# Are sharks actually fish? **URL:** \ **Category:** Factual Questions\ **Created:** [July 25, 2005, 3:40am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999 "2005-07-25T03:40:36Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [July 25, 2005, 3:40am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/1 "2005-07-25T03:40:36Z")
Mrs. RickJay and I recently got the special 30th anniversary edition of “Jaws” and watched it over two bowls of popcorn. After enjoying the movie I fired up some pictures of Great Whites (the shark, not the band) on the Internet. It suddenly crossed my mind that sharks, as well as their relatives the rays and skates, are in some ways not at all like fish. Specifically, of course, they don’t have bones made of bone. I also found that sharks, rays, and skates are in an altogether different class (Chondrichthye) than other fish. So is a shark actually a fish? Or is it a different kind of animal? ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 25, 2005, 3:53am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/2 "2005-07-25T03:53:50Z")
Well, “fish” is not really a technical scientific term. According to Merriam Webster, a fish is: > [@](#): > > any of numerous cold-blooded strictly aquatic craniate vertebrates that include the bony fishes and usually the cartilaginous and jawless fishes and that have typically an elongated somewhat spindle-shaped body terminating in a broad caudal fin, limbs in the form of fins when present at all, and a 2-chambered heart by which blood is sent through thoracic gills to be oxygenated “Fish” thus normally includes three different living classes of vertebrates: the Osteoichthyes, or bony fish; the Chondrichthyes, or cartilaginous fish (sharks and rays, as well as some odder groups such as chimeras), and the Agnata, or jawless fish (lampreys, hagfish, plus many early fossil forms). There is yet another class, the Placoderma, which includes armored fish that are all now extinct. So yes, sharks are indeed fish, but a quite different kind of fish than a trout. The two are about as closely related as an elephant is to a turtle. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 25, 2005, 3:54am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/3 "2005-07-25T03:54:57Z")
Sorry, that should be Agnatha. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [July 25, 2005, 4:10am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/4 "2005-07-25T04:10:42Z")
> [@Colibri](#): > > So yes, sharks are indeed fish, but a quite different kind of fish than a trout. The two are about as closely related as an elephant is to a turtle. Wouldn’t any two land vertibrates be much more closely related than a trout and a shark, if we measure relatedness by the amount of time since the two species diverged? I realize you weren’t making an exact comparison, but it might have sounded that way… ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [July 25, 2005, 4:17am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/5 "2005-07-25T04:17:02Z")
> [@John Mace](#): > > Wouldn’t any two land vertibrates be much more closely related than a trout and a shark, if we measure relatedness by the amount of time since the two species diverged? I realize you weren’t making an exact comparison, but it might have sounded that way… Yes, after I posted that I thought better of it. Elephants and turtles are much more closely related to each other than sharks are to trout. And trout are more closely related to elephants than they are to sharks. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [July 25, 2005, 4:17am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/6 "2005-07-25T04:17:59Z")
> [@RickJay](#): > > So is a shark actually a fish? Or is it a different kind of animal? Sharks are most certainly fish, belonging to class _Chondrichthyes_ (and according to this article subclass [Elasmobranchii](http://en.wikipedia.org/wiki/Chondrichthyes), though that doesn’t appear in traditional taxonomy). They are distinct from what we generally think of as fish in that, not only are their skeletons cartilaginous (though the jaws are typically proper bone) but that they do not have scales, preferring instead a surprisingly rough skin. (The roughness actually reduces drag underwater, which seems counterintuitive to most people not versed in fluid dynamics.) Sharks are typically considered to be “primitive” in that their evolutionary “progress” has essentially halted–most sharks have effectively the same form and features today as their ancestors tens of millions of years ago–but it is more properly considered that they are so finely adapted to their environment that selective pressures have virtually ceased to have any net impact upon them. Having dispensed with the need for baggage like temperature regulation, unnecessary appendages, and an unwieldy oversized brain, they have proceeded to dominate more than three quarters of the planet, which compares favorably with the Mongols, the Romans, and the Moonies, not to mention Donald Trump. Amazing creatures, they are. Stranger ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [July 25, 2005, 4:52am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/7 "2005-07-25T04:52:57Z")
