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The Patagonian toothfish or Chilean sea bass, Dissostichus eleginoides, is an ecological and commercially important species captured by the Equatorian fleet in the Southeast Pacific Ocean. This study aimed to determine this species' diet composition and feeding habits captured in three geographical zones from Ecuador during 2017 and 2018. The total length and corporal mass were measured during this period, and the sex and sexual maturity states were determined from 328 individuals. A hypoallometric growth was evidenced by the size‐weight relationship in D. eleginoides, with an allometry coefficient b = 2.34, suggesting that it increases in size more than in weight. The stomach content analysis expressed as the Prey Specific Index of Relative Importance (PSIRI) indicated that D. eleginoides mainly feeds on teleost fish (88.2%) and less on cephalopods (9%) and crustaceans (2.8%). Males and females evidenced a similar diet; however, adults consumed more teleost fish than juveniles. The trophic position ⁓ 4 indicates that the Patagonian toothfish is a secondary carnivore predator with a wide geographic and diet variation related to prey availability. This is the first study regarding the trophic ecology of D. eleginoides in Ecuador, as other studies are lacking. Understanding nutrient and energy flows in ecosystems is crucial for effective fishing management with an ecosystemic approach. [ABSTRACT FROM AUTHOR]

Cryonotothenioids constitute a subgroup of notothenioid fishes endemic to the Southern Ocean that are specialized to exist in a narrow range of near-freezing temperatures. Due to the challenges of reliably collecting and maintaining larval cryonotothenioids in good condition, most thermal tolerance studies have been limited to adult and juvenile stages. With increasing environmental pressures from climate change in Antarctic ecosystems, it is important to better understand the impacts of a warming environment on larval stages as well. In this study, we determine the critical thermal maxima (CTmax) of cryonotothenioid larvae collected in pelagic net tows during three research cruises near the western Antarctic Peninsula. We sampled larvae of seven species representing three cryonotothenioid families—Nototheniidae, Channichthyidae, and Artedidraconidae. For channichthyid and nototheniid species, CTmax values ranged from 8.6 to 14.9 °C and were positively correlated with body length, suggesting that younger, less motile larvae may be especially susceptible to rapid warming events such as marine heatwaves. To our knowledge, this is the first published test of acute thermal tolerance for any artedidraconid, with CTmax ranging from 13.2 to 17.8 °C, which did not correlate with body length. Of the two artedidraconid species we collected, Neodraco skottsbergi showed remarkable tolerance to warming and was the only species to resume normal swimming following trials. We offer two hypotheses as to why N. skottsbergi has such an elevated thermal tolerance: (1) their unique green coloration serves as camouflage within near-surface phytoplankton blooms, suggesting they occupy an especially warm near-surface niche, and (2) recent insights into their evolutionary history suggest that they are derived from taxa that may have occupied warm tide-pool habitats. Collectively, these results establish N. skottsbergi and larval channichthyids as groups of interest for future physiological studies to gain further insights into the vulnerability of cryonotothenioids to a warming ocean. [ABSTRACT FROM AUTHOR]

Abstract Background Patagonian toothfish (Dissostichus eleginoides) is an economically and ecologically important fish species in the family Nototheniidae. Juveniles occupy progressively deeper waters as they mature and grow, and adults have been caught as deep as 2500 m, living on or in just above the southern shelves and slopes around the sub-Antarctic islands of the Southern Ocean. As apex predators, they are a key part of the food web, feeding on a variety of prey, including krill, squid, and other fish. Despite its importance, genomic sequence data, which could be used for more accurate dating of the divergence between Patagonian and Antarctic toothfish, or establish whether it shares adaptations to temperature with fish living in more polar or equatorial climes, has so far been limited. Results A high-quality D. eleginoides genome was generated using a combination of Illumina, PacBio and Omni-C sequencing technologies. To aid the genome annotation, the transcriptome derived from a variety of toothfish tissues was also generated using both short and long read sequencing methods. The final genome assembly was 797.8 Mb with a N50 scaffold length of 3.5 Mb. Approximately 31.7% of the genome consisted of repetitive elements. A total of 35,543 putative protein-coding regions were identified, of which 50% have been functionally annotated. Transcriptomics analysis showed that approximately 64% of the predicted genes (22,617 genes) were found to be expressed in the tissues sampled. Comparative genomics analysis revealed that the anti-freeze glycoprotein (AFGP) locus of D. eleginoides does not contain any AFGP proteins compared to the same locus in the Antarctic toothfish (Dissostichus mawsoni). This is in agreement with previously published results looking at hybridization signals and confirms that Patagonian toothfish do not possess AFGP coding sequences in their genome. Conclusions We have assembled and annotated the Patagonian toothfish genome, which will provide a valuable genetic resource for ecological and evolutionary studies on this and other closely related species.

Background: Patagonian toothfish (Dissostichus eleginoides) is an economically and ecologically important fish species in the family Nototheniidae. Juveniles occupy progressively deeper waters as they mature and grow, and adults have been caught as deep as 2500 m, living on or in just above the southern shelves and slopes around the sub-Antarctic islands of the Southern Ocean. As apex predators, they are a key part of the food web, feeding on a variety of prey, including krill, squid, and other fish. Despite its importance, genomic sequence data, which could be used for more accurate dating of the divergence between Patagonian and Antarctic toothfish, or establish whether it shares adaptations to temperature with fish living in more polar or equatorial climes, has so far been limited. Results: A high-quality D. eleginoides genome was generated using a combination of Illumina, PacBio and Omni-C sequencing technologies. To aid the genome annotation, the transcriptome derived from a variety of toothfish tissues was also generated using both short and long read sequencing methods. The final genome assembly was 797.8 Mb with a N50 scaffold length of 3.5 Mb. Approximately 31.7% of the genome consisted of repetitive elements. A total of 35,543 putative protein-coding regions were identified, of which 50% have been functionally annotated. Transcriptomics analysis showed that approximately 64% of the predicted genes (22,617 genes) were found to be expressed in the tissues sampled. Comparative genomics analysis revealed that the anti-freeze glycoprotein (AFGP) locus of D. eleginoides does not contain any AFGP proteins compared to the same locus in the Antarctic toothfish (Dissostichus mawsoni). This is in agreement with previously published results looking at hybridization signals and confirms that Patagonian toothfish do not possess AFGP coding sequences in their genome. Conclusions: We have assembled and annotated the Patagonian toothfish genome, which will provide a valuable genetic resource for ecological and evolutionary studies on this and other closely related species. [ABSTRACT FROM AUTHOR]

