Fishes… a strange, scrambled, barely official group of animals that belong to the phylum Chordata. They breathe using gills and have limbs with no digits, and beyond that can have thousands of strange and wonderfully quirky adaptations. Until the last few hundred years, cetaceans were also considered fish (or sea monsters). They spent their whole lives in the water, died if they came ashore and had fins. But now we know cetaceans as smart, complex mammals who give birth to live young, have hair and are warmblooded. This week we look at the ways of our closest marine relatives!
FISH are a group of only somewhat related vertebrates (animals with backbones), that are all part of the phylum Chordata. In general they have limbs with no digits, gills for breathing (therefore are aquatic) and a closed, one-loop circulatory system They include groups like sharks, rays, hagfish, lampreys, ray-finned fish and lobe-finned fish. Their specialized organs including swim bladders, pyloric caeca, kidneys and a lateral line system, which make them well-adapted to marine conditions.
CETACEANS are marine mammals who live their entire lives in the water, using one or two blowholes to breathe. This group, which includes whales, dolphins and porpoises, shares a common ancestor with the hippopotamus. The two general types of cetacean are the toothed whales, who use teeth to hunt fish and sometimes other marine mammals, and baleen whales who use large plates of sieve like hairs to take plankton out of the water.