Slender Suckerfish

Slender Suckerfish, Phtheirichthys lineatus

Slender Suckerfish, Phtheirichthys lineatus. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, January 2010. Length: 15.5 cm (6.1 inches). Identification courtesy of H.J. Walker, Scripps Institution of Oceanography, La Jolla, California.

The Slender Suckerfish, Phtheirichthys lineatus, is a member of the the Remora or Echeneidae Family, and is known in Mexico as rémora delgada or simply pega pega. Globally, this is only one species in the genus Phtheirichthys, this species which is found in Mexican waters of both the Atlantic and the Pacific Oceans.

The Slender Suckerfish has a very elongated body whose width is less than 10% of standard length. They are an overall dark blue color with three prominent light blue stripes along their flank. Their anal and dorsal fins are transparent and their pectoral and pelvic fins are dark; and, their caudal fin is dark brown with narrow upper and lower white margins. Their head has a convex lower and a flat upper profile with mid-sized black eyes and a short disc that is 20% to 22% of standard length and reaches the center of the pectoral fins with 9 to 11 lamellae. They have 1 to 3 gill rakers above and 14 to 17 below. Their lower jaw is projecting and their mouth is oblique with numerous small pointed teeth. Their anal and dorsal fins are of similar size and shape with very long bases that are approximately 3 times longer than the length of the head; their caudal fin margin is “W” shaped; their pectoral fins are pointed; and their pelvic fins are joined to the belly.

The Slender Suckerfish is an oceanic pelagic fish that either travel attached to their hosts (large dead fish, slow moving fish, slow moving sharks, and turtles) or are free swimming. Due to their small disc, they are not as strongly host-dependent as the other Remoras for feeding and are known to consume planktonic crustaceans. They are normally found very close to the surface and range to depths up to 330 feet. They reach a maximum of 76 cm (2 feet 6 inches) in length. The Slender Suckerfish is poorly studied and very little is known about the behavioral paterns as they require fast moving water for survival, making study in captivity difficult.

The Slender Suckerfish is a resident of all Mexican waters of the Pacific Oceans with the exception that in the Pacific they are absent from the northern 20% of the Sea of Cortez. They are more common in southern waters.

The Slender Suckerfish is an easy fish to identify due to its lamellae count and the stripes along its flank. It is, however, somewhat similar to the Whitefin Sharksucker, Echeneis neucratoides (18 to 28 disc plates, wide white bars on flanks).

From a conservation perspective the Slender Suckerfish is currently considered to be of Least Concern with stable, widely distributed populations. They are seldom encountered by humans and are of limited interest to most. They are most definitely a “catch-and-release”.