Juvenile pollack (Pollachius pollachius). Fish specimen 'cleared and stained' to reveal internal structure. The cartilage of the fish is first stained with alcian, turning it blue. It is then placed into an enzyme solution that dissolves away the muscle before alizarin is used to stain the bones red. This technique allows for in situ viewing of the skeleton and study of bone development. The younger fish are more blue due to the dominance of cartilage, but as the skeleton ossifies more mature specimens appear redder. Specimen from the Scilly Isles, May 2013