Bluestreak cleaner wrasse

Evolution

All cleaner wrasses start their lives as females. A group of six to eight cleaner wrasses contains only one male, as the rest are females or juveniles. When the male dies, the strongest female changes her sex, an occurrence known as sequential hermaphroditism.

Cleaner wrasses sleep in crevices between rocks or corals, covered in a slime layer they secrete at dusk and which can be seen floating on the surface in the morning. Cleaner wrasses live for about four years, and can grow to up to four inches.