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Beneath the surface of the Southern Ocean, in the deep waters of the continental shelf and continental slope of Antarctica, a magnificent fauna consisting of over 320 known species of fish thrives in the cold and dark. These fish are uniquely adapted to the extreme environment in which they live. Over the course of millennia, they have evolved a remarkable range of physiological and biochemical features, the most visually stunning of which is that some lack haemoglobin (Fig 1). Yet, these species are under threat from global climate change and fishing, and the secrets they might unlock for science could be lost in the next decades if action is not taken. Figure 1. The blackfin icefish Chaneocephalus aceratus . Photo credit: Steve Untracht. A human can survive in freezing water for around 15 min before their organs begin to shut down. The fauna of the Southern Ocean spend their entire lives at these extreme temperatures. The fish species present are dominated by members of the Notothenioidei, which comprises 50% and 90% of the Antarctic finfish diversity and biomass, respectively [1,2,3]. The notothenioids are a suborder of perch‐like fishes that are mainly benthic and highly endemic to the Antarctic region. They are divided into eight families that have radiated from an ancestral stock during the last 20 million years to fill a variety of niches. These families include the Nototheniidae—the most diverse and specious family of the notothenioids—the Bathydraconidae—the dragonfishes, so‐named because of their especially long and narrow body forms—and the Channichthyidae—the icefishes, known for their colourless blood. > …the Antarctic and its spectacular fauna are suffering a fate similar to others on the planet—their survival is threatened by anthropogenic activities The composition of today's Antarctic fish fauna has been strongly influenced by the distinctive oceanographic features of …

Antarctic barbeled plunderfishes of the genus Pogonophryne are the most speciose notothenioid group, comprising about 20 poorly known recognized species. The interspecific systematics within the genus is complex, because the various species vary little morphologically. One of these previously unknown forms captured as by-catch of the Antarctic toothfish (Dissostichus mawsoni) fishery during the Antarctic summer 2009–2010 in deep waters of the western Ross Sea is described herein as new species Pogonophryne tronio. The description is based on 2 adult specimens, captured at depths 900–1,015 m: the holotype (male, 290 mm TL, 234 mm SL), paratype (female, 315 mm TL, 260 mm SL). This species, a short-barbeled form of the dorsally spotted “P. mentella” group of species, is compared morphologically to the closely related P. brevibarbata and P. ventrimaculata, using type specimens of both species. P. tronio sp. n. is characterized by the following combination of characters: a short (about 10–12 % SL), slender, tapered and bicolored (dark basally, light distally) mental barbel without a conspicuous terminal expansion; tip of barbel slightly flattened and covered by short tapered finger-like processes basally and flattened, leaf-like processes distally; a slightly protruding lower jaw; a relatively low (about 18 % SL) second dorsal fin lacking the elevated anterior lobe occurring in males of some species in the genus, sharply striped pectoral and caudal fins; the dorsal surface of the head and the area anterior to the first dorsal fin covered with large dark-brown blotches and spots.

In fish, haemoglobin adaptations govern survival and biodiversity under specific environmental conditions and physiological requirements. The study of haemoglobins is aimed at identifying key links between molecular and eco-physiological adaptations. Differences in haemoglobin properties arise from the interaction of the heme with specific residues in the primary structure, but modulation in regulatory processes and altered protein synthesis may be additional adaptations in response to environmental changes. Fish experience variations in oxygen availability, salinity, ionic composition, pH and temperature. Compared to the dominant suborder Notothenioidei in Antarctica, many Arctic species possess multiple haemoglobins with different functional properties, which might be selectively and differentially expressed to secure oxygen unloading in peripheral tissues including swim bladder and retina, suggesting a mechanism of labour sharing. Haemoglobin polymorphism may further increase the repertoire of oxygen-b...

An isolated partial right dentary (BAS D.515.2) collected by the British Antarctic Survey prompted a re-evaluation of gadiform remains from the La Meseta Formation (conventionally middle Eocene) of Isla Marambio (Seymour Island), Antarctic Peninsula. Modern gadiforms (hakes and cods) range from the Arctic to Antarctic, inhabiting deep sea benthic, shore, estuarine, and freshwater environments. Based on a fossil record primarily composed of otoliths, they are known to extend back to the Eocene and Oligocene. The new specimen was recovered from the fossil penguin locality D.515. It is characterized by a single row of sharp, ankylosed teeth set upon robust bony pedestals. The surface anterior to the mental foramen exhibits ascending and descending ridges with slightly rugose texture. The ascending ridge is fractured, but partially covers the lateral aspect of the tooth row. BAS D.515.2 is unlike the dentary of macrourid gadiforms, also recovered from the Eocene of Antarctica. BAS D.515.2 preserves several features similar to previously published accounts of the gadiform “†Mesetaichthys” from Isla Marambio. These specimens are probably the same taxon and their combined character suite indicates it is a member of Merluccidae. Thus, these are the only non-otolithic skeletal specimens of an Eocene hake known outside of the London Clay's †Rhinocephalus.

The Antarctic fish fauna is characterized by high endemism and low species diversity with one perciform suborder, the Notothenioidei, dominating the whole species assemblage on the shelves and slopes. Notothenioids diversified in situ through adaptive radiation and show a variety of life history strategies as adults ranging from benthic to pelagic modes. Their larval development is unusually long, lasting from a few months to more than a year, and generally includes a pelagic larval stage. Therefore, the advection of eggs and larvae with ocean currents is a key factor modulating population connectivity. Here, we compare the genetic population structures and gene flow of seven ecologically distinct notothenioid species of the southern Scotia Arc based on nuclear microsatellites and mitochondrial DNA sequences (D-loop/cytochrome b). The seven species belong to the families Nototheniidae (Gobionotothen gibberifrons, Lepidonotothen squamifrons, Trematomus eulepidotus, T. newnesi) and Channichthyidae (Chaenocephalus aceratus, Champsocephalus gunnari, Chionodraco rastrospinosus). Our results show low-population differentiation and high gene flow for all investigated species independent of their adult life history strategies. In addition, gene flow is primarily in congruence with the prevailing ocean current system, highlighting the role of larval dispersal in population structuring of notothenioids.

Trematomus newnesi is a common inshore species with a circum-Antarctic distribution. It provides the only known example of phenotypic plasticity in Antarctic notothenioid fish, existing as populations of typical, large mouth and intermediate morphs that can be difficult to identify. Using specimens from both Potter Cove, King George/25 de Mayo Island, and from McMurdo Sound, we found that the morphometric measurements gape width/head length (HL), upper jaw length/HL and, to a lesser extent, orbit diameter/HL reliably separated the morphs. For use in a key, we converted the ratios into the qualitative characters head shape, head width and upper jaw length relative to middle of the eye. To increase the reliability of the key, we also assessed intra-morph variability in these characters. The key is supplemented with colour photographs illustrating the distinctive features for separation of the morphs. We discovered that, in the case of the specimens from Potter Cove, each morph had a distinct pattern of colouration: typical—trunk blotched, with yellow or orange-brown predominating especially on pectoral and caudal fins; large mouth—trunk blotched, with green predominating especially in pectoral and opercular regions; and intermediate—trunk less blotched, with homogeneous dark brown-grey on trunk, pectoral and caudal fins. We also discuss the ecological implications of colour in the morphs.

