Antarctic Toothfish Dissostichus Mawsoni Research Articles

Antarctic toothfish Dissostichus mawsoni as a bioindicator of trace and rare earth elements in the Southern Ocean

The Antarctic toothfish Dissostichus mawsoni is a Southern Ocean long-lived top predator which is regularly captured on an annual fishery operating in the region. By its biological and ecological characteristics, it is a potential bioindicator for the concentrations of trace and rare earth elements in the Antarctic. As these elements are mainly transferred through the diet and a deficiency or excess of these elements can lead to diverse health problems, it is important to measure their concentrations on the organisms. This study provides, for the first time, the concentration of 27 trace (major essential, minor essential and non-essential) and rare earth elements in the muscle of D. mawsoni captured in three areas of the Amundsen and Dumont D'Urville Seas (Antarctica). Major essential elements had the highest concentrations, with potassium (K) as the most concentrated, and rare earth elements the lowest. Significant differences between areas were found for most of the studied elements. No bioaccumulation nor biomagnification potential was found for the studied elements, with several elements decreasing concentrations towards larger individuals. Decreasing trends are related with the different habitats occupied by D. mawsoni through their life, suggesting that elements' concentrations in the water is determinant for the concentrations in this top predator, and/or there is a dilution effect as the fish grows. Our results also support that Se presents a detoxification potential for Hg in D. mawsoni, but only when Hg concentrations are higher to unhealthy levels. This study supports D. mawsoni as a potential bioindicator for the concentrations of the different trace and rare earth elements in the Southern Ocean, though only when comparing individuals of similar size/age, but also to evaluate annual changes on their concentrations. Furthermore, D. mawsoni can be a good source of major essential elements to humans with concentrations of major essential elements above some of other marine fish worldwide.

Contrasting life-history traits of two toothfish (Dissostichus spp.) species at their range edge around the South Sandwich Islands

The South Sandwich Islands (SSI), a chain of volcanic islands in the Atlantic sector of the Southern Ocean, are home to two large notothenoid species: the Patagonian toothfish Dissostichus eleginoides and the Antarctic toothfish Dissostichus mawsoni. Both species support valuable fisheries throughout the Southern Ocean under management of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The SSI region, which is located south of the Southern Antarctic Circumpolar Current Front, has a diverse and distinct biodiversity and it represents a range edge for the distribution of both toothfish species. In this paper we have updated and expanded previous biological analyses with recent data, explored the stock hypotheses and links of these species to other regions, and investigated the role of the SSI archipelago in the life cycles of both toothfish species, where they overlap in their distribution. We conclude that Patagonian toothfish around the SSI are linked to the adjacent South Georgia population, but have some unique characteristics, including faster growth and better somatic condition, possibly reflecting ‘Bergmann's rule’ which states that body size increases with decreasing temperature and increasing latitude. By comparison, the Antarctic toothfish at the SSI appear to be the northern extent of a larger stock connecting further south towards the Antarctic continent. Finally, we consider the relative importance of the SSI in the life cycle of both species, including in the context of climatic changes to this region.

Genome-wide analysis reveals striking lack of genetic differentiation over long distances for the Antarctic toothfish Dissostichus mawsoni: High genetic connectivity or shared spawning grounds?

The giant Antarctic toothfish Dissostichus mawsoni is one of the most economically valued fishery resources from the Southern Ocean. However, the distinctive biological characteristics and life history of this species, including large body size, long life span, late sexual maturity, and specialization to freezing polar waters, make it particularly vulnerable to overfishing and global climate change. It is therefore of fundamental importance to administer sound management and conservation actions to avoid depletion of this unique species. The crucial issue of whether this species consists of distinct biological units or stocks, which is needed to inform appropriate management and conservation, is currently unresolved. We report here the first RAD-seq analysis of Antarctic toothfish populations, a powerful approach of genome-wide discovery of SNP loci, to assess genetic differentiation between the geographically distant individuals from CCAMLAR Subarea 48.1 locations (South Shetland Islands and West Antarctic Peninsula coasts) and Subarea 88.1 (Ross Sea and McMurdo Sound). We recovered 19,611 SNPs belonging to 13,251 widely shared loci. Comprehensive population structure analyses unambiguously indicated absence of any significant level of population differentiation, thus the null hypothesis of panmixia cannot be rejected. Together with currently known life history traits of D. mawsoni, we suggest this striking lack of genomic differentiation likely reflects high degrees of contemporary and/or historical gene flow rather than shared spawning grounds. Complementary analyses, particularly otolith microchemistry, would contribute useful inference of natal origins.

