The Inky Depths #1: The Whalefish
December 31, 2021 7:43 AM   Subscribe

More than a century ago, in 1895, two Smithsonian scientists described a new kind of deep sea creature living at least 1000 m (3,280 ft) below the ocean’s surface. (This section of ocean is called the Bathyal zone, or "midnight zone.") The scientists named their find the whalefish because of its whale-like appearance. Little did they know that this fish would become one of the prime suspects in a mystery that took scientists from around the world decades to solve.

There are other examples of males and females with very different shapes (sexual dimorphism) and of animals changing from one shape to another as they grow older (metamorphosis). But this is one of the most amazing examples of sexual dimorphism combined with metamorphosis ever found among vertebrates. It may be hard to believe because they look so different, but tapetails, bignose fish, and whalefish are actually all members of the same family (Cetomimidae).

A rare whalefish sighting - video and photo gallery

"Its eyes are poorly developed and small—in fact, they lack lenses and are not even capable of forming images. Instead, a whalefish relies on a network of sensory pores that run over the head and down the length of the body. Those pores feel vibrations in the water and allow a whalefish to detect when predators or prey are near. Many fishes have these sensory pores, usually arranged into the lateral line running along their sides. In the whalefish, the pores are quite large and lie along ridges that give the fish a crocodile-like appearance."

This is fish is also bright red (for dark water camoflauge), the juvenile males in some species appear to have their jaws fused shut, and none of them really "see" and instead rely on a series of sensory pores that run the length of their bodies that detect vibrations in the water.
posted by tiny frying pan (29 comments total) 53 users marked this as a favorite
 
This post is intended to be the first in a series of posts I want to make about spooky creatures in the sea. Enjoy!
posted by tiny frying pan at 7:43 AM on December 31, 2021 [55 favorites]


Thanks, tiny frying pan! Can’t wait for more of these!
posted by heyitsgogi at 7:52 AM on December 31, 2021 [1 favorite]


I see I repeated some info in a sense near the end there. Oh well. Working on it!
posted by tiny frying pan at 7:53 AM on December 31, 2021


Spooky sea creatures are awesome! I nominate Hank Green's anglerfish song to be on the official soundtrack of this post series.
posted by Wretch729 at 8:23 AM on December 31, 2021 [1 favorite]


How crazy is that? Very crazy!
Also, how horrific that the males die of starvation because they can’t consume any new food once they mature. There is so much horror in the animal kingdom - maybe we should be less surprised that humans inflict such horrors on themselves and other creatures.
Also! Why are these fish brightly-colored if nobody down there can see that?
posted by Glinn at 8:52 AM on December 31, 2021 [1 favorite]


The oceans are weird. I love the weirdness of them. Looking forward to more.
posted by jacquilynne at 8:59 AM on December 31, 2021 [1 favorite]


omg, the photo of the Smithsonian that looks like the final scene in Indiana Jones except it's all preserved fish specimens...
posted by gwint at 9:07 AM on December 31, 2021 [5 favorites]


Their bright red color is not distinguishable to other animals in the darkness, which I love.
posted by tiny frying pan at 9:26 AM on December 31, 2021 [3 favorites]


So cool, thank you!
posted by It's Raining Florence Henderson at 9:32 AM on December 31, 2021




This is so cool. Finding out about earth creatures with such strange lifeways always makes me want to imagine how the culture of intelligent aliens with similar adaptations would work.

Looking forward to more!

Also, how horrific that the males die of starvation because they can’t consume any new food once they mature.

Some species of moths (luna, cecropia, and others), the adults have only vestigial mouthparts and no digestive systems. No time to waste eating, they just mate, lay eggs, and starve to death.
posted by BrashTech at 9:32 AM on December 31, 2021 [4 favorites]


Also! Why are these fish brightly-colored if nobody down there can see that?

This one I can answer! So many deep sea animals are bright red because, remember, things have color when they reflect light of specific wavelengths.

I reblogged a cool Tumblr post about it the other day that has pictures and shit, but basically what it is is that red light penetrates the worst into deep water. A red animal absorbs all the wavelengths that aren't red, so since there is very little red light in the deep sea anyway, a red animal is pretty similar to a black one. So a lot of deep sea animals evolve to be bright red as camouflage. (I suspect it's metabolically cheaper than being melanistic, very dark, for pigment reasons, because deep sea animals often specialize on a veeeeeeeeery precarious metabolic curve. Remember, almost everything that lives in the deep sea is carnivorous, because very little light penetrates and plants need that shit to be able to exist, and the density of potential prey items is very very low. I don't study deep sea organisms though, so take all that with a grain of salt; I just have a lot of experience with sensory biology and animal communication).

