Longfin Damselfish

Longfin Damselfish, Stegastes diencaeus

The Longfin Damselfish, Stegastes diencaeus, whose common Spanish name is jaqueta miel, 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 Longfin Damselfish have deep oval compressed bodies with a depth that is 48 – 52% of standard length, thus similar in nature to freshwater bluegills. Adults are a blackish gray color with the snout and nape of their neck having a yellow-brown cast and the outer margin of their anal fin having a bright blue margin. Juveniles have bright blue bodies, however, their fins, snout, nape of neck, and back are gray-brown; they also have blue lines along their snout, top of their head and upper back, and a large black and blue ocellus spot at the base of the rear of their spinous dorsal fin on their upper body. Their head has a small protrusible mouth that opens in the front with a single row of teeth. Their anal fin has two spines and 13 rays; their caudal fin is bluntly forked with large rounded lobes; and their dorsal fin is singular and continuous with 12 spines and 14 to 17 rays. They have 10 or 11 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 Longfin Damselfish are found in shallow reefs within sheltered areas at depths up to 65 feet. They reach a maximum length of 12.5 cm (4.9 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 Longfin Damselfish are found in all waters of the Atlantic.

The Longfin Damselfish can be confused with a series of other Damselfish including the Beaugregory, Stegastes leucostictus (tan yellow base color), the Cocoa Damselfish, Stegastes variabilis (yellow caudal and pectoral fins), the Dusky Damselfish, Stegastes adustus (uniform reddish-brown color), and the Threespot Damselfish, Stegastes planifrons (yellow tail, body depth 56-60%).

The Longfin Damselfish are caught and retained by subsistence fishermen using nets and traps. They are classic nibblers and difficult to catch by hook and line. Being small and colorful they are used by the aquarium trade at a minor level. They are abundant and widespread with stable populations and are of limited interest to most which affords them a conservation status of Least Concern. The juveniles are consumed by the invasive Red Lionfish, Pterois volitans, but at present not at a level to effect the global population.

Longfin Damselfish, Stegastes diencaeus. Fish caught off the Anglins Pier, Lauderdale-by-the-Sea, Florida, January 2015 Length: 10.0 cm (3.9 inches). Catch and photo courtesy of George Brinkman, Guelph, Ontario, Canada.

Longfin Damselfish, Stegastes diencaeus. Fish caught from coastal waters off Key West, Florida, April 2017. Length: 11.2 cm (4.4 inches). Catch and photo courtesy of Dean Kimberly, Atlanta, GA.

Longfin Damselfish, Stegastes diencaeus. Fish caught from coastal waters off Key West, Florida, March 2017. Length: 12.5 cm (4.9 inches). Note the atypical blue spotting ventrally. Catch and photo courtesy of Dean Kimberly, Atlanta, GA.