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Hybridization and introgression are recognized as mechanisms promoting genetic variability during evolutionary radiations. We examined the impact of introgression in the process of speciation, focusing on the Antarctic icefish genus Chionodraco. Our analyses confirmed that the three Chionodraco species (Chionodraco hamatus, Chionodraco myersi , and Chionodraco rastrospinosus) were genetically distinctive, despite signals of past interspecific gene flow between C. hamatus and C. myersi that likely occurred during interglacial periods. However, in this study, no recent hybrids were identified. The lack of contemporary hybridization may be due to life-history traits and the type of marker used in the analysis. Our study emphasizes the importance of genomic approaches to detect subtle patterns of past hybridization accurately and highlights the significance of historical climate events in the demographic and evolutionary history of Antarctic notothenioids. Polar regions, and especially the Antarctic Peninsula, are now experiencing the fastest climate changes due to global warming. Understanding the impact of past climate events is fundamental to trace current modifications in species' genetic variability and distributions and predict future evolutionary trajectories. This knowledge is also vital for conservation efforts, including the implementation of marine protected areas. [ABSTRACT FROM AUTHOR]

This research was conducted to study length–weight relationships (LWR) and condition factors of six Antarctic notothenioidei fish species including blackfin icefish (Chaenocephalus aceratus), single-angle icefish (Chionodraco hamatus), marbled rockcod (Notothenia rossii), black rockcod (Notothenia coriiceps), emerald rockcod (Trematomus bernacchii), and dusky rockcod (Trematomus newnesi) from the King Sejong Station on King George Island and Jang Bogo Station on the Northern Victoria Land. A total of 232 specimens were collected by fishing on the icebreaking research vessel ARAON from December 2020 to February 2021. The LWR parameters and condition factors differed depending on species, which can be affected by their distribution, species characteristics, and gravidity status. The exponent b values in LWR (W = aLb) ranged from 2.593 to 5.184. Four species including C. aceratus, C. hamatus, N. rossii, and T. bernacchii followed positive allometric growth, T. newnesi followed negative allometric growth, and only N. coriiceps showed isometric growth. These results can be helpful in understanding the ecological and growth conditions of six fish species living in the Antarctic Ocean, providing more information for future research on Antarctic fish. [ABSTRACT FROM AUTHOR]

The fish incidence, particularly notothenioids and myctophids, in the diet of non-breeding male Arctocephalus gazella in the western Antarctic Peninsula (AP) region is widely variable according to the studied locality. We made a comparative diet analysis on 158 fecal samples collected in summer 2005 at Hope Bay (HB), AP and at Stranger Point (SP), South Shetland Islands (SSI). The frequency of occurrence of Antarctic krill Euphausia superba and fish as prey was similar at HB, whereas krill was predominant at SP. For each fish species identified based on the otoliths found, their relative importance in the diet was evaluated using the IRI index. Notothenioid fish prevailed at HB, Pleuragramma antarctica being the most important prey. Contrarily, the myctophids Gymnoscopelus nicholsi and Electrona antarctica predominated at SP. Both benthopelagic and pelagic fish species were represented at HB, while the latter were more important at SP. Demersal nototheniid species (e.g., Trematomus spp.) were scarcely represented and only at HB, which might be related to a preference of fur seals for the more abundant pelagic prey there. At SP, demersal nototheniids were not represented in the scats. The fish species consumption was higher in diversity at SP in comparison with HB but low in overlap between the two sites. We surmise that the differences found in the dietary composition of fur seals from both sites could be related to 1—different topographical and hydrological conditions associated to the study areas; 2—historical finfish fisheries, which took place during the late 1970s at the SSI, but not in the AP. Our findings are compared with studies from other localities of the AP and the Scotia Arc. [ABSTRACT FROM AUTHOR]

This study provides the first description of the morphology (geometric morphometric analysis), condition (Fulton index), and diet (stomach content analyses) of the rockcod Patagonotothen tessellata from the coast of Chilean Central Patagonia. We found low but significant intersexual variability in the snout extension, mouth size, and the insertion of the pelvic fin supporting the presence of sexual shape dimorphism in P. tessellata. The diet of the males showed a preference for Patagonotothen spp., unidentified crustaceans, and polychaetes (Chaetopteridae), while the diet of females was comprised primarily of unidentified fish and crustaceans. Significant differences in the consumption of algae, other invertebrates, and fishes were observed between sexes, and a significant negative correlation between fish length and the ingestion of amphipods was found. Diet composition showed significant differences between sexes, but not among size groups. Finally, a partial least square analysis showed a weak but significant covariance between diet and morphology: individuals with shorter snouts and smaller eyes had more unidentified crustaceans, amphipods, and fish in their stomach contents, while individuals with narrower trunks contained more unidentified crustaceans, the shrimp Betaeus truncatus, and gastropods; and individuals with slenderer heads had more Patagonotothen spp. in their stomachs. [ABSTRACT FROM AUTHOR]

The notothenioid family Bathydraconidae is a poorly understood family of fishes endemic to the Southern Ocean. There is especially little information on Akarotaxis nudiceps, one of the deepest‐dwelling and least fecund bathydraconid species. Using genetic and morphological data, we document and describe the larval stages of this unique species, offer a novel characteristic to distinguish it from the morphologically similar bathydraconid Prionodraco evansii and use the sampling locations to infer a possible spawning area of A. nudiceps along the western Antarctic Peninsula. These results provide important baseline information for locating, identifying and studying the biology of A. nudiceps, an important component of the Southern Ocean ecosystem. [ABSTRACT FROM AUTHOR]

Patagonia is an understudied area, especially when it comes to population genomic studies with relevance to fishery management. However, the dynamic and heterogeneous landscape in this area can harbor an important but cryptic genetic population structure. Once such information is revealed, it can be integrated into the management of infrequently investigated species. Eleginops maclovinus is a protandrous hermaphrodite species with economic importance for local communities that are currently managed as a single genetic unit. In this study, we sampled five locations distributed across a salinity cline from Northern Patagonia to investigate the genetic population structure of E. maclovinus. We used restriction site‐associated DNA (RAD) sequencing and outlier tests to obtain neutral and adaptive loci, using FST and GEA approaches. We identified a spatial pattern of structuration with gene flow and spatial selection by environmental association. Neutral and adaptive loci showed two and three genetic groups, respectively. The effective population sizes estimated ranged from 572 (Chepu) to 14,454 (Chaitén) and were influenced more by locality than by salinity cline. We found loci putatively associated with salinity suggesting that salinity may act as a selective driver in E. maclovinus populations. These results suggest a complex interaction between genetic drift, gene flow, and natural selection in this area. Our findings also suggest several evolutionary significant units in this area, and the information should be integrated into the management of this species. We discussed the significance of these results for fishery management and suggest future directions to improve our understanding of how E. maclovinus has adapted to the dynamic waters of Northern Patagonia. [ABSTRACT FROM AUTHOR]

Abstract Patagonia is an understudied area, especially when it comes to population genomic studies with relevance to fishery management. However, the dynamic and heterogeneous landscape in this area can harbor an important but cryptic genetic population structure. Once such information is revealed, it can be integrated into the management of infrequently investigated species. Eleginops maclovinus is a protandrous hermaphrodite species with economic importance for local communities that are currently managed as a single genetic unit. In this study, we sampled five locations distributed across a salinity cline from Northern Patagonia to investigate the genetic population structure of E. maclovinus. We used restriction site‐associated DNA (RAD) sequencing and outlier tests to obtain neutral and adaptive loci, using FST and GEA approaches. We identified a spatial pattern of structuration with gene flow and spatial selection by environmental association. Neutral and adaptive loci showed two and three genetic groups, respectively. The effective population sizes estimated ranged from 572 (Chepu) to 14,454 (Chaitén) and were influenced more by locality than by salinity cline. We found loci putatively associated with salinity suggesting that salinity may act as a selective driver in E. maclovinus populations. These results suggest a complex interaction between genetic drift, gene flow, and natural selection in this area. Our findings also suggest several evolutionary significant units in this area, and the information should be integrated into the management of this species. We discussed the significance of these results for fishery management and suggest future directions to improve our understanding of how E. maclovinus has adapted to the dynamic waters of Northern Patagonia.