As the Southern Ocean cooled to -1.8 °C over the past 40 My, the teleostean clade Notothenioidei diversified and, under reduced selection pressure for an oxygen-transporting apparatus, became less reliant on hemoglobin and red blood cells. At the extreme of this trend, the crown group of Antarctic icefishes (Channichthyidae) lost both components of oxygen transport. Under the decreased selection scenario, we hypothesized that the Antarctic dragonfishes (Bathydraconidae, the red-blooded sister clade to the icefishes) evolved lower blood hemoglobin concentrations because their globin gene complexes (α- and β-globin gene pairs linked by a regulatory intergene) transcribe globin mRNAs less effectively than those of basal notothenioids (e.g., the Nototheniidae [notothens]). To test our hypothesis, we 1) sequenced the α/β-intergenes of the adult globin complexes of three notothen and eight dragonfish species and 2) measured globin transcript levels in representative species from each group. The typical nototheniid intergene was ∼3-4 kb in length. The bathydraconid intergenes resolved into three subclasses (long [3.8 kb], intermediate [3.0 kb], and short [1.5-2.3 kb]) that corresponded to the three subclades proposed for the taxon. Although they varied in length due to indels, the three notothen and eight dragonfish intergenes contained a conserved ∼90-nt element that we have previously shown to be required for globin gene transcription. Using the quantitative polymerase chain reaction, we found that globin mRNA levels in red cells from one notothen species and from one species of each dragonfish subclade were equivalent statistically. Thus, our results indicate that the bathydraconids have evolved adult globin loci whose regulatory intergenes tend to be shorter than those of the more basal nototheniids yet are equivalent in transcriptional efficacy. Their low blood hemoglobin concentrations are most likely due to reduction in hematocrit.

We have investigated the immunoglobulin molecule and the genes encoding it in teleosts living in the Antarctic seas at the constant temperature of −1.86 °C. The majority of Antarctic teleosts belong to the suborder Notothenioidei (Perciformes), which includes only a few non-Antarctic species. Twenty-one Antarctic and two non-Antarctic Notothenioid species were included in our studies. We sequenced immunoglobulin light chains in two species and μ heavy chains, partially or totally, in twenty species. In the case of heavy chain, genomic DNA and the cDNA encoding the secreted and the membrane form were analyzed. From one species, Trematomus bernacchii, a spleen cDNA library was constructed to evaluate the diversity of VH gene segments. T. bernacchii IgM, purified from the serum and bile, was characterized. Homology Modelling and Molecular Dynamics were used to determine the molecular structure of T. bernacchii and Chionodraco hamatus immunoglobulin domains. This paper sums up the previous results and broadens them with the addition of unpublished data.

Ichtyoplankton surveys were carried out in the western Ross Sea by the R/V Italica in the austral summer 1996 and 1997-1998 to study species composition and spatial distribution of larval stages of fish. One of the most abundant icefish caught was Dacodraco hunteri, a poorly known channichthyid inhabiting the high-Antarctic Zone. Based on 382 yolk-sac larvae and 13 preflexion larvae, the study was focused to estimate spatial distribution and abundance, as well as diet and growth rate. The pigmentation pattern and some morphometric measurements were also recorded for comparative purposes. The specimens were caught in relatively restricted areas located in Terra Nova Bay and north of the Ross Ice Shelf on the Challenger and Joides Basins. The standardized abundance of early larvae ranged between 0.03 and 1.72 individuals 10(-3) m(3) in 1996 and 0.16-4.53 individuals 10(-3) m(3) in 1997-1998, respectively. Fitting a linear model to the mean length increase in larvae collected in subsequent catch dates, the growth rate was estimated to be approximately 0.11 mm/day. Based on back calculation of growth rate and presumed hatch size of 11 mm, larval hatching probably took place in mid-December. Diet of preflexion larvae consisted exclusively of larvae of the pelagic nototheniid Pleuragramma antarcticum, a key species of the high-Antarctic pelagic food web. Hence, D. hunteri probably plays a more important role than previously thought in the pelagic community of the Ross Sea.

The RSV Aurora Australis survey allowed the first comprehensive study of the demersal ichthyofaunal environment and of the diversity of the Dumont d’Urville Sea. We observed a high dominance of the Notothenioidei in both the number of species and in integrated abundances. The Nototheniidae was the most abundant family with 44.7% of the total integrated abundance, followed by Bathydraconidae (18.8%). Trematomus eulepidotus was the dominant species with 19.9% of the total individuals catch. Nevertheless, 43 of the 53 species caught could be considered as very rare. The Bathydraconidae was the most diversified family with 11 species caught. The highest integrated abundances of fish were found from 400 to 800 m. Well-structured species communities were observed, with high species richness from 570 to 681 m. The richest zones were located along the basins and along their upper-sides. Statistical analyses indicated large-scale spatial patterns in species composition, with clear differences in fish communities from the continental slopes, the basins and on the shelf. At a finer spatial scale, the current in the George V Basin and iceberg scouring on the banks and their sides tended to create locally heterogeneous small-scale habitats. We suggest that the glacial history and the structured habitats allowed successive colonisations of the seabed by demersal fish.

The Southern Ocean is home to two major types of fishes: the largely endemic suborder Notothenioidei and representatives of oceanic fish families that are widely distributed in the midwater and benthic environments elsewhere (e.g. bathylagids, myctophids, liparids, and zoarcids). In most regions of the coastal Antarctic, e.g. the Ross Sea, there is a distinct separation in the pelagic communities at the shelf break between the oceanics (off-shelf) and the endemics (on-shelf). Coincidentally, in much of the coastal Antarctic, the shelf break also marks the boundary between a water column entirely composed of the very cold (−2 °C) Ice Shelf Water and an oceanic profile that includes warmer circumpolar deep water (2 °C at 200 m) at intermediate depths. The distinct separation in pelagic communities observed in most coastal regions of the Antarctic is not seen on the western Antarctic Peninsula (WAP), where circumpolar deep water intrudes to form a warmer midwater and oceanic species are strongly represented. It was hypothesized that the cold ice-shelf water, lethal to fishes without antifreeze glycoproteins (AFGPs) in their blood, was excluding the oceanic species from most of the Antarctic continental shelf waters. To test the hypothesis, nine species of fish captured in WAP shelf waters were tested for the presence of AFGPs. The oceanic fish families analyzed: Myctophidae (Electrona and Gymnoscopelus), Zoarcidae (Melanostigma), Gempylidae (Paradiplospinus), Paralepididae (Notolepis), and Bathylagidae (Bathylagus) showed no antifreeze activity. Two endemic species captured in the same sampling program did show antifreeze activity: the important pelagic species Pleuragramma antarcticum (Nototheniidae) and the Bathydraconid species Vomeridens infuscipinnus. The absence of AFGPs in the blood of Antarctic oceanic species makes a strong case for temperature exclusion of oceanic fishes in the coastal Antarctic.

The radiation of notothenioid fishes (Perciformes) in Antarctic waters was likely the result of an absence of competition in the isolated Antarctic waters and key traits such as the production of antifreeze glycoprotein and buoyancy modifications. Although notothenioids lack a swim bladder, the buoyancy of Antarctic species, ranging from neutrally buoyant to relatively heavy, corresponds to diverse life styles. The buoyancy of South American notothenioids has not been studied. Static buoyancy was measured in adult notothenioids (n = 263, from six species of the sub-order Notothenioidei, families Bovichtidae, Eleginopidae, Nototheniidae, and Harpagiferidae) from the Beagle Channel. Measurements were expressed as percentage buoyancy (%B). Buoyancy ranged from 3.88 to 6.96% (median, 4.0–6.7%), and therefore, all species could be considered benthic consistent with previous studies that found that neutral buoyancy in notothenioids is rare. Harpagifer bispinis, Patagonotothen cornucola, and Cottoperca gobio were significantly less buoyant than Paranotothenia magellanica. The buoyancy values of most species were concordant with known habitat preferences. These data, especially the data of C. gobio (sister lineage of all other nototehnioids) and E. maclovinus (sister lineage of the Antarctic clade of notothenioids), could be useful for understanding the diversification of this feature during the notothenioid radiation.

Artedidraconids (Plunderfishes) are small benthic notothenioid fishes of the Antarctic and South Georgia shelf and slope. The family Artedidraconidae is monophyletic; however, the relationships within the family have remained poorly explored until now, and based on a small sample of the genus Artedidraco. The present study focuses on the interrelationships among the artedidraconid genera and the phylogeny of the genus Artedidraco. 2,353 base pairs from 77 specimens were sequenced from the partial mitochondrial cytochrome oxidase I gene and cytochrome b gene, the partial mitochondrial control region and the partial nuclear rhodopsin retrogene. The genus Artedidraco is not monophyletic, confirming the preliminary relationships found by Derome et al. (Mol Phylogenet Evol 24:139–152, 2002): Pogonophryne, Dolloidraco and Histiodraco are well embedded within the genus Artedidraco. From Artedidraco skottsbergi and A. loennbergi to A. orianae and A. mirus, the tree shows that there is an increasing number of upper lateral line tubular scales and decreasing number of disc-shaped scales. There is also a trend toward a decrease in the number of epipleural ribs and an increase in number of pleural ribs along the tree.

