H. K. Johnsen
Norwegian College of Fishery Science
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Featured researches published by H. K. Johnsen.
Journal of Thermal Biology | 1995
Malcolm Jobling; H. K. Johnsen; G.W. Pettersen; R.J. Henderson
Abstract 1. 1. Female broodstock Arctic charr were held at 4, 8, 12 or 16°C from mid-June until late-September, and oocyte development and ovulation examined. 2. 2. Thermal environment influenced the deposition of lipids during oocyte development, with oocytes sampled from fish held at the highest temperature containing the highest proportion of triacylglycerols and the lowest proportion of phospholipids. 3. 3. Exposure to high temperature during the summer months resulted in ovulation being delayed by approximately 3–4 weeks. 4. 4. The phospholipids of the ovulated eggs produced by females held at 16°C contained lower proportions of the essential (n-3) fatty acids DHA and EPA than did eggs produced by females that had been exposed to lower temperatures. 5. 5. Thermal environment did not appear to have had any marked influence on egg size, lipid class composition or the fatty acid compositions of the storage triacylglycerols.
Aquaculture | 1998
Arne M. Arnesen; H. K. Johnsen; Atle Mortensen; Malcolm Jobling
Abstract Acclimation of Atlantic salmon ( Salmo salar L.) smolts to sea water at low temperatures has been studied in groups of fish transferred directly from fresh water (6°C) to sea water at 2°, 4° and 6°C. Temperatures were maintained until day 54 when water temperature was switched to ambient (approximately 7°C) in all groups. The following parameters were monitored on days 8, 29, 50 and 72 after transfer: plasma osmolality and electrolyte concentrations, gill Na + –K + ATPase activity, individual feed intake and growth. By the end of the experiment cumulative mortality was 18.1%, 12.5% and 5.0% in the groups of smolt transferred to sea water at 2°, 4° and 6°C, respectively. Plasma osmolality and the concentrations of chloride and sodium were inversely related to water temperature, but values for all groups (osmolality: 324–344 mosM kg −1 ; [Cl − ]: 147–162 mM; [Na + ]: 164–171 mM) fell within the range considered to be normal for seawater-acclimated salmonids. Gill Na + –K + ATPase activity increased in all groups of fish following transfer to sea water, the rate of increase being correlated with water temperature. Feed intake and growth were very low for the first few weeks following the transfer of the fish from fresh to sea water, but increased thereafter. On day 50 the percentages of nonfeeding fish were 23%, 5% and 1% in the groups of smolt transferred to sea water at 2°, 4° and 6°C, respectively. Accordingly, highest rates of feed intake and growth were recorded for the fish held at the highest temperature. The results indicate that Atlantic salmon smolts are more tolerant of low seawater temperatures than earlier believed, and the negative effects of low temperature upon feeding and growth do not seem to be directly related to an impaired ability of the fish to hypoosmoregulate.
Journal of Fish Biology | 2010
H. Tveiten; P. A. Bjørn; H. K. Johnsen; B. Finstad; R. S. McKinley
Groups of mature (5+ year old) Arctic charr Salvelinus alpinus held in sea water were exposed for 34 days to either a high (mean +/-s.e. 0.15 +/- 0.01 sea lice Lepeophtheirus salmonis g(-1) fish mass) (HI), medium (0.07 +/- 0.00 sea lice g(-1) fish mass) (MI) or no [control (C)] sea-lice infection during early stages of gonad development (June to July). Infection with sea lice resulted in increased plasma cortisol concentrations and this was related to intensity of infection; females tended to have higher cortisol concentrations than males at high infection intensities (HI group: female c. 130 ng ml(-1); male c. 80 ng ml(-1)). Plasma osmolality (C c. 330, MI c. 350 and HI c. 415 mOsm) and chloride concentrations (C c. 135, MI c. 155 and HI c. 190 mM) increased significantly with infection intensity, indicating osmoregulatory problems in infected fish. A strong positive relationship between plasma osmolality and cortisol concentration was recorded. Plasma sex-steroid concentrations were influenced negatively by sea-lice infection, particularly in the HI group, and were inversely related to plasma cortisol concentrations. The most heavily infected fish postponed the initiation of reproductive development until exposed to fresh water and timing of ovulation tended to be delayed in these fish. Growth rate and condition were negatively influenced by sea-lice infection and growth rate was inversely related to plasma cortisol concentrations. Sea-lice infection resulted in mortality among females in the HI group, and the proportion of maturing females was lower in the MI group (46%) than in the controls (85%). Egg production in the MI and HI groups was c. 50 and 30% of the C group. Egg size, embryonic survival and fry mass did not differ across groups. Sea lice influence reproductive development and egg production in S. alpinus, and consequently these parasites may influence populations via sublethal effects on broodfish, affecting growth and condition, and their reproductive output.