The IgM and IgT classes were previously identified and characterized in the Antarctic teleost Trematomus bernacchii, a species belonging to the Perciform suborder Notothenoidei. Herein, we characterized the gene encoding the polymeric immunoglobulin receptor (pIgR) in the same species and compared it to the pIgR of multiple teleost species belonging to five perciform suborders, including 11 Antarctic and 1 non-Antarctic (Cottoperca gobio) notothenioid species, the latter living in the less-cold peri-Antarctic sea. Antarctic pIgR genes displayed particularly long introns marked by sites of transposable elements and transcription factors. Furthermore, analysis of T. bernacchii pIgR cDNA unveiled multiple amino acid substitutions unique to the Antarctic species, all introducing adaptive features, including N-glycosylation sequons. Interestingly, C. gobio shared most features with the other perciforms rather than with the cold-adapted relatives. T. bernacchii pIgR transcripts were predominantly expressed in mucosal tissues, as indicated by q-PCR and in situ hybridization analysis. These results suggest that in cold-adapted species, pIgR preserved its fundamental role in mucosal immune defense, although remarkable gene structure modifications occurred. [ABSTRACT FROM AUTHOR]

Although the extent of near-shore and coastal habitats around the Antarctic Continent is limited, they host an abundant and diversified fish fauna dominated by notothenioids. Nevertheless, the spatial distribution of fishes at small scales and their relationships with the surrounding habitat are still poorly known. The purpose of this study is to provide new insights on the inshore fish community of Terra Nova Bay, Ross Sea, which is now part of the largest marine protected area established so far in the Southern Ocean. As a low-impact and effective methodology of investigation, an underwater photographic survey was conducted through two remotely operated vehicle (ROV) transects set down to 300 m depth. The faunistic inventory consisted of twelve species of notothenioids, which complements previous data obtained by conventional samplings. The most abundant species exhibited wide depth distribution ranges, and they were generally associated with areas with a rich benthic macrofauna composed of alcyonaceans, sponges, bryozoans, polychaetes, and echinoderms. Nesting behavior was documented in two species, Trematomus bernacchii and Pagetopsis macropterus. The present data provide further evidence of the importance of inshore waters for the local fish community, representing a proper habitat for settling, foraging, and spawning activities. [ABSTRACT FROM AUTHOR]

In the last three decades, several interdisciplinary studies investigated the marine ecosystems off the West Antarctic Peninsula (WAP), one of the most impacted areas of the Southern Ocean by the global warming. Although the extent of near-shore habitats along the WAP is wider than elsewhere in Antarctica, the coastal fish communities have been rarely studied. Complementing these previous studies, we provide new data on the species composition, population structure and relative abundance of the inshore fish community living off the Argentine Islands (Bellingshausen Sea). Fish samples were caught all the year round during four different periods spread over ten years (from 2006 to 2017). The fish fauna consisted of fourteen high-Antarctic and low-Antarctic species of notothenioids, most of them belonging to the Nototheniidae. Notothenia coriiceps was by far the most abundant species, followed in decreasing abundance by Chaenocephalus aceratus, Notothenia rossii, Trematomus newnesi and Trematomus bernacchii. Our findings provide context for future ecological studies as this area represents either a spawning and nursery area for multiple species in this study. More generally, the inshore waters off the Argentine Islands represent the southern limit of distribution for several low-Antarctic species, and our results provide critical baseline data for assessing possible disruptions in population dynamics driven by the ongoing climate change. [ABSTRACT FROM AUTHOR]

The yellowfin notothen Patagonotothen guntheri is an important fish species in the Marine Protected Area Namuncurá-Burdwood Bank (MPAN-BB) due to its high abundance and significant ecological role. Thus, diet composition and feeding habits were analyzed. To fulfill this purpose, percentage frequency of occurrence, prey-specific abundance, and prey-specific index of relative importance (%PSIRI) were calculated. Generalized linear models were built for the defined prey categories to assess changes in feeding associated with total length, sex, depth, and zone of capture. Two hundred fifty-two specimens were sampled (69–256 mm total length), of which 186 contained food (73.41%). According to PSIRI, ophiuroids (23.28%), unidentified polychaetes (17.92%), and Munida gregaria (12.73%) were the main prey items. However, yellowfin notothen showed variations in diet composition according to their length and the depth of capture. The consumption of decapods and other invertebrates increased with depth, while the ingestion of ophiuroids decreased. Also, the number of polychaetes was higher in the stomach content of larger specimens. The present work provides the first description and analysis of P. guntheri trophic ecology in the MPAN-BB, concluding that it is a species with a generalist diet, which feeds on a great diversity of both benthic and pelagic organisms depending on availability. [ABSTRACT FROM AUTHOR]

The study presents data about the two dominant fish species Notothenia rossii Richardson, 1844 and N. coriiceps Richardson, 1844 in the shallow coastal waters of the Livingston Island. Length-weight relationship, as well as the Fulton’s and the relative condition factors and the diet of both species were studied. A total of 115 specimens of N. rossii and 18 of N. coriiceps were caught near the Bulgarian Polar Base in the South Bay. The average total length and weight of N. rossii were 232.8 mm and 180.4 g, respectively, while in N. coriiceps they were 324.4 mm and 556.8 g. The exponent b values of the length-weight relationship in both species were close to 3, indicating an isometric growth, but not statistically different from 3 since the calculated p -value was above 0.05. The average values of the Fulton’s and the relative condition factors in N. rossii were 1.32 and 1.65, respectively, while the values of the same factors in N. coriiceps were 1.50 and 2.10, respectively, which indicated very good general condition of the fish. Overall, ten dietary classes were recorded in N. rossii and five in N. coriiceps, but only two of them (krill and amphipods) formed a total of 84.1% and 79.3% of the species diet, respectively. [ABSTRACT FROM AUTHOR]

BackgroundAntarctic notothenioids are an impressive adaptive radiation. While they share recent common ancestry with several species-depauperate lineages that exhibit a relictual distribution in areas peripheral to the Southern Ocean, an understanding of their evolutionary origins and biogeographic history is limited as the sister lineage of notothenioids remains unidentified. The phylogenetic placement of notothenioids among major lineages of perciform fishes, which include sculpins, rockfishes, sticklebacks, eelpouts, scorpionfishes, perches, groupers and soapfishes, remains unresolved. We investigate the phylogenetic position of notothenioids using DNA sequences of 10 protein coding nuclear genes sampled from more than 650 percomorph species. The biogeographic history of notothenioids is reconstructed using a maximum likelihood method that integrates phylogenetic relationships, estimated divergence times, geographic distributions and paleogeographic history.ResultsPercophis brasiliensis is resolved, with strong node support, as the notothenioid sister lineage. The species is endemic to the subtropical and temperate Atlantic coast of southern South America. Biogeographic reconstructions imply the initial diversification of notothenioids involved the western portion of the East Gondwanan Weddellian Province. The geographic disjunctions among the major lineages of notothenioids show biogeographic and temporal correspondence with the fragmentation of East Gondwana.ConclusionsThe phylogenetic resolution of Percophis requires a change in the classification of percomorph fishes and provides evidence for a western Weddellian origin of notothenioids. The biogeographic reconstruction highlights the importance of the geographic and climatic isolation of Antarctica in driving the radiation of cold-adapted notothenioids.

