Search

Kuzmina, T. A., Salganskiy, O. O., Vishnyakova, K. O., Ivanchikova, J., Lisitsyna, O. I., Korol, E. M., Kuzmin, Yu. I. (2022): Helminth Diversity In Teleost Fishes From The South Orkney Islands Region, West Antarctica. Zoodiversity 56 (2): 135-152, DOI: 10.15407/zoo2022.02.135, URL: http://dx.doi.org/10.15407/zoo2022.02.135

The Antarctic dragonfish, Parachaenichthys charcoti is a notothenioid teleost fish endemic to the Southern Ocean surrounding Antarctica. It is a relatively rare fish species; therefore, published data on the parasite communities of P. charcoti are limited. The present study was performed on the Ukrainian Antarctic Station "Akademik Vernadsky", Argentine Islands, West Antarctica and the purpose was to examine the species diversity of the parasites of P. charcoti and to identify the parameters of helminth infection and helminth component community. Fifteen specimens of P. charcoti were caught at a depth of 10–30 m and examined using standard parasitological techniques. All helminths (6251 specimens) were collected manually, fixed in 70% ethanol and identified based on their morphology. All examined specimens of P. charcoti were found to be infected with helminths; each fish harboured 10–20 helminth species (mean 13.2; median 13) and 237–804 helminth specimens (mean 417; median 401). Twenty-seven helminth species were found, including nine species of trematodes, 4 of cestodes, 4 of nematodes and 10 of acanthocephalans. P. charcoti is the definitive host for 11 out of 27 helminth species recorded. In the helminth component community, the diversity indices were 2.03 (Shannon's index) and 0.79 (Simpson's index); Pielou evenness index was 0.61, and Berger–Parker dominance index was 0.38. Our results indicate a high species diversity and complex structure of the helminth community in Antarctic dragonfish P. charcoti in the Argentine Islands.

Antarctic dragonfishes (Bathydraconidae) of the suborder Notothenioidei are found only in the Southern Ocean where they diversified in habitats from the surface to the bathypelagic zone thousands of meters deep. Among dragonfishes, the pelagic Gymnodraconinae sister species Acanthodraco dewitti and Psilodraco breviceps remain poorly known. Although A. dewitti is thought to be restricted to Antarctic waters and P. breviceps to be endemic to South Georgia Island, several P. breviceps specimens have occasionally been reported in coastal Antarctica. Here we investigated the molecular genetic identity of the two species and their geographic distribution. Three mitochondrial genetic markers (mt-cyb, mt-co1, and mt-nd2) identified two dragonfish larvae collected on the West Antarctic Peninsula as A. dewitti and showed that all six specimens with available genetic data and reported to be P. breviceps collected in Antarctic waters were also A. dewitti. These results support the allopatric distribution of the two species, with P. breviceps being endemic to South Georgia Island and A. dewitti being endemic to Antarctic waters, potentially with a circumpolar distribution. The biogeography of the sister species A. dewitti and P. breviceps is likely similar to the allopatric distribution of the congeneric sister dragonfish species Parachaenichthys charcoti and P. georgianus. These considerations suggest that the Antarctic Circumpolar Current may geographically isolate the sub-Antarctic and Antarctic species of both sister species pairs, limiting gene flow and promoting speciation. Furthermore, we provide a detailed description of the A. dewitti larvae to supply characteristic morphological features differentiating A. dewitti and P. breviceps larvae.

