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Bjorn Thrandur Bjornsson

Publications and source records attributed to Bjorn Thrandur Bjornsson.

15 recordsLinked to original sources
USGS2019

The evolutionary consequences for seawater performance and its hormonal control when anadromous Atlantic salmon become landlocked

Populations of anadromous fish have become landlocked in relatively recent geological history (<14,000 years), but the evolutionary impacts of this altered lifecycle on traits underlying seawater performance have not been established. In order to examine the effects of relaxed selection on seawater traits, anadromous and landlocked Atlantic salmon were reared under identical conditions and examined for differences in seawater performance and its underlying physiological and endocrine control during the time of spring downstream migration. Salinity tolerance, survival and initial growth in seawater were greater in anadromous than in landlocked salmon. Abundance of the seawater isoform of gill Na+/K+-ATPase increased in spring in both strains but was greater in anadromous salmon. Hormones associated with seawater acclimation (adrenocorticotropic hormone, cortisol and growth hormone) increased in spring in both strains but were higher in anadromous salmon, whereas plasma thyroid hormones did not differ. Hypothalamic urotensin I mRNA levels also increased in spring and were higher in the anadromous strain. The results provide evidence that salinity tolerance and associated physiological traits are regulated by seasonal stimulation of the hypothalamic-pituitary-interrenal axis, and that relaxed selection on seawater entry traits has decreased this stimulation in landlocked salmon.

Scientific Reports↗
USGS2019

In vivo effects of 17α-ethinylestradiol, 17B-estradiol and 4-nonylphenol on insulin-like growth-factor binding proteins (igfbps) in Atlantic salmon

Feminizing endocrine disrupting compounds (EDCs) affect the growth and development of teleost fishes. The major regulator of growth performance, the growth hormone (Gh)/insulin-like growth-factor (Igf) system, is sensitive to estrogenic compounds and mediates certain physiological and potentially behavioral consequences of EDC exposure. Igf binding proteins (Igfbps) are key modulators of Igf activity, but their alteration by EDCs has not been examined. We investigated two life-stages (fry and smolts) of Atlantic salmon ( Salmo salar ), and characterized how the Gh/Igf/Igfbp system responded to waterborne 17α-ethinylestradiol (EE 2 ), 17β-estradiol (E 2 ) and 4-nonylphenol (NP). Fry exposed to EE 2 and NP for 21 days had increased hepatic vitellogenin ( vtg ) mRNA levels while hepatic estrogen receptor α ( erα ), gh receptor (ghr) , igf1 and igf2 mRNA levels were decreased. NP-exposed fry had reduced body mass and total length compared to controls. EE 2 and NP reduced hepatic igfbp1b1 , -2a , -2b1 , -4 , -5b2 and -6b1 , and stimulated igfbp5a . In smolts, hepatic vtg mRNA levels were induced following 4-day exposures to all three EDCs, while erα only responded to EE 2 and E 2 . EDC exposures did not affect body mass or fork length; however, EE 2 diminished plasma Gh and Igf1 levels in parallel with reductions in hepatic ghr and igf1 . In smolts, EE 2 and E 2 diminished hepatic igfbp1b1 , -4 and -6b1 , and stimulated igfbp5a . There were no signs of compromised ionoregulation in smolts, as indicated by unchanged branchial ion pump/transporter mRNA levels. We conclude that hepatic igfbps respond (directly and/or indirectly) to environmental estrogens during two key life-stages of Atlantic salmon, and thus may modulate the growth and development of exposed individuals.

Aquatic Toxicology↗
USGS2011

Environmental endocrinology of salmon smoltification

Smolting is a hormone-driven developmental process that is adaptive for downstream migration and ocean survival and growth in anadromous salmonids . Smolting includes increased salinity tolerance, increased metabolism, downstream migratory and schooling behavior, silvering and darkened fin margins, and olfactory imprinting. These changes are promoted by growth hormone, insulin-like growth factor I, cortisol , thyroid hormones, whereas prolactin is inhibitory. Photoperiod and temperature are critical environmental cues for smolt development, and their relative importance will be critical in determining responses to future climate change. Most of our knowledge of the environmental control and endocrine mediation of smolting is based on laboratory and hatchery studies, yet there is emerging information on fish in the wild that indicates substantial differences. Such differences may arise from differences in environmental stimuli in artificial rearing environments, and may be critical to ocean survival and population sustainability. Endocrine disruptors, acidification and other contaminants can perturb smolt development, resulting in poor survival after seawater entry.

