A juvenile emperor angelfish changes color as it grows. Its electric blue and white rings gradually turn into yellow stripes, and as an adult it has a yellow tail and a pale blue face.
Baby emperor angelfish usually hang out in protected areas, while adults swim out in the open reef. Babies eat parasites and pick off the dead skin of larger fish, and adults feed on sponges or algae. In fact, the adults have such strong jaws that they can chew up sponge skeletons, which are made up of sharp, needle-like silica. They’re practically chewing on shards of glass!
While sea hares don’t undergo such a stunning transformation (or eat glass), they also change colors throughout their lives. Their color depends mostly on the type of algae that they eat, but I’ve also noticed that they’re light red as young babies and a deeper purple when they’re older.