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.