Cortez Rainbow Wrasse, Thalassoma lucasanum
The Cortez Rainbow Wrasse, Thalassoma lucasanum, whose common Spanish name is arcoiris de Cortés, is a member of the Wrasse or Labridae Family, known collectively as doncellas, señoritas, and viejas in Mexico. 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.
The Cortez Rainbow Wrasses have elongated slender compressed bodies 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 (one pair above and one pair below). Their caudal fin is concave and their dorsal fin has 8 spines and 13 rays.
The Cortez Rainbow Wrasses are found in aggregations in and around rocky and coral reefs from tidal pools at depths up to 210 feet. They reach a maximum length of 15.0 cm (5.9 inches). 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 within tidal pools and in intertidal waters adjacent to large coastal rocks, however, they virtually disappear when water temperatures dip below 27oC (80oF). They are a small and poorly studied species and very little is known about their behavioral patterns.
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).
The Cortez Rainbow Wrasses are too rare and too small to be of interest to most. However, they can make an interesting foe on exceedingly light tackle. I catch them in abundance off the beach in heavy rock structure on a Carolina rig utilizing size 8 or size 10 hooks baited with cut shrimp or cut squid. They are easily caught during surf fishing in the greater Los Cabos area during warm water periods and are most definitely a “catch and release”.
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 photo courtesy of Isais Ruiz, San Carlos, Sonora.