Well, the Darwin fish is funny, and clever, and irreverent...
Well the remarkable thing is that it is not incredibly complex - it is reducible to just three closely related genotypes and is therefore rather incomplex genetically while seemingly very complex phenotypically.
No, it's descended from three genotypes. I have no idea what 'reducible' means in this context. Polyploidy does remarkable things to plants, something stoners realized a long time ago.
Heck, look at dogs. There you have Chihuahuas and great Danes descended from one or maybe two species, even without polyploidy.
Which reinforces the point I was trying to make - enormous phenotypical diversity can arise from a small and stable genotypic pool.
However, this phenotypical diversity is limited by the genotypic pool and dogs in all their wonderful variety do not give rise to cabbage in one or one million generations.
Again the issue here is the facile nostrum that amoebae can become, given enough time and interesting enough circumstances, elephants.
Dogs in all their variety have an irreducible dogness which does not, by chance, become cabbageness or armadilloness.