Is there a way to define fish without calling myself one?

[Gelatinous squid]

Is it possible that not all the creatures we call fish are actually fish? 

[Kane]

There are a number of animals that have "fish" in their names that are not fish, such as starfish, crayfish, jellyfish, etc. 

 

This brief article discusses what is and is not considered a fish: http://eol.org/info/442

[Gelatinous squid]

I mean, could we say that lungfish and coelocanths are not fish? Or that sharks are not fish? Because it seems a bit silly to say that all tetrapods must be included among the fish. 

[Fossildude19]

This paper's abstract States that these three - (Lungfish, Coelacanths, and tetrapods ):

 

"Apparently, the coelacanth, lungfish, and tetrapod lineages diverged within such a short time interval that at this level of analysis, their relationships appear to be an irresolvable trichotomy."

 

And while they do share characteristics with tetrapods, ... they share many features of fish as well.  Interesting question.

 

@doushantuo should be along shortly, with a plethora of papers concerning cladistics and phylogeny. 

 

[Kane]

Speaking very generally and conceptually here  : 

 

I've always taken the view that taxonomic divisions are sometimes a bit like cutting up the spectrum of light, and that our very human tendency is to group or cluster certain objects according to a set list of similarities and box 'em all up as distinct categories.

 

There are still open debates about how to classify and categorize certain organisms. Even as recently as when I was in elementary school in the 80s, there were only five recognized kingdoms (animalia, planta, fungi, monera, protozoa) and now there are a few more.

 

In the end, however, it is a little like trying to cut something continuous (such as time) into discrete units so that we can have some basis of consensus when we talk about certain things, like what qualifies as a "fish." Where to put those "cuts" was definitely one of the big challenges Linnaeus faced. And, problematizing things further, as genetic change over time is a continuous process, what is the threshold by which we will assign a new species name?

 

An interesting French philosopher by the name of Henri Bergson held the view that our human understanding of time is not aligned with its nature as something continuous, but that we see it as a kind of film (several still shots combined to show the illusion of motion). Of course, we can probably set aside his other view of orthogenesis as that implies teleology (and the later variant, typostrophism as advanced by the paleontologist Schwindewolf, seems to beg the question a bit too much!). 

[Fossildude19]

And, just as an aside - you don't have to call yourself a fish, unless you really , REALLY like swimming.  

[doushantuo]

no,Tim,coz I don't respond well to irony

Nor to steely,BTW

What's with the "plethora",anyway?

You know i hate fancy talk

Kane,you're thinking along the line of "crownward plesion""and "stemward plesion" there.

And Tim posting a molphyl article.

Now i've seen everything

[doushantuo]

so the question is really "Are the Pisces para-or polyphyletic?

[Mediospirifer]

Ray finned fishes (teleosts) are, I think, a clade, and do not include lobe-finned fishes (lungfish, coelacanth, us, etc.) or cartilagenous fishes (sharks and rays). Asking for a grouping of 'fish' that doesn't include tetrapods is like asking for a group 'reptiles' that doesn't include mammals and birds!

 

Amusingly, if you like the all-inclusive cladistics grouping, that means whales are fish!

 

[JohnBrewer]

Well there's Billy the Fish who's a character in a well know UK comic http://britishcomics.wikia.com/wiki/Billy_the_Fish 

[FossilDAWG]

Related to this topic, I highly recommend "Your Inner Fish" by Neil Shubin.  We may no longer be fish, but there is a lot of fish in our anatomy.

 

Also I'm curious why someone who self-identifies as a slimy cephalopod doesn't want to be a fish?

 

Don

[Gelatinous squid]

I gravitate towards intelligence. Cephalopods will rule the world once the humans are gone. Splatoon and the Future Is Wild have said so. I'm just thinking ahead. True, there are a few intelligent fish, like mantas, but on the whole they're not a spark of light in the universal void. 

[verydeadthings]

It gets even worse, you can't define invertebrate as a monophyletic group without calling yourself one! Another example is class Reptilia, which traditionally defined included both lizards and crocodiles, however, to make the group monophyletic, you'd have to include birds in there as well. As traditionally defined, the Kingdom Protista is paraphyletic because it excludes plants, animals, and fungi, and is no longer valid except as an informal term. 

 

Things get really hairy when you think about whether we (and animals and all other eukaryotes) are technically bacteria (or possibly archea), because we evolved from bacteria. Therefore, defining bacteria without including humans leads to a paraphyletic group. Then you can go down the rabbit hole of how eukaryotes might have evolved from fusion or endosymbiosis of different prokaryotes. I think although paraphyletic groups may not be "natural" groups, they are still useful for informal classification.