This is an interesting criiter, IMHO. The blue ribbon eel starts out all the same sex, and are black with yellow stripes when a juvenile. As they mature, they are males that are a bright blue with yellow stripes. When and if they become a more aged eel, they will have the opportunity to turn female, and all yellow, such as this one. Also known as the “Old maid eel”. However, this is when they reproduce, so these eels are essential to the survival of the species. However, the yellow ones are much more rare than the blue or black ones.