Cryonotothenioidea is the main group of fishes that thrive in the extremely cold Antarctic environment, thanks to the acquisition of peculiar morphological, physiological and molecular adaptations. We have previously disclosed that IgM, the main immunoglobulin isotype in teleosts, display typical cold-adapted features. Recently, we have analyzed the gene encoding the heavy chain constant region (CH) of the IgT isotype from the Antarctic teleost Trematomus bernacchii (family Nototheniidae), characterized by the near-complete deletion of the CH2 domain. Here, we aimed to track the loss of the CH2 domain along notothenioid phylogeny and to identify its ancestral origins. To this end, we obtained the IgT gene sequences from several species belonging to the Antarctic families Nototheniidae, Bathydraconidae and Artedidraconidae. All species display a CH2 remnant of variable size, encoded by a short Cτ2 exon, which retains functional splicing sites and therefore is included in the mature transcript. We also considered representative species from the three non-Antarctic families: Eleginopsioidea (Eleginops maclovinus), Pseudaphritioidea (Pseudaphritis urvillii) and Bovichtidae (Bovichtus diacanthus and Cottoperca gobio). Even though only E. maclovinus , the sister taxa of Cryonotothenioidea, shared the partial loss of Cτ2 , the other non-Antarctic notothenioid species displayed early molecular signatures of this event. These results shed light on the evolutionary path that underlies the origins of this remarkable gene structural modification. [Display omitted] • All analyzed cryonotothenioid species have an IgT gene with a Cτ2 exonic remnant. • Conserved donor/acceptor splice sites allow the expression of the exonic remnant. • The exon loss event took place prior to the radiation of Cryonotothenioidea. • The exon loss is shared by the non-Antarctic sister lineage of Cryonotothenioidea. • The nearly total loss of the Cτ 2 exon occurred in a stepwise mode. [ABSTRACT FROM AUTHOR]

Continuous monitoring of fish fauna is important for evaluating effects of fisheries and environmental changes on the Antarctic marine ecosystem. In January 2019, we collected 52 individuals of 5 species of notothenioid species in Kita-no-ura cove, Lützow-Holm Bay, East Antarctica. The emerald rockcod Trematomus bernacchii was the most dominant (N＝39), while the sharp-spined notothen T. pennellii was the second most common species (N＝10). The number of T. pennellii was larger, but the number of T. hansoni (N＝1) was smaller than previous studies. The relationship between body weight and total length of T. bernacchii and T. pennellii indicated that the body weight of T. pennellii tends to be higher than that of T. bernacchii of equal total length. Body weight is in proportion to total length to the power of 3.23 (95% confidence interval: 3.003.46); therefore, the deviation from isometry, the power of 3.33, was not observed.

Although the extent of near-shore and coastal habitats around the Antarctic Continent is limited, they host an abundant and diversified fish fauna dominated by notothenioids. Nevertheless, the spatial distribution of fishes at small scales and their relationships with the surrounding habitat are still poorly known. The purpose of this study is to provide new insights on the inshore fish community of Terra Nova Bay, Ross Sea, which is now part of the largest marine protected area established so far in the Southern Ocean. As a low-impact and effective methodology of investigation, an underwater photographic survey was conducted through two remotely operated vehicle (ROV) transects set down to 300 m depth. The faunistic inventory consisted of twelve species of notothenioids, which complements previous data obtained by conventional samplings. The most abundant species exhibited wide depth distribution ranges, and they were generally associated with areas with a rich benthic macrofauna composed of alcyonaceans, sponges, bryozoans, polychaetes, and echinoderms. Nesting behavior was documented in two species, Trematomus bernacchii and Pagetopsis macropterus. The present data provide further evidence of the importance of inshore waters for the local fish community, representing a proper habitat for settling, foraging, and spawning activities.

The vertebrate mitochondrial genomes generally present a typical gene order. Exceptions are uncommon and important to study the genetic mechanisms of gene order rearrangements and their consequences on phylogenetic output and mitochondrial function. Antarctic notothenioid fish carry some peculiar rearrangements of the mitochondrial gene order. In this first systematic study of 28 species, we analyzed known and undescribed mitochondrial genome rearrangements for a total of eight different gene orders within the notothenioid fish. Our reconstructions suggest that transpositions, duplications, and inversion of multiple genes are the most likely mechanisms of rearrangement in notothenioid mitochondrial genomes. In Trematominae, we documented an extremely rare inversion of a large genomic segment of 5,300 bp that partially affected the gene compositional bias but not the phylogenetic output. The genomic region delimited by nad5 and trnF , close to the area of the Control Region, was identified as the hot spot of variation in Antarctic fish mitochondrial genomes. Analyzing the sequence of several intergenic spacers and mapping the arrangements on a newly generated phylogeny showed that the entire history of the Antarctic notothenioids is characterized by multiple, relatively rapid, events of disruption of the gene order. We hypothesized that a pre-existing genomic flexibility of the ancestor of the Antarctic notothenioids may have generated a precondition for gene order rearrangement, and the pressure of purifying selection could have worked for a rapid restoration of the mitochondrial functionality and compactness after each event of rearrangement. [ABSTRACT FROM AUTHOR]

Although many notothenioid fishes are primarily carnivorous, some species consistently feed on macroalgae and are therefore omnivorous. Among fish, the degree of herbivory is usually reflected in the morphology of the gastrointestinal system especially intestine length. We examined a large number of juvenile and adult specimens of nine sympatric notothenioid species collected sequentially over eight summer seasons at Potter Cove, South Shetland Islands. We provide relative intestine lengths (RIL), distinct proportions of algae and animal prey in the diets (W%), and numbers of pyloric caeca for all species. The sister species Notothenia coriiceps (NOC) and N. rossii (NOR) evidenced significantly different intestinal growth over ontogeny and ate distinctly different proportions of algae and animal prey. We establish a ranking of the degree of herbivory for the fish species in the local ecosystem, and this was found to be related to their distinct feeding types and strategies. There is a correspondence between intestine length/RILs and degree of herbivory in six of the nine species analysed but no clear association between the number of pyloric caeca and degree of omnivory or carnivory. Compared to other teleosts, our results, and those in the literature, indicate modest divergence in notothenioids that include a phylogenetic decrease in the number of pyloric caeca, from 6 to 7 in most nototheniids to 2–3 in channichthyids, and a 1.8-fold difference in average relative intestine lengths which are most frequently 50–70% of body length and never exceed body length. This is consistent with the unspecialized gastrointestinal morphology that reflects the dietary and ecological plasticity of many notothenioids, exemplified by the high degree of omnivory in species such as NOC and NOR. [ABSTRACT FROM AUTHOR]

