Glassy Sweeper, Pempheris schomburgkii
Glassy Sweeper, Pempheris schomburgkii. Underwater photographs taken in the coastal waters off Akumal, Quintano Roo, December 2020. Photographs and identification courtesy of Bob Hillis, Ivins, Utah.
Glassy Sweeper, Pempheris schomburgkii. Fish caught from coastal waters off Ft. Lauderdale, Florida, March 2022. Length: 11 cm (4.3 inches). Catch, photograph and identification courtesy of Dominick Porcelli, Lighthouse Point, Florida.
Glassy Sweeper, Pempheris schomburgkii. Fish caught from coastal waters off Big Pine Key, Florida, April 2019. Length: 14 cm (5.5 inches). Catch, photograph and identification courtesy of Luke Ovgard, Klamath Falls, Oregon.
The Glassy Sweeper, Pempheris schomburgkii, is a member of the Sweepers or Pempheridae Family that is also known as the Copper Sweeper, and in Mexico as barrendero transparente. Globally, there are two species in the genus Pempheris, both of which are found in Mexican waters of the Atlantic Ocean.
The Glassy Sweeper has an oblong very deep high compressed body. They are a coppery red to olive color with a silver sheen dorsally and a dark band along the base of the anal fin. Juveniles are transparent that the background is visible. Their upper head profile is oblique; their dorsal profile is horizontal and they have a keel on their chest before the pelvic fins; and, their ventral profile is deeply curved in front of the anal fin, tapering upward to a slender peduncle. Their head has a disproportionately large eye, a very short snout and a mid-sized mouth that is strongly oblique and opens upward and is equipped with small teeth. Their anal fin has 3 spines and 31 to 34 rays and a long base; their caudal fin is forked; their dorsal fin has 4 to 6 weak spines and 8 or 9 rays and a short base and originates before the anal fin; and, their pectoral fins have 15 to 18 rays and are long and pointed. They have numerous long gill rakers. They are covered with rough scales. They have a complete lateral line that has a high arch along the back and extends almost to the tips of the central caudal fin rays.
The Glassy Sweepers are found in large schools within clear water coral and rocky reefs at depths up to 30 m (100 feet). They reach a maximum of 15 cm (5.9 inches) in length. They are a nocturnal species that take refuge diurnally in caves, under ledges or among dense branching coral. They emerge at night in large schools and forage for zooplankton, and especially the larval stages of invertebrates, in small groups, pairs or as solitary individuals. The Glassy Sweeper 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 Glassy Sweeper 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 with the exception that they are absent from north of Tuxpan, Veracruz within the northwest portion of the Gulf of Mexico.
The Glassy Sweeper can be confused with the Curved or Shortfin Sweeper, Pempheris poeyi (found only along the east coast of the Yucatán Peninsula; pale yellow brown, anal fin 22-26 rays).
From a conservation perspective the Glassy Sweeper is currently considered to be of Least Concern with stable widely distributed populations. They are known to be a component of the diet of the newly introduced Red Lionfish, Pterois volitrans. They are small in stature and of limited interest to most. They have obtained attention from the scientific community in that they are a nocturnal species that will leave their hiding locations during daylight hours risking predation to obtain cleaning of plankton from the Noronha Wrasse, Thalassoma noronhanum.