Bumphead Damselfish, Microspathodon bairdii
The Bumphead Damselfish, Microspathodon bairdii, whose common Spanish name is jaqueta vistosa, is a species in the Damselfish or Pomacentridae Family, known collectively as castañetas and jaquetas in Mexico. Globally, there are only five species in the genus Microspathodon, three of which are found in Mexican waters, one in the Atlantic and two in the Pacific.
The Bumphead Damselfish have deep oblong thick compressed bodies with a depth that is 56 – 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 two 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 lateral line is incomplete and ends under the edge of their dorsal fin base. Their body is covered with large rough scales.
The Bumphead Damselfish are normally found in shallow water within rocky shores at depths up to 65 feet. They reach a maximum length of 31 cm (12 inches). 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.
In Mexican waters the Bumphead Damselfish have a limited distribution being found from Todos Santos 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 adjacent to 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).
The Bumphead Damselfish are exceedingly rare and of limited interest to most. They are classic nibblers, thus difficult to hook.
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).