Understanding the reproductive biology of Antarctic notothenioid fish species is crucial for effective management and conservation efforts. This study investigates the reproductive biology of Notothenia coriiceps , focusing on the location of spawning grounds and the influence of environmental factors on this process. Sampling included 120 specimens caught at Potter Cove, South Shetland Islands, from November to late March of years 2016–2018 (austral spring-summer season). Gonadal macroscopic, histologic and physiologic features are reported. Histological analysis revealed two distinct groups of oocytes in the ovaries: a leading clutch of vitellogenic oocytes for the upcoming reproductive event and a second remnant clutch of smaller oocytes in cortical alveoli and primary growth stages. Photoperiod phases significantly associate with variations in the gonadosomatic index throughout ovarian development, indicating the influence of this parameter on fish reproduction at high latitudes. Elevated plasma levels of estradiol during vitellogenesis support its role in stimulating yolk precursor synthesis and incorporation into oocytes. In March, an increase in testosterone levels during late vitellogenesis suggests the proximity of final maturation, ovulation, and spawning. A sharp increase in both sex steroids and accelerated gonadal development of N. coriiceps was particularly evident after water temperature reached maximum values (∼2 °C), suggesting that high temperature acts as a driver of the physiological mechanisms that allow to complete vitellogenesis and reach the ovulation. Our results show that (1) N. coriiceps females captured in mid-March at Potter Cove were in late developing, suggesting that spawning likely start on April; (2) Potter Cove is likely a spawning ground for N. coriiceps in part due to its thermal regime, emphasizing the importance of inshore areas as spawning grounds for Antarctic notothenioids. Thus, this study underscores the necessity of investigating the impact of water temperature changes on notothenioids reproductive patterns in the context of global warming at West Antarctic Peninsula region. • First report of the possible role of photoperiod and water temperature on the reproductive physiology in Antarctic fish. • Water temperature increase in Antarctic coastal areas would act as trigger and accelerator of Notothenia coriiceps reproduction. • Sex steroids profiles assessments provide useful information to correctly evaluate the reproductive cycle in Antarctic fish. • Inshore sites serve as spawning grounds for Antarctic notothenioids. [ABSTRACT FROM AUTHOR]

The complete mitochondrial genome of Notothenia rossii was obtained using PacBio Sequel long-read sequencing platform. The mitogenome of N. rossii was circular form and 18,274 bp long, which consists of 13 protein-coding genes, 24 tRNAs, 2 rRNAs, and non-coding control region. Particularly, we found duplicated tRNAThr and tRNAPro in addition to the typical 22 tRNAs. The phylogenetic tree revealed that N. rossii was most closely related to N. coriiceps among species in the Nototheniidae clade within the suborder Notothenioidei.

In this study, we assessed concentrations of 13 trace metals in the scales of Notothenia coriiceps, Trematomus bernacchii and Gobionotothen gibberifrons caught off the coast of James Ross Island (Antarctic Peninsula). Overall, our results for scales broadly match those of previous studies using different fish and different organs, with most metals found at trace levels and manganese, aluminium, iron and zinc occurring at high levels in all species. This suggests that scales can serve as a useful, non-invasive bioindicator of long-term contamination in Antarctic fishes. High accumulation of manganese, aluminium, iron and zinc is largely due to high levels in sediments associated with nearby active volcanic sites. Manganese, vanadium and aluminium showed significant positive bioaccumulation in T. bernacchii (along with non-significant positive accumulation of iron, zinc, cobalt and chromium), most likely due to greater dietary specialisation on sediment feeding benthic prey and higher trophic species. Levels of significance in bioaccumulation regressions were strongly affected by large-scale variation in the data, driven largely by individual differences in diet and/or changes in habitat use and sex differences associated with life stage and reproductive status. Increased levels of both airborne deposition and precipitation and meltwater runoff associated with climate change may be further adding to the already high levels of manganese, aluminium, iron and zinc in Antarctic Peninsula sediments. Further long-term studies are encouraged to elucidate mechanisms of uptake (especially for aluminium and iron) and possible intra- and interspecific impacts of climate change on the delicate Antarctic food web. [ABSTRACT FROM AUTHOR]

Most Antarctic notothenioids exhibit clear geographic structure at large scales of spatial separation, generally between populations off different Ocean sectors. At smaller distances, there is great variation in the extent of population structuring. The Antarctic Peninsula and the archipelago of the South Shetland Islands are separated by a narrow strait of deep water (1000 m). Despite the proximity of these two areas, the confluence of water masses of different origins establishes frontal systems and local gyres which may preclude migration between shelf populations. Among the most abundant fish species in the area, the painted notothen Lepidonotothen larseni and the gaudy notothen Lepidonotothen nudifrons are two of the most numerous and widely distributed. In the present study, the genetic and morphological population structure of these closely related species was evaluated between the Antarctic Peninsula and the South Shetland Islands. Nine meristic counts, 18 inter-landmark distances and a mitochondrial DNA marker (D-loop) were analyzed. Populations of L. nudifrons were significantly different based on both, morphogeometric and genetic analyses, while L. larseni showed no population differentiation. The results showed a moderate structuring not correlated with distance between L. nudifrons populations off the Antarctic Peninsula and the South Shetland Islands. These findings provide evidence that differences between the studied species may be linked to key life history events, such as timing and location of egg development, hatching times and dispersal period of larvae. The present data suggest that notothenioid population structuring at regional scale may be related to a combination of life history traits, oceanographic features and local adaptation. [ABSTRACT FROM AUTHOR]

This study describes the cephalic and trunk lateral line systems in Patagonian blenny Eleginops maclovinus juveniles, providing morphological details for pores, canals and neuromasts. Eleginops maclovinus juveniles possess a complete laterodorsal lateral line that extends from the upper apex of the gill opening along the trunk as far as the caudal fin. The lateral line was ramified through pores and canals. The following pores were recorded: four supraorbital pores, with two along the eye border and two on the snout; seven infraorbital pores, with three on the lacrimal bone and four being infraorbital; five postorbital pores, with three along the preopercular border (upper preoperculum branch) and two on the bone curvature (inferior preoperculum branch); and four mandibular pores aligned along the jaw. Furthermore, five narrow‐simple and interconnected canals were found (i.e. preopercular, mandibular, supraorbital and infraorbital canals). Histologically, the dorsal lateral line presented thin neuromasts (350 μm) with short hair cells. By contrast, the cranial region presented long, thick neuromasts. Infraorbital and mandibular neuromasts had a major axis length of 260 μm and respective average diameters of 200 and 185 μm. Sensory system variations would be due to a greater concentration of neuromasts in the cranial region, allowing for a greater perception of changes in water pressure. Scarce morphological information is available for the lateral sensory system in Eleginopsidae, particularly compared to Channichthyidae, Bovichthydae, Artedidraconidae and Bathydraconidae. Therefore, the presented results form a fundamental foundation of knowledge for the lateral‐line system in juvenile E. maclovinus and provide a basis for future related research in this taxon as well as within the Notothenioidei suborder. [ABSTRACT FROM AUTHOR]

There has been no comprehensive study of body size in notothenioid fishes. Therefore I evaluated maximum total length (TL) as an axis of the evolutionary radiation. Lengths are provided for 141 species that collectively range in maximum adult size from 5.7 cm (Harpagifer nybelini) to 225 cm (Dissostichus eleginoides), a 39-fold difference. For the 138 species analyzed, the mean length is 33.5 cm and the median is 26.6 cm. Based on 10 cm-bins, notothenioids are apportioned into small (< 10 cm), medium (10–39 cm), medium-large (40–91 cm), and large (> 200 cm) size categories. The 20–29 cm bin contains the most species (32%). Most species (71%) are of medium size, 21% of species are medium-large, and 7% and ≈ 1% are small and large, respectively. The median lengths vary among the five cryonotothenioid families as well as among eight clades (genera and families). Among families, median and mean lengths are smallest in the Harpagiferidae and largest in Channichthyidae. Among clades, Harpagifer has the smallest median length (8.3 cm) followed by Artedidraco (12.5 cm). Several middle-sized clades do not differ in median size: Patagonotothen, Trematomus, Pogonophryne, and Bathydraconidae. Two clades of medium-large size species, Notothenia and Channichthyidae, are of similar size. A significant but weak positive relationship exists between maximum length and maximum depth. With the exception of miniature species (≤ 1 cm), the 126 species of cryonotothenioids (the Antarctic clade) encompass the range in size categories in actinopterygians in general, and the disparity in maximum lengths among individual species indicates that body size is an axis of the radiation. I discuss the size of notothenioids relative to other teleosts, the ecological implications of large species in the food web, and the similarity of the cryonotothenioid axes of diversification to those of Lake Baikal sculpins. [ABSTRACT FROM AUTHOR]

