A new record and biological evidence supporting the establishment of Beryx splendens (Actinopterygii: Beryciformes: berycidae) in the western Mediterranean basin

A new specimen of splendid alfonsino, Beryx splendens Lowe, 1834, was caught by trawling in July 2016 in the Ligurian Sea at the depth of 350 m, in the proximity of a submarine canyon. It represents the 10th documented record of B. splendens in the Mediterranean. Because of the rarity of the records in the basin, there could be doubts whether to consider or not such species as established in the area. However, some fndings may support the hypothesis of the possible establishment of the species in the Mediterranean Sea. For example, the stomach of the specimen was nearly full, with rests of one crustacean decapod, one fsh, and some cephalopods, which are commonly reported prey items for the species. Macroscopic observation and histological analysis of the gonads revealed that the specimen was a male in an advanced stage of gonadal development. Finally, the coherence of habitat type and prey items with that of extra-Mediterranean populations coupled with gonadal maturation consistent with the observations on other specimens caught in the Mediterranean

The Arrangement of the Peripheral Olfactory System of Pleuragramma antarcticum: A Well-Exploited Small Sensor, an Aided Water Flow, and a Prominent Effort in Primary Signal Elaboration

The olfactory system is constituted in a consistent way across vertebrates. Nasal structures allow water/air to enter an olfactory cavity, conveying the odorants to a sensory surface. There, the olfactory neurons form, with their axons, a sensory nerve projecting to the telencephalic zone\u2014named the olfactory bulb. This organization comes with many different arrangements, whose meaning is still a matter of debate. A morphological description of the olfactory system of many teleost species is present in the literature; nevertheless, morphological investigations rarely provide a quantitative approach that would help to provide a deeper understanding of the structures where sensory and elaborating events happen. In this study, the peripheral olfactory system of the Antarctic silverfish, which is a keystone species in coastal Antarctica ecosystems, has also been described, employing some quantitative methods. The olfactory chamber of this species is connected to accessory nasal sacs, which probably aid water movements in the chamber; thus, the head of the Antarctic silverfish is specialized to assure that the olfactory organ keeps in contact with a large volume of water\u2014even when the fish is not actively swimming. Each olfactory organ, shaped like an asymmetric rosette, has, in adult fish, a sensory surface area of about 25 mm2, while each olfactory bulb contains about 100,000 neurons. The sensory surface area and the number of neurons in the primary olfactory brain region show that this fish invests energy in the detection and elaboration of olfactory signals and allow comparisons among different species. The mouse, for example\u2014which is considered a macrosmatic vertebrate\u2014has a sensory surface area of the same order of magnitude as that of the Antarctic silverfish, but ten times more neurons in the olfactory bulb. Catsharks, on the other hand, have a sensory surface area that is two orders of magnitude higher than that of the Antarctic silverfish, while the number of neurons has the same order of magnitude. The Antarctic silverfish is therefore likely to rely considerably on olfaction

Feeding strategy of Pleuragramma antarctica investigated by using ecological and ecomorphological approaches

Antarctic silverfish Pleuragramma antarctica is a keystone species of the coastal ecosystems of the Sothern Ocean. This species is the most abundant pelagic fish in the coastal waters of Antarctica, where it plays a pivotal role in the trophic web as the major link between lower and higher trophic levels. Due to the ecological importance of this species, over the last decades many studies on biology and ecology of P. antarctica were carried out. Despite previous studies have provided an overall picture of the trophic ecology of the Antarctic silverfish, important questions remain. Among them, the opportunistic versus selective feeding habit of the species wasn't still investigated, even if this information holds potential to highlight mechanisms and dynamics of the Antarctic silverfish relationship with the other components of its environment. The investigations on the capability of the species at using food resources can give information about its adaptability to ecological changes. Such a piece of information gains further value if contextualized in the frame of the environmental changes ongoing at a rapid pace in polar regions. The aim of my work is to improve present knowledge on the feeding ecology of the Antarctic silverfish highlighting its feeding habits to assess its possible ability to adapt to variations in the availability of prey caused by climate change or overfishing of krill. The research developed within my PhD program contributes to the PNRA (Italian National Program for Research in Antarctica) project RAISE (Integrate Research on Antarctic Silverfish Ecology in the Ross Sea). The study was divided in two parts, the first one was a purely ecological analysis based on the stomach contents of samples collected in different sectors of the Southern Ocean, the second one was an ecomorphological focus on traits involved in feeding activity of the species. In the ecological analysis, I detected evident differences in the diet of the specimens coming from three different zones (Ross Sea, Dumont d’Urville Sea, sea near Antarctic Peninsula). The diets were composed exclusively by planktonic organisms, which belong to different taxa depending on the area, mainly composed by copepods and euphausiids. Depending on the case, the range of prey items found was significantly broader or narrower. The observation of the condition of the different schools of fish and the investigation of selectivity versus generalism of the species let we deduce what item of the diet represented the preferential prey (through my results they appear to be the euphausiids) and if the species was able to adapt to situations of availability of prey different from the optimal ones. The ecomorphological study consisted in a depth study of the biomechanics of the buccal apparatus of P. antarctica. I measured some features of jaws, head and gill rakers and calculated significant index of jaws movements. The comparison of the values obtained with that of the same parameters found in other two species of the same family of nototheniids, Dissostichus mawsoni and Trematomus bernacchii, which live in different habitats and have different feeding habits, highlighted the adaptation to planktofagy and the feeding strategies of P. antarctica. It was relevant the confirmation of the capability of the species to feed on different planktonic items, having both structures to catch relatively large size zooplanktonic organisms and gill rakers conformation to particulate feeding. Both studies carried out lead us to the conclusion that P. antarctica is a plastic predator. Its preferential prey seem to be the euphausiids, towards which it performs a selective predation. In the case of paucity or absence of these organisms, it is able to vary its diet and feed on smaller zooplanktonic species, preyed by means of a less selective particulate feeding activity

