Rainbow Scorpionfish, Scorpaenodes xyris

Rainbow Scorpionfish, Scorpaenodes xyris. Fish caught from coastal waters off Santa Catalina Island, California, September 2016. Length: 13.0 cm (5.1 inches). Catch courtesy of Marty Dufek, Huntington Beach, California. Photograph and identification courtesy of Chris Wheaton, Fullerton, California. This catch documents the northerly extension for the range of the Rainbow Scorpionfish.

Rainbow Scorpionfish, Scorpaenodes xyris. Fish caught from coastal waters off Santa Catalina Island, California, May 2018. Length: 13.5 cm (5.3 inches). Catch, photograph and identification courtesy of Eli (obsessiveangling.wordpress.com). Identification reconfirmed by Milton Love, University of California, Santa Barbara, Goleta, California.

Rainbow Scorpionfish, Scorpaenodes xyris. Underwater photographs taken in Zihuantanejo Bay, Guerrero, February 2023. Photographs courtesy of Ron Woheau, Zihuantanejo.

The Rainbow Scorpionfish, Scorpaenodes xyris, is a member of the Rockfish and Scorpionfish or Scorpaenidae Family, and known in Mexico as escorpión arcoiris. Globally, there are twenty-six species in the genus Scorpaenodes, of which three are found in Mexican waters, two in the Atlantic and one in the Pacific Ocean.

The Rainbow Scorpionfish has a relatively slender compressed body with a depth that is 29% to 31% of standard length. They are various shades of red and brown with a significant amount of mottling often with three to five irregular dark bars on their sides. Their fins have white broken stripes except for the first dorsal fin which is a more uniform color. They have a white bar below their eyes that extends across their upper jaw and a prominent black spot on the lower portion of their gill cover. Their head is large but streamlined and has a terminal mid-sized mouth with teeth only on the roof. Their eyes are relatively large. They lack the “pit” after the eyes found in most other Scorpionfish. They have a longitudinal ridge under their eyes with 2 or 3 spines. Their anal fin has 3 spines, the second being exceedingly long and stout, and 5 rays; their caudal fin is rounded with a ragged margin; their dorsal fin has 13 spines and 10 rays; and, their longest pectoral fin is in the center. They are covered with rough scales and they do not have skin flaps. Their lateral line is complete.

The Rainbow Scorpionfish is a fairly common but inconspicuous species found in cracks, crevices and under ledge overhangs within rocky reefs, steep slopes, and on walls from the intertidal zone to depths of 50 m (165 feet). They reach a maximum 15.0 cm (5.9 inches) in length. Juveniles are found in close proximity to the Long Spined Urchin, Diadema mexicanum, presumably for protection against predation. They are common but seldom seen by humans. The Rainbow Scorpionfish is poorly studied with very limited information available about their lifestyle and behavioral patterns including specific details on age, growth, longevity, movement patterns, diet, habitat use, and reproduction.

The Rainbow Scorpionfish is a resident of all Mexican waters of the Pacific Ocean with the exception that they are absent from of the extreme northern portions of the Sea of Cortez.

The Rainbow Scorpionfish is most likely confused with the California Scorpionfish, Scorpaena guttata (dorsal fin with 12 spines and 9 rays; large bulbous head; pit behind eyes) and juvenile Stone Scorpionfish, Scorpaena mystes (dorsal fin with 12 spines and 9 rays; large bulbous head; pit behind eyes).

From a conservation perspective the Rainbow Scorpionfish is currently considered to be of Least Concern with stable, widely distributed populations, however, their populations are poorly monitored. They are too small to be of interest to most and difficult to handle, thus are a “catch and release”. Caution: As with all Scorpionfish, the Rainbow Scorpionfish should be treated as hazardous and released as soon as possible, being careful not to allow their poisonous spines to penetrate the skin.