Notothenioids are among the most intensively studied lineages of marine fishes. However, notothenioid research is predominately focused on the approximately 100 species of Antarctic cryonotothenioids. Far less attention is devoted to the non-Antarctic lineages Bovichtidae, Pseudaphritis urvillii, and Eleginops maclovinus, all of which originated prior to the diversification of cryonotothenioid species. Here we utilize DNA sequence data from mitochondrial and nuclear genes, as well as meristic trait morphology to investigate the evolutionary history of Bovichtidae. Bovichtus is the only polytypic lineage of early diverging non-Antarctic notothenioids providing a unique opportunity to contextualize the diversification dynamics of cryonotothenioids with their non-Antarctic relatives. We find strong evidence that species of Bovichtus represent a recent evolutionary radiation with divergence times similar to those estimated among the most closely related species of cryonotothenioids. The divergence in traditional meristic trait morphology among species of Bovichtus is consistent with their phylogenetic relationships. The phylogeny of Bovichtus implies the wide geographic distribution of species in the clade is likely the result of West Wind drift-driven dispersal. The phylogeny and divergence time estimates results reject a hypothesis that species persistence in Bovichtus reflects long periods of evolutionary stasis. Instead, we hypothesize that patterns of extinction and diversification in Bovichtus closely mirror those observed in their Antarctic relatives. [ABSTRACT FROM AUTHOR]

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Antarctic specimens collected during various research expeditions are preserved in natural history collections around the world potentially offering a cornucopia of morphological and molecular data. Historical samples of marine species are, however, often preserved in formaldehyde which may render them useless for genetic analysis. We sampled stomachs and hindguts from 225 Trematomus specimens from the Natural History Museum London. These samples were initially collected between 20 and 100 years ago and fixed in either formaldehyde or ethanol. A 313 bp fragment of the cytochrome c oxidase subunit I (COI) was amplified and sequenced for prey item identification in the stomach and a 450 bp region of the 16S rRNA gene to investigate microbiome composition in the gut system. Both data sets were characterized by large dropout rates during extensive quality controls. Eventually, no unambiguous results regarding stomach content (COI) were retained, possibly due to degraded DNA, inefficient primers and contamination. In contrast, reliable microbiome composition data (16S rRNA) was obtained from 26 samples. These data showed a correlation in change of microbiome composition with fish size as well as year of the catch, indicating a microbiome shift throughout ontogeny and between samples from different decades. A comparison with contemporary samples indicated that the intestinal microbiome of Trematomus may have drastically changed within the last century. Further extensive studies are needed to confirm these patterns with higher sample numbers. Molecular analyses of museum stored fish can provide novel micro evolutionary insights that may benefit current efforts to prioritize conservation units in the Southern Ocean.

A combination of stomach content and nitrogen (δ15N) and carbon (δ13C) stable-isotope analysis was used to assess the trophic interactions and feeding habits of three notothenioid coastal fish (Champsocephalus esox, Patagonotothen tessellata and Patagonotothen cornucola) and one exotic salmon species (Oncorhynchus tschawytscha) with diverse life habits (benthic and benthopelagic) in the Francisco Coloane Coastal Marine Protected Area, southern Chile. The stomach contents of C. esox were mainly fish; those of P. cornucola and O. tschawytscha were crustacean decapods, Munida gregaria. A cluster analysis on isotope data and stable-isotope Bayesian ellipses detected two different predator groups, one with benthopelagic habits (C. esox and O. tshawytscha) and one with benthic habits (P. cornucola and P. tessellata). These results were supported with similar isotopic trophic level of each group. We suggest that the exotic salmon O. tschawytscha is a generalist predator with a broad trophic niche that may compete with the native notothenioid C. esox, as both have equivalent trophic levels with substantial overlap. This preliminary study is the first on trophic relationships of a subtidal fish assemblage within a remote ecosystem of fjords and channels in Chile’s southern Patagonia.

The complete mitochondrial genome of Trematomus pennellii was determined by MiSeq platform. The mitogenome of T. pennellii was 15,976 bp in length and encoded 37 genes (13 proteins, 22 tRNAs, 2 ribosomal RNAs) and a non-coding control region (D-Loop). Overall A + T contents (54.10%) in the mitogenome was higher than G + C contents (45.90%). Twenty-nine genes were located on H strand, whereas eight genes were identified on L strand. Among 13 protein-coding genes, unusual start codons were identified in COX1 (GTG), ND6 (ATT), COX2 (ATC), and ATP6 (ATC). The incomplete stop codon (T–) was identified in six genes including COXII, COXIII, NAD2, NAD3, NAD4, and Cytb. The phylogenetic tree of complete genome indicated that Trematomus pennellii was most closely related to Trematomus bernacchii with 91.65% DNA sequence identity.

Graphical abstract Highlights • Analysis of ∼100,000 RADseq loci provide unprecedented phylogenetic resolution of notothenioid fishes. • The new phylogenomic tree resolves several long-standing problems in notothenioid systematics. • We provide a quantification of the predicted utility of RADseq loci for Cenozoic phylogenetic inferences. Abstract Notothenioids are a clade of ∼120 species of marine fishes distributed in extreme southern hemisphere temperate near-shore habitats and in the Southern Ocean surrounding Antarctica. Over the past 25 years, molecular and morphological approaches have redefined hypotheses of relationships among notothenioid lineages as well as their relationships among major lineages of percomorph teleosts. These phylogenies provide a basis for investigation of mechanisms of evolutionary diversification within the clade and have enhanced our understanding of the notothenioid adaptive radiation. Despite extensive efforts, there remain several questions concerning the phylogeny of notothenioids. In this study, we deploy DNA sequences of ∼100,000 loci obtained using RADseq to investigate the phylogenetic relationships of notothenioids and to assess the utility of RADseq loci for lineages that exhibit divergence times ranging from the Paleogene to the Quaternary. The notothenioid phylogenies inferred from the RADseq loci provide unparalleled resolution and node support for several long-standing problems including, (1) relationships among species of Trematomus , (2) resolution of Indonotothenia cyanobrancha as the sister lineage of Trematomus , (3) the deep paraphyly of Nototheniidae, (4) the paraphyly of Lepidonotothen s.l., (5) paraphyly of Artedidraco , and 6) the monophyly of the Bathydraconidae. Assessment of site rates demonstrates that RADseq loci are similar to mtDNA protein coding genes and exhibit peak phylogenetic informativeness at the time interval during which the major Antarctic notothenioid lineages originated and diversified. In addition to providing a well-resolved phylogenetic hypothesis for notothenioids, our analyses quantify the predicted utility of RADseq loci for Cenozoic phylogenetic inferences. [ABSTRACT FROM AUTHOR]