Cephalopod fauna of the Pacific Southern Ocean using Antarctic toothfish (Dissostichus mawsoni) as biological samplers and fisheries bycatch specimens

Cephalopods are an important component of Southern Ocean food webs but studies analysing their habitat and trophic ecology are scarce. Here, we use the Antarctic toothfish Dissostichus mawsoni as a biological sampler of Southern Ocean's cephalopods in the Ross, Amundsen, and D'Urville Seas. Ten cephalopod taxa were identified in the diet of the Antarctic toothfish, with Pareledone turqueti and Moroteuthopsis longimana being the only species present in all the three studied areas. DNA analysis conducted on squid flesh samples allowed identification of eight and two specimens of Mesonychoteuthis hamiltoni and M. longimana, respectively, proving this technique as a potential tool to improve the knowledge of cephalopods biodiversity and biogeography in the Southern Ocean. Stable isotopes were used to compare the habitat (δ13C) and trophic ecology (δ15N) between two life-stages of the two most abundant squid species (M. longimana and Psychroteuthis glacialis) from the D'Urville Sea (both squid species) and Amundsen Sea (only P. glacialis). Higher δ13C values in M. longimana suggest that this species inhabits waters near the Antarctic Polar Front, with incursions into sub-Antarctic waters, whilst P. glacialis spends its entire life in Antarctic waters. The most recently deposited part of the beak is enriched in 15N suggesting an increase in trophic level during squid growth. These results give us the first insights into the bathyal distribution of cephalopods in the Amundsen and D'Urville Seas, as well as into the ontogenetic changes of two of the most consumed squid species by top predators in this region. Such results are an important step towards improving the biogeography of Antarctic cephalopods, being of utmost importance to understand the biodiversity, food web structure, and functioning of this region.

High mercury levels in Antarctic toothfish Dissostichus mawsoni from the Southwest Pacific sector of the Southern Ocean

Mercury is a bioaccumulating toxic pollutant which can reach humans through the consumption of contaminated food (e.g. marine fish). Although the Southern Ocean is often portrayed as a pristine ecosystem, its fishery products are not immune to mercury contamination. We analysed mercury concentration (organic and inorganic forms – T-Hg) in the muscle of Antarctic toothfish, Dissostichus mawsoni, a long-lived top predator which supports a highly profitable fishery. Our samples were collected in three fishing areas (one seamount and two on the continental slope) in the Southwest Pacific Sector of the Southern Ocean during the 2016/2017 fishing season. Mercury levels and the size range of fish varied between fishing areas, with the highest levels (0.68 ± 0.45 mg kg−1 wwt) occurring on the Amundsen Sea seamount where catches were dominated by larger, older fish. The most parsimonious model of mercury concentration included both age and habitat (seamount vs continental slope) as explanatory variables. Mean mercury levels for each fishing area were higher than those in all previous studies of D. mawsoni, with mean values for the Amundsen Sea seamount exceeding the 0.5 mg kg−1 food safety threshold for the first time. It might therefore be appropriate to add D. mawsoni to the list of taxa, such as swordfish and sharks, which are known to exceed this threshold. This apparent increase in mercury levels suggests a recent contamination event which affected the Southwest Pacific sector, including both the Amundsen and Dumont D'Urville seas.

Distribution of Antarctic toothfish Dissostichus mawsoni along East Antarctica: Environmental drivers and management implications

As Antarctic fish species experience increasing anthropogenic pressures there is a growing need to characterise the structure and function of their populations and understand how they may respond to changes in their environment. We integrated fishery-dependent and environmental data from years 2003–2017 to investigate the distribution of Antarctic toothfish Dissostichus mawsoni along a c. 3000 nm expanse of the shelf and slope along East Antarctica (30–150 °E). Spatially-explicit generalised additive mixed models were used to characterise the environmental drivers of relative abundance, mean individual weight, maturity-stage composition and sex ratio. Antarctic toothfish were not randomly distributed across the region, and spatial variations were characterised by complex relationships involving topography, temperature, salinity and sea ice. In particular, catch rates were highest at depths between 1000–1700 m. Mean weight and the proportion of fish that were mature both increased with depth and decreased with bottom temperature. Model predictions were also used to develop hypotheses relating to population function, including the location of nursery and spawning areas. This characterisation of the population can facilitate evaluation of fishing impacts in East Antarctica, and improve our understanding of the role of toothfish in Antarctic and Southern Ocean ecosystems.