Comparative Biochemistry and Physiology B | 1999
H. K. Johnsen; Helge Tveiten; Nils Peder Willassen; Arne M. Arnesen
Vitellogenin (Vtg) was isolated from plasma of estradiol-17 beta-treated Arctic charr males by double precipitation with MgCl2-EDTA and distilled water, followed by ion-exchange chromatography. The monomeric form of Vtg, as revealed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 158 kDa. The purified Vtg was used to raise a polyclonal antibody for Vtg (AbVtg), and the specificity of the AbVtg was assessed by Western blot analysis. No cross-reactivity was observed with plasma from control males. Using this AbVtg, a competitive enzyme-linked immunosorbent assay was developed. The detection limit of the assay was 2 ng ml-1, and the intra- and inter-assay variations determined from plasma samples were 8.6 and 13.3%, respectively. The assay was validated by quantification of Vtg in plasma samples obtained during a reproductive cycle of Arctic charr. Vtg of females increased gradually from 3 mg ml-1 in early March to a peak value of 22 mg ml-1 in late August, followed by a rapid drop to 2 mg ml-1 at the time of spawning in mid-October. The temporal changes in plasma Vtg of females correlate well with the reproductive cycle. Vtg was undetectable in males, except on some sampling dates during July-September when minute amounts (3-13 micrograms ml-1) were detected in some individuals.
Aquaculture | 1998
Robert A Eliassen; H. K. Johnsen; Ian Mayer; Malcolm Jobling
Abstract The osmoregulatory capacities of two north Norwegian strains of Arctic charr, Salvelinus alpinus L., have been compared. Groups of fish were either held in fresh water from late-February to September, or were exposed to full-strength sea water (33–34‰) during the period (mid-May–late-June) at which anadromous charr would usually be at sea. The charr (4+ years old, 400 g initial body weight) used in the experiment were all hatchery-reared fish, either of an anadromous strain originating from the Hammerfest area (70°N), or of a landlocked strain originating from the Skjomen area (68°N). The growth of the two strains of charr was similar for fish held in fresh water. There were temporal changes in gill Na+/K+-ATPase activity and chloride cell numbers that seemed to be typical of a parr-smolt transformation, but charr of the landlocked Skjomen strain were not able to osmoregulate effectively and survive in sea water. Fish of the anadromous Hammerfest strain displayed increased gill Na+/K+-ATPase activity following transfer from fresh water to sea water in May. Charr of this strain were able to regulate plasma osmolality and plasma ion concentrations, and grew at similar rates to the fish maintained in fresh water. The results show that there are distinct differences in osmoregulatory capacity between fish of the anadromous Hammerfest strain and charr of the landlocked Skjomen strain.