Summary: There is no information about the characteristics of early cleavage in the Patagonian blennie (Eleginops maclovinus), which can be used as a diagnostic tool for embryo quality. The purpose of this investigation, therefore, was to characterize the first blastomeres of E. maclovinus morphologically. Of a 'pool' of incubated eggs at 10.7 ± 0.5°C, 100 microphotographs of blastodiscs were extracted at different incubation periods from 0.25 to 5 h after fertilization and analyzed. Blastodiscs taken at 3.5, 4.0 and 5.0 h were characterized and classified into symmetric or asymmetric groups according to their morphology. The proportions of length (L) and width (W) of each blastomere were determined to establish its symmetry. Additionally, 20 microphotographs of blastodiscs of normal appearance were analyzed morphologically (control blastodisc: CB) and compared other blastodiscs (4.0 and 5.0 h). The results showed that before fertilization oocytes presented a somehow turgid aspect (maximum average diameter of 987 ± 41 µm) and after fertilization and hydration, their diameter increased to 1001.5 ± 11 µm (but not statistically significant) and presented a spherical shape. First cleavage ends after 3.5 h of development, forming two blastomeres 467 ± 45 μm length (L) and 328 ± 21 μm width (W) with a L/W ratio of 1.43 ± 0.19. The second cleavage ends after development at 4.5 h forming four blastomeres 238 ± 65 μm length and 227 ± 65 μm width with a ratio L/W of 1.06 ± 0.09. Five categories were identified during the blastomere characterization: 70% normal or symmetric; 8% with odd numbers of blastomeres; 6% unequal; 6% 'pie shaped' and 10% amorphous. [ABSTRACT FROM AUTHOR]

At Potter Cove, King George Island/Isla 25 de Mayo, South Shetland Islands, significant ichthyological research has been conducted in the last three decades, mainly on the general ecology of notothenioid species in demersal stages from young juveniles to adults. Nevertheless, the knowledge of the ichthyoplankton composition in the cove, necessary for the overall comprehension of the dynamics of the fish species life-cycles, remained unexplored. Here, we report the first record of the early stages of Antarctic notothenioids collected in pelagic hauls at Potter Cove in summer 2014 and 2016 at depths of 6-9 m where total bottom depth ranged 30-190 m. The ichthyoplankton was represented by members of the families Harpagiferidae, Nototheniidae and Bathydraconidae. It consists of (1) 37 larval stages (preflexion and postflexion) of the species Harpagifer antarcticus (the most abundant), Psilodraco breviceps, Lepidonotothen squamifrons, Pleuragramma antarcticum and Trematomus scotti, and (2) 15 eggs of Notothenia coriiceps, of which two larvae hatched in the aquarium. Part of this material is illustrated by photographs. The presence of early life stages of fish in the cove is linked to the major influx from the Bransfield Strait and also depends on local environmental conditions (i.e., hydrologic, water circulation). In addition to being a spawning site for Parachaenichthys charcoti, already reported in the literature, nearshore localities of the South Shetland Islands such as Potter Cove appear to also be spawning sites for N. coriiceps, H. antarcticus and Chaenocephalus aceratus. [ABSTRACT FROM AUTHOR]

Abstract Recent studies have confirmed historic atmospheric deposition of uranium in Antarctica, with a steep and significant increase in levels deposited since the 1980s in Antarctic Peninsula ice core samples. To date, however, there has been little or no attention paid to uranium in the Antarctic food web. Here, we present results for uranium content in scales of three common nototheniid species (Trematomus bernacchii , Gobionotothen gibberifrons , Notothenia coriiceps) from coastal waters off James Ross Island (Antarctic Peninsula). While mean total uranium levels (mean ± SD) were low and similar between species (N. coriiceps 0.08 μg g−1 ± 0.01, T. bernacchii 0.17 μg g−1 ± 0.10; G. gibberifrons 0.11 μg g−1 ± 0.04), linear regressions against standard length indicated bioaccumulation in T. bernacchii (ANOVA, F = 7.8349, P = 0.0076). We suggest this may be the result of dietary specialisation on prey with calcareous shells that accumulate uranium. To the best of our knowledge, this paper provides the first quantitative baseline data on uranium levels in coastal Antarctic nototheniids. While the low levels recorded are unlikely to represent a threat within the food chain, we suggest that further long-term trophic studies (including stable isotope analysis) are needed, recognising that the feeding ecology of individual species (and even individuals) can have a strong effect on overall trends. Graphical abstract Image 1 Highlights • First quantitative baseline uranium levels presented for Antarctic nototheniids. • Levels low but emerald rockcod show evidence of bioaccumulation. • Bioaccumulation linked with dietary specialisation on molluscs? • Possible links with atmospheric deposition and climate change. • In depth trophic studies needed on Antarctic food-web dynamics. [ABSTRACT FROM AUTHOR]

Abstract Eleginops maclovinus is a eurythermic fish that under natural conditions lives in environments with temperatures ranging from 4 to 18 °C and can be usually captured near salmon farming areas. The aim of this study was to evaluate the effect of temperature over the innate and adaptive immune response of E. maclovinus challenged with Piscirickettsia salmoni s following different treatments: C (control injection with culture medium at 12 °C), C+ (bacterial injection at 12 °C), 18 °C c/A + B (injection with culture medium in acclimation at 18 °C), 18 °C c/A + B (bacterial injection in acclimation at 18 °C), 18 °C s/A + M (injection with culture medium without acclimation at 18 °C) and 18 °C s/A + B (bacterial injection without acclimation at 18 °C). Each injection had 100 μL of culture medium or with 100 μL at a concentration 1 × 108 of live bacteria, sampling six fish per group at 4, 8, 12, 16 and 20 days post-injection (dpi). Expression of the mRNA related with the innate immune response gene (TLR1, TLR5, TLR8, NLRC3, NLRC5, MyD88 and IL-1β) as well as the adaptive immune response gene (MHCI, MHCII, IgMs and IgD) were measured in spleen and head kidney. Gene expression profiles were treatment-type and time dependent. Levels of Immunoglobulin M (IgM) increased in challenged groups with P. salmonis from day 8–20 post challenge, which suggest activation of B cells IgM + through P. salmonis epitope detection. Additionally, a rise in temperature from 12 °C (C+) to 18 °C (with/without acclimation) also resulted in antibody increment detected in serum with significant differences between "18 °C c/A + B" and "18 °C s/A + B" groups. This is the first study that evaluates the effect of temperature changes and mRNA expression related with immune system gene over time on E. maclovinus, a native wild life fish that cohabits in the salmon farming environment. Highlights • The increase in temperature affects the gene transcription related with innate and adaptive immune response. • The increase in temperature (with and without acclimatation) increased the amount of antibodies detected in serum. • The temperature is modulating the immune response in Eleginops maclovinus. [ABSTRACT FROM AUTHOR]

Studies on reproduction of the dragonfishes, Bathydraconidae, are scarce, and within this family, the reproductive biology of Parachaenichthys charcoti was poorly understood. Herein we present a histologic analysis of P. charcoti ovaries together with data on reproductive effort using fish collected with trammel nets in austral summer at Potter Cove, South Shetland Islands (SSI), and compare this information with that reported for the South Georgia congener Parachaenichthys georgianus. In gravid females of P. charcoti, GSI of 16-31%, mature oocytes of 1.8-3.9 mm and total fecundity (TF) of 9025-18,937 oocytes/individual (X ± SD = 12,617 ± 4019, n = 7) were recorded. The histology of the ovaries confirmed the common characteristics of the Notothenioidei observed macroscopically, i.e., two distinct batches of oocytes, one in the previtellogenic stage (primary growing or cortical alveoli stages) and the other in vitellogenesis and likely to be released in the current season. A longer incubation period of P. charcoti compared with P. georgianus is associated to the colder waters at the SSI. Based on our sampling and reproductive effort data, together with the reported nesting behavior for P. charcoti, it is assumed that this species spawns in nearshore, sheltered waters in summer, presumably from late December to February. Spawning periods of both congeners differ from those reported for other notothenioids in the same Seasonal Pack-ice Zone, suggesting divergence in some aspects of the life strategies in the genus Parachaenichthys. Likewise, although there are no substantial differences between P. charcoti and other notothenioids regarding gonadal development, the genus Parachaenichthys shows distinct features in its reproductive strategies (e.g., higher TF) compared with other bathydraconid species. [ABSTRACT FROM AUTHOR]

