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."
See-through Frog (Hyperolius Leucotaenius)
Hyperolius leucotaenius is a species of frog in the Hyperoliidae family. It is endemic to Democratic Republic of the Congo. At one time thought to be extinct, in 2011 Hyperolius leucotaenius was found and photographed on the banks of the Elila River, a tributary of the Lualaba, during an expedition led by Eli Greenbaum of the University of Texas El Paso.