Marine Genomics | 2014
Even H. Jørgensen; H. K. Johnsen
High latitudes are characterized by strong seasonal changes in environmental conditions, including temperature and food availability. To cope with these changes, many high latitude species have developed circannual oscillators that enable them to anticipate and prepare for forthcoming environmental changes and synchronize seasonal events (e.g. reproduction) to environmental fluctuations. The Arctic charr (Salvelinus alpinus) is the worlds northernmost freshwater fish species with a distribution largely confined within the Arctic. In the northernmost part of its distribution they have developed an anadromous life-history strategy implying annual, seaward migrations in the summer to utilize the rich feeding opportunity in the sea. Overwintering in freshwater is characterized by anorexia and energy conservation. The seaward migration in early summer is preceded by physiological and behavioral changes (smolting), by which they develop seawater tolerance (hypoosmoregulatory ability) and migratory behavior. When migrating to the sea, Arctic charr have regained a strong appetite and within 4-6weeks in the sea they may have doubled their body weight and increased their body fat stores several-fold, in anticipation of the resources needed for reproduction in the autumn and overwintering. All these processes are regulated independently of environmental changes; captive offspring of anadromous charr kept in freshwater displays seasonal changes in seawater tolerance and strong seasonal changes in food intake and growth even when they are continuously fed in excess and held at a constant water temperature in freshwater. A correct timing of these events is crucial for their survival in the Arctic and the Arctic charr seems to possess timing mechanisms that include endogenous, circannual oscillator(s) entrainable by photoperiod. The entrainment mechanism may be linked to diel melatonin rhythms, which in this species exactly mirror overground photoperiod, even during the winter residence in lakes with thick ice and snow. Little is known, however, about how photoperiod, melatonin and putative endogenous clock(s) interact in the generation of seasonal rhythms in fish, and downstream neuroendocrine mechanisms leading to physiological changes. The anadromous Arctic charr seems ideal as a model for studying such mechanisms.
Aquaculture | 2003
Øyvind Aas-Hansen; H. K. Johnsen; Mathilakath M. Vijayan; Even H. Jørgensen
Abstract Anadromous Arctic charr cease feeding and rely on endogenous energy stores during overwintering in fresh water. During spring, they undergo seasonal development of seawater (SW) tolerance (hypoosmoregulatory capacity) and seaward migratory behaviour. As hormones known to be involved in smoltification are also prime regulators of growth and metabolism, the present study set out to investigate whether the seasonal development of hypoosmoregulatory capacity and accompanying changes in cortisol, thyroid hormones and insulin-like growth factor-I (IGF-I) levels are influenced by metabolic and nutritional status. In addition, the present study also investigated the effect of early spring water temperatures (1.5-month advance) on the above parameters. Hatchery-reared offspring of anadromous Arctic charr were either fed or fasted from October 1998 to July 1999. In fish held at ambient water temperature, hypoosmoregulatory capacity improved from March, and reached a level indicating prime SW tolerance in late June. Hypoosmoregulatory development was accompanied by significantly higher gill Na+,K+-ATPase activity, and low levels of thyroid hormones and total IGF-I in the fed and fasted groups. Of the hormones investigated, only plasma cortisol levels in fasted fish resembled the pattern typically seen in smolting salmonids, with peak levels coinciding with development of SW tolerance and increased gill Na+,K+-ATPase activity. Elevation of water temperature in early spring seemed to impair the development of hypoosmoregulatory capacity in this high-Arctic species. It is concluded that long-term fasting associated with overwintering does not impair seasonal development of SW tolerance in Arctic charr, but elevated temperatures in early spring may compromise this developmental process. The lack of hormonal changes regarded as typical for parr–smolt-transforming salmonids may reflect regulatory adjustments at other levels (receptor concentration/affinity, hormone turnover and binding proteins). Furthermore, the hormonal changes seen in the present study may resemble a seasonal resmoltification typical of repeat migrants of this species, rather than parr–smolt-transforming first-time migrants.
Aquaculture | 2000
H. K. Johnsen; Robert A Eliassen; Bjørn-Steinar Sæther; Jørund S Larsen
Abstract Effects of photoperiod manipulation on the development of seawater tolerance were studied in Arctic charr. Three groups of fish, previously reared under natural photoperiod and ambient water temperature conditions, were subjected to a constant short daylength, 4L:20D, from 21 December to 30 January, followed by exposure to either 4L:20D, continuous light (24L:0D) or simulated natural photoperiod (nLD). Temperature of the fresh water was held constant at 4°C until mid-May, after which it increased gradually to reach 8.5°C at the termination of the experiment on 2 July. All groups displayed improved seawater tolerance during the course of the study, assessed as changes in plasma chloride and osmolality concentrations following 72-h exposure to seawater (33–34‰). The tolerance to seawater was positively related to fork length within some sampling dates in all groups. Exposure to 24L:0D advanced the development of seawater tolerance by approximately 6 weeks, compared to the nLD group. Both groups displayed increases in gill Na + /K + -ATPase activity that coincided with the period of improved seawater tolerance. Seawater tolerance of the 4L:20D group was delayed by 6 weeks in comparison with that of the nLD group, but without any concomitant increase in gill Na + /K + -ATPase activity. The results corroborate previous findings, and suggest that the seasonal changes in seawater tolerance of Arctic charr are controlled by an endogenous, circannual timing mechanism that is entrainable by artificially extended daylengths in spring. Our data further suggest that development of seawater tolerance in Arctic charr may occur independently of changes in gill Na + /K + -ATPase activity.
