I'm surprised to learn that it is surprising that eels are fish. I mean, they live in water, they have fins, they're generally fish-shaped... What's more surprising is their incredible life cycle and reproductive journey. I'm surprised the author didn't put that in the title.
It's a brilliant title. I thought: huh, surely that's not a surprise? If that's a surprise, there must be more to eels than I know - which of course is what the article is actually about. If the title was just "eels have an interesting life cycle, actually", I probably wouldn't have realised how interesting it actually was.
QI said (roll podcast title) There is no such thing as a fish, since that group is unbelievably diverse.
Strange that birds are dinosaurs, while Pterosaurs are not. Where is the bipedal fish that looks like a reptile or mamal, but is secretely a fish, too?
I think it's not about diversity, but lineage. The phenotype for "fish" is so tight and well defined; a salmon is closer related to a human in the tree of life than to a coelacanth even though both are categorised as "fish".
Oh, but you should not classify living beings according to their habitat and behaviour; classification based on the degree of the phylogenetical relationship is obviously superior and the only truly reasonble one.
You should classify living beings according to a system that is helpful to understand and discuss the livings beings in a given context. "Fish" isn't a specific taxon in the standard biological taxonomy, but is rather a description of a specific set of common physical attributes and behaviors that is helpful to differentiate some organisms from other organisms. Regardless of official taxonomy, for 99.99% of people it's helpful to describe eels as fish.
Now, there’s something wrong with saying “whales are phylogenetically just as closely related to bass, herring, and salmon as these three are related to each other.” What’s wrong with the statement is that it’s false. But saying “whales are a kind of fish” isn’t.
