Jørgen S. Christiansen

Effects of stocking density on food intake, growth performance and oxygen consumption in Arctic charr (Salvelinus alpinus)

Abstract Food intake, growth rates, and rates of oxygen consumption were measured in Arctic charr (Salvelinus alpinus), stocked at low (15 kg·m−3), medium (60 kg·m−3) and high (120 kg·m−3) densities. Growth rates were similar for fish stocked at the medium and high densities, but were markedly depressed at the lowest stocking density. Differences in growth were probably the result of similar differences in food intake. Low levels of food intake were probably also the prime reason for the low oxygen consumption rates recorded in the groups of fish stocked at low density. Stocking density affected the behaviour of the fish, and schooling behaviour was observed in the groups subjected to the medium and high stocking density. No significant correlations were found between initial body size, food intake and growth rates in the groups of fish held at any stocking density. Consequently, social constraints due to the formation of dominance hierarchies may not have been the prime reason for the appetite and growth reduction seen in groups stocked at low density.

Arctic marine fishes and their fisheries in light of global change

In light of ocean warming and loss of Arctic sea ice, harvested marine fishes of boreal origin (and their fisheries) move poleward into yet unexploited parts of the Arctic seas. Industrial fisheries, already in place on many Arctic shelves, will radically affect the local fish species as they turn up as unprecedented bycatch. Arctic marine fishes are indispensable to ecosystem structuring and functioning, but they are still beyond credible assessment due to lack of basic biological data. The time for conservation actions is now, and precautionary management practices by the Arctic coastal states are needed to mitigate the impact of industrial fisheries in Arctic waters. We outline four possible conservation actions: scientific credibility, ‘green technology’, legitimate management and overarching coordination.

The effects of prolonged exercise training on growth performance and production parameters in fish

When juvenile salmonids are reared in water flowing with currents equivalent to swimming speeds of about 0.75–1.5 BL s−1, the fish tend to grow faster and make more efficient use of the food provided than do conspecifics held in standing water. There may be a more even distribution of food within a group of exercised fish leading to uniformity of growth rates and a reduced size range of the fish at harvest. In addition, frequencies of aggressive interactions may be lower in exercised fish than in those reared in standing water, leading to fewer exercised fish having fin damage. Thus, several benefits may be expected to accrue from growing salmonids in flowing water. The ‘training’ of salmonids by exposing them to moderate water currents for prolonged periods leads to improvements in physiological performance, so rearing such fish in flowing, rather than standing, water may be particularly beneficial when they are destined for release in connection with restocking or ‘ranching’ programmes.

PAH biomarker responses in polar cod (Boreogadus saida) exposed to benzo(a)pyrene

With expanding oil and gas activities into the Arctic region, there is a need to evaluate the induction capacity of polycyclic aromatic hydrocarbon (PAH) biomarkers on Arctic marine organisms and to test analytical methods that have been optimized for their temperate counterparts. Polar cod Boreogadus saida were injected intraperitoneally with cod liver oil (solvent control), 6.6+/-3.7, 85+/-48 or 378+/-190 microg kg(-1) wet weight of benzo(a)pyrene (B(a)P), or not injected (control), and liver and bile were sampled at 0 and 16 h and 1, 2, 4 and 7d. The mRNA expression of cytochrome P4501A1 (cyp1a1) and glutathione S-transferase (gst) genes showed a dose-dependent induction in the first 16 h following the injection and a return to basal levels after 4d. The aryl hydrocarbon receptor 2, however, showed no change in mRNA expression. The protein quantification of cytochrome P4501A (CYP1A), through Western blot analysis and the enzyme-linked immunosorbent assay (ELISA), presented similar but weaker and time-delayed responses (4-7d) compared to the gene (16 h to 2d). Ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) activities increased significantly at day 7 following the gene induction and increase in protein levels. Overall, these biomarkers showed dose-dependent but weak responses to B(a)P and low levels of bile metabolites. The mRNA expressions of oxidative stress genes, superoxide dismutases (sod(Cu/Zn) and sod(Mn)), catalase (cat) and glutathione peroxidase (gpx), were all up-regulated between 16 h and 2d of B(a)P exposure with cat (72-fold) and sod(Cu/Zn) (20-fold) giving the strongest responses in the highest dose. Finally, CAT protein level and enzyme activities showed less clear responses than the genes. The mRNA expression showed the earliest responses, followed by the protein levels. The enzymatic activities were the least sensitive and responded to the exposure after 7d. The study shows the induction capability of biomarkers in polar cod at very low bioavailable doses of B(a)P and provides new information on the selected biomarkers for use in oil monitoring in the Arctic.

Effects of sustained exercise on growth and body composition of first-feeding fry of Arctic charr, Salvelinus alpinus (L.)

Abstract Arctic charr, Salvelinus alpinus, fry (initial length 26 mm) exercised at 2.3–1.1 body length per second grew faster than fry reared in standing water. By day 189 the weights of the exercised fry exceeded those of the controls by 21%. Exercising of fry resulted in a small but significant decrease in body lipid level with a concomitant increase in body protein level compared with controls. No differences in lipid classes and fatty acid composition were observed between exercised and control fry but marked changes in body composition, lipid classes and fatty acid composition occurred within treatment groups during the experiment. Periodic observations indicated that schooling behaviour developed in exercising fry while fry reared in standing water displayed undirected swimming activity.

Biomarker responses in polar cod (Boreogadus saida) exposed to the water soluble fraction of crude oil.

