Shape-Shifting Whalefish That Dissolves Into Sperm Delivery Service Caught On Camera


Rachael Funnell

Social Editor and Staff Writer

clockAug 17 2021, 13:05 UTC
Shape-Shifting Whalefish That Dissolves Into Sperm Delivery Service Caught On Camera

The 4K footage is thought to be the best and most detailed ever captured of whalefish. Image credit: © 2021 MBARI

When diving into the deep with the assistance of remotely operated vehicles (ROVs), marine scientists have a rare opportunity to spot species that we humans would otherwise go our whole lives never seeing. One such rare deep ocean beastie is the whalefish, a bright scarlet fish of the order Cetomimiformes who was recently caught on camera for your viewing pleasure.

Spotted by the Monterey Bay Aquarium Research Institute’s (MBARI) ROV Doc Ricketts alongside Steve Haddock and his team on their recent R/V Western Flyer expedition, the whalefish was seen cruising along at a depth of 2,013 meters (6,604 feet) in offshore Monterey Bay.


“We've only encountered these obscure fish 18 times in 34 years of deep-sea exploration with our remotely operated vehicles (ROVs),” wrote the MBARI in a Facebook post.

While they are a rare sight and little known to the research community, what we do know about whalefishes demonstrates that they are really quite strange, even by the standards of the already bizarre benthic.

“The “shapeshifter” name refers to the three different body forms that were observed in net-caught fish,” said Dr Steve Haddock of the MBARI to IFLScience. “These are not changing shape immediately, but they change as they grow from babies to adults, and males look very different from females. There are lots of examples in the ocean — even among jellyfish — where two different stages of development are thought to be two different species, until someone can connect the dots.”


It’s easy to see why connecting the three dots of whalefish proved challenging when you find out quite how dramatically this fishes’ form changes throughout its life. According to MBARI, whalefish begin life in their larval form with functional eyes, but as they progress to adults the lens is lost, and they lose the ability to see.

Fortunately, they’ve got a backup sensory organ in the form of a lateral line festooned with sensory pores. These enable them to “see” by detecting vibrations in their surroundings, arguably a more effective way of navigating your environment when that environment sits at a depth where light is in short supply anyway.

whalefish video

Unidentified whalefish (order Cetomimiformes) observed during a recent MBARI expedition off the coast of central California. © 2021 MBARI

What happens to the whalefish body plan as it matures depends on their sex. The grisly fate for males sees their jaws dissolve into nothing, a good thing too since they also lose their esophagus, gut and intestines. They prepare for the change by gorging on copepods so that as their body fills with sexual organs it also gets a surge in liver tissue which acts as an energy source for the whalefishes’ sperm delivery service while it’s unable to eat. They’ll share their sperm with whoever will take it until their energy runs out and they die.


Females also undergo their own makeover, instead ballooning to a shape that mimics that of a baleen whale (hence the name). They also become what would be a dazzling shade of orange-red if it weren’t that light of this wavelength doesn’t penetrate the water column to their depth, so this conspicuous coloration actually leaves them near-invisible in their environment.

So, what did we learn from this encounter?

“I don’t think we learned anything new scientifically, but I do think we were able to get the highest-resolution video thus far of a live specimen,” continued Haddock.


“Too often you see the damaged unnatural remains of a net-captured deep-sea animal. Even in Finding Nemo, the anglerfish was shown with gray, opaque eyes, indicating that it was modeled on a dead specimen. I think showing the organisms in their true healthy state is important for helping people appreciate deep-sea animals a bit more.”

[H/T: Live Science]

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