Rolling-circle (RC) eukaryotic transposons, known as helitrons, are found in a wide range of organisms, from protist to mammals. Autonomous helitrons have a distinctive open reading frame (ORF) encoding a polypeptide that contains typical domains for RC replication (RCR): the Rep (RCR initiator) and the DNA helicase domains. These elements are believed to have an important role in the host genome evolution, owing to their frequent capture of host genes, some of which can evolve into novel genes or become essential for helitron transposition. We conducted a molecular analysis of the suborder Notothenioidei, a group of Perciformes that currently dominate the Antarctic waters by virtue of their remarkable cold-adaptation ability. A novel helitron from the genome of the icefish species Chionodraco hamatus, belonging to the Channichthyidae, the most derived Notothenioids family, was isolated, characterized and designated as HeliNoto (8.9 kb). Its ORF was compared to homologous sequences from different species in a comprehensive phylogenetic analysis. For the first time the putative functional domains of a helitron were subjected to a well accurate structural analysis including chromosomal localization. Finally, the distribution of HeliNoto among Notothenioids was investigated.

Understanding molecular adaptations evolved in response to environmental temperature changes is essential, because temperature affects the kinetic energy of molecules and modifies molecular interactions, macromolecular stability/functioning and membrane features. Environmental oxygen availability may also play an important role in the evolution of polar marine organisms, as suggested by the physiological and biochemical strategies adopted by these organisms to acquire, deliver and scavenge oxygen.This review summarises the current knowledge on the structure and function of hemoglobins of fish living in Antarctic habitats. The variety of adaptations underlying the ability of Antarctic fish to survive at temperatures permanently close to freezing is unique among teleosts. The dominant perciform suborder Notothenioidei affords an excellent study group for elaborating the evolution of biochemical adaptation to temperature. The availability of notothenioid taxa living in a wide range of latitudes (Antarctic, sub-Antarctic, and temperate regions) offers a remarkable opportunity to study the physiological and biochemical characters gained and, conversely, lost in response to cold and to reconstruct the likely evolutionary events modulating the ability to carry oxygen in freezing habitats. Although oxygen can be transported in freely dissolved form most animals rely on one or more protein carriers to deliver it to the respiring tissues. Compared to temperate and tropical species, high-Antarctic notothenioids have evolved reduced hemoglobin concentration/multiplicity. The Antarctic family Channichthyidae (the notothenioid crown group) is devoid of hemoglobin. All extant icefish species lack hemoglobin and many have lost myoglobin expression. In these species, oxygen delivery to tissues occurs by transport of the gas physically dissolved in the plasma .

Current climate change has raised concerns over the fate of the stenothermal Antarctic marine fauna (animals that evolved to live in narrow ranges of cold temperatures). The present paper focuses on Notothenioidei, a taxonomic group that dominates Antarctic fish. Notothenioids evolved in the Southern Ocean over the last 20 million years, providing an example of a marine species flock with unique adaptations to the cold at morphological, physiological and biochemical levels. Their phenotypic modifications are often accompanied by 'irreversible' genomic losses or gene amplifications. On a micro-evolutionary scale, relatively 'shallow' genetic variation is observed, on account of past fluctuations in population size, and a significant genetic structure is evident, suggesting low population connectivity. These features suggest that Antarctic fish might have relatively little potential to adapt to global warming, at least at a genetic level. The extent of their phenotypic plasticity, which is evident to some degree, awaits further research.

Antarctic plunderfishes (Notothenioidei, Artedidraconidae) are important components of the Southern Ocean fish fauna. As a contribution to the Victoria Land Transect Project, we performed a cytogenetic analysis of six species from three of the four artedidraconid genera,Artedidraco glareobarbatus,A. orianae,A. skottsbergi,A. shackletoni,Histiodraco velifer, andPogonophrynesp. We investigated the species-specific cytogenetic features and highlighted patterns of chromosomal evolutionary change using a molecular phylogeny based on mitochondrial and nuclear genes. Despite a conserved diploid number, some important karyotypic traits account for major differences among artedidraconid species. Specific cytogenetic features, including the chromosomal organization of ribosomal genes and the occurrence of sex chromosomes, are characteristics ofA. skottsbergi, making this species distinct among those studied. These chromosomal peculiarities are consistent with the phylogenetic hypothesis resolvingA. skottsbergias the sister lineage of all other Artedidraconidae. A karyological similarity was found betweenA. glareobarbatusandA. shackletoniconsistent with their inferred sister species relationship in the phylogeny. The results indicate that artedidraconids are not conservative in their genomic organization at the chromosomal level and provide new evidence for the degree of biological diversity in this notothenioid group.

Antarctic icefishes (Family: Channichthyidae) are the only adult vertebrate animals that do not express the circulatory oxygen-binding protein, hemoglobin. Six species of icefishes, including Dacodraco hunteri, also do not express myoglobin (Mb), an oxygen-binding protein found in ventricular tissue of Antarctic notothenioids. Sequence of the Mb gene from D. hunteri contains a duplicated TATA box in the promoter region of the Mb gene that is absent in Chionodraco rastrospinosus, an icefish species known to express Mb. The 15-base pair insertion in D. hunteri is identical to the duplicated TATA box that is thought to be directly responsible for preventing transcription of the Mb gene in C. aceratus, another icefish species that lacks Mb expression. Sequencing of the Mb promoter from the remaining channichthyid species revealed the duplicated TATA box in 14 of 16 icefish species, including 8 species known to express Mb. Based on the presence of the duplicated TATA box in promoters of both Mb-expressing and Mb-lacking species, loss of Mb expression in D. hunteri and C. aceratus is either independent of the duplicated TATA box, or the duplicated TATA box requires presence or absence of a distant regulatory element to prevent transcription.

While many Antarctic organisms possess only limited ability to respond to environmental temperature change, there is now substantial evidence to confirm that the notothenioid fish, Pagothenia borchgrevinki, has retained some thermal flexibility and can successfully acclimate to a 5°C increase in temperature. Previous research demonstrated that after acclimation to 4°C, resting cardiac output in this species was thermally independent, while cold-adapted fish demonstrated thermal dependence of cardiac output. Here, we extend this research into cardiovascular plasticity and report the following: (1) The mechanisms responsible for the thermal independence of cardiac output in warm-acclimated (4°C, for 4 weeks) fish include a combination of warm-induced bradycardia and cold-induced tachycardia bouts. (2) These acute responses are under cholinergic control. (3) Changes to the thermal sensitivity of heart rate and ventilation rate result in concomitant changes to cardio-respiratory coupling in warm-acclimated fish.

Nineteen specimens of the rare dragonfishVomeridens infuscipinniswere evaluated for meristic counts, morphometric measurements, vomerine teeth and the supratemporal canal, anatomical and histological observations of bone, cartilage and lipid, diet, and reproductive status. Seven individuals were measured for buoyancy. All specimens had small vomerine teeth that varied in number. There was also variability in the arrangement of the supratemporal pores and canals.Vomeridenspossess a body with little bone and considerable amounts of cartilage and lipid. A mean percentage buoyancy of 1.61% indicated thatVomeridensis nearly neutrally buoyant. Inferences from measurements of buoyancy and from morphological data suggest thatVomeridenslives in an epibenthic water column habitat at 400–900 m. Facilitated by its reduced body density,Vomeridensare likely to forage in the water column by hovering above the substrate. The stomach contents consisted of krill (Euphausia superba), some as large as 46–50 mm.The absolute and relative fecundity in seven female was 1576–2296 oocytes (mean 1889) and 21.3–28.9 oocytes g-1body weight (mean 25.3), respectively. The reproductive effort in terms of egg diameter, GSI, and absolute and relative fecundity is similar to that for other bathydraconids.

