What evidence places fish as the first vertebrates?

Can a hippo breathe underwater? Would a cichlid mate with a gourami? How fast does the seat altea go? What is the sail fish known for? Are there seahorses in the Arctic Ocean? How many types of accessiores? Will ghost fish eat neon tetras guppies or kill mollies? How many times do a hammerhead shark eat a day? What is the animal from which pearl is extracted? What are the top ten ways to prevent a shark attack? Why does your air conditioner smell fishy? Where do the people from tanked get there fish? What are the different methods of fish cultivation in Visayas? How many babies does a dogfish shark have? Does a fishes brain tell it to stop eating? Would beaver eat wild rice? Do eels have paired appendages? Does it hurt a great white to close its mouth? Why are bull sharks the most aggressive sharks? Why do you have so many flies at your pool?