Evolving Thoughts

A croc is a fish?

Lawmakers ponder the meaning of fish

Here is a case in which taxonomic categories are defined by political and legal considerations. In order to regulate the use of marine species for commercial reasons, to enforce export controls over crocodile (archosaurian) products, shellfish (molluscs), and prawns (arthropods). So the Bill (currently not online, due it seems to a Microsloth IIS error, *sigh*) treats these all as “fish”. Reuters notes wryly that this is somewhat in contradiction to the definition in the Australian English dictionary, but that is less of concern than the fact that we seem to be returning now to the medieval definition of “fish” as being anything that lives in water, which used to include whales, crocodiles, and so forth.

But “fish” is no longer a taxonomically valid category, and here’s why. Under modern taxonomic conventions (which exist because they make the taxa more natural), something is a group if it includes an ancestral species (whether we know what that is or not) and all its descendents.

And of course, we are descendents of the last common ancestor of all fish too. So, taxonomically, we as well as crocodiles are fishes. Well, to be more accurate, we are Sarcopterygians; there are a few things that get called “fishes” that aren’t in our group, such as ray finned fishes, sharks and placoderms, but it gets the point across.

The point being, that vernacular terms like “fish” really have no scientific meaning, as such, and are the result of the sorts of practical and social conventions that this Bill deals with. So I say, despite the apparent oddity of the political decision, it is actually quite OK.

Comments

  1. #1 RPM
    August 19, 2006

    I’ve come to consider fish to be a synonym for vertebrate.

    there are a few things that get called “fishes” that aren’t in our group, such as ray finned fishes, sharks and placoderms, but it gets the point across.

    Considering that ray finned fishes are what most people consider “fishes”, I don’t think it gets the point across.

    Thanks for fighting the good fight against paraphyly.

  2. #2 John Wilkins
    August 19, 2006

    Well Sarcopterygians are Gnathostomatans, and all fishes fall within that group…

  3. #3 Snail
    August 19, 2006

    Phylogenetic issues aside, I suspect that categorizing crocs as fish also means there are fewer restrictions on how they are slaughtered and processed. Presumably the rules applying to mammals and birds don’t apply to fish.

  4. #4 arensb
    August 20, 2006

    we seem to be returning now to the medieval definition of “fish” as being anything that lives in water, which used to include whales, crocodiles, and so forth.

    …and penguins?

    As far as I know, there are no bats that have adapted to aquatic life (though with so many species of the little buggers, I could easily be mistaken). But if there were, presumably they’d be birds by the Biblical definition, and fish by the Australian legal definition.

    What was your point again? That biology has no obligation to comply with our doggie-horsie-fishy folk taxonomy?

  5. #5 Bob O'H
    August 20, 2006

    Are there any ardent Aquatic Ape Theory supporters in Oz who should be told about this?

    And does this mean that the blue whale is no longer considered an insect?

    Bob

  6. #6 John Wilkins
    August 20, 2006

    What was your point again? That biology has no obligation to comply with our doggie-horsie-fishy folk taxonomy?

    The world is not ony queerer than we imagine, but it is queerer than we can imagine…

  7. #7 Steve Watson
    August 21, 2006

    My favorite examples of taxonomic disconnects: to a botanist, the tomato is a fruit. To a cook, it’s a vegetable, and so are with broccoli and cauliflower.