The Mystery Of The Oceanic Sunfish (Mola Mola)

One of my most impactful experiences happened aboard the American Star on May 26, 2022. It was my third day as an intern at the Cape May Whale Watch and Research Center and I
could not wait to get out into the open waters. As we were leaving the inlet to enter the Atlantic
Ocean, that’s when it was spotted. The Mola mola.

The Mola mola, otherwise known commonly as the oceanic sunfish, is a mysterious fish that is most
commonly known for its basking behavior in the sun. This species is also known as the heaviest
fish in the entire world and can grow to be 5,000 pounds and 14 feet long. Along with holding
the title for the heaviest fish in the world, the oceanic sunfish is one of the most prolific species
meaning one female can produce 300 million tiny eggs (Smith 2017).

Their bodies are round with elongated dorsal and anal fins accompanied with large eyes.
In fact, the word “mola” is Latin for millstone due to round shape of their bodies (Bowen 2018).
Their appearance has given rise to names such as the German name “schwimmender kopf”
translating to “swimming head” (Bowen 2018). When at the surface of the water the Mola mola
is laying horizontally, so the giant eye is looking right back at you like a face. On the other hand, the large fish orients itself vertically when moving throughout the water column. However, the
physical characteristics are not the only unique features of the sunfish.

Along with their unusual appearance, sunfish have unique diving habits. The behavior
and biology of this particular pelagic zooplanktivor (Fraser-Bruner 1951) are relatively
unknown. This pelagic species can be found in both temperate and tropical oceans (Potter 2011).
Sunfish have been spotted circumglobally in all five oceans (Bowen 2018). The oceanic sunfish
are most commonly seen sunbathing at the surface of the water, yet the reason for this surfacing
is still unknown. There are hypotheses that these creatures may be sunbathing to warm their
bodies after deep dives, making their trips to the surface rather rare. Other hypotheses include
sleeping and eliminating the body of parasites that may inhabit their skin (Nakamura 2015). New
studies have tracked the sunfish as active swimmers that dive to depths up to 800 meters, but like
surfacing, the reason is still unknown (Watanabe & Sato 2008, Houghton 2009). The ongoing
study on the Mola mola allows the creature to remain a mystery of the ocean.

-Ceara Reilly, Intern at Cape May Whale Watch and Research Center

Stockton University ’24

References:

Bowen, Devon. “Mola 101: Everything You Need to Know about Ocean Sunfish.” Two Oceans
Aquarium, 9 Jan. 2018, https://www.aquarium.co.za/blog/entry/everything-you-need-to-know-
about-ocean-sunfish.

Fraser-Bruner, A., 1951. The ocean sunfishes (Family Molidae). Bulletin of the British Museum of
Natural History 1, 89–121.

Houghton, J.D.R., Liebsch, N., Doyle, T.K., Gleiss, A.C., Lilley, M.K.S., Wilson, R.P. et al. (2009)
Harnessing the sun: testing a novel attachment method to record fine scale movements in ocean
sunfish (Mola mola). Tagging and Tracking of Marine Animals with Electronic Devices,
Reviews: Methods and Technologies in Fish Biology and Fisheries, 9, 229–242.

Nakamura, Itsumi, Yusuke Goto, and Katsufumi Sato. “Ocean sunfish rewarm at the surface after
deep excursions to forage for siphonophores.” Journal of Animal Ecology 84.3 (2015): 590-603.

Potter, Inga F., and W. Huntting Howell. “Vertical movement and behavior of the ocean sunfish,
Mola mola, in the northwest Atlantic.” Journal of Experimental Marine Biology and Ecology
396.2 (2011): 138-146.

Smith, Richard. “13 Facts You Didn’t Know about Sunfish.” Sport Diver, 11 Mar. 2017,
https://www.sportdiver.com/13-facts-you-didnt-know-about-sunfish-mola-mola.

Watanabe, Y. & Sato, K. (2008) Functional dorsoventral symmetry in relation to lift-based
swimming in the ocean sunfish Mola mola. PLoS ONE, 3, e3446.