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

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

Studies on reproduction of the dragonfishes, Bathydraconidae, are scarce, and within this family, the reproductive biology of Parachaenichthys charcoti was poorly understood. Herein we present a histologic analysis of P. charcoti ovaries together with data on reproductive effort using fish collected with trammel nets in austral summer at Potter Cove, South Shetland Islands (SSI), and compare this information with that reported for the South Georgia congener Parachaenichthys georgianus. In gravid females of P. charcoti, GSI of 16–31%, mature oocytes of 1.8–3.9 mm and total fecundity (TF) of 9025–18,937 oocytes/individual (X ± SD = 12,617 ± 4019, n = 7) were recorded. The histology of the ovaries confirmed the common characteristics of the Notothenioidei observed macroscopically, i.e., two distinct batches of oocytes, one in the previtellogenic stage (primary growing or cortical alveoli stages) and the other in vitellogenesis and likely to be released in the current season. A longer incubation period of P. charcoti compared with P. georgianus is associated to the colder waters at the SSI. Based on our sampling and reproductive effort data, together with the reported nesting behavior for P. charcoti, it is assumed that this species spawns in nearshore, sheltered waters in summer, presumably from late December to February. Spawning periods of both congeners differ from those reported for other notothenioids in the same Seasonal Pack-ice Zone, suggesting divergence in some aspects of the life strategies in the genus Parachaenichthys. Likewise, although there are no substantial differences between P. charcoti and other notothenioids regarding gonadal development, the genus Parachaenichthys shows distinct features in its reproductive strategies (e.g., higher TF) compared with other bathydraconid species. Fil: Novillo Estofan, Julio Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Moreira, María Eugenia. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Macchi, Gustavo Javier. Instituto de Investigaciones Marinas y Costeras (iimyc); Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Barrera Oro, Federico Esteban. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

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

Our knowledge on distribution, habitats and behavior of Southern Ocean fishes living at water depths beyond scuba-diving limits is still sparse, as it is difficult to obtain quantitative data on these aspects of their biology. Here, we report the results of an analysis of seabed images to investigate species composition, behavior, spatial distribution and preferred habitats of demersal fish assemblages in the southern Weddell Sea. Our study was based on a total of 2736 high-resolution images, covering a total seabed area of 11,317 m2, which were taken at 13 stations at water depths between 200 and 750 m. Fish were found in 380 images. A total of 379 notothenioid specimens were recorded, representing four families (Nototheniidae, Artedidraconidae, Bathydraconidae, Channichthyidae), 17 genera and 25 species. Nototheniidae was the most speciose fam- ily, including benthic species (Trematomus spp.) and the pelagic species Pleuragramma antarctica, which was occasionally recorded in dense shoals. Bathydraconids ranked second with six species, followed by artedidraconids and channichthyids, both with five species. Most abundant species were Trematomus scotti and T. lepidorhinus among nototheniids, and Dol- loidraco longedorsalis and Pagetopsis maculatus among artedidraconids and channichthyids, respectively. Both T. lepi- dorhinus and P. maculatus preferred seabed habitats characterized by biogenous debris and rich epibenthic fauna, whereas T. scotti and D. longedorsalis were frequently seen resting on fine sediments and scattered gravel. Several fish species were recorded to make use of the three-dimensional structure formed by epibenthic foundation species, like sponges, for perching or hiding inside. Nesting behavior was observed, frequently in association with dropstones, in species from various families, including Channichthyidae (Chaenodraco wilsoni and Pagetopsis macropterus) and Bathydraconidae (Cygnodraco mawsoni).

This study presents data on fish assemblage structure for the relatively pristine and understudied Antarctic coastal zone (5-25 m). A total of 545 Notothenioidei and Bathydraconidae fish (eight species) were caught in the Prince Gustav Channel (James Ross Island, eastern Antarctic Peninsula) using Nordic multi-mesh benthic gill nets between January and February 2014. Trematomus hansoni dominated at 5 m and T. bernacchii at 15 m, with Gobionotothen gibberifrons and T. newnesi subdominant. Dominance at 25 m resembled that at 15 m. Despite relatively low numbers, species richness, abundance and biomass appeared to increase with depth. While T. bernacchii, T. hansoni, G. gibberifrons and Notothenia coriiceps all displayed multiple size (and probably age) groups, most T. newnesi ranged between 10-15 cm. Sub-samples of G. gibberifrons and T. bernacchii showed a 1:1 adult/immature ratio, with minimum adult and maximum immature length/weight overlapping. Females outnumbered males, with a ratio of 2.8:1 for G. gibberifrons and 4.8:1 for T. bernacchii. The diet comprised mostly benthic taxa (isopods, gammarids, gastropods, polychaete worms). While G. gibberifrons appeared opportunistic, T. bernacchii specialised more on isopods. Our results highlight the possible importance of the Antarctic inshore zone as feeding habitat; despite frequent ice cover/scouring. We suggest that recent prolonged summer ice cover over the eastern side of the Antarctic Peninsula could have important impacts on inshore fish communities and food webs, though further in-depth studies are needed to confirm our results.

