Threespot Damselfish

Threespot Damselfish, Stegastes planifrons

The Threespot Damselfish, Stegastes planifrons, whose common Spanish name is jaqueta de tres puntos, is a species in the Damselfish or Pomacentridae Family, known collectively as castañetas and jaquetas in Mexico. Globally, there are forty species in the genus Stegastes, eleven of which are found in Mexican waters, seven in the Atlantic and four in the Pacific.

The Threespot Damselfish have deep oval compressed bodies with a depth that is 45 to 49% of standard length, thus similar in nature to freshwater bluegills. Adults are gray-brown with their lower head and lower body being tan in color. They have three distinct black spots with thin blue rims (after which they are named): the first at the base of their dorsal fin between the spines and the rays; the second on top of their caudal fin peduncle; and the third at the base of their pectoral fin. Their head and upper body have a few tiny blue spots and the top of their eyes is yellow. Juveniles have a bright yellow body, bright yellow fins, and a large black spot at the base of their dorsal fin under the last spines. They also have a smaller black spot on their upper caudal fin base. Their head has a small protrusible mouth that opens in the front with a single row of long and close-set incisor teeth. They have serrated gill covers. 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 to 17 rays. Their anal and dorsal fins are long, extend past the tail base, and have large rounded lobes. They have 8 or 9 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 Threespot Damselfish are found demersal in shallow reefs at depths up to 100 feet. They prefer staghorn coral and take shelter in caves at night. They reach a maximum length of 12.5 cm (4.9 inches). They are diurnal feeders consuming primarily algae, plankton, and benthic invertebrates. They are very aggressive with their feeding habits and when defending their territory. Reproduction is oviparous with pairing of individuals. Eggs are distributed demersal adhering to the substrate due to their stickiness and are guarded by the males. Very little is known about their behavioral patterns.

In Mexican waters the Threespot Damselfish are found in all waters of the Atlantic.

The Threespot Damselfish can easily be confused with the Cocoa Damselfish, Stegastes variabilis (yellow anal, caudal, and pectoral fins) and the Longfin Damselfish, Stegastes diencaeus (anal fin with blue margin).

The Threespot Damselfish are small, poorly documented, and poorly studied fish, and of limited interest to most. They are classic nibblers, thus difficult to catch by hook and line. They are sold on a very limited basis by the aquarium trade.

Threespot Damselfish, Stegastes planifrons. Fish caught off the Channel 5 Bridge (MM 71.4), Florida Keys, Florida, December 2015. Length: 12 cm (4.7 inches). Catch, photo and identification courtesy of George Brinkman, Guelph, Ontario, Canada.