Monitoring Antarctic toothfish in McMurdo Sound to evaluate the Ross Sea region Marine Protected Area

AbstractWe developed a random, stratified, vertical longline survey in McMurdo Sound, Antarctica, to compare the local age and size composition, diet and reproductive status of Antarctic toothfish (Dissostichus mawsoni) with those observed from a vessel-based survey of the southern Ross Sea shelf that includes a McMurdo Sound stratum. Results indicated that southern McMurdo Sound toothfish were larger and older than those a short distance away in northern McMurdo Sound. These data, in addition to recoveries of tagged fish, suggest that the large toothfish in McMurdo Sound may have limited mixing with the rest of the population. The potential effects of climate change and fishing in northern areas on toothfish abundance in McMurdo Sound will depend on the mechanism of toothfish recruitment to McMurdo Sound. Understanding the ecological relationships between McMurdo Sound toothfish and the larger population is required to predict these impacts. Furthermore, because toothfish predators (type C killer whalesOrcinus orca, Weddell sealsLeptonychotes weddellii) are abundant in the south-west margins of the Ross Sea, it is important to monitor toothfish in McMurdo Sound as part of the monitoring programme for the Ross Sea region Marine Protected Area.

Olfaction in the Antarctic toothfish Dissostichus mawsoni: clues from the morphology and histology of the olfactory rosette and bulb

The Antarctic notothenioid fish Dissostichus mawsoni (Antarctic toothfish) is an important piscine top predator in the Southern Ocean. Good olfactory capability has been hypothesized for this species on the basis of morphological (size of its olfactory bulb compared to other notothenioids) and behavioral (long distance migrations for food search and reproduction) traits. Here, we provide new information on the structure and function of the olfactory rosette and bulb of D. mawsoni using histology. Adult specimens (total length 136.2 ± 11.6 cm) were collected from McMurdo Sound. The rosettes had an average of 39 lamellae, without secondary folds and with a total surface area of about 1000 mm2. Both putative ciliated and microvillous receptor neurons were present in the sensory epithelium. Their projections to clustered glomeruli in the olfactory bulb were observed using antibodies against G-proteins. Numerous rodlet cells were observed in the epithelium and Gαi2-like immunoreactivity was present in their cytoplasm. This deserves further investigation given the still-debated nature of this cell type. Through the isotropic fractionator method, we showed 116,000 cells (mg of tissue)−1 in the olfactory bulb of D. mawsoni, a density that is similar to those found in mammals. Taken together, these data describe a well-developed olfactory system in this species, where olfaction is key sensory system.

Response to the opinion paper by Ainley et al.

We respond to comments made in the opinion paper by Ainley et al. (Hydrobiologia, 10.1007/s10750-015-2607-4, 2016) regarding our recent publication on the biology, ecology and life history of Antarctic toothfish (Dissostichus mawsoni) in the Ross Sea region. We focus in particular on the spatial and temporal extent of data collected from the fishery; results of research to date on changes in abundance and size of Antarctic toothfish at McMurdo Sound; and the subject of neutral buoyancy and inferences about vertical distribution. We conclude by re-iterating the need for well-designed, standardised research programmes to address remaining uncertainties in its life history.

Alien vs. Predator: interactions between the colossal squid (Mesonychoteuthis hamiltoni) and the Antarctic toothfish (Dissostichus mawsoni)

Data collected onboard two South Korean longliners in 2011–2014 targeting Antarctic toothfish provided insights into trophic interactions between two Antarctic top predators: the colossal squid Mesonychoteuthis hamiltoni and the Antarctic toothfish Dissostichus mawsoni. Adults of each species opportunistically prey upon weakened representatives of the other species: squid will feed on longline-caught toothfish, and toothfish on dying and dead squid. The highest occurrence of squid attacks was recorded in the Davis Sea and Commonwealth Sea, and the lowest in the Ross Sea. Squid depredation rates were around 1% on average, though regionally they might rise to 2–3%, which is of a similar magnitude to rates caused by sperm whales and killer whales in some areas.

