high-Antarctic Fish Research Articles

Xenobiotic metabolism and its physiological consequences in high-Antarctic Notothenioid fishes

The Antarctic ecosystem is progressively exposed to anthropogenic contaminants, such as polycyclic aromatic hydrocarbons (PAHs). So far, it is largely unknown if PAHs leave a mark in the physiology of high-Antarctic fish. We approached this issue via two avenues: first, we examined the functional response of the aryl hydrocarbon receptor (Ahr), which is a molecular initiating event of many toxic effects of PAHs in biota. Chionodraco hamatus and Trematomus loennbergii served as representatives for high-Antarctic Notothenioids, and Atlantic cod, Gadus morhua as non-polar reference species. We sequenced and cloned the Ahr ligand binding domain (LBD) of the Notothenioids and deployed a GAL4-based luciferase reporter gene assay expressing the Ahr LBD. Benzo[a]pyrene (BaP), beta-naphthoflavone and chrysene were used as ligands for the reporter gene assay. Second, we investigated the energetic costs of Ahr activation in isolated liver cells of the Notothenioids during acute, non-cytotoxic BaP exposure. In the reporter assay, the Ahr LBD of Atlantic cod and the Antarctic Notothenioids were activated by the ligands tested herein. In the in vitro assays with isolated liver cells of high-Antarctic Notothenioids, BaP exposure had no effect on overall respiration, but caused shifts in the respiration dedicated to protein synthesis. Thus, our study demonstrated that high-Antarctic fish possess a functional Ahr that can be ligand-activated in a concentration-dependent manner by environmental contaminants. This is associated with altered cost for cellular protein synthesis. Future studies have to show if the toxicant-induced activation of the Ahr pathway may lead to altered organism performance of Antarctic fish.

Temperature-dependent metabolism in Antarctic fish: Do habitat temperature conditions affect thermal tolerance ranges?

Climatic warming is most pronounced in the polar regions. For marine ectotherms such as fish, temperature is a key abiotic factor, influencing metabolic processes. Species distribution and abundance are driven by reproduction and growth, which depend on available energy exceeding baseline maintenance costs. These routine metabolic costs make up a large part of the energy expenditure. Thermal stress can increase routine metabolism, affecting an organism’s fitness. Data of routine metabolic rates of Antarctic fish are scarce, and comparability of existing data sets is often problematic due to ecological differences between species and in experimental protocols. Our objective was to compare routine metabolism and thermal sensitivity of species with similar ecotypes but different thermal environments to assess possible ecological implications of warming waters on energy expenditure in Antarctic fish, a fauna characterised by geographic isolation, endemism and putative thermal adaptation. We measured routine metabolic rates of three benthic Antarctic fish species from low- and high-Antarctic regions at habitat temperature and during acute temperature increase. Our analysis revealed differences in metabolic rates at the same temperature suggesting local adaptation to habitat temperature. Acute thermal stress induced a comparable response of metabolic rates to increasing temperature. We conclude that higher metabolic rates and thus higher energetic costs could be associated with narrower thermal windows, a potential disadvantage to the endemic high-Antarctic fish fauna facing the challenge of climate change.

Elevated temperature causes metabolic trade-offs at the whole-organism level in the Antarctic fish Trematomus bernacchii.

As a response to ocean warming, shifts in fish species distribution and changes in production have been reported that have been partly attributed to temperature effects on the physiology of animals. The Southern Ocean hosts some of the most rapidly warming regions on earth and Antarctic organisms are reported to be especially temperature sensitive. While cellular and molecular organismic levels appear, at least partially, to compensate for elevated temperatures, the consequences of acclimation to elevated temperature for the whole organism are often less clear. Growth and reproduction are the driving factors for population structure and abundance. The aim of this study was to assess the effect of long-term acclimation to elevated temperature on energy budget parameters in the high-Antarctic fish Trematomus bernacchii. Our results show a complete temperature compensation for routine metabolic costs after 9 weeks of acclimation to 4°C. However, an up to 84% reduction in mass growth was measured at 2 and 4°C compared with the control group at 0°C, which is best explained by reduced food assimilation rates at warmer temperatures. With regard to a predicted temperature increase of up to 1.4°C in the Ross Sea by 2200, such a significant reduction in growth is likely to affect population structures in nature, for example by delaying sexual maturity and reducing production, with severe impacts on Antarctic fish communities and ecosystems.

