Whitetail Damselfish, Stegastes leucorus
The Whitetail Damselfish, Stegastes leucorus, whose common Spanish name is jaqueta rabo blanco, 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 Whitetail Damselfish have oval compressed bodies with a depth that is 42 to 46% of standard length, thus similar in nature to freshwater bluegills. The adults have deeper bodies than the juveniles. Adults are dark brown in color with darker outlines on their scales. Most adults have a subtle white band on their caudal fin after which they are named. The iris of their eyes is blue. They have a narrow blue band on the margin of their anal fin (a key to the identification) and a white margin on their pectoral fins. Juveniles are dark with an olive-green tinge and have a dark ocellus at the rear base of their dorsal fin and a broad white bar across their caudal base. Their head has a small protrusible mouth that opens in the front with a single row of long and closely set teeth. Their anal fin has two spines and 12 or 13 rays; their caudal fin is bluntly forked; and their dorsal fin is singular and continuous with 12 spines and 14 to 16 rays. They have 10 to 12 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 Whitetail Damselfish are found in shallow reefs within the surge zone at depths up to 60 feet. They reach a maximum length of 17.0 cm (6.7 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 and adhere to the substrate due to their stickiness. They are a poorly studied species and very little is known about their behavioral patterns.
In Mexican waters the Whitetail Damselfish have a limited and poorly documented range being found only along the extreme northwest coast of Baja, around the southeast tip of Baja, and in and around the greater Mazatlán area. The second photo below extends the known range for this species.
The Whitetail can easily be confused with the Acapulco Damselfish, Stegastes acapulcoensis (front half of body lighter in color), the Beaubrummel, Stegastes flavilatus (yellow tip fins; 11 or 12 gill rakers on lower arch), and the Cortez Damselfish, Stegastes rectifraenum (white tip fins).
The Whitetail Damselfish are small, poorly documented, and poorly studied, therefore of limited interest to most. They are classic nibblers, thus difficult to catch by hook and line.
Whitetail Damselfish, Stegastes leucorus. Fish caught out of a tidal pool from coastal waters of Mazatlán, Sonora, April 2015. Length: 6.4 cm (2.5 inches). Catch and photo courtesy of George Brinkman, Guelph, Ontario, Canada.
Whitetail Damselfish, Stegastes leucorus. Fish caught from coastal waters off Acapulco, Guerrero, February 2017. Length: 12.8 cm (5.0 inches). Catch and photo courtesy of Ben Cantrell, Peoria, IL.