Cortez Rainbow Wrasse

Cortez Rainbow Wrasse, Thalassoma lucasanum

Cortez Rainbow Wrasse, Thalassoma lucasanum, Initial Phase (IP) Female. Fish caught from shore at Km 17, El Tule, Baja California Sur, August 2005. Length: 7.0 cm (2.8 inches).

Cortez Rainbow Wrasse, Thalassoma lucasanum, Initial Phase (IP) Female. Underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2018. Photographs courtesy of Ron Woheau, Zihuantanejo.

Cortez Rainbow Wrasse, Thalassoma lucasanum, Terminal Phase (TP) Male. Fish caught from shore at Neuvo Guaymas, Sonora. Length: 16 cm (6.3 inches). Catch and photograph courtesy of  Isais Ruiz, San Carlos, Sonora.

Cortez Rainbow Wrasse, Thalassoma lucasanum, Terminal Phase (TP) Male. Underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2018. Photographs courtesy of Ron Woheau, Zihuantanejo.

Cortez Rainbow Wrasse, Thalassoma lucasanum. Underwater photograph taken off Km 15, Chileno Bay, Baja California Sur, February 2015. Photograph courtesy of Larry Rothblum.

Cortez Rainbow Wrasse, Thalassoma lucasanum. Underwater photo taken in coastal waters of San Agustin Bay, Huatulco, Oaxaca, January 2018. Photograph courtesy of Jason Quick, Winnipeg, Manitoba, Canada.

Cortez Rainbow Wrasse (Juveniles) Blenny mimicking a Sabertooth Blenny, Plagiotremus azaleus. Underwater photograph taken in Zihuantanejo Bay, Guerrero, February 2023. Photograph courtesy of Ron Woheau, Zihuantanejo.

The Cortez Rainbow Wrasse, Thalassoma lucasanum, is a member of the Wrasse or Labridae Family, that is known in Mexico as known collectively as arcoiris de Cortés. Globally, there are twenty-eight species in the genus Thalassoma, four of which are found in Mexican waters, one in the Atlantic and three in the Pacific Ocean.

The Cortez Rainbow Wrasse has an elongated slender compressed body with a depth that is 25% to 28% of standard length. Females and males of the Initial Phase (IP) have a striped body with a yellow stripe that runs from their eye to before the caudal fin base, a wider dark blue-green stripe that runs from the tip of their snout through the eye and into the tail, a yellow line that runs the entire length of the middle of their body, a red line that runs from their pectoral fin base into the caudal fin, and a white belly. Terminal Phase (TP) males have a dark blue head, a broad yellow bar just behind their head, a bluish tail, and a purple mid-body that transitions into a bluish caudal fin. Their pectoral fins are yellow with a blue margin. They have a small terminal mouth equipped with enlarged canine teeth at the front of both jaws (1 pair above and 1 pair below). Their anal fin has 3 spines and 11 rays; their caudal fin is concave; their dorsal fin has 8 spines and 13 rays; and, their pectoral fins have 15 rays. They are covered with large smooth scales. Their lateral line bends abruptly down behind the dorsal fin.

The Cortez Rainbow Wrasse is found in aggregations in and around rocky and coral reefs from tidal pools at depths up to 76 m (210 feet). They reach a maximum 15.0 cm (5.9 inches) in length. They feed on plankton, benthic crustaceans, and fish eggs. Juveniles are known to clean parasites from larger fish. They are abundant in the greater Los Cabos area  of Baja California Sur, within tidal pools and in intertidal waters adjacent to large coastal rocks, however, they virtually disappear when water temperatures dip below 27oC (80oF). The Cortez Rainbow Wrasse 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.

In Mexican waters the Cortez Rainbow Wrasse are found in all Mexican waters of the Pacific with the exception that they are absent from Cedros Island northward along the central and northwest coasts of Baja.

The Cortez Rainbow Wrasse is a fairly easy species to identify despite its many different colors. Males are, however, somewhat similar to the Sunset Wrasse, Thalassoma grammaticum (green head and body; light purple head stripes).

From a conservation perspective the Cortez Rainbow Wrasse is currently considered to be of Least Concern with stable, widely distributed populations. They are very small in stature and of limited interest to most. However, they can make an interesting foe on exceedingly light tackle as they are exceedingly difficult to catch. I can catch them in abundance off the beach in heavy rock structure on a Carolina rig utilizing size 10 hooks baited with cut shrimp or cut squid.