General and Comparative Endocrinology↗
USGS2008

Effects of short-term acid and aluminum exposure on the parr-smolt transformation in Atlantic salmon (Salmo salar): Disruption of seawater tolerance and endocrine status

Episodic acidification resulting in increased acidity and inorganic aluminum (Ali) is known to interfere with the parr-smolt transformation of Atlantic salmon (Salmo salar), and has been implicated as a possible cause of population decline. To determine the extent and mechanism(s) by which short-term acid/Al exposure compromises smolt development, Atlantic salmon smolts were exposed to either control (pH 6.7-6.9) or acid/Al (pH 5.4-6.3, 28-64 ??g l-1 Ali) conditions for 2 and 5 days, and impacts on freshwater (FW) ion regulation, seawater (SW) tolerance, plasma hormone levels and stress response were examined. Gill Al concentrations were elevated in all smolts exposed to acid/Al relative to controls confirming exposure to increased Ali. There was no effect of acid/Al on plasma ion concentrations in FW however, smolts exposed to acid/Al followed by a 24 h SW challenge exhibited greater plasma Cl- levels than controls, indicating reduced SW tolerance. Loss of SW tolerance was accompanied by reductions in gill Na+,K+-ATPase (NKA) activity and Na+,K+,2Cl- (NKCC) cotransporter protein abundance. Acid/Al exposure resulted in decreased plasma insulin-like growth factor (IGF-I) and 3,3???,5???-triiodo-l-thyronine (T3) levels, whereas no effect of treatment was seen on plasma cortisol, growth hormone (GH), or thyroxine (T4) levels. Acid/Al exposure resulted in increased hematocrit and plasma glucose levels in FW, but both returned to control levels after 24 h in SW. The results indicate that smolt development and SW tolerance are compromised by short-term exposure to acid/Al in the absence of detectable impacts on FW ion regulation. Loss of SW tolerance during short-term acid/Al exposure likely results from reductions in gill NKA and NKCC, possibly mediated by decreases in plasma IGF-I and T3. ?? 2008 Elsevier Inc.

General and Comparative Endocrinology↗
USGS2007

Larval exposure to 4-nonylphenol and 17β-estradiol affects physiological and behavioral development of seawater adaptation in Atlantic salmon smolts

Population declines of anadromous salmonids are attributed to anthropogenic disturbances including dams, commercial and recreational fisheries, and pollutants, such as estrogenic compounds. Nonylphenol (NP), a xenoestrogen, is widespread in the aquatic environment due to its use in agricultural, industrial, and household products. We exposed Atlantic salmon yolk-sac larvae to waterborne 10 or 100 &mu;g L -1 NP (NP-L or NP-H, respectively), 2 &mu;g L -1 17&beta;-estradiol (E 2 ), or vehicle, for 21 days to investigate their effects on smolt physiology and behavior 1 year later. NP-H caused approximately 50% mortality during exposure, 30 days after exposure, and 60 days after exposure. Mortality rates of NP-L and E 2 fish were not affected until 60 days after treatment, when they were 4-fold greater than those of controls. Treatment with NP-L or E 2 as yolk-sac larvae decreased gill sodium-potassium-activated adenosine triphosphatase (Na + ,K + -ATPase) activity and seawater (SW) tolerance during smolt development, 1 year after exposure. Exposure to NP-L and E 2 resulted in a latency to enter SW and reduced preference for SW approximately 2- and 5-fold, respectively. NP-L-exposed fish had 20% lower plasma insulin-like growth factor I (IGF-I) levels and 35% lower plasma triiodothyronine (T 3 ). Plasma growth hormone and thyroxine (T 4 ) were unaffected. Exposure to E 2 did not affect plasma levels of IGF-I, GH, T 3 , or T 4 . Both treatment groups exhibited increased plasma cortisol and decreased osmoregulatory capacity in response to a handling stressor. These results suggest that early exposure to environmentally relevant concentrations of NP, and other estrogenic compounds, can cause direct and delayed mortalities and that this exposure can have long term, &ldquo;organizational&rdquo; effects on life-history events in salmonids.