Other tidbits: Chondrichthyes (to which sharks and their allies belong) is a sister clade to Teleostomi (to which more traditional fish belong, as well as ourselves). The common clade (Chondricthyes + Teleostomi) is called Eugnathostomata, and its ancestors (within Gnathostomata - the jawed fishes) had bony skeletons, just as the teleostomes do. This means that sharks, etc., are secondarily cartilaginous, having evolved from bony ancestors. > [@Stranger On A Train](#): > > but that they do not have scales Actually, they do. They are called [“placoid scales”](http://www.amonline.net.au/fishes/what/scales/placoid.htm), and have an outermost layer of enamel, dentine and pulp. Very much like teeth, in fact. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 25, 2005, 5:41am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/8 "2005-07-25T05:41:26Z")
> [@Stranger On A Train](#): > > (The roughness actually reduces drag underwater, which seems counterintuitive to most people not versed in fluid dynamics.) > > Stranger Like the dimples on a golf ball. My fluid mechanics book shows a reduction in coefficient of drag by a factor of up to three for roughened cylinders after a critical Reynolds number is passed. ---
**Author:** ![betenoir](https://avatars.discourse-cdn.com/v4/letter/b/258eb7/32.png) [@betenoir](https://boards.straightdope.com/u/betenoir)\ **Post date:** [July 25, 2005, 6:01am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/9 "2005-07-25T06:01:55Z")
What about eels? I thought I read somewhere that some of the creatures called eels were fish and some were a more distinctly seperate species. (Who I guess may still be fish given the broadness of the characterization.) Are there “real” eels and “faux” eels? Or am I completely off on this? (Sorry for the hijack, but it’s 2 am, I saw this thread, and now I must know what I ate at that sushi place the other night.) ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [July 25, 2005, 6:13am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/10 "2005-07-25T06:13:20Z")
[Eels](http://en.wikipedia.org/wiki/Eel) > [@](#): > > Electric eels are not true eels. They are more closely related to catfish. > > The Anguilliformes (true eels) are an order of bony fishes. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [July 25, 2005, 6:20am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/11 "2005-07-25T06:20:24Z")
> [@Darwin's Finch](#): > > Chondrichthyes (to which sharks and their allies belong) is a sister clade to Teleostomi (to which more traditional fish belong, as well as ourselves). The common clade (Chondricthyes + Teleostomi) is called Eugnathostomata, and its ancestors (within Gnathostomata - the jawed fishes) had bony skeletons, just as the teleostomes do. Is there a standard regulating organization for taxonomies? Looking even briefly online I’ve found at least three distinct and mutally incompatible taxonomies for sharks, any my rather old (and not really authoritative) reference is incompatible with all of them. > [@Darwin's Finch](#): > > This means that sharks, etc., are secondarily cartilaginous, having evolved from bony ancestors. That’s very interesting. Is this some kind of developmental retardation of the process of endochondral ossification or is skeletal development replaced by something completely different? > [@Darwin's Finch](#): > > Actually, they do. They are called “placoid scales”, and have an outermost layer of enamel, dentine and pulp. Very much like teeth, in fact. Your link isn’t working for me, but I’m guessing that placoid scales are the same as denticles which, while they are the precursors to cycloid and ganoid scales, don’t function the same way as the what are commonly thought of as scales, just as scales don’t confer the same benefits as feathers. Stranger ---
**Author:** ![SkipMagic](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skipmagic/32/20706_2.png) [@SkipMagic](https://boards.straightdope.com/u/SkipMagic)\ **Post date:** [July 25, 2005, 7:23am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/12 "2005-07-25T07:23:25Z")
Give it a try again; I fixed the link. ---