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

The Antarctic dragonfish Gerlachea australis is one of the most common bathydraconid species within the fish community of the Filchner Depression in the Weddell Sea. Nevertheless, several biological aspects of this species remain poorly known. The aim of this study was to provide new data on its population structure in terms of size, sex and age through sagittal otolith readings, as well as some reproductive traits based on macroscopic and histological analyses of gonads. The sex ratio in the sampled population was 1:1, with males being significantly smaller than females. Both sexes attained maximum age estimates of 14years. Based on a von Bertalanffy growth model, females showed a higher asymptotic length than males at a comparable growth rate, thus reaching a higher growth performance. The spawning season was spread over a relatively long period, lasting at least from late December through late February. The reproductive effort in terms of fecundity and egg size diameter was similar to that of other bathydraconids, ranging from 739 to 1260 eggs/female and 3.2mm after hydration, respectively. The fish size at first spawning (TL50) was 18.5 and 22.5cm in males and females, corresponding to 80% of their maximum size. G. australis exhibited a combination of life history traits found in other high-Antarctic notothenioids, such as long gametogenesis, large eggs associated with low fecundity, relatively rapid body growth until reaching a delayed sexual maturity, moderate longevity and maximum size, and overall low growth performance.

Background As members of the Notothenioidei - the dominant fish taxon in Antarctic waters - the family Bathydraconidae includes 12 genera and 17 species. The knowledge of these species inhabiting an isolated environment is rather fragmentary, including their parasite fauna. Studies on fish hosts and their associated parasites can help gain insights into even remote ecosystems and be used to infer ecological roles in food webs; however, ecological studies on the Bathydraconidae are scarce. Results In this study, stomach contents and parasite fauna of the Antarctic dragonfish species Parachaenichthys charcoti (n = 47 specimens) as well as of Gerlachea australis (n = 5), Gymnodraco acuticeps (n = 9) and Racovitzia glacialis (n = 6) were examined. The parasite fauna of P. charcoti consisted of eight genera represented by 11 species, with three of them being new host records. Overall, 24 parasite genera and 26 species were found in the sampled fish, including eleven new host records. Conclusion Analyses revealed that the majority of the parasite species found in the different fish hosts are endemic to Antarctic waters and are characterized by a broad host range. These findings are evidence for the current lack of knowledge and the need for further parasitological studies of fish species in this unique habitat. Electronic supplementary material The online version of this article (doi:10.1186/s13071-017-2176-7) contains supplementary material, which is available to authorized users.

The digenean fauna of fishes found in the Southern Ocean is described based on a database derived from the literature and new observations. A total of 60 digenean species allocated to 28 genera in ten families have been described or reported from fishes in the three provinces of the Southern Ocean, i.e. the Sub-Antarctic Islands, the Scotia Sea and the Continental High Antarctic (Province 61) The most prevalent digenean families are the Opecoelidae, the Lepidapedidae and the Hemiuridae. Digeneans have been reported from 76 fish species of 41 genera in 13 families. The fish family with the highest number of records of digeneans is the Nototheniidae with the Channichthyidae, Bathydraconidae and Artedidraconidae also frequently infected. The taxonomic diversity in the Continental High Antarctic Province and the Scotia Sea Province is higher than that of the Sub-Antarctic Islands. It was found that these data suggest that digeneans in fishes of the Southern Ocean typically exhibit low levels of host-specificity. The faunas of Weddell Sea and the distantly separated Ross Sea are highly similar, suggesting that, in geological terms, the regions had been recently connected by a collapse of the West Antarctic Ice Sheet. Phylogenetic inferences derived from 28S rDNA sequences for newly collected Antarctic representatives of the three commonest families are presented and discussed. It was found that the Hemiuridae could only be considered monophyletic if the family Lecithasteridae is included within it. In the Opecoelidae it was found that the genus Macvicaria is polyphyletic and that the two Antarctic species included formed a clade isolated from other putative congeners. In the Lepidapedidae, the Antarctic species clustered with related worms from deep-sea species.