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]

The Antarctic toothfish (Dissostichus mawsoni Norman 1937) is the largest notothenioid inhabiting high-latitude Antarctic waters, where it is an important fishery resource and plays a key ecological role at a high trophic level. Despite the considerable amount of data on D. mawsoni biology and distribution developed since the fishery began in 1997, crucial aspects of the life cycle, including spawning and early life history, remain undescribed. During the first winter longline survey to the northern Ross Sea region in 2016, ripe male and female D. mawsoni were collected for the first time, and in vitro fertilisation of eggs was performed. Here, we report on the first characterisation of D. mawsoni egg structure and initial embryonic development. The duration of the egg cleavage period was similar to that of other nototheniid species releasing pelagic eggs. The structural features of fertilised eggs, including chorion thickness and structure, support the hypothesis that eggs of D. mawsoni are pelagic. The data presented here contribute to the description of the potential habitat of the eggs of this species, and provide the first diagnostic information to recognise the eggs of D. mawsoni. [ABSTRACT FROM AUTHOR]

Notothenioid fish and invertebrate samples from Antarctica were collected in the austral summer of 2009, and analyzed for persistent organic pollutants (POPs), including polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polybrominated diphenylethers (PBDEs), as well as δ13C and δ15N stable isotopes for trophic level determination. In this study, the POP levels in the Antarctic biota samples were found to be ranked in the following order: OCPs > PAHs >> PBDEs. The POP levels in notothenioid fish and krill correlate to trophic levels; however, the POP concentrations in intertidal benthic invertebrates are higher than in notothenioid fish implying that specific biogeochemical factors may affect bioaccumulation in the Antarctica ecosystem. Biomagnification of POPs may have a smaller role than bioconcentration in Antarctica environment. In addition to the source, transport, exposure, and absorption for each group of POPs in the short food chain in Antarctica, the biological variation among species, interaction habitats, diet and metabolism are also factors for future studies on contaminant bioaccumulation. [ABSTRACT FROM AUTHOR]

It has been suggested that High-Antarctic waters, despite their remoteness from human activities, are impacted by anthropogenic pollution, and that the local biota are accumulating the contaminants. At present, no data exist on persistent organic pollutant (POP) body burdens for notothenioid fish inhabiting the High-Antarctic Weddell Sea. We determined the pollutant load in white muscle tissue of red- and white-blooded notothenoids from the Weddell Sea ( Trematomus loennbergii and Chionodraco hamatus , respectively), and compared them to our previous measurements of POPs in Low-Antarctic notothenioids. Analytes included various organochlorine pesticides (OCPs), polychlorinated biphenyls (indicator (i) PCBs, dioxine-like (dl) PCBs) and polybrominated diphenyl ethers (PBDEs). The analytical concentrations were converted into 2,3,7,8-TCDD toxic equivalents (TEQs). Compared to T. loennbergii, C. hamatus had lower levels of β-HCH (0.45 vs. 4.5 ng g −1 lipid weight), and Σ iPCBs (30 vs. 39 ng g −1 lipid weight), as well as lower levels of Σ PBDEs (131 vs. 261 ng g −1 fresh weight). POP body burdens and TEQs were mostly similar to those of Low-Antarctic notothenioids analysed previously, and not related to the trophic positions of the species. The variations in POP levels between and within High- and Low-Antarctic notothenioids only marginally corresponded to sampling site, ecological differences or trophic levels of the species, and might rather be related to metabolism or age effects. The present findings suggest that fishes of High-Antarctic waters, although this area is more remote and less influenced by local human activities, do not show lower POP body burdens than fishes from Low-Antarctic waters. [ABSTRACT FROM AUTHOR]

Eleginops maclovinus is a sub-Antarctic fish endemic to the South American coast and is a monotypic species of the Eleginopidae family. A scarce amount of scientific information exists regarding the effects of temperature on E. maclovinus physiology. In this study, E. maclovinus specimens were acclimated for 2 weeks at 10 °C (control), 14, and 18 °C. Posterior assessments were performed for the intermediary metabolism of carbohydrates, lipids, and amino acids (in the plasma, liver, gills, and kidney) and on the osmoregulatory capacity [plasma osmolality and gill, kidney, and foregut Na, K-ATPase (NKA) activities]. In the plasma, only lactate and total amino acid levels were affected by the temperature. NKA activity presented a linear relationship with the increased temperatures. The liver exhibited no change in the carbohydrates metabolism, but the glycogen/glucose metabolite levels did differ. Amino acid metabolism showed a direct relationship between temperature and GDH and Asp-AT activities, and an inverse relationship between temperature and Ala-AT activity. Lipid metabolism was similar to Ala-AT. In the gills, carbohydrate metabolism (G6PDH and HK activities) presented a direct relationship with the increased temperatures. In the kidney, carbohydrate metabolism (only G6PDH activity) was greater at higher temperatures, and amino acid metabolism (GDH activity) showed a direct relationship with temperature. Lipid metabolism (G3PDH activity) was greatest at 14 °C, presenting significant differences compared to 10 °C. The obtained results suggest that E. maclovinus can acclimate to the projected thermal increase of climate change, with a reorganization of the intermediary metabolism components being tissue-dependent and osmoregulatory effects being affected by NKA activity and greater rates of nitrogenous waste extrusion. [ABSTRACT FROM AUTHOR]

Short-term storage of semen is a useful strategy for preservation of fish spermatozoa in reproductive management, however, no information is available on Patagonian blenny ( Eleginops maclovinus ) semen. This study was designed to evaluate the effects of in vitro storage on sperm function parameters in Patagonian blenny. Samples of undiluted (C: control) and diluted semen 1:1 v/v (DS1) and 1:3 v/v (DS2) in Storfish® were stored at 4 °C for 7 days. Motility, viability, mitochondrial membrane potential (ΔΨMit), DNA fragmentation and ATP content were assessed at 0, 3 and 7 days. The results demonstrated that sperm function parameters were affected significantly by the time of storage, and that dilution allows better preservation of sperm motility. On the third day of storage, spermatozoa showed a motility > 56% in DS1 and DS2, nevertheless, in C it significantly decreased as well as its ATP content ( P < 0.05), whereas viability was maintained > 70% and ΔΨMit > 45%. However, a significant decline in the percentage of sperm function parameters ( P < 0.05) was observed at 7 days of storage for all samples of undiluted and diluted semen. DNA fragmentation showed no significant increase in all groups, demonstrating < 5% at day 7. In vitro storage conditions maintain better sperm motility in diluted than undiluted semen, preserving the sperm function in all groups assessed during 3 days. In conclusion, the results provide new data on Patagonian blenny sperm quality with respect to in vitro short-term storage evaluated by flow cytometry, this information must be considered for implementing in aquaculture reproductive strategies for the conservation of this species. [ABSTRACT FROM AUTHOR]

Calmodulin (CaM) is a highly conserved calcium sensor protein associated with chilling tolerance in living organisms. It has four EF-hand domains for binding of four Ca, two of them located in the N-terminus, and the other two in the C-terminus. A notothenioid CaM gene fragment ( CaMm), which only codes for N-terminus of CaM (with two EF-hand domains), was introduced into Nicotiana benthamiana. Effects of its overexpression on chilling tolerance in plants were explored. During 4◦C or 0◦C chilling treatment, both CaMm and CaM transgenic plants showed higher PSII maximum quantum yield, actual quantum yield, and soluble protein content, lower electrolyte leakage and malondialdehyde content than that of the control. The changes in these physiological indices were comparable between the CaMm and CaM transgenic plants during the treatments. These results indicate that the N-terminus of calmodulin is likely the key functional domain involved in the adaptive response to cold stress. [ABSTRACT FROM AUTHOR]

