Longfin Damselfish, Stegastes diencaeus

Longfin Damselfish, Stegastes diencaeus, Juvenile. Underwater photograph taken with coastal waters off Cozumel Island, Quintana Roo, March 2021. Photograph and identification courtesy of Marina Sutormina, Stockholm, Sweden.

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

Longfin Damselfish, Stegastes diencaeus. Fish caught off the Channel 5 Bridge (MM 71.4), Florida Keys, Florida, March 2014. Length: 10.1 cm (4.0 inches). Catch and photograph courtesy of Ryan Crutchfield, Tampa, Florida.

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

Longfin Damselfish, Stegastes diencaeus. Fish caught off the Anglin’s Fishing Pier, Lauderdale-by-the-Sea, Florida, January 2015. Length: 12.0 cm (4.7 inches). Catch, photograph and identification courtesy of Josh Leisen (joshadventures.com), Gaylord, Michigan.

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 photograph courtesy of Dean Kimberly, Atlanta, Georgia.

Longfin Damselfish, Stegastes diencaeus. Fish caught from coastal waters off Big Pine Key, Florida, July 2020. Length: 12.5 cm (4.9 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.

The Longfin Damselfish, Stegastes diencaeus, is a member of the Damselfish or Pomacentridae Family, and is known in Mexico as jaqueta miel. Globally, there are forty species in the genus Stegastes, of which eleven are found in Mexican waters, seven in the Atlantic and four in the Pacific Ocean.

The Longfin Damselfish has a deep oval compressed body that has a depth that is 48% to 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 2 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 is found in shallow reef habitats within sheltered areas at depths up to 20 m (65 feet). They reach a maximum 12.5 cm (4.9 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 Longfin 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 Longfin Damselfish is a resident of all Mexican waters of the Atlantic Ocean including the Gulf of Mexico and the east coast of the Yucatán Peninsula in the Caribbean.

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%).

From a conservation status the Longfin Damselfish is currently consider to be of Least Concern with stable, widely distributed populations. The juveniles are consumed by the invasive Red Lionfish, Pterois volitans, but at present not at a level to effect the global population. They are small in stature and of limited interest to most however they are caught and retained by subsistence fishermen utilizing 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.