Notothenioid fish were collected in the coastal part of the James Ross Island (Antarctica) mainly during Austral summer in 2012. In this paper, we report the list of species records and their basic biometric measurements as a reaction to missing ichthyofaunal investigation of this particular area. Collected fishes belong to the families Nototheniidae (Trematomus bernacchii Boulenger, 1902; T. eulepidotus Regan, 1914; T. newnesi Boulenger, 1902; Gobionotothen gibberifrons (Lönnberg, 1905); Notothenia coriiceps Richardson, 1844) and Bathydraconidae (Gymnodraco acuticeps Boulenger, 1902).

Although carbonic anhydrase is a ubiquitous enzyme involved in a variety of physiological processes, the information on its evolution and cold adaptation among Antarctic fish is still limited: the only Antarctic fish carbonic anhydrase characterized up-to-date is from Chionodraco hamatus, a member of the Channichthyidae family. In this work, we characterized orthologous genes within two other fish families: Nototheniidae (Trematomus eulepidotus, Trematomus lepidorhinus, Trematomus bernacchii) and Bathydraconidae (Cygnodraco mawsoni). The cDNAs of epithelial gill carbonic anhydrases were cloned and sequenced. Both coding and deduced amino acid sequences were used in phylogenetic analyses. The group of enzymes preferentially expressed in fish erythrocytes (CAIIb) represented the most conserved variant. This result suggests that, although the two variants derived from the same ancestor, CAIIc genes have a more complex evolutionary history than CAIIb. The peculiar distribution of Antarctic CAs among fish CAIIcs suggests that the CAIIc gene appeared at different times through independent duplication events, even after the speciation that led to the differentiation of Antarctic fish families. Using the new CA sequences, we built homology models to trace the expected consequences of sequence variability at the protein structure level. From these analyses, we inferred that sequence variability in Antarctic fish CAs affect important physicochemical properties of these proteins and consequentially influence their reactivity. Furthermore, we searched and tested the validity of various potential molecular trademarks for cold adaptation: significant features that can be related to cold adaptation in fish CAs include reduction of positively charged solvent accessible surfaces and an increased flexibility of N-terminal and C-terminal regions.

Gymnodraco acuticepsis is an Antarctic fish living in the Southern Ocean. Until now, studies on G. acuticeps are still limited. As an Antarctic fish, obtaining and characterization of the mitochondrial genome of G. acuticeps will be important for elucidation of the mechanism of cold-adapting evolution in mitochondrion. In this study, we first isolated and characterized the mitochondrial genome sequence of G. acuticeps with 15,987 bp in length. It contained of 34 genes (12 protein-coding genes, 20 transfer RNA genes, 2 ribosomal RNA genes) and a partial putative control region. Gene organization and nucleotide composition of obtained mito-genome were similar to those of other Antarctic fish. Twenty-eight genes were encoded by heavy strand, while six genes were encoded by light strand. Further, the phylogenetic tree, which based on 12 protein-coding genes, revealed that the G. acuticeps was genetically closest to species Parachaenichthys charcoti among 18 species. We hope this work would be helpful for the population genetics and molecular evolution studies.

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.

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.

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.

A total of nine Antarctic fish species belonging to five families were examined for their endohelminth parasite fauna. The fishes Parachaenichthys charcoti (Bathydraconidae), Chaenocephalus aceratus (Channichtyidae), Paradiplospinus gracilis (Gempylidae), Muraenolepis microps (Muraenolepididae), Gobionotothen gibberifrons, Lepidonotothen larseni, L. nudifrons, L. squamifrons, and Trematomus eulepidopus (Nototheniidae) were caught between 80 and 608 m trawling depth off the Antarctic Peninsula (Elephant Island, King George Island) in 1996. Nineteen different parasites species comprising five Digenea, two Cestoda, four Nematoda, and eight Acanthocephala were found. Pseudophyllidean cestodes, the nematodes Contracaecum radiatum and C. osculatum as well as the acanthocephalan Corynosoma bullosum were the most common, infesting eight of the fish species studied with prevalences reaching 100%. Pseudoterranova decipiens s.l. was the only parasite that was isolated from all studied fish species; however, at a lower intensity. The observed parasite host specificity was low, and the species richness in a single fish ranged from one to eleven in a C. aceratus. This icefish and the moray cod M. microps were the most heavily infested fish, harbouring many adult and larval parasitic stages. The benthodemersal P. gracilis had only two larval parasite species, while the nototheniids had very similar parasite communities, harbouring a total of 8–14 species. Larval mammalian parasites were found to utilize fish, especially the nototheniids and channichthyids, as a common transmission route into their final hosts. The fish parasites parallel explored different benthic host systems to reach the most suitable host. In contrast to the coast and continental shelf, the meso/bathypelagiac zone appears to be species poor and is inhabited by few larval forms. The fish parasite fauna off the South Shetland Islands can be characterized by generalistic parasites that distribute within Antarctic waters according to the feeding ecology and depth range of their teleost hosts, not only horizontally but also extending vertically into the deep sea.