Hybridization between species and the establishment of hybridization barriers can influence the diversification of species. Antarctic notothenioid fishes represent a prime example of marine adaptive radiation that diversified in the icy waters of Antarctica from an ancestral population that innovated antifreeze glycoproteins. The processes by which Antarctic notothenioid species evolved, however, remain elusive, and interspecific hybridization or the establishment of hybridization barriers between lineages may have influenced species diversification. To evaluate the current hybridization potential of notothenioids, we performed an experimental in vitro fertilization cross between two sympatric and congeneric notothen species using oocytes from the bullhead notothen Notothenia coriiceps and sperm from the marbled notothen N. rossii. Resulting embryos developed to late gastrula/early neurula stages and then suddenly died. Genetic analyses of embryos and parents demonstrated that the embryos lacked detectable paternal DNA and were thus gynogenetic. While premating barriers are likely to exist between the two species, this experiment suggests a strong postmating, prezygotic reproductive barrier preventing hybridization between the sister species due to gametic incompatibility in this directional cross. Our study provides novel information on mechanisms that may have contributed to the divergence and maintenance of these two ecologically important congeneric species. [ABSTRACT FROM AUTHOR]

Abstract Gelatinous zooplankton (GZP), i.e., ctenophores, cnidarian medusae, chaetognaths, appendicularians and salps, are considered climate change winners. This becomes particularly obvious in the Southern Ocean, which has undergone a significant shift from a krill‐based to a salp‐based ecosystem over the last decades. A better knowledge on the role of gelatinous invertebrates as prey is needed to predict the impact of such a gelatinous shift. Until recently, GZP was considered as a “trophic dead end”. However, their true importance in diets has remained unresolved due to the rapid digestion of their watery and soft tissues in predators' stomachs. In this study, we want to validate the paradigm shift from GZP being considered as “survival food” to be considered a “regular” prey item for two demersal fish species (Notothenia rossii and N. coriiceps) of Potter Cove, South Shetland Islands, using a multimarker (COI and 18S) metabarcoding approach. We found that GZP taxa commonly occurred in the diets of both species, represented by pelagic tunicates (appendicularians, salps), cnidarians, chaetognaths and ctenophores. Salps were the most abundant prey group, preyed upon by each individual of both species, reaching 98.7% relative read abundance for 18S. We recovered a wide range of different taxa in their diets, from primary producers to highly abundant invertebrates, thus the two nototheniid species can be regarded as “natural samplers” of the ecosystem in study. Finally, we want to point out the importance of multimarker metabarcoding approaches for broad ecological assessments, given the differential amplification and sequencing success of different markers for specific groups and the unequal taxonomic coverage of the reference databases. The output of each marker was highly complementary, since an important prey item such as salps, was only detected with 18S, while other taxa (e.g., Arthropoda) were represented with a higher taxonomic resolution with COI.

The Heteracanthocephalidae Petrochenko, 1956 is a rare family of acanthocephalans mainly parasitic in fishes. The pattern of mitogenomic evolution of the Heteracanthocephalidae is still unknown, and the phylogenetic relationships of the Heteracanthocephalidae with the other 14 families within the order Echinorhynchida remain unclear. In the present study, the complete mitochondrial genome of Aspersentis megarhynchus (von Linstow, 1892) Golvan, 1960 was sequenced and annotated for the first time, which represents the first mitogenomic data for the genus Aspersentis and also for the family Heteracanthocephalidae. The mitogenome of A. megarhynchus has 14,661 bp and includes 36 genes, containing 12 protein-coding genes (PCGs) (missing atp8), 22 tRNA genes, and 2 ribosomal RNAs (rrnS and rrnL), plus two non-coding regions. Comparative mitochondrial genomic analysis revealed that the presence of translocations of several tRNA genes (trnV, trnE, and trnT) and the gene arrangement in the mitogenome of A. megarhynchus represents a new type in Acanthocephala. Moreover, the mitogenomic phylogenetic results based on concatenated amino acid sequences of 12 protein-coding genes strongly supported the validity of the Heteracanthocephalidae and suggested close affinity between the Heteracanthocephalidae and Echinorhynchidae in the order Echinorhynchida.

The aim of our study was to update the information on taxonomic diversity and structure of the parasite community of Antarctic rockcod, Notothenia coriiceps in the coastal water off the Argentine Islands (Wilhelm Archipelago, Graham Land, West Antarctica). The material for this study was collected in 2014-2015 at the Ukrainian Antarctic station "Akademik Vernadsky". More than 8,500 specimens of parasites from 106 host specimens were collected and identified. All fishes were found to be infected with helminths; 25 helminth species were identified. Acanthocephalans were recorded in 93.4 % of hosts; eight species of acanthocephalans (Metacanthocephalus rennicki, M. johnstoni, M. campbelli, M. dalmori, Aspersentis megarhynchus, Corynosoma hamanni, C. pseudohamanni, and C. evae) were found. Nematodes were found in 96.2 % of fishes; larval stages of Pseudoterranova sp., Contraceacum sp., Anisakis sp. and adults Ascarophis nototheniae and Dichelyne fraseri were identified. Trematodes were found in 94.3 % of fishes; seven species (Macvicaria georgiana, Neolebouria antarctica, Lepidapedon garrardi, Genolinea bowersi, Elytrophalloides oatesi, Lecithaster macrocotyle, Derogenes johnstoni) were identified. Larval stages of cestodes (Diphyllobothrium sp. and tetraphyllidean metacestodes) and the monogenean species Pseudobenedenia nototheniae were found. Our studies revealed significant changes in the structure of the parasite community of N. coriiceps during the last decade. [ABSTRACT FROM AUTHOR]

