Cortez Damselfish, Stegastes rectifraenum
The Cortez Damselfish, Stegastes rectifraenum, whose common Spanish name is jaqueta de Cortés, is a member of a group of small, very colorful reef fishes found throughout the subtropical and tropical regions of the world’s oceans and is a member of the Damselfish or Pomacentridae Family, known collectively as castañetas and jaquetas in Mexico. There are 40 global members of the Stegastes Genus of which seven are found in Mexican waters of the Atlantic and four in Mexican waters of the Pacific.
The Cortez Damselfish has an oval, compressed body that has a depth that is 51 to 55% of standard length, similar in nature to a freshwater bluegill. The adults are dark brown grading to lighter brown on the head with scattered paler spots on the body. The body scales have blackish margins and the 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 the head and nape. They have a black ocellated spot at the base of the spiny and soft dorsal fin junction and a small blue-edged black spot on the upper caudal fin base. The head has a small protrusible mouth that opens in the front with a single row of teeth. The anal fin has two spines and 12 to 14 rays; the caudal fin is bluntly forked; the dorsal fin is singular and continuous with 12 spines and 15 or 16 rays, and they have 14 or 18 gill rakers on the lower arch. The body is covered with large rough scales. The lateral line is incomplete and ends under the end of the dorsal fin base.
The Cortez Damselfish is 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 which is photographed below. They are diurnal feeders consuming primarily algae, plankton and benthic invertebrates. They are very aggressive in its feeding habits and when defending its territory. Reproduction is oviparous with pairing of individuals; the eggs are distributed demersal and are sticky and adhere to the substrate.
The Cortez Damselfsih can easily be confused with the Acapulco Damselfish, Stegastes acapulco (front half of body is lighter in color), the Beaubrummel, Stegastes flavilatus (yellow tip fins, 11 or 12 gill rakers on the lower arch), the Giant Damselfish, Microspathodon dorsalis (white tipped fins), and the Whitetail Damselfish, Stegastes leucorus (yellow pectoral fin boarder).
The Cortez Damselfish are found in all Mexican waters of the Pacific with the exception that they are absent from north of Guerrero Negro on the northwest coast of Baja and in the northern 20% of the Sea of Cortez.
The Cortez Damselfish is small and of limited interest to most. They are a classic nibbler and difficult to catch by hook and line.