We analysed histological characteristics of gonads and reproductive effort of the small deep-living dragonfishes Akarotaxis nudiceps (Waite) and Bathydraco marri Norman collected in the south-western Ross Sea. From a macroscopic point of view, most specimens of B. marri were juveniles in early stages of gonad maturity, except for a maturing female. Conversely, the sample of A. nudiceps was composed of both immature and adult fish in different stages of maturity. A single A. nudiceps female was mature with a gonadosomatic index of 9.8%. Its absolute and relative fecundity was 260 oocytes and 31.5 oocytes g−1 TW, respectively, with a mean size of ripe oocytes of 1.9 mm. Gametogenesis in both species closely resembled that observed in other notothenioids, with females possessing two well-defined groups of oocytes. One group consisted of previtellogenic oocytes as a reserve stock while the other group was maturing oocytes to be ovulated in the current spawning season. A distinctive feature of oogenesis in recovering and maturing females of A. nudiceps was the presence of both postovulatory follicles in different stages of reabsorption and atretic oocytes. Based on low absolute fecundity, it is possible that A. nudiceps provides parental care and egg guarding.

The predominantly non-Antarctic family Bovichtidae is phyletically basal within the perciform suborder Notothenioidei, the dominant component of the Antarctic fish fauna. In this article we focus on the South Atlantic bovichtids Bovichtus diacanthus, the klipfish from tide pools at Tristan da Cunha, and Cottoperca gobio, the frogmouth from the Patagonian shelf and Falkland Islands. We document the anatomy and histology of the brains, olfactory apparatus, retina, and cephalic lateral line system. We also use the microvascular casting agent Microfil to examine ocular vascular structures. We provide detailed drawings of the brains and cranial nerves of both species. Typical of perciforms, the brains of both species have a well-developed tectum and telencephalon and robust thalamic nuclei. The telencephalon of C. gobio is prominently lobed, with the dorsomedial nucleus more conspicuous than in any other notothenioid. The corpus cerebelli is relatively small and upright and, unlike other notothenioids, has prominent transverse sulci on the dorsal and caudal surfaces. Areas for lateral line mechanoreception (eminentia granularis and crista cerebellaris) are also conspicuous but olfactory, gustatory, and somatosensory areas are less prominent. The anterior lateral line nerve complex is larger than the posterior lateral line nerve in B. diacanthus, and in their cephalic lateral line systems both species possess branched membranous tubules (which do not contain neuromasts) with small pores. These are especially complex in B. diacanthus where they become increasingly branched and more highly pored in progressively larger specimens. Superficial neuromasts are sparse. Both species have duplex (cone and rod) retinae that are 1.25-fold thicker and have nearly 5-fold more photoreceptors and than those of most Antarctic notothenioids. Convergence ratios are also high for bovichtids. Bovichtus diacanthus has a yellow intraocular filter in the dorsal aspect of the cornea. Both species are unique among notothenioids in possessing all three vascular structures present in the generalized teleostean eye: the choroid rete mirabile, the lentiform body (also a rete), and the falciform process. When comparing the phyletically derived Antarctic clade exemplified by the families Artedidraconidae, Bathydraconidae, and Channichthyidae to the phyletically basal bovichtids, we observe phyletic regression and reduction in some regions of the brain and in some sensory modalities that are well displayed in bovichtids. In the phyletically derived families the brain is less cellular and nuclei are smaller and less prominent. In some species reduction in the size of the telencephalon, tectum, and corpus cerebelli imparts a "stalked" appearance to the brain with the neural axis visible between the reduced lobes. There is also a phyletic reduction in the number of ocular vascular structures from three in bovichtids to one or none in artedidraconids, bathydraconids, and channichthyids. There are no morphological features of bovichtid brains and sense organs that presage the divergence of the phyletically derived members of the clade in the Antarctic marine environment with its cold and deep continental shelves. We conclude that this environment does not require sensory or neural morphology or capabilities beyond those provided by the basic perciform body plan.