Fisheries ecosystem-based management is an important tool for sustainable harvesting of fisheries worldwide. Knowledge of trophic interactions is crucial since changes in trophic balances can induce severe changes in the structure of marine communities. While advocated for deep-sea fisheries, a lack of studies in the benthopelagic area persist. The Antarctic toothfish, Dissostichus mawsoni, is a top predator inhabiting the Southern Ocean deep-sea and a high-value species in a fishery managed by CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources). Previous studies suggested a geographical variability in its diet, but never studying it in the same year. We analysed stomach contents and stable isotopes of δ15N and δ13C in the muscle of D. mawsoni captured in three fishing areas from the Amundsen and Dumont D'Urville Seas, during the 2016/17 fishing season. Although significant spatial differences were found, five taxa were found in all sites, Antimora rostrata, Macrourus spp., Muraenolepis spp., Moroteuthopsis longimana and Psychroteuthis glacialis. High diversity of prey confirms D. mawsoni as a generalist feeder. Values of δ15N showed similar trophic position across areas, in contrast to the differences found in δ13C values. GLM showed that δ15N and δ13C values varied with otolith length, latitude and the opposite isotope, i.e. δ13C and δ15N respectively. Implications for D. mawsoni fisheries management are discussed considering different predation release scenarios. [ABSTRACT FROM AUTHOR]

Purpose: The parasitic diversity on the intertidal fish of the Southern American Cone is barely known. The present study describes two new parasitic copepod species, a Clavella and a Haemobaphes found on the nototheniid fish Patagonotothen cornucola. Methods: The fish were collected from the intertidal zone of the Strait of Magellan, Southern Chile. The copepods were found on the fins and in the gill chamber of the fish, which were morphologically analyzed using optical and electronic microscopy. Results: Clavella cornucola sp. nov. and Clavella bowmani are similar but differ in the number of setae found on the maxillule (two setae on the inner lobe vs. three on C. bowmani), and a pad of spinules on the dorsal margin as opposed to the outer lobe (no pad vs. one pad, respectively). Haemobaphes puntaarenensis sp. nov. is distinguished from its congeners based on the lobe shapes of the head and the clear separation between the pedigerous somites (first, second, and third). The maxilla on H. puntaarenensis sp. nov. lacks a pad of spinules on the second segment, but it is found in all the other congeneric species. Conclusion: Clavella cornucola sp. nov. is the 10th species of the genus in Chile, whereas Haemobaphes puntaarenensis sp. nov. is the first species of the genus recorded in Chile and the Southern Cone coasts. [ABSTRACT FROM AUTHOR]

Abstract Background Chromosomal rearrangements are thought to be an important driving force underlying lineage diversification, but their link to speciation continues to be debated. Antarctic teleost fish of the family Nototheniidae (Notothenioidei) diversified in a changing environmental context, which led to ecological, morphological, and genetic differentiation among populations. In addition, extensive chromosomal repatterning accompanied species divergence in several clades. The most striking karyotypic changes involved the recent species radiation (about 10 My) of the genus Trematomus, with chromosomal pair numbers ranging between 29 and 12. These dramatic reductions in chromosome number resulted mostly from large-scale chromosome fusions. Multiple centric and/or tandem fusions have been hypothesized in at least seven of the twelve recognized Trematomus species. To reconstruct their evolutionary history, we employed comparative cytogenomics (BAC-FISH and chromosome painting) to reveal patterns of interspecific chromosomal orthologies across several notothenioid clades. Results We defined orthologous chromosomal segments of reference, termed Structural Units (SUs). SUs were identified in a total of 18 notothenioid species. We demonstrated for the first time that SUs were strongly conserved across every specimen examined, with chromosomal syntenies highlighting a paucity of intrachromosomal macro-rearrangements. Multiple independent fusions of these SUs were inferred in the Trematomus species, in contrast to the shared SU fusions in species of the sister lineage Notothenia. Conclusions The SU segments were defined units of chromosomal rearrangement in the entire family Nototheiidae, which diverged from the other notothenioid families 20 My ago. Some of the identified chromosomal syntenies within the SUs were even conserved in their closest relatives, the family Eleginopsidae. Comparing the timing of acquisition of the fusions in the closely related genera Notothenia and Trematomus of the nototheniid species family, we conclude that they exhibit distinct chromosomal evolutionary histories, which may be relevant to different speciation scenarios.

Patagonotothen cornucola is one of the most abundant intertidal fishes off the Patagonian shores of central Argentina that live under rocks, among algae and in tidal pools. This study was aimed to analyze its dietary composition and feeding strategy in two sites of the coast of San Jorge Gulf, Argentina. Samples were taken monthly between 2008 and 2012. The stomach contents were identified at the lowest possible level, counted and weighed. The most numerous group found in the stomachs were crustaceans, followed by annelids. Among crustaceans P. cornucola feeds principally on the isopod Exosphaeroma sp. and amphipods, and polychaetes represented the most important prey among annelids. There was no single predominating prey item across the studied area, and the occurrences of each prey were different in each site. Our study demonstrated that P. cornucola is mainly carcinophagous opportunistic ambush predator exhibiting seasonal and spatial variability of the feeding spectrum. [ABSTRACT FROM AUTHOR]

Abstract This study analyzed the effect of thermal stress on erythrocytes of Notothenia rossii and Notothenia coriiceps, abundant notothenioids in Admiralty Bay, Antarctic Peninsula. In both species, the antioxidant defense system enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione-S transferase, glutathione reductase were punctually altered (8°C for 1, 3 and 6 days) in erythrocytes, indicating that these markers are not ideal for termal stress. However, under the influence of thermal stress, morphological changes in Notothenia coriiceps erythrocytes were observed at all exposure times (1, 3 and 6 days at 8°C), and in Notothenia rossii occurred in 6 days. These results suggest that Notothenia corriceps presents a lower tolerance to thermal stress at 8°C for up to 6 days, since the cellular and nuclear alterations recorded are pathological and may be deleterious to the cells. Among the morphological markers analyzed in this work, we believe that the shape change and nuclear bubble formation may be good stress biomarkers in erythrocytes of Notothenia rossii and Notothenia coriiceps.

