The Fish Olympics: Pitting Giants Against Each Other

Two contestants fight it out for the very official title of the WORLD’S BEST BIG FISH.

Meet the Contestants!



The categories they are competing in today: Names, size, free time, parasites, eggs, number of species, life competency, and edibility.

Aaand we are off! Let’s start with the names of our lovely contestants:
- Oarfish: also known as Regalecus: “King of the herrings.”
- Ocean sunfish: the Mola mola, or “Millstone millstone.”



So… half of a Mola mola?
Pic: Flickr, Earthwatcher

Winner: Oarfish. “Millstone millstone,” really?

What about their sizes?
- Oarfish: The longest bony fish in the world, at 8 meters long.*
- Ocean sunfish: The heaviest bony fish in the world, with one found to be 5,071 pounds (or the weight of two small cars).
Winner: Neither. How do you choose between two world records?
*The oft-quoted length of 17 meters was actually a rotting basking shark… (Roberts 2012). The longest oarfishes actually in museums are about 8 meters long.

What do they like to do in their free time?
- Oarfish: Spends it masquerading as the basis of hundred of years of sea serpent legends.

Terrifying people for fun. Wikimedia Commons

Terrifying people for fun.
Wikimedia Commons

Ocean sunfish: Spends it masquerading as floating rocks.

Activate rock mode! Pic: Flickr, k schneider

Uhh. Not quite as impressive as “king of the herrings.”
Pic: Flickr, k schneider

Winner: Oarfish.

Personal hygiene?
- Oarfish: Contain parasites but despite all the media hype, not that big of a deal.
- Ocean sunfish: Molas are one of the most heavily parasitized fish in the world, with so many hitchhikers that it actually seeks out birds and small fish to help remove get them off. Gross (and pretty brilliant!).
Winner: Molas. (Does it count as winning if you have more parasites?)

Baby-making capabilities?
- Oarfish: Hundreds of thousands” of eggs.
- Ocean sunfish: Famously the most fecund of all fishes, with one female found to be carrying up to 300 million eggs! To put that in some perspective, America’s population is 316 million. Wow.
Winners: Molas, for sure.

Ever experienced any identity crises?
- Oarfish: Originally thought to be only 1 species; now DNA points to 2-4 that are separated geographically.
- Ocean sunfish: Used to be thought of as just Mola mola but DNA evidence  now indicates there are 2 with overlapping geographic distributions.

Among other differences, the two species of Mola have different clavuses, with one being wavy and the other flat. Figure from Yoshita et al. 2008.

Among other differences, the two species of Mola have different clavuses (tails), with one being wavy and the other flat. However, the morphological differences are not always apparent, so DNA testing is the only way of being sure of the exact species.
Figure from Yoshita et al. 2008.

Winner: Oarfish. (Molas, why you gotta live all together and be confusing for scientists? The two separate species were only recognized in 2009 and are still not named, unless ‘species A’ and ‘species B’ counts… nah.)

Special talents:
- Oarfish: Losing a part of their body. Yes, you read that right. They flipping self-amputate; losing anywhere from just a little bit of their tail to 2/3 or 3/4 of their bodies. Pretty cool? Yes. Generally competent? Not so much.*

From Roberts et al. 2012.

He just looks so CHOPPED OFF.
From Roberts 2012.

- Ocean sunfish: They don’t cut anything off their own bodies.
Winner: Ocean sunfish.
*Of course there has to be a reason why the oarfish would lop off part of themselves (aka automize); scientists theorize** that it has to do with permitting “large fish to readjust the body proportions so that elongate larvae and juvenile stages, sometimes with excessively long caudal fin rays, are transformed into relatively short-bodied adults consisting mainly of head, abdomen, vital organs, and gonads” (Roberts 2012).
**What they don’t say but I think is obvious: losing different parts of your hind-end repeatedly is a pretty nifty party trick.

- Oarfish: Alright taste (although some have said ‘even dogs would not eat the flesh’), flaccid texture, apparently “might taste better if steamed or made into soup by a Chinese cook*” (Roberts 2012).
- Ocean sunfish: Conflicting opinions: have been described as gelatinous and disgusting, but there is a market for them in Taiwan and Japan.
Winner: Unfortunately for her, the ocean sunfish.
*Why a Chinese cook? No, seriously, I’m confused.



For an astonishingly entertaining and extremely comprehensive paper on oarfish, check out:
Roberts TR. 2012. Systematics, biology, and distribution of the species of the ocanic oarfish genus Regalecus. Mémoires du Muséum national d’Histoire naturelle 202.

For a discussion of the two different species of Mola mola, refer to:
Yoshita et al. 2008. Phylogenetic relationship of two Mola sunfishes (Tetraodontiformes: Molidae) occurring around the coast of Japan, with notes on their geographical distribution and morphological characteristics. Ichthyol Res 56(3): 232-244.