Oxidative challenge is an important factor affecting the adaptive strategies of Antarctic fish, but data on antioxidant defences in these organisms remain scarce. In this investigation, individual antioxidants and the total oxyradical scavenging capacity (TOSC) were characterised in three notothenioid species, Trematomus bernacchii, Trematomus hansoni and Trematomus newnesi; seasonal fluctuations were further analysed in T. bernacchii sampled during different periods of the reproductive cycle, ice melting and phytoplanktonic blooms. The overall results revealed only limited differences between the three notothenioids, with greater TOSC values in T. hansoni and T. newnesi. The capacity for decomposing hydrogen peroxide via catalase was not particularly enhanced in these fish, in contrast to the prominent role of the enzyme in Antarctic invertebrates. An alternative antioxidant strategy, based on the efficiency of low molecular mass scavengers was suggested, especially for T. bernacchii which had higher lev...

Marine organisms, living in the cold waters of the Southern Ocean, are exposed to high oxygen concentrations. Cold-adapted organisms have developed networks of defence mechanisms to protect themselves against oxidative stress. The dominant suborder Notothenioidei of the Southern Ocean is one of the most interesting models, within vertebrates, to study the evolutionary biological responses to extreme environment. Within bacteria, the psychrophilic Antarctic bacterium Pseudoalteromonas haloplanktis TAC125 gives the opportunity to explore the cellular strategies adopted in vivo by cold-adapted microorganisms to cope with cold and high oxygen concentration. Understanding the molecular mechanisms underlying how a range of Antarctic organisms have responded to climate change in the past will enable predictions as to how they and other species will adapt to global climate change, in terms of physiological function, distribution patterns and ecosystem balance.

The Trematominae are a particularly interesting subfamily within the antarctic suborder Notothenioidei (Teleostei). The 14 closely related species occupy a large range of ecological of niches, extremely useful for evolutionary and biogeography studies in the Antarctic Ocean. But some Trematomus species can be difficult to identify by using morphological criteria, specially young stages and damaged specimens. Molecular identification would therefore be highly useful, however the suitability of the cytochrome oxidase Igene in a barcodingapproach needs to be assessed. We evaluated species delineation withinthegenusTrematomus comparing morphological identification, nuclear markers (the rhodopsin retrogene and a new nuclear marker pkd1: polycystic kidney disease 1) and COI. We show that Trematomus vicarius is not distinguishable from Trematomus bernacchii with the molecular markers used, and neither is Trematomus loennbergii from Trematomus lepidorhinus. We suggest that until this is investigated further, studies including these species list them as T. loennbergii/T. lepidorhinus group, and keep voucher samples and specimens. Generally, COI gives a congruent result with the rhodopsin retrogene, and except for the previously cited species pairs, COI barcoding is efficient for identification in this group. Moreover pkd1 might not be suitable for a phylogenetic study at this scale for this group. 2010 Elsevier B.V. and NIPR. All rights reserved.

Antarctic notothenioid fishes possess high oxidative capacities, large amounts of intracellular lipid combined with biological membranes enriched in polyunsaturated fatty acids, all of which could make these animals susceptible to oxidative injury, particularly in the form of lipid peroxidation. The central objective in this study was to examine capacities for oxidative metabolism and total antioxidant defense in Antarctic and non-Antarctic notothenioids in order to test the hypothesis that the cold-bodied Antarctic fishes possess elevated activities of citrate synthase (CS), matched by a more robust antioxidant (AOX) defense, than non-Antarctic species. CS activities and total AOX capacities were measured in brain and heart of 4 Antarctic species and 2 non-Antarctic species collected on the 2004 ICEFISH cruise. While no statistical differences are found among Antarctic and non-Antarctic fishes in either CS or AOX capacities, AOX capacity in both tissues expands with CS activity among individuals measured when all species are combined. There is also a 4.5-fold greater AOX capacity, when normalized to CS activity, in brain than in heart indicating the requirement for extra AOX defense in a tissue well known for its particularly high levels of phospholipids more prone to lipid peroxidation.

Many Antarctic notothenioid species endemic to the Seasonal Pack-ice Zone have converged on adult blood serum freezing points that are several tenths of a degree above the freezing point of seawater. While these fishes share high adult serum freezing points, the development of their freeze avoidance during ontogeny has not been studied. We investigated this in wild caught juveniles of one such species, Chaenocephalus aceratus (family Channichthyidae), using blood serum antifreeze activity as a proxy for their freeze avoidance. Juvenile serum antifreeze activity was significantly below that of adults through the oldest year 2+ specimens collected. This increased at an estimated rate of 0.368 × 10−3 ± 0.405 × 10−4°C day−1 which, if sustained, would leave C. aceratus below their adult serum antifreeze activity levels of 0.57 ± 0.08°C until 4.2 years after hatching. Underlying the 2.7-fold increase in their serum antifreeze activity from late year 0+ juveniles to adults was an even greater 10.4-fold increase in the concentration of their serum antifreeze glycopeptides, which increased proportionally across all of their serum AFGP size isoforms. With insufficient antifreeze activity to avoid freezing in the ice-laden surface waters, both adult and juvenile C. aceratus are most likely restricted to the year round ice-free waters where a metastable supercooled state can be maintained.