The genome evolution of Antarctic notothenioids has been modulated by their extreme environment over millennia and more recently by human-caused constraints such as overfishing and climate change. Here we investigated the characteristics of the immune system in Notothenia rossii and how it responds to 8 h immersion in viral (Poly I:C, polyinosinic: polycytidylic acid) and bacterial (LPS, lipopolysaccharide) proxies. Blood plasma antiprotease activity and haematocrit were reduced in Poly I:C-treated fish only, while plasma protein, lysozyme activity and cortisol were unchanged with both treatments. The skin and duodenum transcriptomes responded strongly to the treatments, unlike the liver and spleen which had a mild response. Furthermore, the skin transcriptome responded most to the bacterial proxy (cell adhesion, metabolism and immune response processes) and the duodenum (metabolism, response to stress, regulation of intracellular signal transduction, and immune system responses) to the viral proxy. The differential tissue response to the two proxy challenges is indicative of immune specialisation of the duodenum and the skin towards pathogens. NOD-like and C-type lectin receptors may be central in recognising LPS and Poly I:C. Other antimicrobial compounds such as iron and selenium-related genes are essential defence mechanisms to protect the host from sepsis. In conclusion, our study revealed a specific response of two immune barrier tissue, the skin and duodenum, in Notothenia rossii when exposed to pathogen proxies by immersion, and this may represent an adaptation to pathogen infective strategies. Interleukin (il), interferon regulatory factor 2 binding protein 1 (irf2bpi), protein disulphide isomerase family A member 2 (pdia2), lysosomal alpha-glucosidase (gaa), peroxisome proliferator-activated receptor alpha (pparα), macrophage (M or MR), Liver X receptor alpha (LXRα), toll-like receptor 3 (tlr3), receptor (r), NLR Family CARD Domain Containing 3 (nlrc3), leucine rich repeat and pyrin domain containing (nlrp), nuclear factor (NF), interferons (IFNs), tumour necrosis factor (TNF), alpha (α), beta (β), gamma (γ), interferon alpha/beta receptor 2 (ifnra2), immunoglobulin (Ig), major histocompatibility complex (MHC), T-cell receptor (TCR), isocitrate dehydrogenase [NADP], mitochondrial (idh2), tricarboxylic acid cycle (TCA), scavenger receptor class B member 1 (scarb1), signal transducer and activator of transcription (STAT), endoplasmatic reticulum (ER). [Display omitted] • Four tissues transcriptomes were responsive to bacterial and viral proxies. • The skin was more responsive to LPS and the duodenum to poly I:C. • The main processes involved were related to metabolic pathways and immune system. • PRRs and other antimicrobial compounds were observed as defence mechanisms. [ABSTRACT FROM AUTHOR]

The spatio-temporal delimitation of fish reproduction is essential for the appropriate management and conservation strategies in populations. Assessing this feature in Antarctic Ichthyology is particularly difficult because harsh environmental conditions limit sample collection. This study shows how physiology can contribute compelling evidence to understand reproduction in Antarctic fish using the notothenioid Lepidonotothen nudifrons as a model species. Sampling included 121 specimens caught at Potter Cove (PC), South Shetland Islands (SSI), from November to late March of 2016–2018. Gonadal macroscopic and histologic features are reported. Oocyte growth and change in testosterone and estradiol plasma levels throughout the ovarian growth of L. nudifrons adult females is provided. In March, females (n = 17) attained gonado-somatic index of 13–20% (16.73 ± 4.20), total fecundity of 2196–4652 oocytes/female, the leading clutch oocytes measured 1.7–2.1 mm, and males (n = 5) showed spermatozoids in their testicles. The leading clutch growth was significantly associated with photoperiod, with no diameter variation until the summer solstice, when it began to grow linearly with an estimated rate of 0.01 mm/day. Testosterone and estradiol increased together with the oocyte growing throughout the analysed months, with a higher rate of increase during March. The reproductive effort data, and especially the significant plasma level increase in both sex steroids observed in March, suggest that (1) females were at a late vitellogenesis stage, just prior to the oocyte final maturation, and thus L. nudifrons spawning period might begin in March at SSI; (2) PC is likely a spawning site for L. nudifrons, which indicates that nearshore areas are spawning grounds for some notothenioids. [ABSTRACT FROM AUTHOR]

The Notothenioidei are a typical example of stenothermal fishes since most species have evolved and lived in Antarctic waters, where the water temperature is low and stable. This fact enabled them to evolve physiological characteristics related to cold. Nevertheless, some species came out of Antarctic waters a few million years ago and coped with more variable thermal regimes. This work aims to determine the thermal tolerance and preference of two sub-Antarctic notothenioid species found in Southern South America, Patagonotothen tessellata and Harpagifer bispinis, adding valuable information about thermal adaptation mechanisms. Experiments were conducted after exposing their juveniles for three weeks at 4, 7, 10 and 12 °C. Their thermal tolerance limits were established using the Critical Thermal Methodology and their acute thermal preferenda, employing a horizontal thermal gradient tank. Fishes acclimated to different exposure temperatures had small to intermediate thermal tolerance polygons (P. tessellata: 593.85°C2, H. bispinis: 475.40 °C2) and positive relationships between preferred and acclimation temperatures. The Final Temperature Preferenda were estimated to be 14.25 °C for P. tessellata and 13.05 °C for H. bispinis, allowing to characterize them as cold eurythermal species, with P. tessellata more tolerant to heat and H. bispinis more tolerant to cold. Their different thermal sensitivities are in agreement with their different thermal histories and distributions. In a climate change context, the increase of sea surface temperatures is likely to reduce the northern boundaries of their distributions. Conversely, it can potentially enhance both species' performances at their southernmost distribution limits since those environments are cooler than their maximum thermal tolerances. [ABSTRACT FROM AUTHOR]

