Question: acording to QI fish don't exist is this true?

David Pyle answered on 20 Mar 2011:

No! I didn’t see this on QI, but it is a philosophical argument about whether you can define what it is to be a ‘fish’, rather than whether there are creatures that have backbones, scales and gills but no legs that swim in the sea. Fish do exist – and all modern examples can fit into one of three ‘classes’: those with bony skeletons, those with skeletons made of cartilage (e.g. sharks), and those that don’t have jaws (e.g. lampreys).

Looking at the geological record, fish have a long and very diverse history, They may well extend back to over 500 million years ago, and are one of the most diverse group of living organisms. In terms of size, fish go from the enormous filter-feeders who were cruising the oceans during the age of the dinosaurs, down to the few-mm long fish recently discovered in some swamps in Indonesia. In terms of shape, they range from needlefish, flat fish and rays to the exotically-decorated fish you can see on tropical reefs.