The long evolution of the Antarctic perciform suborder of Notothenioidei in the icy, oxygen-rich waters of the Southern Ocean may have reduced selective pressure to maintain a hypoxic response. To test this hypothesis, cDNA of the key transcriptional regulator of hypoxic genes, hypoxia-inducible factor-1α (HIF-1α), was sequenced in heart ventricles of the red-blooded notothenioid, Notothenia coriiceps, and the hemoglobinless icefish, Chaenocephalus aceratus. HIF-1α cDNA is 4500 base pairs (bp) long and encodes 755 amino acids in N. coriiceps, and in C. aceratus, HIF-1α is 3576 bp long and encodes 779 amino acids. All functional domains of HIF-1α are highly conserved compared to other teleosts, but HIF-1α contains a polyglutamine/glutamic acid (polyQ/E) insert nine amino acids long in N. coriiceps and 34 amino acids long in C. aceratus. Sequencing of this region in four additional species, representing three families of notothenioids, revealed that the length of the polyQ/E insert varies with phylogeny. Icefishes, the crown family of notothenioids, contain the longest polyQ/E inserts, ranging between 16 and 34 amino acids long, whereas the basal, cold-temperate notothenioid, Eleginops maclovinus, contains a polyQ/E insert only 4 amino acids long. PolyQ/E inserts may affect dimerization of HIF-1α and HIF-1β, HIF-1 translocation into the nucleus and/or DNA binding. [ABSTRACT FROM AUTHOR]

In the present study, the possible associations between selected persistent organic pollutants (POPs) and biological factors were assessed in different tissues of two Antarctic notothenioid fish: Notothenia rossii (NOR) and Trematomus newnesi (TRN) collected at Potter Cove, King George Island/Isla 25 de Mayo, South Shetland Islands. Specifically, association patterns between biological factors (body size, lipid content, body condition) and POP concentrations (polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and metabolites, polybrominated diphenyl ethers (PBDEs), and hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), chlordanes (CHLs) and methoxylated polybrominated diphenyl ethers (MeO-PBDEs)), were explored by using two approaches: multivariate analyses (principal component analysis: PCA) and intraspecific correlations. Integrating results suggest that biological factors such as size, KI and tissue type seemed to be associated to selective accumulation of POPs for immature specimens of N. rossii , and KI and tissue type for mature specimens of T. newnesi . Each particular factor should be considered when choosing N. rossii or T. newnesi as sentinels for POPs pollution in Antarctic marine environments. Further, both nototheniids showed a selective accumulation pattern in their gonads of penta-chlorinated biphenyls ( penta- CBs; 55.5 and 29 ng g −1 lw for N. rossii and T. newnesi , respectively) and organochlorine pesticides such as DDTs (199 and 13.3 ng g −1 lw, for N. rossii and T. newnesi respectively), and of polybrominated diphenyl ethers (PBDEs) in gills (97.2 and 22.1 for ng g −1 lw, for N. rossii and T. newnesi , respectively), highlighting the importance of these tissues in monitoring studies of pollution in fish. The current study expands the knowledge concerning the biological factors to be investigated when specific pollutants are monitored and supports the importance of tissue type for the selective accumulation of POPs in Antarctic fish. Additionally, a contribution to the scarce data on concentration of MeO-PBDEs in Antarctic marine organisms, particularly in the highly diverse perciform suborder Notothenioidei is provided. [ABSTRACT FROM AUTHOR]

Owing to commercial fishing during the late 1970s/early 1980s, targeted notothenioid species had become depleted around the South Shetland Islands. Herein we report subsequent changes in the prevalence of three species, Notothenia rossii, Gobionotothen gibberifrons and Notothenia coriiceps in Potter Cove, King George Islands/Isla 25 de Mayo, in a 33-year effort to monitor recovery. N. rossii and G. gibberifrons had been severely impacted by industrial fishing but in offshore waters N. coriiceps had never been commercially fished; however, all three species exhibit similar nearshore habitats and life history. We examined composition in trammel net catches during 2012-2016, augmenting a time series started in 1983. Our inshore results were consistent with those from offshore bottom trawl sampling in 2007 and 2012 around the South Shetland Islands: (1) continued increase in the abundance of N. rossii; (2) further decline in G. gibberifrons recruitment evidenced by low proportions of juvenile fish; and (3) a high abundance of N. coriiceps. Reasons for lack of recovery in G. gibberifrons remain obscure but seemingly relate to the dramatically changing ecosystem of the region due in part to climate as well as recovery among previously depleted upper trophic level species. Our results are also consistent with trends reported in seabirds that feed on juveniles of these notothenioids: decrease in the areas commercially fished. Under the regulation of CCAMLR, commercial fishing for finfish in the South Shetland Islands region (FAO Subarea 48.1) remains prohibited since 1991; results indicate that it cannot be reinstated. [ABSTRACT FROM AUTHOR]

There has been no comprehensive study of the bathymetry of notothenioid fishes. Therefore, I analyzed minimum and maximum depths and depth ranges for 128 of 142 species that collectively range from 0 to ≈3000 m. Means (and medians) for maximum depths are 176 m (75 m) for non-Antarctic, 511 m (360 m) for sub-Antarctic, and 963 m (899 m) for Antarctic species; medians are significantly different. Means (and medians) for depth ranges for the three groups are 140 (55 m), 470 (345 m), and 727 m (714 m), respectively, with significantly different medians. The mean maximum depths for the Cryonotothenioidea are: Nototheniidae-525 m, Harpagiferidae-88 m, Artedidraconidae-906 m, Bathydraconidae-1165 m, and Channichthyidae-910 m. If five species of Bathydraco, with a mean of 2098 m are excluded, the mean for the Bathydraconidae is 741 m. With the exceptions of the harpagiferids and Bathydraco, there is overlap of the 95% confidence intervals for the means of other families. Thirteen Antarctic and sub-Antarctic species with maximum depths and/or depth ranges ≥1500 m are especially deep-living: four nototheniids, four species of Bathydraco, three species of Pogonophryne, and two channichthyids. The most common depth range is 0-50 m for non-Antarctic, 200-400 m for sub-Antarctic and 600-800 m for Antarctic species. Three species have depth ranges >2000 m. Species diversity peaks at 50 m for non-Antarctic, 100 m for sub-Antarctic, and 500 m for Antarctic species. Notothenioids are not eurybathic compared with older deep-sea taxa but are eurybathic relative to marine percomorphs. [ABSTRACT FROM AUTHOR]

The Antarctic spiny plunderfish Harpagifer antarcticus is a common species distributed along the southern Scotia Arc, representing one of the most important components of the littoral benthic fish community there. Compared to adulthood, the early life history traits of H. antarcticus are poorly known, especially for the population inhabiting the shallow waters off the South Shetland Islands. Through the analysis of sagittal otolith microstructure, we estimated age and growth from early larvae collected during the austral summer at Chile Bay, Greenwich Island. An exponential model fitted to the age-length data provided estimates of hatching size and mean larval growth of the local population, being, respectively, 5.36 mm and 0.17 mm day (range 0.12-0.22 mm day), corresponding to a daily percentage increase in body size of 2.2%. Back-calculated hatch dates were positively correlated to wind intensity, especially in case of northeast wind dominance. Based on this evidence, we suggest that hatching of H. antarcticus might be triggered by wind-induced turbulence in nearshore subtidal environments of the South Shetland Islands. From an ecological perspective, the early life history strategy of this species consisted of a spring-summer hatching of small, fast-growing larvae, which develop into a demersal juvenile stage before their first winter of life. [ABSTRACT FROM AUTHOR]