California Smoothtongue, Leuroglossus stilbius

California Smoothtongue, Leuroglossus stilbius. Fish collected in a deep water trawl net off Point Loma, California, August 2010. Length: 10.5 cm (4.1 inches). Collection and identification courtesy of H.J. Walker, Jr., Scripps Institution of Oceanography, La Jolla, California.

The California Smoothtongue, Leuroglossus stilbius, is a member of the Pencilsmelt or Microstomatidae Family, and is known in Mexico as lengualisa californiana and peces boquita. Their common name is derived from their relative absence of teeth. Globally, there are three species in the genus Leuroglossus with the species described herein being the only one found in Mexican waters of the Pacific Ocean.

The California Smoothtongue has a slender and laterally compressed body that tapers to toward the tail that has a wide base, with a depth that is 20% to 22% of standard length. They are silvery to brassy in color being darker ventrally and having pale to transparent fins. Their head has a pointed snout that is greater in length than their eye diameter. Their anal fin has 11 to 14 rays; their caudal fin is deeply forked; their dorsal fin is set well back on the body and has 9 to 12 rays; their small pectoral fins are located ventrally and have 8 or 9 rays; and, their pelvic fins have 8 to 10 rays. They have 21 to 26 gill rakers.

The California Smoothtongue is a bathypelagic species that is found from the surface to depths up to 854 m (2,800 feet). They reach a maximum of 17.2 cm (6.8 inches) in length. They are vertical migrators that move to the surface at night to feed and return to the ocean depths for protection during the day. They consume copepods, larvaceans, ostracods, salps, and fish eggs. In turn they provide a valuable food source for a wide variety of marine life including birds, dolphins, the Humboldt Squid, sea lions, and numerous fish. They have a double-chambered stomach, the first chamber having a lining with a black pigment that prevents the light from digested luminescent prey from being visible from the exterior. Reproduction is oviparous with planktonic eggs and larvae. They have lifespans of five 5 years. The California Smoothtongue 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 California Smoothtongue is a resident of all Mexican waters of the Pacific with the exception that they are absent from along the coast of the mainland south to Guatemala.

The California Smoothtongue is straightforward to identify and cannot be confused with any other species.

From a conservation perspective the California Smoothtongue is currently considered to be of Least Concern with stable, widely distributed populations. They are a small and very deep-water species that are abundant but seldom seen by humans and of limited interest to most.