Giant Damselfish, Microspathodon dorsalis
The Giant Damselfish, Microspathodon dorsalis, whose common Spanish name is jaqueta gigante, 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 71 global members of the Microspathodon Genus of which one is found in Mexican waters of the Atlantic and two in Mexican waters of the Pacific.
The Giant Damselfish has a deep, oblong, thick, compressed body that has a depth that is 58 – 62% of standard length. They are a dark gray-blue with the head and anterior part of the body slightly lighter than the posterior part. The margins of the anal, caudal and soft dorsal fin have narrow white or light blue margins. Breeding males have very pale whitish coloration in the head and anterior part of the body. Juveniles are totally different in coloration being blue-gray with neon-blue marking on the face and fin boarders and a line of four blue spots above the lateral line. The heads are relatively small with a slanted long profile. 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 13 or 14 rays; the caudal fin is lunate; the dorsal fin is singular and continuous with 12 spines and 13 or 14 rays, and they have 18 to 20 gill rakers on the lower arch. The anal, caudal and dorsal fins have pointed filamentous rear tips. The body is covered with large rough scales. The lateral line is incomplete and ends under the end of the dorsal fin base.
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; the eggs are distributed demersal and are sticky and adhere to the substrate. They exhibit very aggressive habits when feeding or defending its territory.
Adult Giant Damselfish are an easy identification due to white or light blue margins to their anal, caudal and soft dorsal fin. This fish species 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 trailing anal, caudal and dorsal fins. The Giant Damselfish 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 Giant Damselfish are exceedingly rare and of limited interest to most. They are a classic nibbler and difficult to hook.