The modern ichthyofauna of the Southern Ocean is uniquely depauperate with respect to species diversity (Eastman, 2005). Although the Southern Ocean constitutes approximately 10% of our planet’s oceanic waters, the number of fish species is quite small (~300 species vs. a global diversity of ~25,000 species), and almost half belong to a single perciform suborder, the Notothenioidei. The origin of this taxonomic restriction results from the dramatic paleoclimatic and paleogeographic history of Antarctica (Eastman, ’93) during the Cenozoic Era. The opening of the Drake Passage, which separates Antarctica from South America, occurred via tectonic rifting ~40–34 million years (Myr) ago (Kennett, ’77; Livermore et al., 2005; Scher and Martin, 2006). The onset of widespread glaciation of Antarctica ~34 Myr ago (Zachos et al., 2001), which is attributable to declining atmospheric CO2 (DeConto and Pollard, 2003), the establishment of the Antarctic Circumpolar Current and the development of the Antarctic Polar Front (between ~50 and 60°S), decoupled the Southern Ocean from warmer, subtropical waters to the north (Kennett, ’77). A cooling trend that began in the late Paleocene/early Eocene (~55 Myr ago), when water temperatures were 15–20°C, accelerated during the Miocene until the Southern Ocean approached the freezing point of seawater (−1.9°C) ~14–5 Myr ago (Clarke, ’90). As the Southern Ocean cooled, the shallow water, cosmopolitan, and temperate fish fauna of late Eocene (38 Myr ago) became largely extinct owing to the destruction of inshore habitat and changes in trophic structure caused by repeated ice sheet scouring of the continental margin (Eastman, 2005). Thus, fish diversity was reduced and new ecological niches became available to taxa, such as the notothenioid fishes, which were diversifying in situ. Today, species of the notothenioid suborder constitute 46% of all the fish species of the Southern Ocean. At the highest latitudes, notothenioid species dominance is particularly clear, encompassing 77% of species diversity and 90% of biomass (Eastman, 2005). The ancestral notothenioid stock probably arose as a sluggish, bottom-dwelling perciform species some 40–60 Myr ago in the cool temperate shelf waters of the Antarctic continent (DeWitt, ’71; Eastman, ’93; Eastman and Clarke, ’98). With the elimination of most of the Eocene ichthyofauna, the notothenioids diversified to fill the many vacated niches. Lacking swim bladders, the Notothenioidei evolved toward pelagic or partially pelagic zooplanktivory and piscivory by reduction of skeletal mineralization and enhancement of lipid deposition. Termed pelagization, the tailoring of morphology for life in the water column is the hallmark of the notothenioid radiation, has arisen independently several times in different clades (Eastman, ’97, ’99; Near et al., 2007), and reflects the retention of larval characteristics in the adult (pedomorphism) (Eastman, ’97). In the dominant family Nototheniidae, ~50% of the Antarctic species are semipelagic, epibenthic, cryopelagic, or pelagic (Eastman, 2005). On the basis of their rapid speciation (average time for speciation of 0.76–2.1 Myr), geographical restriction, and high endemism, the Notothenioidei are the best described example of a marine species flock (Eastman, 2000; Eastman and McCune, 2000). Absence of niche competition alone would not have guaranteed the radiation of the notothenioids had they not evolved biochemical and physiological adaptations to their frigid environment. One key evolutionary adaptation of the notothenioids was the de novo acquisition of antifreeze glycoproteins, which bind to the surfaces of ice crystals that form in these fishes to inhibit ice propagation in their hyposmotic fluids (Cheng, ’98; Cheng and Detrich, 2007). The evolution of the antifreeze glycoprotein genes from a pancreatic, trypsinogen-like gene (Chen et al., ’97; Cheng and Chen, ’99) is a remarkable exemplar of a critical genetic innovation that fostered an extensive species radiation (Montgomery and Clements, 2000). The notothenioids are notable not only for their resistance and compensatory adaptations to the extreme Antarctic marine environment, but also for their regressive evolutionary changes or losses of function [the “disaptations” of Montgomery and Clements (2000) and references therein]. Antarctic notothenioids are cold stenotherms—these high latitude species typically live at temperatures between −1.9 and +2°C and have incipient lethal temperatures near 5°C that cannot be raised by acclimation in the laboratory (Somero and DeVries, ’67). This stenothermality results in part from adaptive alterations to the biochemical, cellular, and physiological systems of these fishes. Major examples of compensatory adaptation include efficient microtubule assembly (Williams et al., ’85; Detrich et al., ’89, ’92, 2000; Paluh et al., 2004) and protein translocation at cold temperatures (Romisch et al., 2003), homeoviscous adaptation of membrane lipids to preserve membrane fluidity (Logue et al., 2000), and cold-stable lens crystallins that prevent cataract formation (Kiss et al., 2004). Consistent with their long isolation in a constantly cold environment, the Antarctic notothenioids have lost the inducible heat shock response (Hofmann et al., 2000; Buckley et al., 2004), which seems to have been recruited to an adaptive, constitutive status to deal with elevated denaturation of proteins caused by cold stress (Place et al., 2004; Place and Hofmann, 2005; Todgham et al., 2007). Other striking regressive changes include the loss of erythrocytes (Ruud, ’54) and the respiratory transport protein hemoglobin (Cocca et al., ’95, 2000; Zhao et al., ’98; Near et al., 2006) by all species of the icefish family and independent losses of cardiac myoglobin in a subset of icefish species (Sidell et al., ’97; O’Brien and Sidell, 2000; Sidell and O’Brien, 2006). Recently, Chen et al. (2008) reported a large-scale transcriptomic up-regulation of 177 gene families in the Antarctic toothfish, Dissostichus mawsoni (Nototheniodei: Nototheniidae), with respect to their orthologs in temperate and tropical fish. At the genomic level, they found that 118 gene families in several notothenioid species have undergone substantial gene duplication relative to the temperate/tropical species. Overlap of the duplicated gene set with the transcriptionally up-regulated gene set suggested that gene family expansion may contribute to cold adaptation of cellular and physiological function, a conclusion supported by the augmentation of tubulin genes in the bullhead notothen, Notothenia coriiceps (Parker and Detrich, ’98). It is notable that 17 families of LINEs showed Antarctic-specific duplication, which suggests that LINE expansion may have facilitated gene duplication in Antarctic notothenioids by retrotransposition-mediated gene transduction (Xing et al., 2006). The above findings suggest that the genomes of notothenioids are evolutionarily dynamic and that this plasticity may have contributed to the overall success of the group. The development of genomic resources from these difficult-to-obtain specimens is thus important, well justified, and valuable to a wide community of genomic, evolutionary, and ecological biologists and biomedical scientists. In 2003, we collected high molecular weight (HMW) DNA from a wide assortment of notothenioid fishes, with the aim of enabling genomic studies in this group, and subsequently submitted a white paper to the BAC library network at the National Human Genome Research Institute (NHGRI) to request construction of high-quality and high-representation BAC genomic libraries from selected notothenioid species. We were informed that BAC libraries would be generated from two of the species: Chaenocephalus aceratus (blackfin or Scotia Arc icefish) and N. coriiceps (bullhead notothen or yellowbelly rockcod). The selection of these two species was largely strategic in that C. aceratus represents a lineage (icefishes) devoid of erythrocytes and lacking hemoglobin genes, whereas N. coriiceps represents an erythrocyte-producing species in which hemoglobin genes are intact and functional. Thus, these two species, although not representative of the entire gamut of notothenioids, are extremely useful for genomic comparisons of processes that involve differences in their respective physiologies and anatomies as a result of hemoglobin loss by the icefishes. In this article, we describe the generation of BAC libraries from these 2 representative notothenioid species and further provide genome size estimates for 11 species of notothenioid fishes. Quality assurance data are provided for both BAC libraries that validate the utility of these resources for genomic analyses.

This study describes de novo transcriptome sequencing and annotation analyses for the head kidney of the sub-Antarctic notothenioid fish Eleginops maclovinus, a sister group of the Antarctic notothenioid fish clade. Moreover, E. maclovinus is one of the most eurythermal and euryhaline representatives of the Notothenioidei suborder. RNA-seq data were generated by the 454 GS Junior system, resulting in 11,207 contigs that were then assembled by the Genomic Workbench CLC software. The transcriptome was annotated by BLASTing each sequence against the universal, non-redundant NCBI database (National Center for Biotechnology Information) using the AUSTRAL-omics computer cluster. A significant number of transcripts related to innate and adaptive immunity were found in the sequences, which could be used as references in future immunological studies in E. maclovinus.

Evolution of Antarctic notothenioids in the frigid and oxygen-rich Southern Ocean had led to remarkable genomic changes, most notably the gain of novel antifreeze glycoproteins and the loss of oxygen-binding hemoproteins in the icefish family. Recently, the mitochondrial (mt) NADH dehydrogenase subunit 6 (ND6) gene and the adjacent transfer RNA(Glu) (tRNA(Glu)) were also reportedly lost. ND6 protein is crucial for the assembly and function of Complex I of the mt electron transport chain that produces adenosine triphosphate (ATP) essential for life; thus, ND6 absence would be irreconcilable with Antarctic notothenioids being thriving species. Here we report our discovery that the ND6 gene and tRNA(Glu) were not lost but had been translocated to the control region (CR) from their canonical location between ND5 and cytochrome b genes. We characterized the CR and adjacent sequences of 22 notothenioid species representing all eight families of Notothenioidei to elucidate the mechanism and evolutionary history of this mtDNA rearrangement. Species of the three basal non-Antarctic families have the canonical vertebrate mt gene order, whereas species of all five Antarctic families have a rearranged CR bearing the embedded ND6 (ND6(CR)) and tRNA(Glu), with additional copies of tRNA(Thr), tRNA(Pro), and noncoding region in various lineages. We hypothesized that an initial duplication of the canonical mt region from ND6 through CR occurred in the common ancestor to the Antarctic clade, and we deduced the succession of loss or modification of the duplicated region leading to the extant patterns of mt DNA reorganization that is consistent with notothenioid evolutionary history. We verified that the ND6(CR) gene in Antarctic notothenioids is transcribed and therefore functional. However, ND6(CR)-encoded protein sequences differ substantially from basal non-Antarctic notothenioid ND6, and we detected lineage-specific positive selection on the branch leading to the Antarctic clade of ND6(CR) under the branch-site model. Collectively, the novel mt ND6(CR) genotype of the Antarctic radiation represents another major molecular change in Antarctic notothenioid evolution and may reflect an adaptive change conducive to the functioning of the protein (Complex I) machinery of mt respiration in the polar environment, driven by the advent of freezing, oxygen-rich conditions in the Southern Ocean.

