Cortez Damselfish, Stegastes rectifraenum
The Cortez Damselfish, Stegastes rectifraenum, whose common Spanish name is jaqueta de Cortés, is a species in the family Pomacentridae, the Damselfish, which are known as castañetas and jaquetas in Mexico. This fish is also known as Beaubrummel Major. 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.
The Cortez Damselfish have oval compressed bodies with a depth that is 51 – 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 two spines and 12 to 14 rays; their caudal fin is bluntly forked; and their dorsal fin is singular and continuous with 12 spines and 15 or 16 rays. They have 14 or 18 gill rakers on their lower arch. Their lateral line is incomplete and ends under the edge of their dorsal fin base. Their body is covered with large rough scales.
The Cortez Damselfish are found in shallow reefs within the surge zone at depths up to 40 feet but normally at depths of less than 50 feet. They reach a maximum length of 16.0 cm (6.3 inches), with this maximum established by a fish that I caught (pictured below). They are diurnal feeders consuming primarily algae, plankton, and benthic invertebrates. 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. They are found in all Mexican waters of the Pacific with the exception of north of Guerrero Negro on the northwest coast of Baja and in 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).
The Cortez Damselfish are small and of limited interest to most. They are classic nibblers, thus difficult to catch by hook and line.