Macroscopic and histological analyses of gonads during the spawning season of Chionodraco hamatus (Pisces, Channichthyidae) off Terra Nova Bay, Ross Sea, Southern Ocean

A macroscopic and histological analysis of gonads was carried out during the spawning season of the high-Antarctic channichthyid Chionodraco hamatus in the western Ross Sea. Samples were collected between December and February during several years in the coastal waters of Terra Nova Bay. Gonad maturity stages were described for males and females according to macroscopic and histological scales. Using multi-year data, the estimated length at first spawning of females was about 35 cm TL, very similar to that obtained indirectly for males. Similar to many other high-Antarctic fish, C. hamatus is a summer spawner. The greater part of the stock was indeed in spawning condition between December and February, although a large proportion of females large enough to spawn probably did not spawn in that season. The present data confirm that C. hamatus, as is typical for Antarctic fish, probably spawns a single batch of oocytes once a year. In addition, vitellogenesis is a slow process that extends over at least 1 year. Discrepancies between the macroscopic and histological appearance of gonads were found. These were associated mainly with spent and resting females (maturity stages 5 and 2, respectively). This study demonstrates the importance of histological analysis of gonads in order to confirm the results of the macroscopic analyses routinely carried out in studies of reproductive biology. This is of particular importance in determining size at maturity and spawning stock biomass, for assessment purposes.

Age and growth of high Antarctic notothenioid fish

Available literature data on age and growth of high Antarctic fish is reviewed and discussed in relation to environmental seasonality. Except for Antarctic toothfish Dissostichus mawsoni, with maximum total length (TL) more than 170 cm, high Antarctic notothenioids are predominantly small species of less than 45 cm TL. Maximum ages reported for small Trematomus species were generally high (18–23 years), and probably comparable to those of some larger channichthyids. Highest longevity is attained by large nototheniids, such as Aethotaxis mitopteryx and D. mawsoni, of more than 30 years. Most high Antarctic fish spawn for the first time at 50–80% of maximum age. Males of some Trematomus species reach spawning maturity earlier than females, but at a higher percentage of maximum age. Pauly's index of growth performance P has been used to compare growth. P for nototheniids is typically between 1 and 2, whereas in channichthyids it is between 2 and 3. Generally, high Antarctic notothenioids exhibit a lower P than those further north. In high Antarctic nototheniids, between 19 and 42 cm maximum theoretical length, growth performance seems to increase from pelagic to benthic fish habit. Thus, although low temperature is a constraint on growth, other ecological factors linked to life style, such as food availability and physiological adaptations, may explain differences in growth performance between fish from the seasonal pack-ice zone and the high Antarctic zone.

Growth and age validation in high-Antarctic fish

The growth of three demersal species dominant in biomass and abundance in the Weddell Sea, Chionodraco myersi (channichthyid), Trematomus eulepidotus (nototheniid) and Dolloidraco longedorsalis (artedidraconid), was studied on specimens caught in summer. Ages were determined using ground and polished otolith sections and an image analysis system to measure the otolith radius and distances of each growth increment to the otolith core. Ageing precision and accuracy have been estimated. Indirect validation methods, based on the increment growth pattern, were applied to support the annual periodicity of the increments. Due to the lack of some age classes, back-calculated age-length keys were determined and used to fit the von Bertalanffy growth parameters by sex and species. The determined values showed sexual dimorphism, with females having faster growth rates, except in D. longedorsalis. The growth performance index was between 1 and 2, as in other high-Antarctic fish. For T. eulepidotus, age and growth data were available, but this is the first report for C. myersi and D. longedorsalis. Moreover, this is the first time that accuracy and precision have been estimated for high-Antarctic fish age determination.

Habitat partitioning of dominant high Antarctic demersal fish in the Weddell Sea and Lazarev Sea

Using underwater photography twelve, structural habitat characteristics of the six most abundant demersal high Antarctic fish species were investigated. Two categories of relationships beween fishes and benthos were found: (1) Trematomus lepidorhinus (Pappenheim) and T. loennbergi (Regan) preferred rich epibenthic communities dominated by sessile suspension feeders. The fish used this three-dimensional structure to both settle on and to hide in. (2) Prionodraco evansii (Regan), Dolloidraco longedorsalis (Rhoule) and Trematomus scotti (Boulenger) occurred mostly in areas free of stones and biogenous debris and with generally less epifauna. For Chionodraco myersi (Dewitt and Tyler), no significant link with the benthic habitat was found; it seemed to have an intermediate position between the groups mentioned above.

