Here we have the first creatures with a backbone that started their murky lives some 440 million years ago. “Fishes” scientists often like to say and write to refer to many species of fish, as opposed to the simple plural and singular form of the word “fish”. Among fishes, you will find a big, diverse group of sea animals with heads, fins, gills and backbones. Fish and water are inseparable! Where you find water you will find fish and vice versa. Sea mammals and invertebrates are not fish. Shellfish, cuttlefish, starfish, crayfish and jellyfish, despite the names, are not fish. Most fish are cold-blooded but a few, like tuna for example, are warm-blooded.