I recently revisited the bucket list I started in high school. It mainly includes travel destinations like Japan and Santorini. But it also includes things like learning to play the ukulele and diving with the strange looking but magnificent ocean sunfish.

Measuring at about six feet tall by six feet long and weighing in at about 2,200 pounds, the ocean sunfish (Mola mola), is one of the largest and heaviest bony fish in the world. Honestly, they are a horrifying looking fish; a huge, flat, silver disc, with a tiny face and a mouth with puckered lips that never close. Let’s dive into some ocean sunfish natural history and what makes them unique.

Habitat

Ocean sunfish can be found across the world’s tropical and temperate waters, where they spend a lot of their time either at the surface or hunting. Misconceptions about their capability to survive stemmed from being terribly slow swimmers and were originally thought to be giant drifters because they are often observed lying motionless at the sea surface. However, they are one of the most advanced bony fish, and have survived for over 50 million years and diversified into at least five species across multiple oceans. Ocean sunfish are actually optimized for a very strange yet very effective way of living. Ocean sunfish are capable swimmers but they drift because their prey (mainly jellyfish) drift.

Researchers have found through satellite tagging that ocean sunfish were not just drifting, they were diving. Ocean sunfish can dive hundreds of meters multiple times a day. They are unbelievably athletic! They dive to reach their prey in the diurnal vertical migration. While their prey do rise to the surface at night, they sink during the day, which is when the ocean sunfish do deep dives. After each dive they resurface to warm up by basking in the sun, this is called behavioral thermoregulation. One study found that an ocean sunfish’s core temperature would drop from 20 degrees Celsius to 12, a dangerously cold level for a cold blooded animal, especially one living in tropical and temperate waters.

So why bother going through the trouble of using so much energy to dive into the deep cold waters just to eat low nutrient jellies? Well, probably because they are extremely abundant in the open ocean, especially at depth, and are not sought after by many other predators. Evolving to survive off this niche food group is actually pretty brilliant.

The evidence is clear to me: ocean sunfish are more than just a lazy drifter. 

Conservation & Policy

The ocean sunfish was named so because of the species’ habit of sunbathing. It is listed as vulnerable by the IUCN because as you can probably imagine, this fish is vulnerable to boat collisions and bycatch from drift gillnets. Because these nets are notorious for damaging marine life, I am happy to report that in 2023 the bipartisan Driftnet Modernization and Bycatch Reduction Act mandates phasing out large-mesh drift gillnets in all federal U.S. waters. A small victory in reducing bycatch and saving vulnerable species worthy of celebrating. Notably, the law supports fishermen switching to alternate gear by offering grants. This gear could lead to higher prices for their catch, and ensure consumers that their seafood choices are safer.

Fun fact: The Germans affectionately named ocean sunfish Schwimmender Kopf, or “swimming head.” This is very apt for their strange appearance because they have no true tail! Instead it has a thick, scalloped bridge of skin called a clavus that connects the dorsal and anal fins acting as a powerful rudder.

Relationship with humans and art

Ocean sunfish aren’t just some weird fish to everyone. Apparently, I am not alone in wanting to experience basking in the sun with this fish. They are evidently pretty popular with Scuba diving tourists and have even become familiar with divers.

Ocean sunfish are found in art in many cultures. There are Sarongs worn by women in Lamalera, a village in the island of Lembata in the Lesser Sunda Islands of Indonesia, that have patterns of ocean sunfish, which they know as kebuku.

Ocean sunfish are still widely misunderstood. I think their oddities and magnificence draws many people’s attention. Scientists are only beginning to piece together their migration habits, reproductive cycles, and ecological roles because their oddities are working and we have yet to learn why.

Learn more about how these deep diving fish defy expectations in this video.

Artful Action

Today marks the official start of spring! As the snow starts to melt (finally!) and the grass begins to grow, March reminds us of the importance of protecting our environment. This spring, take action to improve our environment and spread environmental awareness to others, encouraging them to do the same. Conservation is a team effort.

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References & continued reading

Barnes, Ruth (1988). “Ikat Patterns Found in Lamalera”. Ikat Textiles of Lamalera: A Study of an Eastern Indonesian Weaving Tradition. Studies in South Asian Culture. Vol. 14. Leiden, Netherlands: Brill Publishers. pp. 60–63. ISBN 90-04-08753-2.

Breen, P., Cañadas, A., Cadhla, O.Ó. et al. New insights into ocean sunfish (Mola mola) abundance and seasonal distribution in the northeast Atlantic. Sci Rep 7, 2025 (2017). https://doi.org/10.1038/s41598-017-02103-6

Coastal Conservation Association

Face to Face With the Ugly, Marvelous Mola Mola

Mola mola – The Ocean’s Gentle Giant

Nakamura, I., Goto, Y. and Sato, K. (2015), Ocean sunfish rewarm at the surface after deep excursions to forage for siphonophores. J Anim Ecol, 84: 590-603. https://doi.org/10.1111/1365-2656.12346