To predict how the fishing of Antarctic toothfish, Dissostichus mawsoni, would affect the ecosystem, it is necessary to understand the species' ecological niche. Morphological analysis of the stomach contents of 960 D. mawsoni specimens collected at depths of 946–1600 m along the East Antarctic continental slope from December 2016 to March 2017 was used to assess dietary composition according to depth, sex, site, and size. Fishes were the most common prey item for D. mawsoni, comprising 97.8% based on the index of relative importance. Among the nine fish families consumed by D. mawsoni, Macrouridae was the dominant taxon. The size of D. mawsoni increased with depth. The dietary composition of D. mawsoni did not show significant differences by depth or sex, but did differ with site and size. D. mawsoni was the top predator in the ecosystem along the East Antarctic continental slope and can be considered an opportunistic feeder, feeding on abundant food in the environment. Therefore, additional studies of the diet of Antarctic toothfish are necessary to maintain the ecosystem structure and function in a changing environment, and the results of this study can be used as a monitoring baseline. [ABSTRACT FROM AUTHOR]

Se estudiaron trescientos sesenta y tres ejemplares de Eleginops maclovinus (Valenciennes, 1830) para conocer sus hábitos alimentarios en la desembocadura del río Lingue (Chile, 39°25?S; 73°10?W). La proporción de machos y hembras (%) se muestra para cada mes. La muestra refleja estadísticamente la clase de tamaño de los machos entre VII y XI y en las hembras entre VIII y XIV en comparación con otros estudios (Gosztonyi, 1974). El 44% de las muestras de estómago estaban vacías. Los contenidos estomacales fueron 84,32% del peso en animales y 11% en plantas, principalmente algas. Los animales más abundantes fueron los crustáceos. Se presentan figuras en relación con las características de la muestra de peces y en relación con el contenido del estómago. Como conclusión, E. maclovinus es una especie omniporosa que se alimenta principalmente de animales bénticos.

Abstract Background The importance of transposable elements (TEs) in the genomic remodeling and chromosomal rearrangements that accompany lineage diversification in vertebrates remains the subject of debate. The major impediment to understanding the roles of TEs in genome evolution is the lack of comparative and integrative analyses on complete taxonomic groups. To help overcome this problem, we have focused on the Antarctic teleost genus Trematomus (Notothenioidei: Nototheniidae), as they experienced rapid speciation accompanied by dramatic chromosomal diversity. Here we apply a multi-strategy approach to determine the role of large-scale TE mobilization in chromosomal diversification within Trematomus species. Results Despite the extensive chromosomal rearrangements observed in Trematomus species, our measurements revealed strong interspecific genome size conservation. After identifying the DIRS1, Gypsy and Copia retrotransposon superfamilies in genomes of 13 nototheniid species, we evaluated their diversity, abundance (copy numbers) and chromosomal distribution. Four families of DIRS1, nine of Gypsy, and two of Copia were highly conserved in these genomes; DIRS1 being the most represented within Trematomus genomes. Fluorescence in situ hybridization mapping showed preferential accumulation of DIRS1 in centromeric and pericentromeric regions, both in Trematomus and other nototheniid species, but not in outgroups: species of the Sub-Antarctic notothenioid families Bovichtidae and Eleginopsidae, and the non-notothenioid family Percidae. Conclusions In contrast to the outgroups, High-Antarctic notothenioid species, including the genus Trematomus, were subjected to strong environmental stresses involving repeated bouts of warming above the freezing point of seawater and cooling to sub-zero temperatures on the Antarctic continental shelf during the past 40 millions of years (My). As a consequence of these repetitive environmental changes, including thermal shocks; a breakdown of epigenetic regulation that normally represses TE activity may have led to sequential waves of TE activation within their genomes. The predominance of DIRS1 in Trematomus species, their transposition mechanism, and their strategic location in “hot spots” of insertion on chromosomes are likely to have facilitated nonhomologous recombination, thereby increasing genomic rearrangements. The resulting centric and tandem fusions and fissions would favor the rapid lineage diversification, characteristic of the nototheniid adaptive radiation.

The article discusses a study which successfully generated highly contiguous genome sequences of Dissostichus mawsoni, the Antarctic toothfish that belongs to the family Nototheniidae of the order Perciformes and is native to the Southern Ocean. Topics covered include the researchers' use of long-read sequencing and Hi-C technology to provide comprehensive insight into the adaptive mechanisms of D. mawsoni, and the discovery of the features of previously unavailable DNA regions.

This study describes the cephalic sensory canal pores of the Patagonian toothfish's juvenile and adult specimens (Dissostichus eleginoides) from southern Chile. Specimens exhibited four supraorbital, eight infraorbital, and five mandibular pores, followed by six preoperculars, one coronal pore, one supratemporal pore, and four temporal pores. Juveniles exhibited circular pores in the mandibular, infraorbital, and preopercular region. The first two supraorbital pores are circular, the third is rectangular, and the fourth triangular. The coronal pore is circular with a bifurcation; the supratemporal pore is rectangular. In adults, the first mandibular canal pore is circular, and the last four are elongated. The preopercular canal pores are elongated. The two first supraorbital canal pores are circular, unlike the third and fourth, which are rectangular. The coronal pore is rectangular without bifurcation, and the supratemporal pore has a T-shape. The jaw of juveniles does not present all mandibular canal pores; in the infraorbital region, the first five pores extend as a thin canaliculus, while the adjacent pores appear as longer canaliculi in adults. The differences could be related to changes in spatial distribution during larval, juvenile, and adult stages. Adult cephalic sensory canal pores may have an important role in detecting vibratory waves allowing them to capture their prey and perceive potential predators. Our results provide information regarding the cephalic sensory canal pores of the Patagonian toothfish that may stimulate future studies of this species' mechanosensory system. [ABSTRACT FROM AUTHOR]