The Antarctic fish Notothenia rossii and Notothenia coriiceps were selected as target organisms for studies of biomarker responses of environmental monitoring research of Admiralty Bay, King George Island. In this case, molecular taxonomy analysis of the referred population became an important study subject in order to increase the knowledge of especies diversity. The taxonomy of Antarctic fish has been predominantly based on morphological characteristics rather than on genetic criteria. A typical example is the Notothenia group, which consists of N. coriiceps, N. neglecta and N. rossii. The Polymerase Chain Reaction and Restriction Fragment Length Polymorphism (PCR-RFLP) technique was used to determine whether N. neglecta and N. coriiceps are different or whether they are the same species with morphological, physiological and behavioural variability. N. rossii was used as control. Mitochondrial DNA (mtDNA) was isolated from muscle specimens of N. neglecta, N. coriiceps and N. rossii, which were collected in Admiralty Bay, King George Island. The DNA was used to amplify a fragment (690 base pairs) of the coding region of the mitochondrial gene for NADH subunit 2. Further, the amplicon was digested with following restriction enzymes: DdeI, HindIII and RsaI. The results showed a variation of the digestion pattern of the fragment amplified between N. rossii and N. coriiceps or N. neglecta species. No differences were found between N. coriiceps and N. neglecta specimens.

Pogonophryne stewarti, new species, is described from collections made at 1700 m on the continental slope of the Indian Ocean Sector of the Southern Ocean, off Wilkes Land, Antarctica. The new species is assigned to the unspotted P. albipinna species group and is related to P. immaculata. It is distinguished from all other species of the P. albipinna species group by the following combination of characters: a long (about 15–20% SL) mental barbel without a terminal expansion, a shallow head and slender trunk with only slight taper to caudal peduncle, 8–13 middle lateral-line pores, and divergence in the mitochondrial ND2 gene. We discuss the composition and validity of the P. albipinna group, which, up to this point, has been based on three holotype specimens. We provide meristic and morphometric data for seven recently collected adult specimens of P. immaculata. Bayesian analyses of mitochondrial gene sequences for 11 of the now 19 recognized species of Pogonophryne, sampled from all five of the ...

Survival of some polar fishes is associated with high levels of circulating antifreeze glycoproteins (AFGPs). AFGP prevent ice growth giving rise to thermal hysteresis. The inhibiting action of AFGPs implies that polar fish contain ice to which AFGPs adsorb. Cryopelagic Pagothenia borchgrevinki, inhabiting the ice-laden waters of McMurdo Sound, Antarctica, were assayed for ice and ice was found on skin, gills, in the intestine, and in the spleen. Two methods used to assess the number of ice crystals in spleens gave comparable results (12.1 +/− 1.9 and 22 +/− 3.8 per spleen). Attempts were made to measure the rate of uptake of ice by P. borchgrevinki held in cages immediately beneath the sub-ice platelet layer in McMurdo Sound; uptake was sporadic. Introduction of ice into fish by spray freezing a small patch of the integument resulted in detection of splenic ice after 1 h, illustrating that a mechanism exists for ice transport from the periphery to the spleen. Splenic ice did not seem to be eliminated from fish held in ice-free water at − 1.6 °C for approximately two months. The relatively small number of splenic ice crystals and the slow rate of ice uptake suggest efficient ice barriers exist in P. borchgrevinki.

Biogeographic studies separate the Antarctic Notothenioid fish fauna into high- and low-latitude species. Past studies indicate that some species found in the high-latitude freezing waters of the High-Antarctic Zone have low-serum hysteresis freezing points, while other species restricted to the low-latitude seasonal pack ice zone have higher serum hysteresis freezing points above the freezing point of seawater (−1.9°C), but the relationship has not been systematically investigated. Freeze avoidance was quantified in 11 species of Antarctic icefishes by determining the hysteresis freezing points of their blood serum, in addition, the freezing point depression from serum osmolytes, the antifreeze activity from serum antifreeze glycoproteins (AFGPs), and the antifreeze activity from serum antifreeze potentiating protein were measured for each species. Serum hysteresis freezing point, a proxy for organismal freeze avoidance, decreased as species were distributed at increasing latitude (linear regression r 2 0.66, slope −0.046°C °latitude−1), which appeared largely independent of phylogenetic influences. Greater freeze avoidance at high latitudes was largely a result of higher levels of antifreeze activity from serum AFGPs relative to those in species inhabiting the low-latitude waters. The icefish fauna could be separated into a circum High-Antarctic Group of eight species that maintained serum hysteresis freezing points below −1.9°C even when sampled from less severe habitats. The remaining three species with low-latitude ranges restricted to the waters of the northern part of the west Antarctic Peninsula and Scotia Arc Islands had serum hysteresis freezing points at or above −1.9°C due to significantly lower combined activity from all of their serum antifreeze proteins than found in the High-Antarctic Zone icefish.

The presence of the two morphs, “typical” and “large mouth”, in the Antarctic fish species Trematomus newnesi (Perciformes, Notothenioidei) was recorded for the first time in nearshore waters of the South Shetland Islands (Potter Cove) and western Antarctic Peninsula (Petermann Island). The two morphs were distinguishable in specimens of 60–241 mm total length (TL); about 30% of the specimens constituted intermediate forms. In addition to the previously known characters separating the morphs, we found that the “relative size of the eye” can also be used to identify smaller and larger fish of the typical morph. The ecological significance of the two morphs remains unclear. Ratios of diagnostic characters for identification of the species at two size ranges (60–131 and 132–241 mm TL) are provided.

State III respiration rates were measured in mitochondria isolated from hearts of Antarctic notothenioid fishes that differ in the expression of hemoglobin (Hb) and myoglobin (Mb). Respiration rates were measured at temperatures between 2 and 40°C in Gobionotothen gibberifrons (+Hb/+Mb), Chaenocephalus aceratus (–Hb/–Mb) and Chionodraco rastrospinosus (–Hb/+Mb). Blood osmolarity was measured in all three species and physiological buffers prepared for isolating mitochondria and measuring respiration rates. Respiration rates were higher in mitochondria from G. gibberifrons compared to those from C. aceratus at 2°C, but were similar among all species at temperatures between 10 and 26°C. Respiration rates were significantly lower in icefishes at 35 and 40°C compared to G. gibberifrons. The respiratory control ratio of isolated mitochondria was lower in C. aceratus compared to G. gibberifrons at all temperatures below 35°C. At 35 and 40°C, mitochondria were uncoupled in all species. The Arrhenius break temperature of state III respiration was similar among all three species (30.5 ± 0.9°C) and higher than values previously reported for Antarctic notothenioids, likely due to the higher osmolarity of buffers used in this study. These results suggest that differences in mitochondrial structure, correlated with the expression of oxygen-binding proteins, minimally impact mitochondrial function.

The dominant perciform suborder Notothenioidei is an excellent study group for assessing the evolution and functional importance of biochemical adaptations to temperature. The availability of notothenioid taxa in a wide range of latitudes (Antarctic and non-Antarctic) provides a tool to enable identification of physiological and biochemical characteristics gained and lost during evolutionary history. Non-Antarctic notothenioids belonging to the most basal families are a crucial source for understanding the evolution of hemoglobin in high-Antarctic cold-adapted fish. This paper focuses on the structure, function and evolution of the oxygen-transport system of Cottoperca gobio, a sub-Antarctic notothenioid fish of the family Bovichtidae, probably derived from ancestral species that evolved in the Antarctic region and later migrated to lower latitudes. Unlike most high-Antarctic notothenioids, but similar to many other acanthomorph teleosts, C. gobio has two major hemoglobins having the β chain in common. The oxygen-binding equilibria and kinetics of the two hemoglobins have been measured. Hb1 and Hb2 show strong modulation of oxygen-binding equilibria and kinetics by heterotropic effectors, with marked Bohr and Root effects. In Hb1 and Hb2, oxygen affinity and subunit cooperativity are slightly higher than in most high-Antarctic notothenioid hemoglobins. Hb1 and Hb2 show similar rebinding rates, but also show significant dynamic differences that are likely to have functional consequences. Molecular dynamic simulations of C. gobio Hb1 were performed on the dimeric protein in order to obtain a better understanding of the molecular basis of structure/function relationships. Fil: Giordano, Daniela. Consiglio Nazionale delle Ricerche; Italia Fil: Boechi, Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Vergara, Alessandro. Università degli Studi di Napoli Federico II; Italia Fil: Marti, Marcelo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Samuni, Uri. City University of New York; Estados Unidos Fil: Dantsker, David. Albert Einstein College of Medicine; Estados Unidos Fil: Grassi, Luigi. Consiglio Nazionale delle Ricerche; Italia Fil: Estrin, Dario Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química, Física de los Materiales, Medioambiente y Energía. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química, Física de los Materiales, Medioambiente y Energía; Argentina Fil: Friedman, Joel M.. Albert Einstein College of Medicine; Estados Unidos Fil: Mazzarella, Lelio. Università degli Studi di Napoli Federico II; Italia Fil: Di Prisco, Guido. Consiglio Nazionale delle Ricerche; Italia Fil: Verde, Cinzia. Consiglio Nazionale delle Ricerche; Italia