Ecomorphological Differentiation of Feeding Structures within the Antarctic Fish Species Flock Trematominae (Notothenioidei) from Terra Nova Bay (Ross Sea)

The Antarctic endemic fish genus Trematomus (Trematominae, Notothenioidei) includes 15 species very diverse in morphology, lifestyle and feeding ecology. Co-occurring on the continental shelf, they occupy different habitats and a wide range of ecological niches as the result of adaptive radiation during their evolutionary history. Ecomorphological differentiation is a key feature of adaptive radiations, with a general trend for specialization following divergence. Here, we investigated the trophic adaptive morphology and ecology of six Trematomus species from Terra Nova Bay (Ross Sea) through feeding apparatus metrics and geometric morphometrics. The suction index (SI), the mechanical advantage in jaw closing (MA), the relative surface of the adductor mandibulae muscle and nine morphological traits related to feeding structures were analysed. Head shape clearly differentiates the benthic (T. bernacchii, T. hansoni and T. pennellii) from the pelagic (T. eulepidotus and T. borchgrevinki) species. The position of the eyes and the orientation of the mouth also contribute to specific morphological differences and specialization. Interestingly, T. newnesi stands at an intermediate position and the mouth is clearly oriented upwards compared to the other congeneric species

Latitudinal Cline in Chromosome Numbers of Ice Cod A. glacialis (Gadidae) from Northeast Greenland

The ice cod Arctogadus glacialis (Peters, 1872) is one of the few fish species endemic to the Arctic. With a circumpolar distribution, the species is confined to the fjords and shelves of the Arctic seas. Biological information on A. glacialis is scarce, with genomic information restricted to microsatellites. Within the frame of the TUNU-Programme: Arctic Ocean Fishes—Diversity, Adaptation and Conservation, we studied A. glacialis at the chromosomal level to explore fish diversity and evolutionary aspects. The analysis of over 50 individuals from the Northeast Greenland fjords between latitudes 71°09′ N and 76°42′ N revealed a remarkable intraspecific diversity epitomized by chromosome numbers spanning from 28 to 33, the occurrence of putative B chromosomes, and diversified patterns of distribution of heterochromatin and rDNAs. The number of B chromosomes followed a latitudinal gradient from 0–2 in the north to 2–5 in the south. Considering the benthic and rather stationary life history of this species, the observed chromosomal differences might have arisen independently, possibly driven and/or fostered by the dynamics of repetitive sequences, and are being fixed in relatively isolated fjord populations. The resulting latitudinal cline we observe today might have repercussions on the fate of local populations facing the ongoing climate-driven environmental changes

First records of Chionodraco hamatus nests in coastal areas of Terra Nova Bay (Ross Sea): a potential nesting area for the species?

Nests of the icefish Chionodraco hamatus were documented for the first time at about 500 m depth at Terra Nova Bay (Victoria Land, western Ross Sea), in an area included in the Antarctic Specially Protected Area (ASPA) No. 173 within the world's largest established marine area, the Ross Sea Region Marine Protected Area (RSRMPA). Nest building and egg guarding are common parental care behaviours in the Antarctic icefishes (Channichthyidae). Prior to this study, nest building behaviour for C. hamatus was observed only in aquarium experiments. Here we report on the observation of five nests of C. hamatus by remote underwater video systems in November 2021, during an Italian Antarctic expedition. The nests, consisting of gravel and small stones, were circular and bowl-shaped with a consistent diameter of about 30–40 cm. Nest building behaviour, with the icefish individual alternating radial turns in clockwise and counter-clockwise movements was also recorded in situ for the first time. The presence of icefish nests, as well as biotic and abiotic features of the locality, suggest the existence of a C. hamatus nesting area. If confirmed, the occurrence of an icefish nesting area in Silverfish Bay would further strengthen the ecological value of the ASPA 173. Furthermore, documenting nesting icefish in nearshore coastal areas of the RSRMPA reinforces the relevance of the MPA itself and provides an important focus for future research and monitoring in the area

