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Amongst the nototheniid subfamily Pleuragramminae, Aethotaxis mitopteryx is an infrequently collected high Antarctic species with an array of morphological and physiological adaptations supporting an evolutionarily derived benthopelagic lifestyle. The present study deals with some poorly known life history traits of this species, counting on 79 specimens collected in the Weddell Sea during 2014 and 2015 austral summer. Annulation pattern in sagittal otoliths were used to assess population age structure and growth rate, while macroscopic and histological analyses of gonads were performed to estimate reproductive status and features of gametogenesis. The sex ratio of the sampled population was close to parity, with females significantly larger than males. Based on the von Bertalanffy growth model, females attained a larger maximum size (40 vs. 27 cm) at a lower rate (0.05 vs. 0.12 years−1) than males. Individual longevity was remarkable in both sexes, females and males attaining 62 and 32 years of age, respectively. Females showed group synchronous oocyte development and presumed high reproductive effort, as indicated by the large size of residual hydrated oocytes in regressing individuals (4.6-4.8 mm). Body sizes at sexual maturity were 33 and 19 cm in females and males, corresponding to 32 and 11 years of age, respectively. All specimens were caught far from the reproductive season. From an evolutionary perspective, it appears that the process of pelagization similarly influenced the life strategies of the species within the clade Pleuragramminae, which shared high reproductive effort linked to early sexual maturity, slow somatic growth and long life span. [ABSTRACT FROM AUTHOR]

Nototheniid and myctophid fish are primary prey for marine piscivores, yet little is known about their nutritional value. In this study, we characterized the proximate composition [PC: water, fat (neutral lipids), crude protein (CP) and ash] and energy density (ED; kJ g) of fifteen fish species from McMurdo Sound and the Ross Sea, Antarctica. We assayed the entire fish for all species except for the large Antarctic toothfish, Dissostichus mawsoni (muscle tissue only). On a wet mass basis (WM), fish were variable in composition: moisture content ranged from 64.9 to 87.3% WM, fat from 0.5 to 17.4% WM, CP from 7.7 to 16.7% WM, ash from 11.2 to 21.0% FFDM (fat-free dry mass), and ED from 2.9 to 10.3 kJ g. Myctophids and pelagic nototheniids such as Pleuragramma antarcticum and D. mawsoni were high in fat content (7-17% WM), while a bathylagid and benthic nototheniids including most Trematomus spp. and Lepidonotothen squamifrons were low in fat (0.5-4% WM). The epibenthic Trematomus species ( T. eulepidotus and T. lepidorhinus) were intermediate. Energy density tracked fat content, with highest values in myctophids and pelagic nototheniids. The variation in nutrient and energy density confirms that prey composition must be taken into account when modelling energy and nutrient fluxes within the Antarctic ecosystem. Further analyses of prey collected over a number of different locations and seasons are needed in order to determine how the nutritional value of certain species might affect annual or decadal variation in reproductive success or population size of top predators. [ABSTRACT FROM AUTHOR]

The Antarctic silverfish Pleuragramma antarcticum Boulenger is the dominant fish species in the high Antarctic zone, playing a key role in the Ross Sea midwater shelf ecosystem. Unlike other notothenioids, it is holoplanktonic species, spending its entire life cycle in the water column. Early life stages of P. antarcticum are generally found in the upper 200m and their spatial distribution is largely affected by water masses and general circulation. To understand better the mechanisms involved in the geographical distribution of the Antarctic silverfish within the western Ross Sea, an analysis of abundance and distribution was carried out in relation to oceanographic conditions. Samples were collected in summer during the 1998, 2000 and 2004 Italian cruises, covering the majority of the western sector of the Ross Sea. Overall 127 stations were sampled using standard plankton nets for biological samples and CTD and XBT to record abiotic parameters. Although all surveys were in December-January, the yearly results differed in terms of relative abundance of larval developmental stages and of oceanographic characteristics. The 1997-98 samples were characterized by very low abundance overall and by the virtual absence of early larvae. In summers 1999-2000 and 2003-04 the abundance of P. antarcticum was one order of magnitude higher than in the earlier season. In 1999-2000 catches were mainly composed of pre-flexion larvae and late postlarvae, while in 2003-04 catches were made up of pre-flexion larvae and juveniles. In January 2000 the Ross Sea summer polynya was fully open as the pack ice was almost completely melted, whereas in January 1998 and 2004 the opening of the polynya was considerably delayed. As a consequence, a delay in phytoplankton blooms and a decrease in primary production were observed in the summer seasons 1998 and 2004 with respect to 2000. The spatial distribution of early life stages, that were confined to the continental shelf and shelf break of the Ross Sea, generally appeared to be positively influenced by transition zones (oceanographic fronts). In addition, most of catches were recorded on or in close proximity to the banks (Pennell, Mawson, Ross and Crary) that characterize the continental shelf of the Ross Sea. On the basis of present findings and literature data, a link between the general circulation in the western Ross Sea and the distribution pattern of the early life stages of P. antarcticum has been developed. [ABSTRACT FROM AUTHOR]

Two species of Antarctic fish were stressed by moving them from seawater at −1 °C to seawater at 10 °C and holding them for a period of 10 min. The active cryopelagic species Pagothenia borchgrevinki maintained heart rate while in the benthic species Trematomus bernacchii there was an increase in heart rate. Blood pressure did not change in either species. Both species released catecholamines into the circulation as a consequence of the stress. P. borchgrevinki released the greater amounts, having mean plasma concentrations of 177 ± 54 nmol · l−1 noradrenaline and 263 ± 131 nmol · l−1 adrenaline at 10 min. Plasma noradrenaline concentrations rose to 47 ± 14 nmol · l−1 and adrenaline to 73 ± 28 nmol · l−1 in T. bernacchii. Blood from P. borchgrevinki was tonometered in the presence of isoprenaline. A fall in extracellular pH suggests the presence of a Na+/H+ antiporter on the red cell membrane, the first demonstration of this in an Antarctic fish. Treatment with the β-adrenergic antagonist drug sotalol inhibited swelling of red blood cells taken from temperature-stressed P. borchgrevinki, suggesting that the antiporter responds to endogenous catecholamines. [ABSTRACT FROM AUTHOR]