Brain gangliosides and cold-adaptation in high-antarctic fish

The concentration and composition of gangliosides from the brain of eight species of Antarctic Notothenioid fishes belonging to the class of perciformes and two species of boreal fishes (tropic cichlid fish Oreochromis mossambicus; Codfish Gadus morhua) were investigated. The concentration of whole brain gangliosides in Notothenioid fishes (between 1622 and 2183 μg NeuAc/g dry wt.) was slightly lower than that in the brains of fish species, which live in warm, temperate habitats (2483 μg NeuAc/g dry wt.). The composition of brain gangliosides was completely different from that of warm adapted fish species (e.g. the tropic cichlid fish Oreochromis mossambicus). The relative concentration of polysialogangliosides (GT1b-GH) is strongly increased in all the investigated Antarctic species. They were found to have the most complex and most polar brain ganglioside pattern (high degree of sialylation and alkali-lability) within the teleosts. This may be one of the mechanisms, beside antifreeze proteins, to keep the neuronal membranes functional even below the freezing point.

The amino acid sequence of the single hemoglobin of the high-Antarctic fish Bathydraco marri Norman

1. 1. Bathydraco marri Norman is a cold-adapted Antarctic teleost (Family: Bathydraconidae), living preferably at depths between 400 and 1200 m. 2. 2. The blood of this species contains a single hemoglobin, in which oxygen binding is pH-regulated (Bohr and Root effects). 3. 3. The complete amino acid sequence of the α and β chains of the hemoglobin of B. marri has been elucidated.

Haematological studies on Aethotaxis mitopteryx DeWitt, a high-Antarctic fish with a single haemoglobin

Haematological studies on Aethotaxis mitopteryx DeWitt, a high-Antarctic fish with a single haemoglobin

The primary structure and oxygen-binding properties of the single haemoglobin of the high-Antarctic fish Aethotaxis mitopteryx DeWitt

The primary structure and oxygen-binding properties of the single haemoglobin of the high-Antarctic fish Aethotaxis mitopteryx DeWitt

Aethotaxis mitopteryx, a high-Antarctic fish with benthopelagic mode of life

Aethotaxis mitopteryx DeW~tt is one of the lesser known high-Antarctic fish species of the family Nototheniidae. W~thin the last 7 yr close to 90 % of all reported specimens were caught in the Weddell Sea and the Lazarev Sea , with only 5 % of these in pelagic trawls. Average blomass values of ca 0.69 kg 30 min-l, which is 10 times the biomass values attained in the Weddell Sea , suggest the Lazarev Sea at depths between 400 and 800 m, or narrow shelf areas of the eastern Antarctic in general, to be a major distribution area of this species Due to new maximum values reported for length and weight (total length = 48 cm, fresh weigth = 855 g ) currently recorded growth parameters have to be adjusted Adults are characterized by slow growth, high reproductive effort, a benthopelagic mode of life and regular occurrence in the warmer deep water. Due to the high abundance of A. mitopteryx larvae In the Weddell Sea, spawning migrations are likely. Structural and functional features of blood as well as observations from aquaria indicate a sluggish mode of l ~ f e and a limited scope for activity. This and a number of adaptations to life In the pelagial suggest energy requirements to be low.

Haematological studies on a high-Antarctic fish: Bathydraco marri Norman

This paper presents the first record of the blood parameters of the Antarctic fish Bathydraco marri; the structural and functional characterization of haemoglobin purified from the blood of this species is also reported. One single haemoglobin was detected and the globin chains were purified and subsequently sequenced. The molecular weights of the α- and β-chains were 15552 and 16048, respectively. O 2 binding was measured as a function of pH and a strong Root effect as well as a large, negative, alkaline Bohr effect were observed. The subunit cooperativity was lost at lower pH values, as indicated by the decrease of the Hill coefficient. P 50 was 13.2 mm Hg at 20 °C, pH 7.5. Haematocrit, the number of erythrocytes and the haemoglobin concentration were 14.6, 0.59·10 12·1 −1 and 29.6 g·1 −1, respectively. Mean corpuscular haemoglobin concentration and mean cellular haemoglobin content were 202.7 g·1 −1 and 50.2 pg, respectively. The plasma contribution to the total O 2-carrying capacity was 16.7%. The pH was 7.7; the mean venous pressures of CO 2 and O 2 were 3.8 and 58.5 mm Hg, respectively. For comparison, a summary of the available data from other bathydraconids is also presented. Special attention is given to the mode of life and the evolution of this teleost in relation to its habitat.