Additional Data on Arctozenus australis Ho et Duhamel, 2019 (Pisces: Aulopiformes, Paralepididae) off Kerguelen Islands

Introduction

When checking the ZIN collection, the author found several specimens of Arctozenus caught on the shelf of the Kerguelen Archipelago in the Southern Ocean, identified as Arctozenus risso confer (Bonaparte, 1840). Upon closer examination, the fish were identified as the recently described species Arctozenus australis Ho, et al. [1]. This article is intended to slightly alleviate the lack of published data on this species, known so far only from the Kerguelen shelf.

Now, only the above two species are known to belong to the genus Arctozenus Gill, 1864, although there is information that Arctozenus risso may consist of two cryptic species from different oceans, the Pacific and Atlantic [2].

Materials and Methods

Examined material: ZIN 56771, 6 specimens SL 258–278 mm, NW off Kerguelen 46°52’S-67°53’E, RV Skif, cruise 3, trawl No. 110, station 1069/158, depth 340–354 m, 02 Jan. 1971 3:00 – 5:30 AM, collector A.F. Pushkin.

Measurements follow Ho et Duhamel [1].

The counting of the predorsal and preanal vertebrae was carried out to the first rays of the fin, and not to the corresponding pterygiophores, which are located 1–3 and 4–6 vertebrae rostrally, respectively (Figure 1). The caudal fin formula is written as upper procurrent rays + principal rays + lower procurrent rays. Isobaths are drawn Figure 2 according to the General Bathymetric Chart of the Oceans (GEBCO), Mercator projection [3].

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Results and Discussion

Fish have been identified as Arctozenus australis according to the description in Ho and Duhamel [1]. Anterior lateral-line scales long; origin of pelvic fin slightly behind dorsal-fin base (Figure 1A); body depth 5.7–6.3 %SL (Table 1); a slender head, its depth at middle of eye 4.1‒4.5 in HL; the ratio of snout length/eye diameter 3.3–3.6. Some questions remain about the presence of teeth in adult Alepisauroids [1, 4, 5] so it is important to mention that all examined specimens have well-developed teeth on the jaws.

Ho, et al. [1] examined a similar size group when describing A. australis, so the data presented here should not be considered a manifestation of allometry. Limit values for predorsal length, prepelvic length, preanal length, D–A, head depth have shifted upwards compared to the original description; D–V values have expanded in both directions; interorbital width, caudal-peduncle depth, snout length, upper-jaw length, and lower jaw (in % HL) expanded downwards. Of the counting parameters, in two cases a smaller number of caudal vertebrae and in one case a greater number of preanal vertebrae were noted, the same fish had a reduced number of anal fin rays (Table 2).

Table 1 (Continuation): Morphometric data of examined Arctozenus australis specimens and of *Ho and Duhamel [1] material. Data in bold is slightly outside the original description.

The presented data do not contradict the data of Ho and Duhamel but expand the known parameter values of the species. Despite the shifted limit of the head height values towards A. risso, the head height in A. australis is still notably slender (19.6–24.4 vs 24.5–28.9 of A. risso [1]). Location and conditions of capture correspond well to previously published data (Figure 2). There is no doubt that A. australis can be caught all around the Kerguelen Archipelago on the continental slope.

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Funding

The study was supported by the State Research Program number 122031100285-3.

Acknowledgments

This research was performed using the equipment of the Core Facilities Centre “Taxon” at the Zoological Institute Russian Academy of Sciences (St Petersburg, Russia).