AT A GLANCE
- Common Name: Barred Flagtail
- Scientific Name: Kuhlia mugil
- Category: Fish
- Subcategory: Bony Fishes
- Range: Circumtropical Indo-Pacific region, from South Africa and the Red Sea east to Hawaii, French Polynesia, and the Pacific coast of Central America (from Mexico to Colombia)
- Habitat Type: Shallow coastal surf zones, surge channels, rocky reef margins, tide pools, lagoons, and clear coastal reef drop-offs exposed to heavy wave action
- IUCN Red List Status: Least Concern
- Lifespan: 4 to 7 years
- Diet: Carnivorous/Planktivorous (nocturnal feeding on zooplankton, pelagic crustaceans, amphipods, small shrimps, crab zoea larvae, and small fish larvae)
- Average Size/Weight: Total length 20 to 30 cm; weight 150 to 350 g
- Key Defining Feature: Sleek, silvery coastal reef fish with colossal dark nocturnal eyes and an unmistakable, deeply forked caudal fin boldly marked with five jet-black horizontal stripes
Overview
The Barred Flagtail (Kuhlia mugil), also commonly known as the Five-band Flagtail, is an agile, beautifully patterned marine teleost in the flagtail family Kuhliidae. Widely distributed across the warm tropical reefs and surf zones of the Indo-Pacific, from the shores of East Africa to the remote Hawaiian archipelago, it is named for its striking tail fin. When swimming in the crystal-clear surge of coral reefs, its deeply notched tail displays five sharp, alternating black-and-white stripes that flash like a waving nautical signal flag.
Biology and Physical Characteristics
Kuhlia mugil possesses a compressed, moderately deep, aerodynamic body covered in smooth, silvery-white cycloid scales with a brilliant metallic mirror-like sheen. Its head is relatively large with a prominent, upturned mouth and colossal, round, dark eyes that provide exceptional night vision for nocturnal hunting in churning water. Its dorsal fin is deeply notched into two sections, armed with stout, sharp spines. Its defining anatomical trademark is its caudal fin: deeply forked and pure white, it is decorated with five bold, solid jet-black bands—a central horizontal stripe running through the fork, and two oblique black bars on each lobe, creating an eye-catching striped pattern that confuses predators in turbulent surf.
Behavior and Ecology
Barred Flagtails are specialized surge-zone swimmers with incredible hydrodynamic control. During the day, they form dense, tight-knit schools that mill calmly inside shaded surge channels, caves, and turbulent white-water zones where crushing waves break over rocky ledges, conditions that deter larger predatory sharks and jacks. As dusk falls, the schools disperse into open water, using their large eyes to hunt pelagic plankton and small nocturnal crustaceans that rise to the surface under moonlight. Juveniles are common in shallow intertidal rock pools, tolerating wide fluctuations in salinity and water temperature.
Conservation and Human Impact
The Barred Flagtail is classified as Least Concern on the IUCN Red List. It is abundant and broadly distributed across thousands of kilometers of tropical coastline. It faces no significant threats and is taken locally by artisanal cast-net and hook-and-line fishermen as a delicious panfish and baitfish.
Interesting Factoid
The Barred Flagtail spends its entire day swimming effortlessly inside violent, foaming wave-break zones that would smash other fish against the rocks, using its five-striped tail to flash visual signals to keep its school together.