Environmental Science & Technology↗
USGS2007

Differential hormonal responses of Atlantic salmon parr and smolt to increased daylength: A possible developmental basis for smolting

In order to elucidate the developmental basis for smolting, Atlantic salmon, Salmo salar, parr (< 11.5??cm) and smolts (> 12.5??cm) were exposed to natural daylength (LDN) and increased daylength (LD16:8) starting in late February and gill Na+,K+-ATPase activity and circulating hormone levels monitored from January to May. Gill Na+,K+-ATPase activity remained low and constant in both groups of parr. In smolts, gill Na+,K+-ATPase began increasing in late February in both photoperiods, but was significantly higher in the LD16:8 group from March through April. Smolts exposed to LD16:8 had dramatically elevated plasma GH within one week of increased daylength that remained high through April, whereas plasma GH of LDN smolts increased steadily beginning in late February and peaking in late April. Plasma GH levels of parr remained low in spring and did not respond to increased daylength. Plasma insulin-like growth factor I (IGF-I) levels were substantially higher in smolts than parr in January. Plasma IGF-I levels of parr increased steadily from January to May, but there was no influence of increased daylength. In smolts, plasma IGF-I of LD16:8 fish initially decreased in early March then increased in late March and April, whereas plasma IGF-I of LDN smolts increased steadily to peak levels in early April. Plasma cortisol was low in parr throughout spring and did not differ between photoperiod treatments. Plasma cortisol of LD16:8 smolts increased in early March and remained elevated through April, whereas in LDN smolts plasma cortisol did not increase until early April and peaked in late April. Plasma thyroid hormones were generally higher in smolts than in parr, but there was no clear effect of increased daylength in parr or smolts. The greater capacity of the GH/IGF-I and cortisol axes to respond to increased daylength may be a critical factor underlying smolt development. ?? 2007 Elsevier B.V. All rights reserved.

Aquaculture↗
USGS2007

Effects of aqueous exposure to polychlorinated biphenyls (Aroclor 1254) on physiology and behavior of smolt development of Atlantic salmon

Polychlorinated biphenyls (PCBs) are a widespread aquatic contaminant and are present in both wild and hatchery raised Atlantic salmon, Salmo salar. The possible sub-lethal alterations in smolt physiology and behavior due to PCB exposure of salmon have not been widely examined. In this study, we examined the effects of the PCB mixture Aroclor 1254 on survival and smolt development of Atlantic salmon. In separate experiments, fish were exposed as yolk-sac larvae or as juveniles just prior to the parr-smolt transformation in April to 1 ??g l-1 (PCB-1) or 10 ??g l-1 (PCB-10) aqueous Aroclor 1254 (A1254), or vehicle for 21 days. After exposure, yolk-sac larvae were reared at ambient conditions for 1 year, until the peak of smolting the following May. Juveniles were sampled immediately after exposure. Both groups were assessed for behavioral, osmoregulatory, and endocrine disruption of smolt development at the peak of smolting. PCB-1 and PCB-10 treated yolk-sac larvae exhibited significant increases in the rate of opercular movement after 14 and 21 days of exposure. At the peak of smolting, prior exposure as yolk-sac larvae to PCB-1 did not affect behavior, while PCB-10 dramatically decreased volitional preference for seawater. Neither concentration of A1254 had long-term effects on the osmoregulatory or endocrine parameters measured in animals exposed as yolk-sac larvae. Juvenile fish exposed to PCB-1 or PCB-10 during smolting exhibited a dose-dependent reduction in preference for seawater. Fish treated with the higher dose of A1254 also exhibited a 50% decrease in gill Na+,K+-ATPase activity and a 10% decrease in plasma chloride levels in freshwater. In addition, plasma triiodothyronine was reduced 35-50% and plasma cortisol 58% in response to exposure to either concentration; whereas plasma thyroxine, growth hormone, and insulin-like growth factor I levels were unaffected. These results indicate that the effects of exposure to A1254 may vary according to developmental stage. Exposure to A1254 in the freshwater environment can inhibit preparatory adaptations that occur during smolting, thereby reducing marine survival and sustainability of salmon populations. ?? 2007 Elsevier B.V. All rights reserved.