This scarcity of things to eat, by the way, is also probably why you see so many weird deep sea things that are all eyes (or other sensory organs) and teeth and stomach and very little else. You never know how long it's going to be before you find another prey item! The kind of extreme sexual and ontogenetic (developmental) dimorphism you see in this species and many others is almost certainly also a byproduct of that resource scarcity.

Usually when we talk about sexual dimorphism, we talk in terms of animals with big differences between males and females because of differences in strategies to find mates or win at intrasexual competition. But there's another potential reason for sexual dimorphism to happen: niche competition. If your males and your females occupy very different niches, you can sustain a much larger effective population size because your species has diversified its strategy so that adult males and females are now not in competition with one another. You see a very similar thing with ontogenetic dimorphism, where juveniles of one species eat very different things than adults of the species, and again one of the advantages of doing that is that juveniles then don't have to compete with adults for resources.

In terms of terrestrial animals, you see a lot of this in amphibians, fish, monitor lizards (where juveniles may climb a lot and spend a lot of time in trees hunting prey that big, potentially cannibalistic adults can't access) and snakes, as well as many kinds of insects. Parental care usually completely obliterates any shot at making ontogenetic niche differentiation work, because by definition it means parents are assisting juveniles to obtain resources, but you do also see a certain amount of sexual niche partitioning among animals with extreme sexual dimorphism as well. I'm pretty sure that for example there's some documentation of it in elephant seals.
posted by sciatrix at 9:36 AM on December 31, 2021 [45 favorites]


Spooky creatures in the sea, yay! Looking forward to more.
I'm going to pretend I have no mouth parts for a few days (after New Years of course).
posted by winesong at 9:37 AM on December 31, 2021 [3 favorites]


oooo a sciencey serial - bring it on
"We know more about the surface of the Moon and about Mars than we do about this habitat [the deep sea floor], despite the fact that we have yet to extract a gram of food, a breath of oxygen or a drop of water from those bodies." [TEDtalk ] Paul Snelgrove.
sciatrix will know better than me, but I have a "memory" that M&F red kangaroos Macropus rufus were long believed to be separate species because their size, and colour, [and habitat?] dimorphism were so extreme among mammals.
posted by BobTheScientist at 9:55 AM on December 31, 2021 [1 favorite]


Also, how horrific that the males die of starvation because they can’t consume any new food once they mature.

I thought naming them “flabby whalefish” was adding insult to injury. Why not “noble whalefish” or “sleek whalefish?”
posted by GenjiandProust at 9:55 AM on December 31, 2021 [1 favorite]


Parental care usually completely obliterates any shot at making ontogenetic niche differentiation work,

I dunno, I feel that human teenagers survive on diets that would kill their parents in about 2 weeks….
posted by GenjiandProust at 9:59 AM on December 31, 2021


Also, how horrific that the males die of starvation because they can’t consume any new food once they mature.

The flip side of this is that anglerfish where the males are like a tenth the size of the females, and spend their whole adult lives as parasites hanging off the female's body. They find a female anglerfish, latch on to her side with their mouth, and then gradually his mouth and her skin just sort of fuse so that he gets all his nutrition from her circulatory system. And then the rest of his body gradually atrophies until it's just his testicles and that's it, he is just a parasitic scrotum the female's carry around with them for when they need it.
posted by EmpressCallipygos at 10:27 AM on December 31, 2021 [7 favorites]


"whale-like appearance" - But tiny!
posted by davidmsc at 10:39 AM on December 31, 2021 [1 favorite]


I love this. Can't wait for more.
posted by Elmore at 10:49 AM on December 31, 2021


I like their tiny fins, they seem so… fussy.
posted by GenjiandProust at 11:09 AM on December 31, 2021 [1 favorite]


The tapetail looks so graceful with their fluttery fins. Makes me think of rhythmic gymnasts with their ribbons. "I used to be so cute! And then I grew up." Heh.

Since there seem to be a lot of science-y folks in his thread, I have a dumb question: how can they tell that something is still in its larval stage and hasn't reached maturity yet? What do they look at, what do they check for?
posted by tinydancer at 12:17 PM on December 31, 2021 [1 favorite]


This post needs a soundtrack, and I have just the thing.
posted by box at 12:20 PM on December 31, 2021 [1 favorite]


This post is intended to be the first in a series of posts I want to make about spooky creatures in the sea. Enjoy!