**Author:** ![Darwins\_Finch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darwins_finch/32/20304_2.png) [@Darwins\_Finch](https://boards.straightdope.com/u/Darwins_Finch)\ **Post date:** [July 25, 2005, 8:08pm UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/13 "2005-07-25T20:08:05Z")
> [@Stranger On A Train](#): > > Is there a standard regulating organization for taxonomies? Looking even briefly online I’ve found at least three distinct and mutally incompatible taxonomies for sharks, any my rather old (and not really authoritative) reference is incompatible with all of them. Generally, it seems to be whatever is accepted by most folks is…whatever is accepted. There are regulatory agencies for binomial nomenclature (e.g., the International Code of Zoological Nomenclature, and it’s botanical brother, the International Code of Botanical Nomenclature), but none for higher groups, so far as I know. For online sources, I generally use [palaeos.com](http://palaeos.com), the Tree of Life Web ([tolweb.org](http://tolweb.org)), or [Mikko’s Phylogeny Archive](http://www.fmnh.helsinki.fi/users/haaramo/). Those are all cladistic sites (I’m no fan of Linnaean taxonomies, but then I 'd guess there are many who aren’t fans of cladistic ones). > [@](#): > > That’s very interesting. Is this some kind of developmental retardation of the process of endochondral ossification or is skeletal development replaced by something completely different? Most likely, the former. While shark bones don’t ossify, they do typically calcify, providing some strength (though not as strong as true bone). > [@](#): > > Your link isn’t working for me, but I’m guessing that placoid scales are the same as denticles which, while they are the precursors to cycloid and ganoid scales, don’t function the same way as the what are commonly thought of as scales, just as scales don’t confer the same benefits as feathers. I’m not sure why that would be relevant; scales are scales. The general evolutionary trend is thought to be placoid -\> cosmoid -\> ganoid -\> ctenoid/cycloid (some fishes can even have multiple scale types, e.g., flounders and other flatfish). And feathers are no longer thought to be derived from reptilian scales. The feather is a whole new animal. So to speak. ---
**Author:** ![Punoqllads](https://avatars.discourse-cdn.com/v4/letter/p/d2c977/32.png) [@Punoqllads](https://boards.straightdope.com/u/Punoqllads)\ **Post date:** [July 25, 2005, 8:36pm UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/14 "2005-07-25T20:36:47Z")
> [@Darwin's Finch](#): > > And feathers are no longer thought to be derived from reptilian scales. The feather is a whole new animal. So to speak. Linky-link? Not that I doubt you, just that I’d like to see a fuller explanation. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [July 26, 2005, 12:00am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/15 "2005-07-26T00:00:25Z")
Eels. I hate eels. I even hate the word “eel”. Is that wrong? ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 26, 2005, 12:06am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/16 "2005-07-26T00:06:46Z")
And of course eel skin is made from slime eels, which also aren’t eels and are even more remotely related to bony fish than sharks or humans are. ---
**Author:** ![RickJay](https://avatars.discourse-cdn.com/v4/letter/r/bb73d2/32.png) [@RickJay](https://boards.straightdope.com/u/RickJay)\ **Post date:** [July 26, 2005, 12:21am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/17 "2005-07-26T00:21:25Z")
This thread is fascinating. I’ve never had a GQ so effectively and thoroughly addressed! I am just floored by the notion that a trout’s more closely related to an elephant than to a shark. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [July 26, 2005, 12:28am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/18 "2005-07-26T00:28:03Z")
> [@David Simmons](#): > > Like the dimples on a golf ball. My fluid mechanics book shows a reduction in coefficient of drag by a factor of up to three for roughened cylinders after a critical Reynolds number is passed. They also have the advantage of being resistant to other marine life such as barnacles. They’re looking at imitating shark skin on Navy ships. [http://www.livescience.com/technology/050715\_shark\_skin.html](http://www.livescience.com/technology/050715_shark_skin.html) ---
**Author:** ![Cervaise](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cervaise/32/16693_2.png) [@Cervaise](https://boards.straightdope.com/u/Cervaise)\ **Post date:** [July 26, 2005, 12:38am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/19 "2005-07-26T00:38:32Z")
> [@Colibri](#): > > Well, “fish” is not really a technical scientific term. Unlike, say, “bug.” 😉 ---
**Author:** ![Blake](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@Blake](https://boards.straightdope.com/u/Blake)\ **Post date:** [July 26, 2005, 12:43am UTC](https://boards.straightdope.com/t/are-sharks-actually-fish/313999/20 "2005-07-26T00:43:30Z")
> [@Cervaise](#): > > Unlike, say, “bug.” > > 😉 Strangely “bug” is more scientifically meaningful than 'fish". The bugs all belong to two closely related orders of insects, whereas the fish span almost an entire phylum. Of course in everyday speech bug means a whole lot of things besides sucking insects, but scientifically the word is fairly rigid. [Next page](https://boards.straightdope.com/t/are-sharks-actually-fish/313999.md?page=2)