The tip of South America extends almost 20° farther south than any of the other continental masses reaching the circum-Antarctic region (Briggs 1974). Both continents were connected until the early Tertiary through the Scotia Arc (Balech and Ehrlich 2008). The Antarctic Convergence, characterized by great stability, is the northern boundary of the Antarctic area; the permanent occurrence of the convergence makes the Antarctic area one of the most isolated regions of the world. At the longitude of the American continent, the Antarctic Convergence sends two branches that flow northward, one along the west coast of South America, the Humboldt Current, and the other along the east coast, the Malvinas Current. Moreover, near the American continent, at the latitude of Tierra del Fuego and Malvinas Islands, the Antarctic Convergence is more meanderous, and those meanders facilitate the water mixture (Balech and Ehrlich 2008). Because of this, the cold-temperate area of South America is strongly influenced by the Southern Ocean.

The Southern Ocean fish fauna is well known through numerous papers based on research cruises carried out by several countries (Headland 1990). On the other hand, the relationship between the ichthyofaunas of the Antarctic region and the cold-temperate waters of South America is less well known.

The aim of this work is to show the presence of Southern Ocean fishes in the Argentinian continental shelf and adjacent areas, as a contribution to the knowledge of the relationship between the Southern Ocean and South American fish faunas from the ichthyological point of view.

The specimens collected came from the cruises indicated in Table 1, carried out between 1968 and 1998 with fishing boats and research vessels, mainly with the Argentine R/V “Capitán Oca Balda” and “Dr. Eduardo L. Holmberg”, both belonging to the Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP).

Table 1 Cruises from which the species were obtained
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Species were identified on board or in the laboratory; we followed Eschmeyer (2010) for an updated taxonomy. The samples are preserved at the INIDEP Fish Collection (Copeia 1996). For each species, information was recorded as follows: catalog number; family; specific scientific name; author; year; number of specimens; size; locality (place name or latitude, longitude and depth); date; collector’s name. Size was recorded as total length and standard length.

The geographical location of the samples is shown in Fig. 1. In order to describe the distribution pattern, fish species were arranged according to two regions or categories. A: Argentine continental shelf and adjacent waters; B: mesopelagic species in the southwestern Atlantic.

Fig. 1
figure 1

Map showing the locations where Southern Ocean fishes were collected in the Argentinian continental shelf and adjacent areas. 1 Magellanic Province; 2 Argentine Province

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From the continental shelf and adjacent areas, 25 species of Southern Ocean fishes were recorded, belonging to 16 families, mainly notothenioids (families Nototheniidae, Harpagiferidae, Bathylagidae, Bathydraconidae and Channichthyiidae) (Table 2). The most interesting case is Paranotothenia magellanica, captured at 38°S in temperate waters of the Argentinian Biogeographic Province, and far from its more usual area of occurrence, the Magellanic Province (Figueroa et al. 2005). Mesopelagic fishes are represented by species of the families Microstomatidae, Stomiidae, Notosudidae, Paralepididae, Myctophidae, Melamphaidae, Melanonidae and Gempylidae (Table 2). In a description of the mesopelagic fish distribution in the southwestern Atlanctic related to water masses, those species were classified as subantarctic by Figueroa et al. (1998). The abovementioned species represent altogether 15% of the Southern Ocean ichthyofauna, according to Gon and Heemstra (1990).

Table 2 Species preserved at the INIDEP Fish Collection, arranged by families and regions
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Balech and Ehrlich (2008) mentioned the close relationship between the ichthyofauna of the Magellanic Province, corresponding to southern South America, and that of the Antarctic continent, characterized by a high endemism at the generic level and also at senior taxonomic categories.

From the comparison of the species listed in Table 2 with those mentioned by Fischer and Hureau (1985) in the FAO species identification sheets for fishery purposes, relating to the Southern Ocean, the results are as follows. Among Agnatha, two species are mentioned, Myxine australis and Geotria australis, as inhabitants of the Argentinian continental shelf. Seven species of chondrichthyans are mentioned, two of them common to both areas. The bony fishes amount to a total of 48 species in the work of Fischer and Hureau (1985), 17 of them (35.4 %) having been captured on the Argentinian continental shelf.

Gon and Heemstra (1990) edited a more detailed list of fishes of the Southern Ocean, with a total of 49 families and 273 species described. The Agnatha are the same as mentioned above; one of the four shark species and three of the seven species of skates are also mentioned for the Argentinian continental shelf and adjacent waters according to the list of Cousseau et al. (2010). Of 44 families of bony fishes mentioned in the work of Gon and Heemstra (1990), 35 (79.54%) are represented on the Argentinian continental shelf and inadjacent waters (Cousseau et al. 2010). Of a total of 260 bony fish species of the Southern Ocean, as mentioned by Gon and Heemstra (1990), 64 (24.61%), are represented on the Argentinian continental shelf and in adjacent waters (Cousseau et al. 2010).

It is interesting to remark that 9 of the families of bony fishes mentioned by Gon and Heemstra (1990), (Notacanthidae, Gonostomatidae, Sternoptychidae, Ophidiidae, Oneirodidae, Lampridae, Congiopodidae, Bovichtidae and Scombridae) are present on the Argentinian continental shelf and in adjacent waters, even though they have no species common to the Southern Ocean and the Argentinian continental shelf and adjacent waters (Menni et al. 1984).

The presence of Somniosus antarcticus on the Argentinian continental shelf and adjacent waters is detailed by Díaz de Astarloa et al. (1999).

The most interesting case of dispersion is that of the notothenids. Eastmann (1991) considered Nototheniidae the most speciose family among the notothenioids, and pointed out that its great diversification allows recognition of species of several ecological niches: pelagic, cryopelagic, benthopelagic and benthic. Figueroa et al. (2003) think that, between the Antarctic fishes, the Family Nototheniidae “could be considered as a family in expansion, exceeding all the geographic barriers that confined its Antarctic ancestral habitat, it has settled in the Patagonian shelf and slope, competing with new fish groups and searching new habitats.”