Unicorn tangs or Naso unicornis are members of the family Acanthuridae commonly refer to as surgeonfish. There are 80 species in 6 different genera in this family. All have one distinguishing characteristic. They have sharp blades at the base of their tails (caudal peduncle) on both sides of their bodies that are used in self-defense. Seventeen of the 80 species are unicornfish. Here we will be elaborating on the unicorn tang. They are endemic to the Indo-Pacific from Indonesia and Christmas Island westward to the Andaman Sea, south to the eastern coast of Africa and east to the Hawaiian Islands.
Unicornfish receive their names from the horn-like projection at the top of their heads. This horn begins to develop in early adulthood. These unicorn horns will grow longer as the fish continues to mature. The function of these horns is not understood. They have yet to be observed using these spinal adaptations as a means of defense. An unmistakable defensive mechanism employed by all members of the family Acanthuridae is the modified scale structures at the base of their tail. These structures are exceedingly sharp. When threatened, this family will thrash their tail about hoping to dissuade their aggressors from further attempts at predation. These blades will slice into flesh as efficiently as a surgeon's scalpel. In addition to self-defense, surgeonfish use their blades to ward off intruders from their feeding grounds. Most surgeonfish have just one set of retractable blades located in a slot on both side of their tail. Unicorn tangs have two fixed blades on either side. These double blades are the defining characteristic of the genus Naso. This distinguishing feature helps to identify the fish's genome. Not all unicornfish develop the horn for which they are commonly named.
Uincorn tangs are among the largest species made available by the aquarium industry. They can grow to a maximum adult length of 27 inches. This is why you will seldom see one in a home aquarium. They require a minimum tank size of 250 gallons and are best suited for large show tanks. Because of their ties to one of the most elegant of all mythological creatures, they are prized additions to public aquaria.
Unicorns have the flat, teardrop shaped bodies common to most tangs. They are bluish-gray in color and have long, flowing lyre shaped caudal fins. They are sold by the aquarium industry under the pseudonyms Naso unicornfish and bluespine unicornfish.
A significant populace of these creatures exists around the shores of the Hawaiian Islands. Unicorn tangs were prized by ancient Hawaiians both as a source of food and for their hides. Their tough skins were used in the construction of drum heads. This species is not considered aggressive to human intrusion. However tourist diving off the Hawaiian Islands should avoid chasing or corning these creatures. Sports fishermen should use extreme caution when removing them from hooks or nets.
Unicorn tangs are herbivores. In nature their diet consists primarily of benthic algae. Since they are unlikely candidates for home aquariums, there seems little point in covering dietary conditioning in captivity.
One of the unique aspects of surgeonfish is their communal mating habits. During spawning seasons they will congregate in large groups. Females and males simply release eggs and sperm into the water for fertilization. There is no thought to courtship or coupling found among surgeonfish in the wild.
Credit To Stephen J Broy