The complete mitochondrial genome of the Antarctic dragonfish, Parachaenichthys charcoti (Vaillant, 1906), is described, representing the first complete mitochondrial genome sequence of the family Bathydraconidae. The mitochondrial genome is 18,202 base pairs in length and encodes 13 protein-coding genes, 23 tRNAs, 2 rRNAs and 2 control regions. The overall base composition is A: 25.8%, T: 25.3%, G: 17.9% and C: 31.0%, with an A:T content of 51.1%. The complete mitochondrial genome sequence will be useful for phylogenetic, evolutionary and functional studies of Antarctic Notothenioids.

Glutathione peroxidases are a family of antioxidant enzymes catalyzing the reduction of H2O2 or organic hydroperoxides. In the present study, we report the molecular characterization and gene expression analysis of a new GPx-1 from the Antarctic fish Trematomus bernacchii. To expand our knowledge on the GPx-1 s evolution within the group of Antarctic fish, in this work, we also presented the cDNA sequencing of this enzyme in other three species, belonging to two families—Nototheniidae (Trematomus eulepidotus, T. lepidorhinus) and Bathydraconidae (Cygnodraco mawsoni). The deduced amino acid sequences were compared with GPx-1 s of other vertebrates by multiple alignment, in order to evaluate the conservation of amino acids involved in the enzyme activity. The results of phylogenetic analyses indicated that fish GPx-1 s possibly originated from independent duplication events, and Antarctic GPx-1 s evolved according to the molecular and morphological phylogeny of Antarctic fish. Basal GPx-1 mRNA expression analyses in various tissues of T. bernacchii specimens indicated that liver and heart displayed the highest mRNA accumulation; probably a protection of these organs against lipid peroxidation is needed.

In comparison with other bathydraconids, all species of the genus Bathydraco are poorly known from an ecological perspective. The diet of juvenile Bathydraco marri Norman, 1938 was studied for the first time in specimens collected in the southwestern Ross Sea during summer 1998. Fish were collected in a single otter trawl catch at 330–340 m depth. The stomach content analysis showed that this species fed exclusively on crustaceans. Overall, 20 prey taxa were identified to genus or species level. Mysids, amphipods and copepods were the most important prey in decreasing order of importance. Other prey, such as Euphausia superba, isopods and tanaids were eaten occasionally and in very small amounts. A multivariate analysis was applied to feeding data to assess ontogenetic or sex-related changes in diet. No difference was detected between sexes, whereas diet of small and large fish differed in some degree. An ontogenetic shift from small and pelagic crustaceans such as copepods to benthic–benthopelagic prey such as amphipods and mysids was observed. Relating present results with published data on physiological characteristics of B. marri, it was possible to infer their feeding behaviour and mode of life. Like other bathydraconids, this species appeared to be an inactive and sluggish fish, which relied on more or less motile benthic or epibenthic prey adopting a “sit and wait” feeding strategy. On the other hand, smaller fish seem to be more active, feeding also on pelagic prey such as copepods that can be seasonally abundant, thus reducing the intraspecific competition for food.

