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Fish not existing

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nix-j-c
778951.  Sat Jan 22, 2011 3:53 pm Reply with quote

I'm not sure which series this was on, but one of the last couple I think.

And Steven stated that in biological terms, 'fish' do not exist. Looking at the family and genus etc of various animals i can see how that's possible, but how did biolgists discover this, I assume by DNA analysis . . .

 
bobwilson
779343.  Mon Jan 24, 2011 1:37 am Reply with quote

It's a claim made by an eminent biologist (I thought it was Pinker but it appears not). The essential thing is that there's no particular reason to describe all swimming things as "fish" any more than there is any reason to describe all flying things as "birds".

Bats fly - and they are mammals. Ladybirds fly - and they are insects. We don't call them all "birds" do we?

 
Posital
779345.  Mon Jan 24, 2011 1:47 am Reply with quote

But then, we don't call whales and dolphins fish either...

 
bobwilson
779371.  Mon Jan 24, 2011 3:36 am Reply with quote

True - but we specifically exclude them for other reasons. The point is that anything that swims is a fish unless it's specifically excluded - and there's no good reason for that. You might as well say anything that has legs is a mammal unless it's specifically excluded.

 
suze
779545.  Mon Jan 24, 2011 11:02 am Reply with quote

I think this has been explained in more detail somewhere, but I can't now find that discussion.

But bob has the essence of it. There is no system of questions under which we can definitively classify any given animal as either "fish" or "not fish". Every definition of "fish" which exists is flawed, in that some creatures which meet it are not generally considered to be fish, or some which are so considered do not meet it.

 
AlmondFacialBar
800716.  Tue Mar 29, 2011 5:23 am Reply with quote

I think it was Stephen Jay Gould who originally stated that and Richard Dawkins explains it very well in The Ancestor's Tale. The idea is basically, that while of course there is a perfectly good convenience term "fish" for swimming vertebrates with gills that doesn't actually mean they're in any way related on an evolutionary level, i.e. they're not a monocladistic group. Think about it - and just looking at a couple of fishies will make it perfectly obvious, too - there are Teleosts (most fishies you'd commonly meet or have for dinner), then there are cartilaginous fish (sharks, rays and the like), then Coelacanths (our closests cousins who we owe our limb arrangements to) and a couple other odds and sods. Looking at them not even that closely you'll notice how different these are from each other already. For instance, Teleost fins don't have muscles but are moved via muscles in the rump, but Coelacanth fins do, leading to the English term lobefinned fish, and our own arm and leg muscles. Cartilaginous fish, then, don't have calcified bones or a swim bladder, and and whole different anatomy again, and are thus also a different kettle of... fish from the rest of us.

These obvious differences are confirmed by molecular analysis that makes very clear that some fish are more related to tetrapods than to other fish, some are more related to other groups and so on. Hence, from a purely evolutionary point of view, there is no such thing as a fish. That won't keep me from turning one into a stir fry tonight, though. ;-)

:-)

AlmondFacialBar

 
Zebra57
807612.  Wed Apr 20, 2011 10:07 am Reply with quote

This issue was raised on the BBC Radio 4 quiz The Unbelievable Truth chaired by David Mitchell. He claimed that fish only existed in a culinary sense.

 
VidovicS
874327.  Sun Jan 01, 2012 4:21 pm Reply with quote

The problem with fish aren't their differences or similarities, but the topology of their evolutionary tree.
If there is a clade recovered through a cladistic analysis it will be difinable. The very princible of a cladistic analysis is to find relationships through the comparison of morphology or DNA.
Taking this into consideration, comparing cartilaginous swimming vertebrates to armoured ones has no bearing if they nest in a clade. The only thing is, the clade containing all the swimming vertebrates also contains everything that evolved from them, including us! So, using the definition fish in a correct sense (as a monophyletic clade containing all animals with heads, back bones and fins, or secondarily lost them) would mean lizards, dinosaurs, mammals, birds and amphibians are fish too. This would make the group "fish" synonymous with vertebrates. Vertebrata has been given priority. The term "fish" is still used in a colloquial sense to descibe what we term a paraphyletic group of vertebrates lacking tetrapod characteristics.
One of the easiest ways to understand the concept is to look at a similar situation with a group not so engrained in your brain, pterosaurs seem a good proxy. Pterosaurs have a paraphyletic group called "rhamphorhynchoids" in the "stem" of the tree followed by the terminal, and therefore monophyletic pterodactyloids. Check it out.
Or alternatively a copy of the ICZN (the code which all biologists name names according to) is freely available from the Natural History Museum UK.

 
jeffcj
887557.  Mon Feb 20, 2012 3:54 pm Reply with quote

Gould's claim is risible; he always was overly fond of the catchy soundbite. The crux is the assumptions that are omitted from that facile statement.....
There's no need to invoke cladistics for an essentially onomastic problem. Common human conceptions rest [necessarily] in essentially pragmatic, gradal terms; hence, the [demonstrably monophyletic] teleosts are for all everyday purposes the 'true fishes'. "Cartilaginous fishes", "shellfish" etc. are all similarly susceptible of relatively specific definition [albeit sometimes only by contradistinction].
One couldn't conduct any informal discussion about organisms in strictly cladistic terms without constantly having to exclude the members of the clade in question not immediately pertinent to the topic.

This is of course why higher taxonomic categories have largely resisted substantial post-cladistic change: to accurately reflect common ancestry the Primates, for example, would have to be downgraded in status to something more equivalent to the current 'value' of the species, or lower :-)

 
dr.bob
887656.  Tue Feb 21, 2012 5:30 am Reply with quote

jeffcj wrote:
Gould's claim is risible


Personally I think it's interesting and thought provoking. I certainly don't think it deserves to be ignored or laughed at.

jeffcj wrote:
There's no need to invoke cladistics for an essentially onomastic problem.


Sometimes there is, particularly when a commonly used term for something has grown up over the years without anyone actually questioning what it really means and then finds its definition rather at odds with the latest scientific research. Hence the discussion at the IAU a few years ago about what we actually mean by the word "planet".

It also brings to light complacency in understanding. People may well be assuming that everyone agrees with their definition of "fish" or "planet", but then be rather surprised when they discover someone who doesn't think that a mussel is a fish, or that Pluto is a planet.

jeffcj wrote:
Common human conceptions rest [necessarily] in essentially pragmatic, gradal terms; hence, the [demonstrably monophyletic] teleosts are for all everyday purposes the 'true fishes'.


So you're saying a sturgeon isn't a true fish?

jeffcj wrote:
One couldn't conduct any informal discussion about organisms in strictly cladistic terms without constantly having to exclude the members of the clade in question not immediately pertinent to the topic.


I don't think that's remotely true. You can easily have a discussion about birds, mammals, hominids, or many, many other clades without having to constantly exclude members of that clade.

jeffcj wrote:
to accurately reflect common ancestry the Primates, for example, would have to be downgraded in status to something more equivalent to the current 'value' of the species, or lower :-)


This bit I really don't understand. Why would you have to downgrade the status of Primates to accurately reflect their common ancestry? Do Primates have a "status" in the first place? If so, what is it?

 

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