Cortez Damselfish, Stegastes rectifraenum

Cortez Damselfish, Stegastes rectifraenum, Juvenile. Fish caught from shore at Buena Vista, Baja California Sur, July 2019. Length: 11.1 cm (4.4 inches). Catch and photograph courtesy of  Dr. Martini Arostegui, Seattle, Washington.

Cortez Damselfish, Stegastes rectifraenum, Juvenile Transitioning To An Adult. Fish caught from shore at Km 21, Cabo Real, Baja California Sur, December 2015. Length: 12.4 cm (4.9 inches).

Cortez Damselfish, Stegastes rectifraenum. Fish caught from shore at Km 21, Cabo Real, Baja California Sur, May 2011. Length: 16.0 cm (6.3 inches). Fish identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.

Cortez Damselfish, Stegastes rectifraenum. Fish caught from shore at Las Frailes, Baja California Sur, March 2022. Length: 16.0 cm (6.3 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

Cortez Damselfish, Stegastes rectifraenum. Fish caught from shore in Acapulco, Guerrero, February 2017. Length: 16.0 cm (6.3 inches). Catch, photograph and identification courtesy of Ben Cantrell, Peoria, Illinois.

The Cortez Damselfish, Stegastes rectifraenum, is a member of the Damselfish or Pomacentridae Family, and is known in Mexico as jaqueta de Cortés. Globally, there are forty species in the genus Stegastes, of which eleven are found in Mexican waters, seven in the Atlantic and four in the Pacific Ocean.

The Cortez Damselfish has an oval compressed body that has a depth that is 51% to 55% of standard length, similar in nature to freshwater bluegills. Adults are dark brown in color and transition to lighter brown on their head with scattered paler spots on their body. Their body scales have blackish margins and their pectoral fins have yellowish margins. Juveniles are bright blue with darker scale margins and a pair of neon-blue stripes on the upper part of their head and nape. They have a black ocellated spot at the base of their spiny and soft dorsal fin junction and a small blue-edged black spot on their upper caudal fin base. Their head has a small protrusible mouth that opens in the front with a single row of teeth. Their anal fin has 2 spines and 12 to 14 rays; their caudal fin is bluntly forked; and their dorsal fin has 12 spines and 15 or 16 rays. They have 14 or 18 gill rakers on their lower arch. They are covered with rough scales. Their lateral line is incomplete and ends under the edge of their dorsal fin base.

The Cortez Damselfish is found in shallow reefs within the surge zone at depths up to 12 m (40 feet). They reach a maximum length of 16.0 cm (6.3 inches), with this maximum established by a fish that I caught (pictured above). They are diurnal feeders consuming primarily algae, benthic invertebrates and plankton. They are very aggressive with their feeding habits and when defending their territory. Reproduction is oviparous with pairing of individuals; eggs are distributed demersal and adhere to the substrate due to their stickiness. The Cortez Damselfish 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 Cortez Damselfish is a resident of all Mexican waters of the Pacific Ocean with the exception that they are absent from Guerrero Negro, Baja California, northward along the central and northwest coasts of Baja and from the northern 20% of the Sea of Cortez.

The Cortez Damselfish can easily be confused with the Acapulco Damselfish, Stegastes acapulco (front half of body lighter in color), the Beaubrummel, Stegastes flavilatus (yellow tip fins; 11 or 12 gill rakers on lower arch), the Giant Damselfish, Microspathodon dorsalis (white tipped fins), and the Whitetail Damselfish, Stegastes leucorus (yellow pectoral fin border).

From a conservation perspective the Cortez Damselfish is currently considered to be of Least Concern with stable, widely distributed populations. They are small in stature and of limited interest to most. They are classic nibblers, thus difficult to catch by hook and line.