We have capitalised on the availability of eggs and adults of the naked dragonfish Gymnodraco acuticeps (Sub-order Notothenioidei, F. Bathydraconidae) near McMurdo Station, Antarctica to examine metabolic energy utilization at different stages of its life cycle. Average egg respiration rates were found to increase from 2.17±1.02 nmol O2 h−1 ind−1 at about 17 h post-fertilization (hpf) to 5.72±0.56 nmol h−1 ind−1 at about 24 hpf, during which time the eggs underwent first cleavage. The respiration rates of embryos from 2–20 days post-fertilization (dpf) averaged 4.11±1.47 nmol O2 h−1 ind−1. About 10 months post-fertilization, oxygen consumption rates of 27.14±3.92 nmol O2 h−1 ind−1 were recorded immediately prior to hatching, with a peak of 112.41±31.38 nmol O2 h−1 ind−1 at the time of hatch. Larvae aged 46–63 days post-hatch had an average respiration rate of 64.4±15.11 nmol O2 h−1 ind−1. Mass-specific respiration rates of hatched larvae (approximately 1–2 months old) were calculated using dry weights (DW) and averaged 16.1±3.4 nmol O2 h−1 mg−1 DW. Adult dragonfish respiration rates (corrected for a 100 g fish and using a 0.8 scaling exponent) averaged 0.91±0.36 mmol O2 kg−1 h−1 after a 48 h acclimatization period, which is not indicative of significant metabolic cold adaptation. The energy contents of dragonfish eggs and larvae were also measured by microbomb calorimetry and used, along with the respiration data, in an initial approach to estimate an energy budget. In order to balance the budget, the bulk of the available post-gastrulation respiratory energy (during 213 days of embryonic incubation) must be consumed at a relatively low average rate (7.1 nmol O2 h−1 ind−1), which supports the possibility that advanced dragonfish embryos overwinter in a relatively quiescent metabolic state while awaiting a suitable stimulus (such as the return of the sun) to initiate hatching.

Oogenesis was examined in nine species of Antarctic fish to verify the existence of morphological peculiarities. The analyses were carried out on specimens belonging to three different families of Notothenioids (Nototheniidae, Channichthyidae and Bathydraconidae), all captured in the Ross Sea, in front of the Italian Station of Terra Nova Bay. Following dissection, the ovaries were processed and examined at the light and electron microscopes to determine the oocyte gross and fine morphology. The attention, in particular, was focused on the presence of cytoplasmic round bodies and on the organization of the cortical alveoli and the vitelline envelope. Results reveal significant specie-specific differences that could be partly correlated to the phylogenetic radiation but not to the peculiar environmental conditions being essentially comparable to those observed among temperate species.

Antarctic fishes were sampled with 41 midwater and 6 benthic trawls during the 1999–2000 austral summer in the eastern Ross Sea. The oceanic pelagic assemblage (0–1,000 m) contained Electrona antarctica, Gymnoscopelus opisthopterus, Bathylagus antarcticus, Cyclothone kobayashii and Notolepis coatsi. These were replaced over the shelf by notothenioids, primarily Pleuragramma antarcticum. Pelagic biomass was low and concentrated below 500 m. The demersal assemblage was characteristic of East Antarctica and included seven species each of Artedidraconidae, Bathydraconidae and Channichthyidae, ten species of Nototheniidae, and three species each of Rajidae and Zoarcidae. Common species were Trematomus eulepidotus (36.5%), T. scotti (32.0%), Prionodraco evansii (4.9%), T. loennbergii (4.7%) and Chaenodraco wilsoni (4.3%). Diversity indices were highest for tows from 450 to 517 m (H′=1.90–2.35). Benthic biomass ranged from 0.7 to 3.5 t km−2. It was generally higher in tows from 450 to 517 m (0.9–2.0 t km−2) although the highest biomass occurred at an inner-shelf station (238 m) due to large catches of T. eulepidotus, T. scotti and P. evansii.

The jaw musculature of notothenioid fishes is described and compared based on a total of 38 species referred to eight families of the suborder Notothenioidei. In the Notothenioidei, the adductor mandibulae, the largest and most conspicuous of the cranial muscles, is generally composed of sections A1, A2, A3 and Aw as in the generalized percoids. The morphology of the adductor mandibulae is similar in most notothenioid families except the Nototheniidae and Bathydraconidae. Notothenia, Paranotothenia and Dissostichus are clearly distinguished from the other nototheniid genera in having A3. Gymnodraco of the Bathydraconidae has a fused A1-A2 complex and the anterior element is segmented by a tendinous intersection from the A1-A2 complex. These features are unique to Gymnodraco and not seen in other bathydraconids. The Harpagiferidae and Artedidraconidae share the same apomorphy, the presence of A1β, with the Nototheniidae and have no synapomorphies with the Bathydraconidae and Channichthyidae. The character distribution, however, shows some inconsistencies with the previous classifications. Based on the limited evidence obtained in this study, the Notothenioidei can be divided into six groups and it seems reasonable to suggest a review of the current classification of the Nototheniidae.

