Giant Damselfish

Giant Damselfish, Microspathodon dorsalis

Giant Damselfish, Microspathodon dorsalis, Juveniles. Underwater photographs taken in Zihuantanejo Bay, Guerrero, March 2018. Photographs courtesy of Ron Woheau, Zihuantanejo.

Giant Damselfish, Microspathodon dorsalis, Juvenile. Fish caught from coastal waters off Mazatlán, Sinaloa, October 2017. Length 10.9 cm (4.3 inches). Catch, photograph and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.

Giant Damselfish, Microspathodon dorsalis, Juvenile. Fish caught out of a tidal pool from coastal waters off Mazatlán, Sinaloa, April 2015. Length: 11.4 cm (4.5 inches). Catch and photograph courtesy of George Brinkman, Guelph, Ontario, Canada.

Giant Damselfish, Microspathodon dorsalis, Juvenile. Fish collected from a tidal pool, 8 km north of Puerto Los Cabos, Baja California Sur, January 2004. Length: 7.4 cm (2.9 inches). First photo was taken immediately on location; second photo was taken a few hours later. Collection made by Dr. Mike Browning, Denver. Identification courtesy Dr. Ross Robertson, Smithsonian Institute, Panama.

 

Giant Damselfish, Microspathodon dorsalis. Fish caught off the beach at Cabo Real, Baja California Sur, July 2021. Length: 19 cm (7.5 inches). Note the white margins of the caudal fin.

Giant Damselfish, Microspathodon dorsalis. Fish caught from coastal waters off Mazatlán, Sinaloa, October 2021. Length: 23 cm (9.1 inches). Catch, photograph and identification courtesy of Bart, The Netherlands  (worldangler.eu).

Giant Damselfish, Microspathodon dorsalis, Breeding Male. Underwater photograph taken in Zihuantanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.

Giant Damselfish, Microspathodon dorsalis. Underwater photograph taken in Zihuantanejo Bay, Guerrero, March 2018. Photograph courtesy of Ron Woheau, Zihuantanejo.

Giant Damselfish, Microspathodon dorsalis. Underwater photograph taken in coastal waters of the greater Los Cabos area, Baja California Sur, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah.

The Giant Damselfish, Microspathodon dorsalis, is a member of the Damselfish or Pomacentridae Family, and is known in Mexico as jaqueta gigante. Globally, there are five species in the genus Microspathodon, of which three are found in Mexican waters, one in the Atlantic and two in the Pacific Ocean.

The Giant Damselfish has a deep oblong thick compressed body that has a depth that is 58% to 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 2 spines and 13 or 14 rays; their caudal fin is lunate; and their dorsal fin has 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 body is covered with large scales. Their lateral line is incomplete and ends under the edge of their dorsal fin base.

The Giant Damselfish is normally found around large boulders and rocky reefs just beyond the surge zone at depths up to 26 m (85 feet). They reach a maximum of 38 cm (15 inches) in length, with this maximum established by a fish in my possession. They are diurnal feeders consuming primarily algae, benthic invertebrates and plankton. 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. The Giant 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 Giant Damselfish is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Magdalena Bay, Baja California Sur, southward 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 Damselfish, 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.

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