In order to mimic the biological effects of an oil spill in Arctic waters, we examined several types of biomarkers (genes, enzymes, metabolites, and DNA damage) in polar cod Boreogadus saida experimentally exposed to the water soluble fractions of crude oil. During 4 weeks of exposure, induction of the studied biomarkers exceeded baseline levels. The mRNA expression of the cytochrome P4501A1 (cyp1a1) gene was the most promising biomarker, with glutathione S-transferase (gst) as a suitable complement. The delayed ethoxyresorufin O-deethylase (EROD) and GST activities and their persistence following 2 weeks of depuration may allow detection of previous exposures in field samples. The composition of PAH metabolites in the bile indicated the bioavailability of different PAH size-classes. Although mRNA expressions of antioxidant defense genes were induced at start of the exposure, with the strongest responses from catalase and cytosolic superoxide dismutase, they were poor for oil monitoring purposes due to their very short response times. Significant DNA damage demonstrated genotoxicity even at low PAH concentrations (<15microgL(-1)) and was correlated with benzo(a)pyrene and pyrene metabolites in the bile.

Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus)

Deep living for centuries We tend to think of vertebrates as living about as long as we do, give or take 50 to 100 years. Marine species are likely to be very long-lived, but determining their age is particularly difficult. Nielsen et al. used the pulse of carbon-14 produced by nuclear tests in the 1950s—specifically, its incorporation into the eye during development—to determine the age of Greenland sharks. This species is large yet slow-growing. The oldest of the animals that they sampled had lived for nearly 400 years, and they conclude that the species reaches maturity at about 150 years of age. Science, this issue p. 702 Greenland sharks can live to be 400 years old and only become sexually mature at 150, raising conservation concerns. The Greenland shark (Somniosus microcephalus), an iconic species of the Arctic Seas, grows slowly and reaches >500 centimeters (cm) in total length, suggesting a life span well beyond those of other vertebrates. Radiocarbon dating of eye lens nuclei from 28 female Greenland sharks (81 to 502 cm in total length) revealed a life span of at least 272 years. Only the smallest sharks (220 cm or less) showed signs of the radiocarbon bomb pulse, a time marker of the early 1960s. The age ranges of prebomb sharks (reported as midpoint and extent of the 95.4% probability range) revealed the age at sexual maturity to be at least 156 ± 22 years, and the largest animal (502 cm) to be 392 ± 120 years old. Our results show that the Greenland shark is the longest-lived vertebrate known, and they raise concerns about species conservation.

The application of X‐radiography in feeding and growth studies with fish: A summary of experiments conducted on arctic charr

Abstract The X‐radiographic method first described by Talbot and Higgins (1983) can, with suitable modifications and in combination with other simple techniques, have a wide range of applications in feeding and growth studies with fish. The method can be used for the accurate determination of feed intake, something that is required for the construction of feed tables for farmed fish. The method also may be used in studies designed for the investigation of feeding behavior and modes of feeding. The most useful application may, however, be related to the study of feed‐growth relationships because the method enables the monitoring of feeding and growth performances of individual fish within groups. The application of the method to the study of feed‐growth relationships is described using the effects of different levels of sustained exercise on these relationships as an example. The data show that exposure of fish to moderate water currents for prolonged periods leads to both higher rates of weight gain and i...

Biomarker responses in polar cod (Boreogadus saida) exposed to dietary crude oil.

Polar cod Boreogadus saida were exposed weekly to two doses of dietary crude oil for 4 weeks followed by 2 weeks of depuration. Administered doses corresponded on average to 4 and 9microgSigmaPAHsg(-1)fishweek(-1). Cytochrome P4501A1 (cyp1a1) and glutathione S-transferase (gst) mRNA expression, ethoxyresorufin O-deethylase (EROD) activity and metabolites in the bile showed strong and dose-dependent inductions at 2 and 4 weeks of exposure. Following 2 weeks depuration, mRNA expression of cyp1a1 and gst and PAH metabolites returned to basal levels while EROD activity and GST activity were still induced in the high oil treatment. The mRNA expressions of antioxidant defense genes (catalase, glutathione peroxidase and cytosolic and mitochondrial superoxide dismutase) did not change significantly during the experiment. Catalase activity was significantly depressed at week 2 in the high oil treatment. We conclude that the cyp1a1 mRNA expression, EROD activities and bile metabolites were the most reliable biomarkers of exposure while gst mRNA expression and GST activity were less sensitive and are considered only as complementary. Antioxidant defenses were poor biomarkers to assess effects of crude oil exposure in polar cod.

A mitogenomic approach to the taxonomy of pollocks: Theragra chalcogramma and T. finnmarchica represent one single species

BackgroundThe walleye pollock (Theragra chalcogramma) and Norwegian pollock (T. finnmarchica) are confined to the North Pacific and North Atlantic Oceans, respectively, and considered as distinct species within the family Gadidae. We have determined the complete mtDNA nucleotide sequence of two specimens of Norwegian pollock and compared the sequences to that of 10 specimens of walleye pollock representing stocks from the Sea of Japan and the Bering Sea, 2 specimens of Atlantic cod (Gadus morhua), and 2 specimens of haddock (Melanogrammus aeglefinus).ResultsA total number of 204 variable positions were identified among the 12 pollock specimens, but no specific substitution pattern could be identified between the walleye and Norwegian pollocks. Phylogenetic analysis using 16.500 homologous mtDNA nucleotide positions clearly identify the Norwegian pollock within the walleye pollock species cluster. Furthermore, the Norwegian pollock sequences were most similar to mitochondrial genotypes present in walleye pollock specimens from the Sea of Japan, an observation supported both by neighbor-joining, maximum parsimony, and maximum likelihood analyses.ConclusionWe infer that walleye pollock and Norwegian pollock represent one single species and that Norwegian pollock has been recently introduced from the Pacific to the Atlantic Oceans.