Early life history traits of the blackfin notothen, Trematomus scotti, were investigated through otolith microincrement pattern and stomach content analyses. Post-larval specimens of 12–20 mm standard length (SL) were collected in the Bransfield Strait and adjacent waters during the 2010–11 summer. Catches were unevenly distributed across the surveyed area, yielding a relative abundance of 0.3–3.6 specimens per 1000 m3 of filtered sea water. Age estimates ranged from 34 to 67 days, with good consistency and no apparent bias between readings. Based on an exponential model fitted to the age-length dataset, the growth rate was 0.17 mm day-1, corresponding to a daily percentage increment in size of 1.07% SL. In agreement with previous studies, larval hatching occurred at a mean size of 9.0 mm and was spread over a relatively short period, lasting from late December to late January. Prey composition consisted exclusively of copepods, mainly larval stages of copepodites. Feeding intensity ranged from 1–14 prey items per stomach, being positively correlated with larval fish size. In summary, T. scotti shares a common early life history strategy with several other notothenioids, consisting of small larvae hatching in summer and overwintering as pelagic early juveniles until the following summer season.

During the research programme conducted on the OV Puerto Deseado in the summers of 2011 and 2013, 36 stations were sampled using a demersal net at depths between 53–590 m in the Antarctic Peninsula and South Shetland Islands. A total 3378 fish specimens belonging to 36 species were recorded. Notothenidae was the best-represented family in species number, with Lepidonotothen nudifrons, L. larseni and Trematomus scotti being the most numerous species. Of the fish assemblages, 20% of the species were considered as dominant, 10% as common, 13% as occasional and 57% as rare. Six groups (and two sub-groups) were obtained by the ordination diagram based on geographical location: group 1=Gerlache Strait, group 2=Deception Islands, group 3=Biscoe Island, group 4=between Elephant and King George islands, group 5=northern Antarctic Peninsula, and group 6=South Shetland Islands, with sub-groups 6a shallower South Shetland Islands and 6b deeper South Shetland Islands. Sampling depth and water temperature significantly explained the spatial pattern. A latitudinal pattern of decreasing abundance from north-east to south-west was found in L. larseni and the opposite in T. scotti. The predictability of fish composition in the assemblages’ areas could be a useful tool for ecosystem-based management.

New information on the biology and ecology of an abundant ‘rockcod’ species, Lepidonotothen squamifrons (family: Nototheniidae), found at South Georgia is presented. Data collected from twenty demersal trawl surveys carried out at South Georgia and Shag Rocks (sub-Antarctic) from 1986–2012 were analysed to investigate distribution, size, maturity and diet. Distribution was patchy with large aggregations in consistent high-density ‘hotspots’ to the east of Shag Rocks and to the west of South Georgia. Fish density was shown to vary between regions of the shelf and between years but there was little evidence of significant changes in catch per unit effort (CPUE) over the duration of the study. Length at first maturity for males and females (37–38 cm, total length) was very similar to that described for the Indian Ocean population. Detailed stomach contents analysis (2005–12) indicated a varied diet dominated by salps/tunicates, but with ontogenetic and depth variations in prey composition. Lepidonotothen squamifrons was shown to be an opportunistic bentho-pelagic forager. Enhanced knowledge of the ecology of L. squamifrons will be valuable in future research on food web modelling and marine spatial management in the Southern Ocean and to provide baseline data on the ecology of the species in a rapidly changing environment.

This study is based on the analysis of the stomach content and the morphology and morphometry of the three pairs of otoliths (sagitta, asteriscus and lapillus) of Lepidonotothen larseni (Lönnberg) collected at the South Shetland Islands and Antarctic Peninsula during summer, in order to find possible relationships between ontogenetic change of sagittal otolith shape and feeding ecology. Length-weight relationship resulted in a positive allometric growth, with juveniles and adults in good nutritional condition (Le Cren condition index > 1), and with a decreasing trend from noon to late evening of the stomach repletion index. The stomach content consisted of several prey, with copepods and amphipods more frequent and abundant in juveniles, whereas euphausiids were in adults. The morphometric analysis of otoliths enabled us to relate different measurements with fish size, and those contributing mostly to separate juveniles from adults were the otolith and rostrum length and their percentage (R index). Juveniles proportionally showed a shorter and wider sagitta than adults reflected in a major E index because of a rounded shape and a minor R index because of a less developed rostrum. This pattern can be tentatively linked to the different habitat of juveniles and adults of this species, being respectively pelagic and epibenthic, as also evidenced by the ontogenetic change of feeding habits.

