The decoy scorpionfish ( Iracundus signifer) is a species of marine ray-finned fish belonging to the family Scorpaenidae, the scorpionfishes. It is native to the Western Indian Ocean and Pacific Ocean oceans. A non-migratory species, I. signifer can be observed in close association with coral at depths of from . This species grows to a length of fish measurement. This species is the only known member of its genus
Taxonomy
The decoy scorpionfish is a ray-finned fish, a member of the class Actinopterygii, belonging to the family Scorpaenidae, also known as the scorpionfish, which are aptly named due to many of its species possessing the capacity to produce a venomous mucus on the tips of their spines.
This species was first formally described in 1903 by the American
David Starr Jordan and Barton Warren Evermann, with the type locality given as
Oahu in
Hawaii.
The decoy scorpionfish is the sole member of the genus
Iracundus.
The genus name
Iracundus means "wrathful" and is an allusion to the red color of this species. The specific name
signifer is a compound of
signa meaning "mark" and
fera which means "to bear", a reference to the black spot on the spiny part of the dorsal fin.
Distribution and habitat
The decoy scorpionfish is native to the
Tropics coral reefs of both the Indian and Pacific oceans. In the Indian Ocean,
I. signifer has been observed along the coast of
South Africa, as well as the islands of
Mauritius and Reunion. In the Pacific, it has been observed in the
Hawaiian Islands, the
Ryukyu Islands, and
Taiwan.
[Santhanam, R. (2019). Biology and Ecology of Venomous Marine Scorpionfishes (Family Scorpaenidae). Biology and Ecology of Venomous Marine Scorpionfishes, 2-9. doi:10.1016/b978-0-12-815475-5.00003-0] Like other scorpionfishes,
I. signifer is a
Demersal fish organism, remaining in close proximity to the seafloor and coral reef for shelter, as well as
camouflage from predators and prey. Its most preferred habitat is within the cavernous, rubble-laden inlets underneath the edges of the coral reefs.
[Shallenberger, R. J., & Madden, W. D. (1973). Luring Behavior in the Scorpionfish, Iracundus signifer. Behaviour, 47(1/2), 33–47. Retrieved from www.jstor.org/stable/4533540]
Morphology
The decoy scorpionfish is a small, spiny fish, much like most other members of the family Scorpaenidae. The reddish-orange to white coloring covering most of the fish's body serves as camouflage along the Indo-pacific coral reefs where it resides. The decoy scorpionfish has a stocky, football-like body that can reach up to 13 cm (total length),
which is an average length for species within the
Scorpaenidae family. Its body is covered in small to medium-sized
Venom, a characteristic trait of all scorpionfish, the venom from which can be lethal to humans. These spines protrude from nearly everywhere across the fish's body, including ones protruding from around the eyes, along a fleshy membrane surrounding the head, and between the scales of the back, concentrated mostly in a stripe on each side running laterally to the spine. The
are broad and fan-like, with deep notches in the membrane between each spine.
[Jordan, David Starr, and Barton Warren Evermann. “Bulletin of the United States Fish Commission.” V.22 (1902) - Bulletin of the United States Fish Commission., The Commission, Govt. Print. Off., 1 Jan. 1970] Like many other members of the family Scorpaenidae,
I. signifer can actively change the color of their bodies in response to their environment.
This behavior usually involves displaying more dull colors when attempting to camouflage itself, and flashing brighter colors in the presence of a predator.
Likely the most unique aspect of this fish is the patterning of the dorsal fin itself. The fourth dorsal spine is nearly twice the length of the others, and there exists a distinct black mark appearing somewhere along the membrane between the first and third dorsal spines, with the combination of the two traits resulting in the dorsal fin having Mimicry. I. signifer utilizes this morphological feature in a coordinated luring mechanism not seen in any other members of the Scorpaenidae family.
Luring behavior
The decoy scorpionfish has been noted on multiple accounts to display a unique prey-luring mechanism, involving the movement of its dorsal fin. The form of
I. signifers dorsal fin strongly resembles that of a small fish, with the fourth dorsal spine representing the dorsal fin of the lure fish, and a small black dot between dorsal spines 1-3 representing the eye.
The decoy scorpionfish has developed a method of moving this fin so that it also behaves like a fish would. By moving the first dorsal spine in a figure-eight like pattern, the rest of the fin follows in a wave-like pattern of movement, while also moving laterally from side to side. This motion causes the dorsal fin to resemble a small fish gyrating in the water. The fish-like shape of the fin is emphasized by the subtle movement between the first and second dorsal spines, which continually move closer and then further apart, mimicking the opening and closing of a fish's mouth.
Another factor to this behavior is the active color-changing between the fin and body, as during luring, the normally deep red dorsal fin becomes much more intense in color, and the body of the fish conversely becomes more dull as a camouflage mechanism.