Yes! Very much looking forward to the rest of them. There are some weird things down there.

I went to a very entertaining talk by a deep sea marine biologist and explorer just before the pandemic, and he called out hello to his friend in the audience who was sat just behind us, who has been to some of the deepest parts of the ocean. Said hello to him as we left, and was such an odd thought that not that many more people have been where this unassuming bloke in a fleece jacket in the audience had, than had walked on the moon.
posted by reynir at 12:56 PM on December 31, 2021 [4 favorites]


sciatrix will know better than me, but I have a "memory" that M&F red kangaroos Macropus rufus were long believed to be separate species because their size, and colour, [and habitat?] dimorphism were so extreme among mammals.

Off the top of my head I don't know, but there's a vague bell of recognition going off in my head at that idea too. (I've never worked directly on niche partitioning in either time or sex myself, but I've spent a little bit of time toying with a side modeling project on the topic.)

how can they tell that something is still in its larval stage and hasn't reached maturity yet? What do they look at, what do they check for?

If it was me, and bearing in mind this bit is quite a bit farther from anything I've ever personally done? I would be doing dissections and looking for something that looked like reproductively mature gonads. When I found something gonad-like in the process of documenting the anatomy of my collections, I would do some microscopy to see if there was anything like sperm or mature eggs present. If I found a tissue that looked like a gonad, I would also be noting whether it looked like a testis or an ovary, and whether it appeared to be producing sperm or egg cells or not. Typically, reproductively mature gonads are much larger than immature ones.

As much as possible, I would be referring to related species with a better known life history as I went, too. So if I wanted to know how to tell if a whalefish was male or female and whether it was reproductively mature, I might make a study of everything I could find out about the gonadal fish as closely related and as well understood as possible relative to my whalefish, so that I was more likely to be able to identify the right tissues quickly and with a minimum of damage to my museum specimen. From a cursory glance, ridgeheads might be a good place to start as a point for comparison. I might also look at one of the commercially fished Bericyformes on the theory that species of commercial importance tend to have a lot more research put into their ecology and development, and therefore more knowledge currently existing, than species without that aspect.
posted by sciatrix at 1:02 PM on December 31, 2021 [5 favorites]


none of them really "see" and instead rely on a series of sensory pores that run the length of their bodies that detect vibrations in the water.

aaaah I missed this in the original FPP and I love it so much! This series of pores will be what's called the "lateral line" in fish, and it's this bizarre but really cool organ that fish use to monitor vibrations in the water around them. It's sort of between hearing (which we use to monitor vibrations in the air or water that are oscillating at a relatively high frequency) and touch (which we use to monitor direct pressure on our bodies that oscillates relatively VERY slowly, if it oscillates at all, but also has more force than we associate with hearing).

So these fish are going through the world primarily relying on feeling/hearing/being in tune with the world around them on a short scale in the way that we use vision on a short scale. Neat!
posted by sciatrix at 1:22 PM on December 31, 2021 [5 favorites]


one of the advantages of doing that is that juveniles then don't have to compete with adults for resources.

I was recently wondering if this is the reason that octopi moms stop eating and die after giving birth; removing themselves from the ecosystem reduces competitive pressure on the young. Especially as they're solitary animals, so that there's no intergenerational advantage to having the elders hang around...
posted by kaibutsu at 2:13 PM on December 31, 2021


And then the rest of his body gradually atrophies until it's just his testicles and that's it, he is just a parasitic scrotum the female's carry around with them for when they need it.

As I get older it seems like quite the opposite happens.
posted by Insert Clever Name Here at 2:36 PM on December 31, 2021


It may be hard to believe because they look so different, but tapetails, bignose fish, and whalefish are actually all members of the same family (Cetomimidae)

In case anyone else was confused (because it sounds like normal evolution) there are multiple Genera/Species exhibiting this pattern of development, all of which are called whalefish, etc.
posted by ChurchHatesTucker at 7:10 PM on December 31, 2021 [1 favorite]


So are those three from the first link the same species as each other or examples from different species?
posted by starfishprime at 2:24 AM on January 1, 2022


So are those three from the first link the same species as each other or examples from different species?

They're the same Species. The confusing thing is that there's several Species and Genera doing the same thing, so you have to go up to Family to talk about them as a group.
posted by ChurchHatesTucker at 5:01 PM on January 2, 2022


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