The nototheniid Pleuragramma antarcticum (Boulenger, 1902), is the dominant pelagic fish in waters of the continental shelf in High Antarctic regions. Larvae and juveniles of this species comprise the majority of ichthyoplankton at many locations around Antarctica including the Weddell Sea and the western Ross Sea, where it may amount to 98% of the ichthyoplankton. Its life cycle has been the subject of a number of studies but spawning and embryological development are still uncertain. Eggs with embryos and newly hatched larvae of P. antarcticum were collected in November 2002 near the Italian Antarctic station at Terra Nova Bay through holes drilled in the sea ice. Eggs and yolk-sac larvae were floating among the platelet ice below the solid cap of congelation ice. Eggs were 2.2–2.5 mm in diameter and contained embryos at an advanced stage of development. Hatching occurred from mid-November onwards, and newly hatched larvae averaged 9.3 mm SL. This paper provides the detailed description of embryos and newly hatched larvae in terms of pigmentation pattern and morphometric characteristics, thus allowing a significant advance in our understanding of the early life history of P. antarcticum in the Ross Sea, and extending the knowledge of the life cycle of this key Antarctic species.

The demersal fish fauna of the southern and eastern Weddell Sea is described. The following species were recorded for the first time in this area: Aethotaxis mitopteryx, Bathyraja eatoni, B. Maccaini, B. sp2 (FAO-list), Bathydraco marri, Dissostichus mawsoni, Macrourus holotrachys, Muraenolepis sp., Notothenia coriiceps, Notothenia kempi, Psilodraco spec. and Trematomus nicolai. In terms of biomass the dominant species on the very narrow eastern continental shelf were Chionodraco myersi (49%), Trematomus eulepidotus (11%), C. hamatus (7%), T. lepidorhinus (6%), Pagetopsis maculatus (5%) and T. scotti, Cryodraco antarcticus, Cygnodraco mawsoni and Pleuragramma antarcticum (4% each). The highest density of individuals and greatest biomass was found between 400 and 650 m water depth. Here, C. myersi, T. eulepidotus and T. lepidorhinus dominated the catches. The shallow shelf area was inhabited by smaller species such as T. scotti, T. centronotus, P. maculatus, Artedidraco skottsbergii, A. shackletoni, and Prionodraco evansii. In the southern Weddell Sea Akarotaxis nudiceps, Dolloidraco longedorsalis, Gerlachea australis, Pleuragramma antarcticum, and Trematomus loennbergi were dominant. Members of the Channichthyidae occurred only occasionally, most of these are Dacodraco hunteri. The biomass of the demersal fish fauna was estimated to be 0.3 to 1.6 t km−2 on the Vestkapp shelf and 0.1 to 0.4 t km−2 for Gould Bay. Biomass values greater than 1.0 t km−2 were found at the shelf edge.

The notothenid species Trematomus bernacchii has previously been shown, by allozyme analysis, to be a complex of two cryptic species, one of which being more closely related to T. hansoni than to the other T. bernacchii cryptic species. Two T. bernacchii colour morphs, “white blotch” and “brown”, at McMurdo Sound, may correspond to these cryptic species. In this study, we present mitochondrial DNA sequences of the 12S and 16S ribosomal regions for six “white blotch” morphs, eight “brown” morphs collected in McMurdo Sound, one individual collected off the Antarctic Peninsula, and two T. hansoni individuals from McMurdo Sound. These sequences were compared with those of T. bernacchii and T. hansoni in the literature. Based on 14 phylogenetically informative sequences, no differences were found between “white blotch” and “brown” morphs. Furthermore, only one substitution separated these sequences from the previously published T. hansoni sequence, while 10 substitutions separated them from the previously published T. bernacchii sequence. Misidentified specimens, and sequence misreadings may be at the origin of these discrepancies. However, the presence of cryptic species within T. bernacchii and T. hansoni is not ruled out.

Trematomus newnesi inhabited inshore (<20 m) subzero waters in McMurdo Sound where it fed in the water column on Euphausia crystallorophias and fishes. This sample included the largest reported specimens of this species. The length–weight relationship was Weight = 3.17 × 10−6 (Standard Length)3.34, n = 67, r2 = 0.95. The population was phenotypically plastic, with two distinct morphs easily separated by visual inspection – the typical morph and a large mouth/broad headed morph comprising 28% of the sample. The large mouth morph had a wider and blunter head, longer upper jaw, wider gape, more heavily ossified jaws and darker colouration. To document this morphology, four views of the head are illustrated. Inference from morphology and measurements suggested that the large mouth morph was more benthic than the typical semipelagic morph. Museum specimens from Cape Adare confirmed the presence of the large mouth morph 700 km north of McMurdo Sound. This is the first clear example of phenotypic plasticity in any species of marine fish and its discovery extends the bounds of the nototheniid adaptive radiation to the population level. This finding suggests ecological and evolutionary parallels between the inshore waters of the high Antarctic shelf and the low diversity ichthyofaunas of Arctic, boreal and some temperate lakes. Although there is no data on genetic diversification, an alternate interpretation of the phenotypic plasticity is that the large mouth morph is a cryptic or sibling species.