The first non-coastal Sub-Antarctic Marine Protected Area (Namuncurá) in Argentina was created in 2013, at Burdwood Bank (MPAN-BB), an undersea plateau located about 200 km south from Malvinas/Falkland Islands, SW Atlantic Ocean. The main contribution of this work was to explore fish species composition and the structure of fish assemblages in three different zones of the MPAN-BB with different conservation strategies and different surrounding areas. Twenty-two fishing trawls were performed using a demersal bottom trawl pilot net at depths between 71 and 608 m. A total of 667 fish belonging to 30 species were collected in the surveyed area. The richest family in terms of species number was Nototheniidae (seven species), followed by Macrouridae, Myxinidae and Zoarcidae (four species each), then Moridae and Arhynchobatidae (three species each), and finally Muraenolepididae and Psychrolutidae (two species each). The remaining families were represented by a single species. Three significantly different fish assemblages were detected. These distinct assemblages were largely circumscribed at the plateau, the shelf-break slope, and the area west of the BB. The results showed that fish diversity in the MPAN-BB is relatively high constituting ~ 10% of the fish composition reported for the Atlantic sector of the Magellanic Province. The present data suggest that fishes are an important component of the benthic community planned to be protected by the implementation of the MPAN-BB. These findings have important implications for habitat preservation and threatened species conservation. [ABSTRACT FROM AUTHOR]

The present study is a valuable contribution to the knowledge of feeding habits of Patagonian toothfish Dissostichus eleginoides in Southwestern Atlantic (53–55°S, 351 to 1073 m depth) near Burdwood Bank/Namuncurá marine-protected area, where diet has not been previously investigated. Based on stomach content analyses of 441 specimens ranging from 38 to 190 cm total length (TL), our study tested the hypotheses that diet was influenced by TL, sex, maturity stage, depth, and region, using generalized linear models and information theory selection criteria. The Patagonian toothfish fed primarily on fish (morid cod Notophycis marginata, myctophids, rattails Macrourus holotrachys and Coelorinchus fasciatus, notothenids Patagonotothen ramsayi, and hoki Macruronus magellanicus), followed by cephalopods (Onykia ingens, Doryteuthis gahi) and shrimps (Acanthephyra pelagica). One case of cannibalism was recorded. The trophic level was 4.57 (4.22 juveniles, 4.78 adults). The pelagic fish and bathypelagic shrimp were more consumed in the east region, whereas demersal fish and cephalopods were more consumed in the west one. Ontogenetic dietary changes associated with TL and maturity stage were reported: pelagic fish and shrimp A. pelagica had the main importance in the diet of intermediate-sized toothfish, reinforcing the hypothesis that juveniles exhibited a bento-pelagic behavior. Demersal fish were more heavily consumed by juvenile specimens, and the size of demersal fish predated by Patagonian toothfish increased according to the predator TL. Cephalopods were more consumed by adults. The preference of sexually mature specimens for cephalopods could have a positive effect on spawning and egg quality. [ABSTRACT FROM AUTHOR]

Th e aim of our study was to update the information on taxonomic diversity and structure of the parasite community of Antarctic rockcod, Notothenia coriiceps in the coastal water off the Argentine Islands (Wilhelm Archipelago, Graham Land, West Antarctica). Th e material for this study was collected in 2014-2015 at the Ukrainian Antarctic station "Akademik Vernadsky". More than 8,500 specimens of parasites from 106 host specimens were collected and identified. All fi shes were found to be infected with helminths; 25 helminth species were identified. Acanthocephalans were recorded in 93.4% of hosts; eight species of acanthocephalans (Metacanthocephalus rennicki, M. johnstoni, M. campbelli, M. dalmori, Aspersentis megarhynchus, Corynosoma hamanni, C. pseudohamanni, and C. evae) were found. Nematodes were found in 96.2% of fi shes; larval stages of Pseudoterranova sp., Contraceacum sp., Anisakis sp. and adults Ascarophis nototheniae and Dichelyne fraseri were identified. Trematodes were found in 94.3% of fi shes; seven species (Macvicaria georgiana, Neolebouria antarctica, Lepidapedon garrardi, Genolinea bowersi, Elytrophalloides oatesi, Lecithaster macrocotyle, Derogenes johnstoni) were identifi ed. Larval stages of cestodes (Diphyllobothrium sp. and tetraphyllidean metacestodes) and the monogenean species Pseudobenedenia nototheniae were found. Our studies revealed signifi cant changes in the structure of the parasite community of N. coriiceps during the last decade. [ABSTRACT FROM AUTHOR]

Background: Chromosomal rearrangements are thought to be an important driving force underlying lineage diversification, but their link to speciation continues to be debated. Antarctic teleost fish of the family Nototheniidae (Notothenioidei) diversified in a changing environmental context, which led to ecological, morphological, and genetic differentiation among populations. In addition, extensive chromosomal repatterning accompanied species divergence in several clades. The most striking karyotypic changes involved the recent species radiation (about 10 My) of the genus Trematomus, with chromosomal pair numbers ranging between 29 and 12. These dramatic reductions in chromosome number resulted mostly from large-scale chromosome fusions. Multiple centric and/or tandem fusions have been hypothesized in at least seven of the twelve recognized Trematomus species. To reconstruct their evolutionary history, we employed comparative cytogenomics (BAC-FISH and chromosome painting) to reveal patterns of interspecific chromosomal orthologies across several notothenioid clades. Results: We defined orthologous chromosomal segments of reference, termed Structural Units (SUs). SUs were identified in a total of 18 notothenioid species. We demonstrated for the first time that SUs were strongly conserved across every specimen examined, with chromosomal syntenies highlighting a paucity of intrachromosomal macro-rearrangements. Multiple independent fusions of these SUs were inferred in the Trematomus species, in contrast to the shared SU fusions in species of the sister lineage Notothenia. Conclusions: The SU segments were defined units of chromosomal rearrangement in the entire family Nototheiidae, which diverged from the other notothenioid families 20 My ago. Some of the identified chromosomal syntenies within the SUs were even conserved in their closest relatives, the family Eleginopsidae. Comparing the timing of acquisition of the fusions in the closely related genera Notothenia and Trematomus of the nototheniid species family, we conclude that they exhibit distinct chromosomal evolutionary histories, which may be relevant to different speciation scenarios. [ABSTRACT FROM AUTHOR]

