#7 European Eel
European Eel
European Eels change colors several times throughout their lives. They start off transparent before turning brownish-yellow on their sides and belly. After 5–20 years in fresh or brackish water, the eels become sexually mature, their eyes grow larger, their flanks become silver, and their bellies white in color. In this stage, the eels are known as "silver eels." (source: wikipedia)