Giant Damselfish, Microspathodon dorsalis
The Giant Damselfish, Microspathodon dorsalis, whose common Spanish name is jaqueta gigante, is a species in the family Pomacentridae, the Damselfish, known as castañetas and jaquetas in Mexico. Globally, there are only five species in the genus Microspathodon, of which three are found in Mexican waters, one in the Atlantic and two in the Pacific.
The Giant Damselfish have deep oblong thick compressed bodies with a depth that is 58 – 62% of standard length. They are dark gray-blue in color with the head and anterior part of their body slightly lighter than the posterior part. The margins of their anal, caudal, and soft dorsal fins have narrow white or light blue margins. In breeding males, the head and anterior part of the body are pale white. Juveniles are totally different in color being blue-gray with neon-blue marking on their face and fin borders and a line of four blue spots above their lateral line. Their heads are relatively small with a slanted long profile and a small protrusible mouth that opens in the front with a single row of teeth. Their anal fin has two spines and 13 or 14 rays; their caudal fin is lunate; and their dorsal fin is singular and continuous with 12 spines and 13 or 14 rays. Their anal, caudal, and dorsal fins have pointed filamentous rear tips. They have 18 to 20 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 Giant Damselfish are normally found around large boulders and rocky reefs just beyond the surge zone at depths up to 85 feet. They reach a maximum length of 38 cm (15 inches), with this maximum established by a fish in my possession. They are diurnal feeders consuming primarily algae, plankton, and benthic invertebrates. Reproduction is oviparous with pairing of individuals; eggs are distributed demersal and adhere to the substrate due to their stickiness. They exhibit very aggressive habits when feeding or defending their territory. They are found in the Pacific from Magdalena Bay south along the southwest coast of Baja, in the lower half of the Sea of Cortez, and along the coast of the mainland south to Guatemala.
The adult Giant Damselfish is easy to identify due to white or light blue margins of its anal, caudal and soft dorsal fin. It is similar in appearance to the Acapulco Major, Stegastes acapulcoensis, the Bumphead Damselfish, Microspathodon bairdii, the Cortez Damselfish, Stegastes rectifraenum, and the Silverstripe Chromis, Chromis alta, but all of the above lack the extended anal, caudal and dorsal fins.
The Giant Damselfish are exceedingly rare and of limited interest to most. They are classic nibblers, thus difficult to hook.