Dissotichus eleginoides has a discontinuous circumpolar geographic distribution restricted to mountains and platforms, mainly in Subantarctic and Antarctic waters of the southern hemisphere, including the Southeast Pacific, Atlantic and Indian oceans and in areas surrounding the peninsular platforms of subantarctic islands. The aim of this work was to determine and characterize the gastrointestinal parasitic and microbial fauna of specimens of D. eleginoides captured in waters of the south-central zone of Chile. The magnitude of parasitism in D. eleginoides captured in waters of the south-central zone of Chile is variable, and the parasite richness is different from that reported in specimens from subantarctic environments. Next-generation sequencing (NGS) of the microbial community associated to intestine showed a high diversity, where Proteobacteria, Firmicutes, and Bacteriodetes were the dominant phyla. However, both parasitic and microbial structures can vary between fish from different geographic regions

In this study, we present first observations on the feeding behaviour of an Antarctic notothenioid fish, the striped rockcod, Trematomus hansoni Boulenger, 1902. During 13 days of feeding experiment onboard RV Polarstern, the striped rockcod consumed an average of 1.0% BM · day-1 of Loligo reynaudii at the temperature around +1.0°C. The daily food ration of T. hansoni turned out to be lower than predicted by theoretical equations derived for fish living at higher temperatures but was similar to values observed in other Antarctic fish in captivity. [ABSTRACT FROM AUTHOR]

Highlights • The thermal stress of 8 °C induces different metabolic adjustments in the brain. • Glycogenolysis in Notothenia coriiceps was to be essential as an immediate source of glucose. • In Notothenia rossii , the anaerobic metabolism and hexokinase were reduced. • Glutathione peroxidase and glutathione-S-transferase appear to be critical enzymes. • There are tissue-specific patterns and species-specific responses. Abstract Antarctic Nototheniidae is an attractive group for studying metabolic and physiological responses at high temperatures. The present work investigated the metabolic responses of the carbohydrate metabolism and antioxidant system to thermal stress at 8 °C (for 2–144 h) in the brains of Notothenia rossii and Notothenia coriiceps. In N. coriiceps , glycogenolysis was essential in the first hours of exposure (2 h) at 8 °C and, in addition to inhibiting glucose-6-phosphatase activity, was important for activating the pentose phosphate pathway. In N. rossii , anaerobic metabolism was reduced in the first hours of exposure (2 and 6 h) at 8 °C, followed by reduced hexokinase activity, suggesting energy regulation between neurons and astrocytes. The antioxidant system results indicated the importance of the actions of the glutathione-dependent antioxidant enzymes glutathione-S-transferase and glutathione peroxidase as well as those of catalase in N. coriiceps and the action of glutathione-S-transferase, glutathione peroxidase and glutathione reductase in N. rossii , especially during the first 12 h of thermal stress exposure. These results indicate tissue-specific patterns and species-specific responses to this stress. [ABSTRACT FROM AUTHOR]

Thermal elevation records in the Austral Ocean have raised questions about the physiological impacts on Antarctic organisms which have evolved under cold and stable water temperatures. Some notothenioid fishes exhibit species-specific responses to elevated temperature, yet the mechanisms involved in restoring homeostasis are unclear. Our study focused on the physiological effects of short-term (2-144 h) exposure to water temperatures of 8 °C on the plasma biochemical profiles of Notothenia coriiceps and Notothenia rossii, species that are abundant in Admiralty Bay, King George Island, Antarctic Peninsula, a region where increasing temperatures have been detected. Despite being phylogenetically similar, these species responded differently to thermal stress. N. rossii showed no changes in cortisol levels, and transient hyperglycemia was likely triggered by elevated catecholamine levels; conversely, metabolic and antioxidant defense parameters were unaffected. Increased gill Na+/K+-ATPase activity was observed only in N. rossii after 24 h at 8 °C, which assists in maintaining ionic homeostasis. In N. coriiceps, cortisol accurately indicated thermal stress. Increased cortisol levels in N. coriiceps additionally resulted in transient secondary responses such as hyperglycemia and hyperlactemia, as well as reduced levels of total protein, globulins and triglycerides. Unlike in N. rossii, catalase activity in N. coriiceps was modulated at 8 °C, and this parameter is thus considered a good biomarker of thermal stress. Results suggest that N. coriiceps is more sensitive to thermal stress than is N. rossii and that the former is a potential bioindicator for Admiralty Bay. [ABSTRACT FROM AUTHOR]

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

During their evolution and speciation in the Antarctic waters, notothenioid fish occupied a variety of habitats and ecological niches. The diversification led to important variations in several morphological features related to particular aspects of their ecologies. We investigated the feeding structures and biomechanics of three phylogenetically related species (family Nototheniidae) with different ecologies: the bentho-pelagic Antarctic toothfish Dissostichus mawsoni, the pelagic Antarctic silverfish Pleuragramma antarctica, and the benthic emerald rockcod Trematomus bernacchii. The suction index (SI), the mechanical advantage in jaw closing (MA), and 14 morphological traits related to their feeding activity were analyzed. Significant differences among the species were found for all the parameters considered, supporting a high level of specialization. [ABSTRACT FROM AUTHOR]

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

Background: The importance of transposable elements (TEs) in the genomic remodeling and chromosomal rearrangements that accompany lineage diversification in vertebrates remains the subject of debate. The major impediment to understanding the roles of TEs in genome evolution is the lack of comparative and integrative analyses on complete taxonomic groups. To help overcome this problem, we have focused on the Antarctic teleost genus Trematomus (Notothenioidei: Nototheniidae), as they experienced rapid speciation accompanied by dramatic chromosomal diversity. Here we apply a multi-strategy approach to determine the role of large-scale TE mobilization in chromosomal diversification within Trematomus species. Results: Despite the extensive chromosomal rearrangements observed in Trematomus species, our measurements revealed strong interspecific genome size conservation. After identifying the DIRS1, Gypsy and Copia retrotransposon superfamilies in genomes of 13 nototheniid species, we evaluated their diversity, abundance (copy numbers) and chromosomal distribution. Four families of DIRS1, nine of Gypsy, and two of Copia were highly conserved in these genomes; DIRS1 being the most represented within Trematomus genomes. Fluorescence in situ hybridization mapping showed preferential accumulation of DIRS1 in centromeric and pericentromeric regions, both in Trematomus and other nototheniid species, but not in outgroups: species of the Sub-Antarctic notothenioid families Bovichtidae and Eleginopsidae, and the non-notothenioid family Percidae. Conclusions: In contrast to the outgroups, High-Antarctic notothenioid species, including the genus Trematomus, were subjected to strong environmental stresses involving repeated bouts of warming above the freezing point of seawater and cooling to sub-zero temperatures on the Antarctic continental shelf during the past 40 millions of years (My). As a consequence of these repetitive environmental changes, including thermal shocks; a breakdown of epigenetic regulation that normally represses TE activity may have led to sequential waves of TE activation within their genomes. The predominance of DIRS1 in Trematomus species, their transposition mechanism, and their strategic location in "hot spots" of insertion on chromosomes are likely to have facilitated nonhomologous recombination, thereby increasing genomic rearrangements. The resulting centric and tandem fusions and fissions would favor the rapid lineage diversification, characteristic of the nototheniid adaptive radiation. [ABSTRACT FROM AUTHOR]

