining dissection, CT scanning, histology, and performance testing—we demonstrate a novel use of pharyngeal teeth in the ocean sunfish (Mola mola), a species for which pharyngeal jaw anatomy had not been described. We show that sunfish possesses only dorsal pharyngeal jaws where, in contrast to their beaklike oral teeth, teeth are recurved spikes, arranged in three loosely connected rows. Fang-like pharyngeal teeth were tightly socketed in the skeletal tissue, with shorter, incompletely-formed teeth erupting between, suggesting tooth replacement. Trichrome staining revealed teeth anchored into their sockets via a combination of collagen bundles originating from the jaw connective tissue and mineralized trabeculae extending from the teeth bases. In resting position, teeth are nearly covered by soft tissue; however, manipulation of a straplike muscle, running transversely on the dorsal jaw face, everted teeth like a cat's claws. Adult sunfish suction feed almost exclusively on gelatinous prey (e.g., jellyfish) and have been observed to jet water during feeding and other activities; flume experiments simulating jetting behavior demonstrated adult teeth caught simulated gelatinous prey with 70%–100% success, with the teeth immobile in their sockets, even at 50x the jetting force, demonstrating high safety factor. We propose that sunfish pharyngeal teeth function as an efficient retention cage for mechanically challenging prey, a curious evolutionary convergence with the throat spikes of divergent taxa that employ spitting and jetting.”

Overview of Mola mola gross anatomy. (a) Photograph of a stranded adult mola. (b) Photograph of left and right pharyngeal jaw lobes, from the fish in A. (c) Grayscale orthoslice from an adult mola CT scan, highlighting the pharyngeal jaws and teeth. Note the simplified oral jaw beak and linear pharynx. (d) T1-weighted MRI scan slice from an adult mola.

#Flaum et al. Functional morphology of the pharyngeal teeth of the ocean sunfish, Mola mola. The Anatomical Record. 2024.

https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25531
Quote: “Smaller sunfish consume a mixed diet of crustaceans, fish, and very small amounts of gelatinous prey. Adults transitions to a much lower-energy density diet of gelatinous zooplankton and squid (>200 cm; Doyle et al., 2007; Phillips et al., 2020; Sousa et al., 2016). Although the curvature of mola pharyngeal jaw teeth does not change with age (Table 1), we suggest that it is only when a mola reaches adulthood with sufficiently long pharyngeal teeth that such a diet shift can occur, as we have demonstrated that only adult pharyngeal teeth can retain gelatinous prey items (Figures 5 and 6). The tooth eversion mechanism we have demonstrated facilitates the shift to a soft food diet, especially since capturing gelatinous prey in a fluid medium is mechanically challenging (Sinatra et al., 2019). In fact, the mola's lack of prehensile oral jaw is an advantage for this specialist diet, as attempting to grab gelatinous prey would only lead to losing pieces externally, making suction and retention a far better strategy.”

– And while it is fun to call them dumb actually they are a highly specialized and resilient species, widely spread throughout the oceans of the world. A marvel of evolution. A truly genius creature.

#Daniel Kemp. The Solar-Powered Fish with Jellies in Their Bellies: Molas. US Fish and Wildlife Service. 2022.
https://www.fws.gov/story/solar-powered-fish-jellies-their-bellies-molas
Quote: “Why Change a Good Thing?

Given the extremely unorthodox appearance, physiology, and diet of ocean sunfish, it can be easy to look at them as an evolutionary oddity that might not have a ton of staying power as a species. However, Dr. Thys offers some counterpoints.

“I think these fish have many, many characteristics to suit them well for longevity in this fast-changing world, most definitely. For one, they have a massive range...the more places you exist, the more likely you are to persist...they have great thermal range and can tolerate today's fast warming ocean. Some of our preliminary data shows that they can tolerate hypoxic conditions for a short period of time. They produce a ton of young; that's a good strategy in a fast-changing ocean…In some areas where we've pulled out all the food fish, the low energy life forms like jellies have moved in and taken up residence…So, we need to keep all our jelly eaters intact. The molas are an important component of that whole gelatinous zooplankton ecosystem. And they're just so darn endearing that I think people are enchanted by them.””

#Breen P, Cañadas A, Cadhla OÓ, Mackey M, Scheidat M, Geelhoed SCV, Rogan E, Jessopp M. New insights into ocean sunfish (Mola mola) abundance and seasonal distribution in the northeast Atlantic. Sci Rep. 2017
https://pubmed.ncbi.nlm.nih.gov/28515419/
Quote: “The ocean sunfish, Mola mola, is the largest teleost fish in the world. Despite being found in all oceans of the world, little is known about its abundance and factors driving its distribution. In this study we provide the first abundance estimates for sunfish in offshore waters in the northeast Atlantic and the first record of extensive sunfish presence in these waters year-round. Abundance estimates and predictive distributions for sunfish in approximately 300,000 km² of the northeast Atlantic were derived from large scale offshore aerial surveys in 2015-2016 using distance sampling techniques. Generalized additive models of sunfish density were fitted to survey data from 17,360 km of line transect effort resulting in minimum abundance estimates of 12,702 (CI: 9,864-16,357) in the summer (Density = 0.043 ind/km²) and 8,223 individuals (CI: 6,178-10,946) (Density = 0.028 ind/km²) in the winter. Density surface models predicted seasonal shifts in distribution and highlighted the importance of the mixed layer depth, possibly related to thermoregulation following deep foraging dives. The abundance estimate and estimated daily consumption of 2,600 tonnes of jellyfish in the northeast Atlantic highlights the need to re-assess the importance of this species in the pelagic ecosystem, and its role in top-down control of jellyfish blooms.”

#Pope, E. C. et al. The biology and ecology of the ocean sunfish Mola mola: a review of current knowledge and future research perspectives. Reviews in Fish Biology and Fisheries. 2010.
https://link.springer.com/article/10.1007/s11160-009-9155-9

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