Total Mercury Contents of Antarctic Toothfish Dissostichus mawsoni Caught in the Antarctic Sea

Abstract Mercury is an element of special concern for human health. Measurements of total mercury levels in fish have been taken into con-sideration to assess risk. In this study, the Antarctic toothfish Dissostichus mawsoni was evaluated as a potential safe food source through measurement of total mercury contents. Total mercury concentrations in Antarctic toothfish ranged from 0.101 ± 0.047 mg/kg to 0.139 ± 0.075 mg/kg. The total mercury concentration was significantly correlated with macroscopic values including total fish length, weight, gonadosomatic index, and maturity ( P < 0.01 or 0.05). Furthermore, according to the risk assessment, the total mercury body exposure rate from Antarctic toothfish ranged from 2.125% to 2.847% of the Provisional Tolerable Weekly Intake. Therefore, the Antarctic toothfish could be used as a potential safe seafood source. Key words: Dissostichus mawsoni , Antarctic toothfish, Mercury, Risk assessment, Safe seafood source Introduction The cod icefish species internationally known as the tooth-fish can be classified into the Antarctic toothfish

Composition of leucocytes in peripheral blood of Antarctic toothfish Dissostichus mawsoni (Nototheniidae)

Composition of leucocytes in peripheral blood of Antarctic toothfish Dissostichus mawsoni (Nototheniidae)

Pogonophryne tronio, a new species of Antarctic short-barbeled plunderfish (Perciformes: Notothenioidei: Artedidraconidae) from the deep Ross Sea with new data on Pogonophryne brevibarbata

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.

Results of investigation of the diet of antarctic toothfish Dissostichus mawsoni (Nototheniidae) in the Lazarev Sea

131 There are few investigations on the diet of the Ant� arctic toothfish Dissostichus mawsoni. The first data on feeding of this species were reported by Andriashev (1967). He found that from the first year of life the Antarctic toothfish is a clearly expressed predator. Most publications on the feeding of Antarctic toothfish deal with the Pacificand Indianocean sec� tors of the Antarctic Regions. Information on food composition of the Antarctic toothfish in open waters and continental seas of two sectors of the Antarctic Regions is available in publications by Calhaem and Christoffel (1969), Yukhov (1971, 1982), Pakhomov and Tseitlin (1992), Fenaughty et al., 2003), Petrov (2006), Petrov and Filippova (2007), and Petrov and Istomin (2008). The obtained results revealed both similarity and some differences in the diet of Antarc� tic toothfish from different regions. The bulk of the food bolus (by the frequency of occurrence and by weight) consists of fish of the families Macrouridae, Channichthyidae, and Nototheniidae, as well of cephalopods—squids (Psychrotheutidae, Onycho� teuthidae, Cranchiidae) and octopuses (Cirrata and Incirrata). The data on the diet of Antarctic toothfish in the Atlantic sector of Antarctic Regions are reported by Yukhov (1982) and Croshler (1992). According to Yukhov (1982) the investigated Antarctic toothfish taken out of stomachs of sperm whales fed in the open pelagial on whole squids and on their remains. Three species of squids were found in stomachs of toothfish: Morotheuthis knipovitchi, Kondakovia longimana, and Psychroteuthis glacialis. In the area of Elephant island (the South Shetlands) in 39% of the investigated fish 11-119 cm long (n = 38), the stomachs contained no food and in 61% of them mysids and amphipods pre� vailed; Champsocephalus gunnari and Gobionothen gib� berifrons fish were present (Crohsler, 1992).

