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 eastern
coast of Africa and
east to the Hawaiian
Islands.
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.
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.
Unicorns
have the flat, teardrop shaped bodies common to most tangs. They are
bluish-grey in color and have long, flowing lyre shaped caudal fins.
They are
sold by the aquarium industry under the pseudonyms Naso unicornfish and
bluespine unicronfish.
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.
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.
