Emperors are a marine species of fish belonging to the Lethrinidae family, often referred to as Lethrinids. About 40 different species inhabit the tropical to temperate waters of the Indo-Pacific region, with more than half of said species found in Australian waters. Their main habitat are coral reefs, but seagrass beds, sandy areas, lagoons and rocky reefs as deep as 200 m are also home to Lethrinids. Juveniles can be found over shallow, inshore waters, near mangroves and over seagrass beds. The most distinctive physical features are their snouts, big eyes and thick lips, the latter attributing to the old name, “sweetlip.” Their teeth are robust at the front and side of their jaws. Emperors are a colorful family with varying types.
The trumpet emperor has a gray body with red near its eyes, mouth and fins. The sweetlip emperor has orange around the eyes with a bright orange dorsal fin, while the rest of the body is usually
light gray with small black scales dotted over the body. Darker colorations appear almost red. The sweetlip emperor’s mouth is also extremely red inside. The spangled emperor has a yellow body with blue spots on scales of its upper body and blue bars drawn from the eyes over the cheeks and snout. Adult emperors can grow to be 90 cm long and weigh up to 9 kg. Species like the spangled emperor can live as long as 30 years.
They are carnivorous bottom feeders with a diet including sea snails, crabs, sea urchins, worms and other small organisms. Sweetlip emperors will usually forage at night and hide during the day. Emperor predators include other larger fish, including sharks. Sweetlip emperors can either be found as singles or in schools. Aggregated spawning tends to occurring during a new moon or full moon for most species of emperors. Emperor fish reach sexual maturity at 30-50 percent of their lifespan. They are hermaphrodites that start their lives as females and change their sex to male as they mature. Most members of the Lethrinidae family, including emperors, have the ability to switch on and off their dark mottled patterns, spots or bars in an effect to deter predators. The spangled emperor changes color by switching on pigment cells in its skin. If it becomes frightened, it will produce blotchy vertical brown bands across its body. This color change can occur within a matter of minutes. Emperors are also very edible for humans and a popular catch fish. Management measures for protecting emperors include limiting the number of people fishing, limiting the amount of fish caught (bag limits or quotas) and restricting the type of fishing gear used. The biggest concern is people fishing during spawning season over breeding grounds. However, there appears to be no major conservation concerns for any species of emperor at this time.