The Challenge to Observe Antarctic Toothfish (Dissostichus mawsoni) under Fast Ice

In situ observation of Antarctic toothfish (Dissostichus mawsoni) is challenging as they typically live at depths greater than 500 m, in dark and ice-covered Antarctic waters. Searching for adequate methodologies to survey Antarctic toothfish in their habitat, we tested a miniaturized Baited Remote Underwater Video camera (BRUV), deployed through holes drilled in the sea ice in the Ross Sea region, over three field seasons. In 2015 three BRUVs were deployed at McMurdo Sound, and paired with a vertical longline sampling. In 2017, three opportunistic deployments were performed at Terra Nova Bay. In 2018 seven deployments at Terra Nova Bay provided preliminary data on the habitat preferences of the species. The design and configuration of the mini-BRUV allowed to collect high-quality video imagery of 60 Antarctic toothfish in 13 deployments from the fast sea ice. The behaviour of fish at the bait, intra-species interactions, and potential biases in individual counting were investigated, setting baselines for future studies on the abundance and distribution of Antarctic toothfish in sea-ice covered areas. This work represents the first step towards the development of protocols for non-extractive monitoring of the Antarctic toothfish in the high-Antarctica coastal shelf areas, of great value in the Ross Sea region where the largest MPA of the world has recently been established

Surface egg structure and early embryonic development of the Antarctic toothfish, Dissostichus mawsoni Norman 1937

The Antarctic tooth sh (Dissostichus mawsoni Norman 1937) is the largest notothenioid inhabiting high-latitude Antarctic waters, where it is an important shery resource and plays a key ecological role at a high trophic level. Despite the consider- able amount of data on D. mawsoni biology and distribution developed since the shery began in 1997, crucial aspects of the life cycle, including spawning and early life history, remain undescribed. During the rst winter longline survey to the northern Ross Sea region in 2016, ripe male and female D. mawsoni were collected for the rst time, and in vitro fertilisa- tion of eggs was performed. Here, we report on the rst 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 rst diagnostic information to recognise the eggs of D. mawsoni

Midtrophic fish feeding modes at the poles: an ecomorphological comparison of polar cod (Boreogadus saida) and Antarctic silverfish (Pleuragramma antarctica)

The polar cod (Boreogadus saida) and the Antarctic silverfish (Pleuragramma antarctica) are pelagic fish endemic to the Arctic and Antarctica sea, respectively. Both species are abundant and play a central role as midtrophic wasp-waist species in polar ecosystems. Due to their biological and ecological characteristics (small size, complex life histories, relatively short generation cycles, movement capability, planktivorous diet, and importance as prey), the polar cod and the Antarctic silverfish are potentially good sentinels of ecosystem change. Changes in polar zooplankton communities are well documented. How changes impact ecosystems as a whole largely depend on the degree of diet specialization and feeding flexibility of midtrophic species. Here, we provide the ecomorphological characterization of polar cod and Antarctic silverfish feeding performances. A comparative functional ecology approach, based on the analysis of morpho-anatomical traits, including calculation of suction index and mechanical advantage in jaw closing, was applied to profile the feeding modes and flexibility of the two species. Ecomorphological evidence supports differences in food acquisition: the polar cod appears able to alternate particulate ram-suction feeding to a pump filter feeding, and the Antarctic silverfish results be both a particulate ram and a tow-net filter feeder. Both species exhibit opportunistic feeding strategies and appear able to switch feeding mode according to the abundance and size of the available prey, which is a clue of potential resilience to a changing environment

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

The Antarctic notothenioid fish Dissostichus mawsoni (Antarctic toothfish) is an important piscine top predator in the Southern Ocean. Good olfactory capability has been hypothesized for this species on the basis of morphological (size of its olfactory bulb compared to other notothenioids) and behavioral (long distance migrations for food search and reproduc-tion) traits. Here, we provide new information on the structure and function of the olfactory rosette and bulb of D. mawsoniusing histology. Adult specimens (total length 136.2 \ub1 11.6 cm) were collected from McMurdo Sound. The rosettes had an average of 39 lamellae, without secondary folds and with a total surface area of about 1000 mm2. Both putative ciliated and microvillous receptor neurons were present in the sensory epithelium. Their projections to clustered glomeruli in the olfac-tory bulb were observed using antibodies against G-proteins. Numerous rodlet cells were observed in the epithelium and G\u3b1i2-like immunoreactivity was present in their cytoplasm. This deserves further investigation given the still-debated nature of this cell type. Through the isotropic fractionator method, we showed 116,000 cells (mg of tissue) 121 in the olfactory bulb of D. mawsoni, a density that is similar to those found in mammals. Taken together, these data describe a well-developed olfactory system in this species, where olfaction is key sensory syste