Cytomorphology of female and male gonads in Antarctic toothfish Dissosctichus mawsoni (Nototheniidae) from the Ross Sea in the summer period

Results of histological analysis of gonads of female and male Antarctic toothfish Dissostichus mawsoni caught in the Ross Sea of the Pacific sector in the period of Antarctic summer (December–February) 2004–2005 are presented. Morphological indices and index of gonad maturity are described and ecological criteria of assessment of maturity stages of ovaries, cytological indices of oocytes, and the type of toothfish oogenesis are determined. It was established that in the period of fishing Antarctic toothfish, females and males with gonads at maturity stage III dominate. Ovaries contain two groups of oocytes of the period of trophoplasmatic growth and large oocytes of the nearest spawning season that comprise the smallest proportion of total sex cells. In the testes of two male toothfish, the primary fusion of renal and generative tissues was revealed. It is suggested that the termination of gonad maturity of toothfish takes place from March to April, and spawning takes place from June to August.

Comparative analysis of crystallins and lipids from the lens of Antarctic toothfish and cow

Animal model systems of senile cataract and lens crystallin stability are essential to understand the complex nature of lens transparency. Our aim in this study was to assess the long-lived Antarctic toothfish Dissostichus mawsoni (Norman) as a model system to understand long-term lens clarity in terms of solubility changes that occur to crystallins. We compared the toothfish with the mammalian model cow lens, dissecting each species' lens into a cortex and nuclear region. In addition to crystallin distribution, we also assayed fatty acid (FA) composition by negative ion electrospray ionization mass spectrometry (ESI-MS). The majority of toothfish lens crystallins from cortex (90.4%) were soluble, whereas only a third (31.8%) from the nucleus was soluble. Crystallin solubility analysis by SDS-PAGE and immunoblots revealed that relative proportions of crystallins in both soluble and urea-soluble fractions were similar within each species examined and in agreement with previous reports for bovine lens. From our data, we found that both toothfish and cow crystallins follow patterns of insolubility that mirror each animals lens composition with more γ crystallin aggregation seen in the toothfish lens nucleus than in cow. Toothfish lens lipids had a large amount of polyunsaturated fatty acids that were absent in cow resulting in an unsaturation index (I(U)) four-fold higher than that of cow. We identified a novel FA with a molecular mass of 267 mass units in the lens epithelial layer of the toothfish that accounted for well over 50% of the FA abundance. The unidentified lipid in the toothfish lens epithelia corresponds to either an odd-chain (17 carbons) FA or a furanoid. We conclude that long-lived fishes are likely good animal models of lens crystallin solubility and may model post-translational modifications and solubility changes better than short-lived animal models.

Molecular diversity and genomic organisation of the α, β and γ eye lens crystallins from the Antarctic toothfish Dissostichus mawsoni

The eye lens of the Antarctic toothfish living in the − 2 °C Southern Ocean is cold-stable. To investigate the molecular basis of this cold stability, we isolated, cloned and sequenced 22 full length crystallin cDNAs. We found two α crystallins (αA, αB), six β crystallins (βA1, βA2, βA4, βB1, βB2, βB3) and 14 γ crystallins (γN, γS1, γS2, γM1, γM3, γM4, γM5, γM7, γM8a, γM8b, γM8c, γM8d, γM8e, and γM9). Alignments of α, β and γ with other known crystallin sequences indicate that toothfish α and β crystallins are relatively conserved orthologues of their vertebrate counterparts, but the toothfish and other fish γM crystallins form a distinct group that are not orthologous to mammalian γ crystallins. A preliminary Fingerprinted Contig analysis of clones containing crystallin genes screened from a toothfish BAC library indicated α crystallin genes occurred in a single genomic region of ~ 266 kbp, β crystallin genes in ~ 273 kbp, while the γ crystallin gene family occurred in two separate regions of ~ 180 and ~ 296 kbp. In phylogenetic analysis, the γM isoforms of the ectothermic toothfish displayed a diversity not seen with endothermic mammalian γ crystallins. Similar to other fishes, several toothfish γ crystallins are methionine-rich (γM isoforms) which may have predisposed the toothfish lens to biochemically attenuate γ crystallin hydrophobicity allowing for cold adaptation. In addition to high methionine content, conservation of αβ crystallins both in sequence and abundance suggests greater functional constraints relative to γ crystallins. Conversely, reduced constraints upon γ crystallins could have allowed for greater evolutionary plasticity resulting in increased polydispersity of γ crystallins contributing to the cold-stability of the Antarctic toothfish lens.