The non-long terminal repeat retrotransposons Rex1 and Rex3 were identified in 13 species of Antarctic fishes from five families of the suborder Notothenioidei. Partial reverse transcriptase gene sequences were characterized for Notothenia coriiceps, Trematomus newnesi and Dissostichus mawsoni (Nototheniidae), and Gymnodraco acuticeps (Bathydraconidae). Rex1 and Rex3 both formed a notothenioid-specific monophyletic group compared to the corresponding elements from other fishes. They globally evolved under purifying selection, showing their activity during notothenioid evolution. Fluorescence in situ hybridization analysis of the chromosomal distribution of Rex1 and Rex3 was performed for several notothenioid fish species. Rex1 was generally less abundant than Rex3, which was widely scattered on the chromosomes with more intense hybridization patterns in some specific zones. Particularly, Rex3 accumulated in Chionodraco hamatus in pericentromeric areas, short arms of some pairs as well as in an intercalary band in the long arm of the Y chromosome similarly to a previously described DNA transposon. Such pattern similarities suggest the presence of autosomal and gonosomal regions of preferential accumulation for different types of repeated elements in notothenioid genomes. To the best of our knowledge, this report is the first description and analysis of retrotransposable elements in Antarctic fish genomes.

The hemolysate of the Antarctic teleost Gobionotothen gibberifrons (family Nototheniidae) contains two hemoglobins (Hb 1 and Hb 2). The concentration of Hb 2 (15–20% of the total hemoglobin content) is higher than that found in most cold-adapted Notothenioidei. Unlike the other Antarctic species so far examined having two hemoglobins, Hb 1 and Hb 2 do not have globin chains in common. Therefore this hemoglobin system is made of four globins (two α- and two β-chains). The complete amino-acid sequence of the two hemoglobins (Hb 1, ; Hb 2, ) has been established. The two hemoglobins have different functional properties. Hb 2 has lower oxygen affinity than Hb 1, and higher sensitivity to the modulatory effect of organophosphates. They also differ thermodynamically, as shown by the effects on the oxygen-binding properties brought about by temperature variations. The oxygen-transport system of G. gibberifrons, with two functionally distinct hemoglobins, suggests that the two components may have distinct physiological roles, in relation with life style and the environmental conditions which the fish may have to face. The unique features of the oxygen-transport system of this species are reflected in the phylogeny of the hemoglobin amino-acid sequences, which are intermediate between those of other fish of the family Nototheniidae and of species of the more advanced family Bathydraconidae.

We investigated the burst swimming performance of five species of Antarctic fish at -1.0degreesC. The species studied belonged to the suborder, Notothenioidei, and from the families, Nototheniidae and Bathydraconidae. Swimming performance of the fish was assessed over the initial 300 ms of a startle response using surgically attached miniature accelerometers. Escape responses in all fish consisted of a C-type fast start; consisting of an initial pronounced bending of the body into a C-shape, followed by one or more complete tail-beats and an un-powered glide. We found significant differences in the swimming performance of the five species of fish examined, with average maximum swimming velocities (U-max) ranging from 0.91 to 1.39 m s(-1) and maximum accelerations (A(max)) ranging from 10.6 to 15.6 m s(-2). The cryopelagic species, Pagothenia borchgrevinki, produced the fastest escape response, reaching a U-max and A(max) of 1.39 m s(-1) and 15.6 m s(-2), respectively. We also compared the body shapes of each fish species with their measures of maximum burst performance. The dragonfish, Gymnodraco acuticeps, from the family Bathdraconidae, did not conform to the pattern observed for the other four fish species belonging to the family Nototheniidae. However, we found a negative relationship between buoyancy of the fish species and burst swimming performance. (C) 2002 Elsevier Science Ltd. All rights reserved.