Mexican lampfish

Triphoturus mexicanus is a small lanternfish of the family Myctophidae that lives in oceanic waters of the eastern Pacific, from the epipelagic to the mesopelagic zone ^[1]. In Peru it is called pez linterna ^[1]. Larvae of its southern population, studied off northern Chile, feed by day on copepods, nauplii and other tiny planktonic organisms ^[2]. The IUCN lists it as Least Concern ^[3]. The valid name and its authority, Gilbert 1890, are recorded in WoRMS ^[4].

The dorsal fin has 13 to 16 soft rays and the anal fin 14 to 17, with no spines in either; the vertebral count is 33 to 35 ^[1]. The largest size on record is 7 cm total length ^[1].

Mitochondrial genome analyses place it as the sister species of Triphoturus nigrescens ^[5]. Off northern Chile the pigmentation of the larvae differed from that of Triphoturus mexicanus and resembled that described for the former Triphoturus oculeus larvae; an earlier study using mitochondrial DNA and pigmentation found differences between the northern and southern Pacific forms and suggested they are probably separate species, so the authors, out of caution, call them Triphoturus mexicanus affinis Triphoturus oculeus ^[2].

It occurs in the eastern Pacific from California and the Gulf of California south to Peru and Chile, between 37° N and 34° S ^[1]. It is a marine, oceanic fish of the epipelagic to mesopelagic zone ^[1].

Off the Mejillones Peninsula in northern Chile (23° S), larvae of the southern population were caught in two strata, 0 to 50 m and 50 to 150 m, and were more abundant in the shallow stratum ^[2]. The authors note that there it is among the most abundant myctophids and that adults and larvae occur through much of the year ^[2].

It is oviparous, with planktonic eggs and larvae; the estimated generation time is 1.8 years ^[1]. Lipids make up about 14.5 % of fresh weight, and wax esters account for around 82.2 % of them ^[1].

Off northern Chile, larvae of the southern population measured 2.45 to 11.87 mm, and the gut contents of 614 were examined. All those caught in the dark hours had empty guts, and the feeding incidence was 17.6 %; the smallest larva with food measured 3.4 mm ^[2]. These larvae have conical teeth ^[2].

Its estimated trophic level is 3.3 ^[1].

Larvae off northern Chile fed mainly on nauplii, copepodids and ostracods, and shared the area with Diogenichthys laternatus. The diets of the two species were similar where food was abundant and differed where it was scarce ^[2].

Mesopelagic fishes, as a group, are described as a link between plankton and larger predators in marine food webs ^[5].

The IUCN lists it as Least Concern, according to the 2018 assessment ^[3]. FishBase estimates a low vulnerability to fishing, 22 out of 100, and a high resilience ^[1].

The taxonomy of the southern Pacific populations is under discussion: they have been suggested to be a species distinct from the northern Pacific one ^[2].