Fish are adapted to living in water and are born in water. They hatch from eggs that are laid in water and spend their entire lives in aquatic environments. Fish are believed to have evolved from ancient sea creatures over 500 million years ago. Through natural selection and evolution, fish developed specialized organs and adaptations that allowed them to breathe, swim, and thrive in water. Over time, fish diversified into a wide range of species that inhabit oceans, rivers, lakes, and other bodies of water around the world.