Bumphead Damselfish, Microspathodon bairdii
Bumphead Damselfish, Microspathodon bairdii, Juvenile. Fish collected from a tidal pool Km 17, El Tule, Baja California Sur, January 2016. Length: 4.2 cm (1.7 inches).
Bumphead Damselfish, Microspathodon bairdii, Juvenile. Fish caught from coastal waters off Acapulco, Guerrero, January 2018. Length: 20 cm (7.9 inches). Catch, photograph, and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.
Bumphead Damselfish, Microspathodon bairdii. Fish caught from shore at Km 21, Cabo Real, Baja California Sur, April 2010. Length: 28 cm (11 inches). This fish was disproportionately heavy for its length.
Bumphead Damselfish, Microspathodon bairdii. Underwater photograph taken in coastal waters of the greater Los Cabos area, Baja California Sur, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah.
Bumphead Damselfish, Microspathodon bairdii. Underwater photographs taken in Zihuantanejo Bay, Guerrero, December 2021 and December 2022. Photographs courtesy of Ron Woheau, Zihuantanejo.
The Bumphead Damselfish, Microspathodon bairdii, is a member of the Damselfish or Pomacentridae Family, and is known in Mexico as jaqueta vistosa. 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 Bumphead Damselfish has a deep oblong thick compressed body that has a depth that is 56% to 60% of standard length. They are generally dusky gray-brown in color with their pectoral and pelvic fins having a golden brown hue. The iris of their eyes is bright blue and some fish have whitish or yellowish heads. Juveniles have a totally different coloration being bright blue on their upper half and orange on their lower half. Their head has a pronounced bump (pictured below) after which they are named, 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 bluntly forked; and their dorsal fin is singular and continuous with 12 spines and 15 or 16 rays. They have 17 to 21 gill rakers on their lower arch. Their body is covered with large rough scales. Their lateral line is incomplete and ends under the edge of their dorsal fin base.
The Bumphead Damselfish is normally found in shallow water within rocky shores at depths up to 20 m (65 feet). They reach a maximum of 31 cm (12 inches) in length. 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. The Bumphead 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 Bumphead Damselfish is a resident of Mexican waters of the Pacific Ocean but has a limited distribution being found from Todos Santos, 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. There are reports of a small colony living in coastal waters of Empalme, Sonora, in the northeast section of the Sea of Cortez.
The adult Bumphead Damselfish is easy to identify due to the large bump on its forehead; younger fish can be confused with the Beaubrummel, Stegastes flavilatus (yellow fin tips) and the Giant Damselfish, Microspathodon dorsalis (straight head profile; white anal, caudal, and dorsal fin tips).
From a conservation perspective the Bumphead Damselfish is currently considered to be of Least Concern with stable, widely distributed populations. They are rare and relatively small in stature and of limited interest to most. They are classic nibblers, thus exceedingly difficult to hook.