After those first ten days the shell is lost and the spines begin to develop. The larvae undergo a metamorphosis approximately three weeks after hatching. During this time all the fins and fin rays are present and the teeth are formed. The red and yellow colors of the larvae do not persist into the juvenile phase and are replaced by the olives and browns characteristic of adults. Dark spots also appear on the juvenile's underside.
Juveniles retain spotting until they move inshore and become adults.
The juvenile balloonfish does not undergo another metamorphosis to become an adult. All changes are now external and include elongation of the spines and normal body growth. They can reach sizes up to a foot. They are shy creatures and will retreat if approached by a diver. In some parts of the world the dried, inflated bodies are sold as tourist novelties.