California smoothtongue

Leuroglossus stilbius is a small pelagic fish of the family Bathylagidae that lives from the surface down into deep water and reaches about 20 cm in total length ^[1]. Its range covers the eastern Pacific from Washington State to Peru, including the Gulf of California ^[1].

Off Peru, its larvae turned up in plankton samples from an IMARPE cruise between Punta Sal and Ilo in the summer of 2020 ^[2].

The checklist of fishes of the North American Pacific coast places the species from Washington to Peru, the Gulf of California included, and describes it as epipelagic to mesopelagic; it gathers records from the surface (at night, with lights) to perhaps 3824 m depth ^[1]. Chilean records attributed to a subspecies urotranus are now treated as Leuroglossus urotranus, and Alaskan specimens in a university collection belong to Leuroglossus schmidti ^[1].

From 26 May to 7 June 1986, off the west coast of Baja California Sur, Mexico, larvae turned up at 13 of 58 stations, in water with a mean temperature between 12.1 and 17.4 °C that the authors consider modified California Current water ^[3].

In Peru, the summer 2020 hydroacoustic survey, which covered Punta Sal (3°S) to Ilo (18°S), recorded larvae in the northern and southern zones of the coast; in the north they were found from Talara to Malabrigo ^[2].

The larvae of this species measure between 4.0 and 21.0 mm standard length, the smaller ones predominating, with a peak at 6.0 mm, in the May–June 1986 sampling off Baja California Sur ^[3]. The authors recall that in the CalCOFI surveys of 1955–1960 off California and Baja California the larvae were caught in great abundance between January and May ^[3].

In a 24-hour sampling off central California between 16 April and 4 May 1989, 40 individuals in early life stages were collected with an opening-closing net: 5 in preflexion, 3 in flexion, 19 in postflexion, 13 in transformation and none as juveniles ^[4]. Bathylagid larvae as a group were centred somewhat deeper by day and closer to the surface at night; the paper also counts it among species considered daily vertical migrators in their juvenile and adult phases ^[4].

Where the larvae were caught in Baja California Sur, the dominant copepods were Calanus pacificus, Pleuromamma abdominalis and Rhincalanus nasutus; the authors note that two of them are herbivores and one an omnivore, and that this could place pressure on the larvae for food ^[3].

Off central California, Leuroglossus stilbius was the third most abundant mesopelagic species among early life stages, with 40 individuals out of 726 mesopelagic larvae and juveniles ^[4].

A study of the diet of the jumbo squid Dosidicus gigas off the Peruvian coast in 2015–2019, based on 954 stomachs analysed, found remains of the genus Leuroglossus in 4.82 % of the stomachs with food, without resolving the species ^[5].

The Peruvian data come from a hydroacoustic survey of pelagic resources carried out in February and March 2020 between Punta Sal and Ilo. There the larvae of Leuroglossus stilbius were present at 19 plankton stations, 7.4 % of the 258 stations, at 3 to 138 individuals per m² ^[2]. These are plankton-net records from a research vessel, not direct observations ^[2].