This study investigated maturation and spawning of Patagonian toothfish Dissostichus eleginoides in the Heard Island and McDonald Islands (HIMI) fishery on the Kerguelen Plateau in the Indian Sector of the Southern Ocean based on gonads and otoliths collected between 2004 and 2015 and using histological analyses and calibration of macroscopic staging criteria. Dissostichus eleginoides at HIMI spawn throughout the austral late autumn and winter months of May-August and spawning activity is concentrated on slopes along the west and south of the plateau around HIMI at depths of 1500-1900 m. Comparison between histological analyses and macroscopic gonad staging indicated that many fish that had spawned, as indicated by the presence of post-ovulatory follicles, returned to a resting stage which was macroscopically indistinguishable from maturing fish. Furthermore, the occurrence of females of all size classes with low gonado-somatic index and low macroscopic gonad stage during the spawning season suggested that a proportion of mature females did not spawn every year. Age-at-maturity estimates, based on the assumption that fish of macroscopic stages ≥2 were mature, decreased between the 2004-2009 and 2010-2015 periods for both sexes. The magnitude of this temporal variation in age at maturity, however, varied between gear types and fishing depths and variable sampling regimes probably influenced these variations. This study highlights the importance of correct interpretation of macroscopic gonad stages and understanding the influence of fishery operations on estimations of life-history parameters. [ABSTRACT FROM AUTHOR]

The Patagonian toothfish Dissostichus eleginoides is one of the most important fisheries from the Southern Ocean. The biology of this species is relatively well studied and some nutritionals issues have also been reported; however there is no information about the composition of the bacterial community of the gastrointestinal tract, which is essential to characterize the microbiota of this fish. The bacterial flora of D. eleginoides is here described for the first time using culturable methods. By applying traditional culture-based techniques and 16S rDNA sequencing methods it was possible to characterize the families Vibronaceae and Moraxellaceae, which were mainly represented by Vibrio and Psychrobacter, respectively. This Patagonian fish shows a microbiota very similar to other cold waters fishes. [ABSTRACT FROM AUTHOR]

Notothenia coriiceps and Notothenia rossii are two widespread nototheniid fishes, that live sympatrically along the southern Scotia Arc from South Georgia to the South Shetland Islands. In this sector of the Southern Ocean, they experienced different exploitation rates in the past and exhibit different habitat and food preferences as adult. Aiming to evaluate the influence of these factors in shaping life history traits of these species, we compare the reproductive investment and the age structure between the species and in N. rossii, between populations inhabiting different areas. Based on histological analyses, the two species share the same pattern of gamete development in both sexes. The potential fecundity was similar and was positively related to fish size in both species, being relatively high with respect to other notothenioids and in terms of egg size at deposition. Based on sagittal otolith readings, the growth rate and maximum age recorded differed significantly between the two species. Notothenia rossii exhibited a higher growth rate and a comparatively lower maximum age than N. coriiceps. Similarly, N. rossii attained sexual maturity at the same age but at a larger size than N. coriiceps. At the intraspecific level, no differences in life history traits were observed between the populations of N. rossii collected from different areas. Consistent with the different levels of fishing pressure exerted on these species and their low resilience, a recent significant decrease over time in the maximum fish size and related reproductive potential has been observed only in the overexploited populations of N. rossii. [ABSTRACT FROM AUTHOR]

The coastal fish community of the southern Scotia Arc, including the South Shetland Islands and the Bransfield Strait, is composed of the genus Lepidonotothen, which consists of three widely overlapping species such as L. kempi, L. larseni and L. nudifrons. The life-history strategies of these species driven by environmental and inter-specific interactions remain poorly known. In this paper, we estimate the maternal contribution to spawning of adult females in terms of fecundity and egg size through macroscopic and histological analyses of gonads. We further investigate the size and timing of hatching, growth rate and duration of the larval stage through microstructure analysis of sagittal otoliths collected from larval samples. All three species produced eggs of relatively small size at hatching, showing a trade-off between egg size and fecundity. Total fecundity was positively related to fish size during growth, as well as to maximum size. Female gonad investment was comparable among the species, as they all start spawning at about 65% of their maximum size with a similar gonadosomatic index. All species generated small larvae (altricial) which hatched over widely different periods, resulting in a temporal succession of larval occurrence. Compared to L. kempi, the other two species had relatively slow-growing larvae. Only L. kempi and L. larseni produced overwintering larvae. Differences in maternal contribution to spawning and early life-history traits of these species contribute to reduce interspecific competition for food through ecological niche partitioning. [ABSTRACT FROM AUTHOR]

The composition of leukocytes in the Patagonian toothfish (Dissostichus eleginoides Smitt, 1898), caught in the Scotia Sea at a depth of more than 1000 m, was studied. Cells with various morphofunctional characteristics and cell structure were found. Lymphocytes were predominant, followed by, in decreasing order, eosinophils, monocytes, blast forms and neutrophils. The composition of leukocytes in the Patagonian toothfish consists of the same types of leukocytes as the earlier studied Antarctic toothfish (Dissostichus mawsoni Norman, 1937), but the percentage of white blood cells in the leukocyte formula differs between the two species.