The present review surveys several recent studies of the aspartic proteinases from Antarctic Notothenioidei, a dominating fish group that has developed a number of adjustments at the molecular level to maintain metabolic function at low temperatures. Given the unique peculiarities of the Antarctic environment, studying the features of Antarctic aspartic proteinases could provide new insights into the role of these proteins in fish physiology. We describe here: (1) the biochemical properties of a cathepsin D purified from the liver of the hemoglobinless icefish Chionodraco hamatus; (2) the biochemical characterization of Trematomus bernacchii pepsins variants A1 and A2 obtained by heterologous expression in bacteria; and (3) the identification of two closely related, novel aspartic proteinases from the liver of the two Antarctic fish species mentioned above. Overall, the results show that Notothenioidei aspartic proteinases display a number of characteristics that are remarkably different from those of mammalian aspartic proteinases, including high turnover number or high catalytic efficiency. We have named the newly identified aspartic proteinases “Nothepsins” and classified them relative to aspartic proteinases from other species.

We investigated intraspecific geographic variation in buoyancy by obtaining percentage buoyancy (%B) measurements for the Antarctic notothenioid speciesPleuragramma antarcticum,Trematomus hansoni,T. bernacchiiandGymnodraco acuticepsfrom both McMurdo Sound in East Antarctica and the South Shetland Islands in West Antarctica. Mean percentage buoyancies in these species ranged from 0.22–0.52% in the neutrally buoyantP. antarcticumto 3.34–3.67% in the benthicT. bernacchii. Dispersion (1 standard deviation) of percentage buoyancy (%B) values around the mean was ± 0.2–0.5 %B units for the entire sample. Although intraspecific differences in mean percentage buoyancy were statistically significant (P P. antarcticumandT. hansoni, we consider these differences as normal variation without substantive biological significance. The dispersion in buoyancy measurements during adult life reflects the density of the fish and this may be influenced, in both the short- and long-term, by gut contents, nutritional condition, and reproductive state. Mitigation of the effects of these variables is not biologically realistic because they constitute normal aspects of the daily and yearly life cycles. The results of our measurements of buoyancy are consistent with what is known about the ecology of these four species and this is considered in the discussion.

Fish skeletal muscle is an excellent model for studying muscle structure and function, since it has a very well-structured arrangement with different fiber types segregated in the axial and pectoral fin muscles. The morphological and physiological characteristics of the different muscle fiber types have been studied in several teleost species. In fish muscle, fiber number and size varies with the species considered, limiting fish maximum final length due to constraints in metabolites and oxygen diffusion. In this work, we analyze some special characteristics of the skeletal muscle of the suborder Notothenioidei. They experienced an impressive radiation inside Antarctic waters, a stable and cold environment that could account for some of their special characteristics. The number of muscle fibers is very low, 12,700-164,000, in comparison to 550,000-1,200,000 in Salmo salar of similar sizes. The size of the fibers is very large, reaching 600 μm in diameter, while for example Salmo salar of similar sizes have fibers of 220 μm maximum diameter. Evolutionary adjustment in cell cycle length for working at low temperature has been shown in Harpagifer antarcticus (111 h at 0°C), when compared to the closely related sub-Antarctic species Harpagifer bispinis (150 h at 5°C). Maximum muscle fiber number decreases towards the more derived notothenioids, a trend that is more related to phylogeny than to geographical distribution (and hence water temperature), with values as low as 3,600 in Harpagifer bispinis. Mitochondria volume density in slow muscles of notothenioids is very high (reaching 0.56) and since maximal rates of substrate oxidation by mitochondria is not enhanced, at least in demersal notothenioids, volume density is the only means of overcoming thermal constraints on oxidative capacity. In brief, some characteristics of the muscles of notothenioids have an apparent phylogenetic component while others seem to be adaptations to low temperature. Fil: Fernandez, Daniel Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Calvo, Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Organisms living in the Southern Ocean are exposed to strong environmental constraints, especially temperature. The Perciform suborder Notothenioidei, today largely endemic to the Antarctic, has developed numerous cold-adapted characters. The most striking peculiarity of this group of fish is the drastic reduction of hemoglobin content in their blood. This condition gives rise to a low metabolic demand of iron. Recently, we have undertaken a study to add new insights on iron metabolism in hemoglobinless fish. By taking advantage to our previous studies on transferrins from Antarctic Notothenioids, in this article we compared the evolutionary properties of these sequences to those from other fish groups and mammals. Our findings based on analysis of dN/dS ratio and on the results of the relative rate ratio test suggest that the transferrin gene has undergone positive selection in fish but not in mammals. The results of type I functional divergence provide statistical evidence for shifted evolutionary rate after speciation. Finally, when superimposed onto the three-dimensional structure of transferrin, the sites identified as responsible of the divergence in Notothenioids appear to cluster preferentially at non-iron binding locations, occupying surface locations that might affect the rate of iron binding and/or release in a cold environment.

Iron is an essential element for metabolic processes intrinsic to life, but the properties that make iron a necessity also make it potentially deleterious. To avoid harm, iron homeostasis is achieved through iron transport, storage and regulatory proteins. The functions of some of these molecules are well described, for example transferrin and ferritin, whereas the roles of others remain unclear. The past decade has seen the identification of new molecules involved in iron metabolism, such as divalent metal transporter-1, and hepcidin. The present review aims at surveying the studies carried out on some of the most important genes involved in transport and storage of iron in Antarctic Notothenioidei, a dominating fish group endowed of a number of striking adaptive characters, including reduced (or absence of) hematocrit. This unique peculiarity among vertebrates makes this fish group a suitable system to studying the relationship between hemoglobin and iron metabolism and to understanding the adaptive changes occurred in Antarctic fish metabolism during their evolution to avoid the deleterious effects of iron overload in the absence of hemoglobin. The results summarised here indicate that the loss of hemoglobin in the most specialized group of Antarctic notothenioids, belonging to the Channychthyidae family, is accompanied by remodulation of the iron metabolism.

A primary objective of the ICEFISH 2004 cruise was to collect and study notothenioid fishes from remote localities in the Atlantic sector of the Southern Ocean. Nearly 1 month was devoted to bottom trawling for fishes on the shelf and upper slope (to 1,000 m) areas around Shag Rocks, South Georgia, South Sandwich Islands and Bouvetoya. The focus was on the latter two locations, because their faunas are more poorly known. Eight species were collected at Shag Rocks with Patagonotothen guntheri most abundant; 17 at South Georgia with Lepidonotothen nudifrons, L. larseni and Gobionotothen gibberifrons most abundant; 13 at the South Sandwich Islands with L. larseni, L. nudifrons and G. gibberifrons most abundant; and 11 at Bouvetoya with L. larseni, Macrourus holotrachys and L. squamifrons most abundant. Ten new locality records were established: Shag Rocks (1), South Georgia (1), South Sandwich Islands (5), South Sandwich Trench at 5,350 m (1) and Bouvetoya (2). Total known demersal fish diversity on the shelf and upper slope at Shag Rocks/South Georgia, South Sandwich Islands and Bouvetoya is 42, 31 and 17 species, respectively. To examine population structure in the four most abundant notothenioids at Bouvetoya (L. larseni, L. squamifrons, Notothenia coriiceps and Chaenocephalus aceratus), we examined the ND2 portion of mitochondrial DNA. Chaenocephalus aceratus, N. coriiceps and L. larseni exhibited no significant genetic differentiation in comparison with samples from localities in the Scotia Sea and the Antarctic Peninsula. However, L. squamifrons showed significant genetic differentiation between the South Shetlands and Bouvetoya populations (F ST = 0.189, P = 0.015). Thus, these data combined with previous studies of two other notothenioids suggest that five of the six notothenioid species at Bouvetoya are not genetically differentiated from other localities in the Atlantic sector of the Southern Ocean. The location of Bouvetoya within the Antarctic Circumpolar Current and the long (1–2 years) pelagic stages of the notothenioids at Bouvetoya may be at least partly responsible for this genetic homogeneity.