Comparative Biochemistry and Physiology A-molecular & Integrative Physiology | 2009
Daisuke Ojima; Roger J. Pettersen; Judith Wolkers; H. K. Johnsen; Even H. Jørgensen
In a comparative experiment the effect of cortisol and growth hormone (GH) on the hypo-osmoregulatory ability of a landlocked and an anadromous strain of Arctic charr (Salvelinus alpinus) was investigated. Cortisol and GH were implanted either alone or in combination, and the fish were exposed to a 24 h seawater challenge test (SWT) on days 14 and 28 after implantation. Hypo-osmoregulatory ability, measured as plasma osmolality and chloride concentration after the SWTs, was better in the anadromous than in the landlocked strain, irrespective of treatment. However, cortisol provided a strong stimulation of hypo-osmoregualtory ability in both strains, and this stimulation seemed to be potentiated by GH in an additive manner. Improved hypo-osmoregulatory ability in GH+cortisol treated anadromous Arctic charr was accompanied by increased gill Na(+), K(+)-ATPase activity and Na(+)-K(+)-2Cl(-) cotransporter protein abundance, but no changes in gill Na(+),K(+)-ATPase alpha1a and alpha1b mRNA levels. For landlocked charr the improved hypo-osmoregulatory ability in GH+cortisol treated fish was accompanied only with an increase in gill Na(+)-K(+)-2Cl(-) cotransporter protein abundance. Hormone treatment caused an improvement of hypo-osmoregulatory ability that was of approximately the same magnitude in the landlocked as in the anadromous Arctic charr. This suggests that the lack of spontaneous development of hypo-osmoregulatory ability often seen in landlocked populations of Arctic charr may depend, at least partly, on a lack of the hormonal activation seen in anadromous populations.
Aquatic Toxicology | 2016
Morgan Lizabeth Bender; Marianne Frantzen; Ireen Vieweg; Inger-Britt Falk-Petersen; H. K. Johnsen; Geir Rudolfsen; Knut Erik Tollefsen; Paul Dubourg; Jasmine Nahrgang
Increasing human activities in the Arctic raise the risk of petroleum pollution, thus posing an elevated risk for Arctic organisms to be chronically exposed to petroleum compounds. The endocrine disrupting properties of some of these compounds (i.e. polycyclic aromatic hydrocarbons [PAHs]) present in crude oil may have negative effects on the long and energy intensive reproductive development of polar cod (Boreogadus saida), an Arctic keystone species. In the present study, selected reproductive parameters were examined in feral polar cod exposed to crude oil via a natural diet (0.11, 0.57 and 1.14μg crude oil/g fish/day [corresponding to low, medium and high treatments, respectively]) for 31 weeks prior to spawning. Fish maturing in the current reproductive period made up 92% of the experimental population while 5% were immature and 3% were identified as resting fish. Phase I metabolism of PAHs, indicated by ethoxyresorufin-O-deethylase (EROD) activity, showed a dose-dependent increase in high and medium crude oil treatments at week 6 and 22, respectively. Decreasing EROD activity and increasing PAH bile metabolite concentrations over the experimental period may be explained by reproductive maturity stage. Significant alterations in sperm motility were observed in crude oil exposed males compared to the controls. The investigated somatic indices (gonad and hepatic), germ cell development and plasma steroid levels (estradiol-17β [females], testosterone [males and females] and 11-ketotestosterone [males]) were not significantly altered by chronic dietary exposure to crude oil. The environmentally realistic doses polar cod were chronically exposed to in this study were likely not high enough to induce adverse effects in this ecologically important fish species. This study elucidated many baseline aspects of polar cod reproductive physiology and emphasized the influence of maturation state on biomarkers of PAH biotransformation (EROD and PAH bile metabolites).