Fish

With an estimated 20,000 different species, there is an immense variety of fish. The variation in size is enormous: the tiny Paedocypris progenetica is only 8 millimetres long, and the whale shark can reach over 12 metres. Fish are adapted to live in many different habitats: trout and catfish can live in freshwater; seahorses and yellow tang fish live in coral reefs; and down on the deep, dark ocean floor are anglerfish and cookie cutter sharks.