Aquatic Toxicology↗
USGS2007

Effects of hexazinone and atrazine on the physiology and endocrinology of smolt development in Atlantic salmon

Exposure to hexazinone (HEX) and atrazine (ATZ), highly mobile and widely used herbicides along rivers in the United States, is potentially harmful to Atlantic salmon, which have been listed as an endangered species. To determine the effects of these contaminants on smolt development, juvenile Atlantic salmon were exposed under flow-through conditions to 100 μg l −1 HEX, 10 and 100 μg l −1 ATZ in fresh water (FW) for 21 days at 10 °C beginning in mid-April. Twelve fish per treatment were sampled in FW, following a 24 h seawater (SW) challenge and after growth for 3 months in SW. Exposure to 100 μg l −1 HEX or 10 μg l −1 ATZ caused no mortalities of smolts in FW or after SW challenge, while 9% of the fish exposed to 100 μg l −1 ATZ died during exposure. Fish exposed to 100 μg l −1 ATZ reduced feeding after 10 days of exposure and had an impaired growth rate in FW and during the first month in SW; compensatory growth occurred in the second and third month in SW. HEX and ATZ at 10 μg l −1 exposure had no effect on plasma levels of cortisol, growth hormone (GH), insulin growth factor I (IGF-I), thyroxine (T 4 ) and plasma 3,5,3′-triiodo- l -thyronine (T 3 ), Cl − , Mg 2+ , Na + , Ca 2+ in FW or after SW challenge. FW smolts exposed to 100 μg l −1 ATZ had decreased plasma Cl − , Mg 2+ , Na + and Ca 2+ ions and increased cortisol. No effect on plasma levels of GH, IGF-I, T 4 or T 3 was found in FW smolts exposed to 100 μg l −1 ATZ. Following SW challenge, fish previously exposed to 100 μg l −1 ATZ had significant increases in hematocrit, plasma cortisol, Cl − , Mg 2+ , Na + , Ca 2+ and a decrease in T 4 and T 3 . It is concluded that under the conditions imposed in this study, HEX does not affect salinity tolerance of Atlantic salmon smolts, while ATZ causes ionoregulatory, growth and endocrine disturbance.

Aquatic Toxicology↗
USGS2007

Differential expression of gill Na + ,K + -ATPaseα - and β-subunits, Na + ,K + ,2Cl - cotransporter and CFTR anion channel in juvenile anadromous and landlocked Atlantic salmon Salmo salar

This study examines changes in gill Na + ,K + -ATPase (NKA) &alpha;- and &beta;-subunit isoforms, Na + ,K + ,2Cl - cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR I and II) in anadromous and landlocked strains of Atlantic salmon during parr-smolt transformation, and after seawater (SW) transfer in May/June. Gill NKA activity increased from February through April, May and June among both strains in freshwater (FW), with peak enzyme activity in the landlocked salmon being 50% below that of the anadromous fish in May and June. Gill NKA-&alpha;1b, -&alpha;3, -&beta; 1 and NKCC mRNA levels in anadromous salmon increased transiently, reaching peak levels in smolts in April/May, whereas no similar smolt-related upregulation of these transcripts occurred in juvenile landlocked salmon. Gill NKA-&alpha;1a mRNA decreased significantly in anadromous salmon from February through June, whereas &alpha;1a levels in landlocked salmon, after an initial decrease in April, remained significantly higher than those of the anadromous smolts in May and June. Following SW transfer, gill NKA-&alpha;1b and NKCC mRNA increased in both strains, whereas NKA-&alpha;1a decreased. Both strains exhibited a transient increase in gill NKA &alpha;-protein abundance, with peak levels in May. Gill &alpha;-protein abundance was lower in SW than corresponding FW values in June. Gill NKCC protein abundance increased transiently in anadromous fish, with peak levels in May, whereas a slight increase was observed in landlocked salmon in May, increasing to peak levels in June. Gill CFTR I mRNA levels increased significantly from February to April in both strains, followed by a slight, though not significant increase in May and June. CFTR I mRNA levels were significantly lower in landlocked than anadromous salmon in April/June. Gill CFTR II mRNA levels did not change significantly in either strain. Our findings demonstrates that differential expression of gill NKA-&alpha;1a, -&alpha;1b and -&alpha;3 isoforms may be important for potential functional differences in NKA, both during preparatory development and during salinity adjustments in salmon. Furthermore, landlocked salmon have lost some of the unique preparatory upregulation of gill NKA, NKCC and, to some extent, CFTR anion channel associated with the development of hypo-osmoregulatory ability in anadromous salmon.