We evaluated the condition factor (K), an index of weight per unit length, in a sample of 49 761 longline-caught specimens of Antarctic toothfish,Dissostichus mawsoni, from the Ross Sea. Our sample consisted of specimens from northern (60–70°S) and southern (70–78°S) regions. Fifty percent of the northern sample and 4.9% of the southern sample were large individuals with a low condition factor (Kah ≤ 1.0182) and displaying an “axe handle (ah)” morphology with a notably thinner trunk. In the northern sample 55.4% of the males and 43.2% of the females were less thanKah.In the southern region 5.3% of the males and 4.5% of the females were less thanKah. The axe handle morphology is attributable to the metabolic loss of muscular and subcutaneous lipid stores, and probably proteins, from white muscle. Our discussion considers energy metabolism as related to migration, feeding and reproduction. We suggest that migration, a life history trait of the phyletically basal notothenioid cladesPseudaphritisandEleginops, persists inD. mawsoni. The spawning migration from the southern shelf to ridges and seamounts in the north may reflect fidelity to historic spawning grounds. As evidenced by the axe handle specimens neutral buoyancy of largeD. mawsonimay be ephemeral, fluctuating over the course of adult life.

We analysed cytochrome oxidase I (COI) barcodes for 35 putative fish species collected in the Scotia Sea, and compared the resultant molecular data with field-based morphological identifications, and additional sequence data obtained from GenBank and the Barcode of Life Data System (BOLD). There was high congruence between morphological and molecular classification, and COI provided effective species-level discrimination for nearly all putative species. No effect of geographic sampling was observed for COI sequence variation. For two families, including the Liparidae and Zoarcidae, for which morphological field identification was unable to resolve taxonomy, DNA barcoding revealed significant species-level divergence. However, the dataset lacked sufficient sensitivity for resolving species within theBathydracoandArtedidracogenera. Analysis of cytochromebfor these two genera also failed to resolve taxonomic identity. The data are discussed in relation to emergent priorities for additional taxonomic studies. We emphasize the utility of DNA barcoding in providing a valuable taxonomic framework for fundamental population studies through assigning life history stages or other morphologically ambiguous samples to parental species.

A new species of notothenioid fish, Pogonophryne bellingshausenensis n. sp., is described from the Bellingshausen Sea, Antarctica. The new species belongs to the dorsally-spotted “mentella” group of the genus and is characterized by having a short (about 13% SL) mental barbel with a short (about 16% of barbel length), narrow (barely wider than the stalk), and relatively inconspicuous terminal expansion composed of short, irregular, fingerlike processes. Compared to most other dorsally-spotted species of Pogonophryne (“barsukovi”, “marmorata”, and “mentella” groups), P. bellingshausenensis has a relatively wide (about 7% SL) interorbital region. An unspotted patch on the median dorsal surface of the head, posterior to the posttemporal ridges and anterior to the first dorsal fin, has not been observed previously in any dorsally-spotted species. The holotype was collected at 1,947 m, one of the deepest records for any species of Pogonophryne. A revised key to the ten species of the “mentella” group of Pogonophryne is also provided.

In the Antarctic, fishes of dominant suborder Notothenioidei have evolved in a unique thermal scenario. Phylogenetically related taxa of the suborder live in a wide range of latitudes, in Antarctic, sub-Antarctic and temperate oceans. Consequently, they offer a remarkable opportunity to study the physiological and biochemical characters gained and, conversely, lost during their evolutionary history. The evolutionary perspective has also been pursued by comparative studies of some features of the heme protein devoted to O(2) transport in fish living in the other polar region, the Arctic. The two polar regions differ by age and isolation. Fish living in each habitat have undergone regional constraints and fit into different evolutionary histories. The aim of this contribution is to survey the current knowledge of molecular structure, functional features, phylogeny and adaptations of the haemoglobins of fish thriving in the Antarctic, sub-Antarctic and Arctic regions (with some excursions in the temperate latitudes), in search of insights into the convergent processes evolved in response to cooling. Current climate change may disturb adaptation, calling for strategies aimed at neutralising threats to biodiversity.

Antarctic marine organisms are considered to have extremely limited ability to respond to environmental temperature change. However, here we show that the Antarctic notothenioid fish Pagothenia borchgrevinki is an exception to this theory. P. borchgrevinki was able to acclimate its resting metabolic rate and resting ventilation frequency after a 5°C rise in temperature. Acute exposure to 4°C resulted in an elevation in metabolic rate (57.8 ± 4.79 mg O2 kg−1 h−1) and resting ventilation rate (40.38 ± 1.61 breaths min−1) compared with fish at −1°C (metabolic rate 34.45 ± 3.12 mg O2 kg−1 h−1; ventilation rate 29.88 ± 3.72 breaths min−1). However, after a 1-month acclimation period, there was no significant difference in the metabolic rate (cold fish 29.52 ± 3.01; warm fish 31.13 ± 2.30 mg O2 kg−1 h−1), or the resting ventilation rate (cold fish 28.75 ± 0.98; warm fish 34.25 ± 2.28 breaths min−1) of cold and warm acclimated fish. Acclimation changes to the rate of oxygen consumption following exhaustive exercise were complex. The pattern of oxygen consumption during recovery from exhaustive exercise was not significantly different in either cold or warm acclimated fish.

The fish species Notothenia angustata inhabits temperate waters (10 °C), yet retains physiological traits that show it once existed at sub-zero temperatures. We determined the free-ranging activity, heart rate and metabolism of N. angustata and compared it with Notothenia coriiceps, an ecologically and morphologically congeneric cousin that still inhabits sub-zero waters. Firstly, the association between heart rate (fH) and oxygen consumption (MO2) was first determined in the laboratory. The fish were then released into their respective environments and fH recorded by a miniature archival electronic tag, from which the metabolic rate of the free-ranging fish was extrapolated. Free-ranging activity of wild fish was monitored throughout the study using implanted acoustic tags and a static hydrophone array. Results showed that the difference in standard metabolic rate (SMR) between N. angustata and N. coriiceps fitted the Arrhenius model for inter-species thermal sensitivity in fish (Q10 = 1.76). However, the inter-species disparity in total metabolic rate (TMR) was far greater. This was attributable to N. angustata swimming at higher speeds and covering a 5-fold greater area over 24 h compared with N. coriiceps. As a result, activity (and associated feeding) comprised a far larger portion of TMR in N. angustata (27.9%) than for N. coriiceps (5.7%). We conclude that the increased time spent swimming by N. angustata was presumably to forage for food to acquire sufficient energy to fuel its elevated SMR. This resulted in a much greater inter-species difference in TMR than may be predicted by the disparity in environmental temperature.

Members of the HSP70 gene family comprising the constitutive (HSC70) and inducible (HSP70) genes, plus GRP78 (Glucose-regulated protein 78 kDa) were surveyed for expression levels via Q-PCR after both an acute 2-h heat shock experiment and a time course assay in the Antarctic plunderfish Harpagifer antarcticus. In general, down regulation of all genes was observed during the course of the heat shock experiments. This thermally induced down regulation was particularly acute for the GRP78 gene, which at one time point was more than 100-fold down regulated. These results demonstrate the loss of the heat shock response in H. antarcticus, a basal member of the Notothenioidei. This finding is discussed with reference to the survival of Notothenioids during observed ocean warming and also the reorganisation of cellular protein mechanisms of species living in extreme environments.