Updated: May 10, 2020
Parrotfish are known collectively as uhu in the Hawai'ian language, and with their heavy beaks and their often times blue bodies, the name suits them. They swim primarily with their pectoral fins and undergo confusing sex and color morph changes as they mature, which is clear evidence that they are related to the Wrasse Family. There are eight species found in Hawai'i including three endemics. Parrotfish are generally active during the day and at night rest in crevices and caves where some species excrete a thick layer of mucus to protect them from predators.
Most parrotfish begin life as females and have the ability to either remain female or transition to male as they mature. This ability is known as hermaphroditism and it is common to the Wrasse family to which all parrotfish are closely related. Their gender at maturity, or terminal gender, is determined by a complex combination of environmental cues and population biology requirements. This ability to change gender is quite unique among vertebrates, and is usually relegated to the invertebrate orders and families.
Most parrotfish are herbivorous, using their fused teeth to scrape algae from the substrate. However, some do consume living coral. Those that do have grinding plates in their throats that pulverize the calcareous skeletons of the coral and the remnants are pooped out as coralline sand. In Hawai'i, there is a distinct difference between the basaltic sand created by the volcanic eruptions that has formed these islands and the calcareous sand created by the parrotfish.
It is typical for parrotfish to establish and defend territories. Usually, these are maintained by adult males and will generally include several to many females in the 'harem' which is the sexually reproductive unit or family. One of the most unusual aspects of the parrotfish lifestyle is when the dominant male of the harem is killed or dies, one of the dominant females will change gender and become a "supermale" and will assume the role of the dominant male in the harem. This supermale is noticeably larger and more aggressive than even the normal males of the same species.