Journal of Experimental Biology↗
USGS2003

Influence of salinity on the localization of Na+/K +-ATPase, Na+/K+/2Cl- cotransporter (NKCC) and CFTR anion channel in chloride cells of the Hawaiian goby (Stenogobius hawaiiensis)

Na+/K+-ATPase, Na+/K+/2Cl- cotransporter (NKCC) and cystic fibrosis transmembrane conductance regulator (CFTR) are the three major transport proteins thought to be involved in chloride secretion in teleost fish. If this is the case, the levels of these transporters should be high in chloride cells of seawater-acclimated fish. We therefore examined the influence of salinity on immunolocalization of Na +/K+-ATPase, NKCC and CFTR in the gills of the Hawaiian goby (Stenogobius hawaiiensis). Fish were acclimated to freshwater and 20??? and 30??? seawater for 10 days. Na+/K +-ATPase and NKCC were localized specifically to chloride cells and stained throughout most of the cell except for the nucleus and the most apical region, indicating a basolateral/tubular distribution. All Na+/K +-ATPase-positive chloride cells were also positive for NKCC in all salinities. Salinity caused a slight increase in chloride cell number and size and a slight decrease in staining intensity for Na+/K +-ATPase and NKCC, but the basic pattern of localization was not altered. Gill Na+/K+-ATPase activity was also not affected by salinity. CFTR was localized to the apical surface of chloride cells, and only cells staining positive for Na+/K+-ATPase were CFTR-positive. CFTR-positive cells greatly increased in number (5-fold), area stained (53%) and intensity (29%) after seawater acclimation. In freshwater, CFTR immunoreactivity was light and occurred over a broad apical surface on chloride cells, whereas in seawater there was intense immunoreactivity around the apical pit (which was often punctate in appearance) and a light subapical staining. The results indicate that Na+/K +-ATPase, NKCC and CFTR are all present in chloride cells and support current models that all three are responsible for chloride secretion by chloride cells of teleost fish.

Journal of Experimental Biology↗
USGS2000

The presence of high-affinity, low-capacity estradiol-17β binding in rainbow trout scale indicates a possible endocrine route for the regulation of scale resorption

High-affinity, low-capacity estradiol-17β (E 2 ) binding is present in rainbow trout scale. The K d and B max of the scale E 2 binding are similar to those of the liver E 2 receptor ( K d is 1.6 ± 0.1 and 1.4 ± 0.1 nM, and B max is 9.1 ± 1.2 and 23.1 ± 2.2 fmol × mg protein -1 , for scale and liver, respectively), but different from those of the high-affinity, low-capacity E 2 binding in plasma ( K d is 4.0 ± 0.4 nM and B max is 625.4 ± 63.1 fmol × mg protein −1 ). The E 2 binding in scale was displaced by testosterone, but not by diethylstilbestrol. Hence, the ligand binding specificity is different from that of the previously characterized liver E 2 receptor, where E 2 is displaced by diethylstilbestrol, but not by testosterone. The putative scale E 2 receptor thus appears to bind both E 2 and testosterone, and it is proposed that the increased scale resorption observed during sexual maturation in both sexes of several salmonid species may be mediated by this receptor. No high-affinity, low-capacity E 2 binding could be detected in rainbow trout gill or skin.

General and Comparative Endocrinology↗
USGS1998

Repeated acute stress reduces growth rate of Atlantic salmon parr and alters plasma levels of growth hormone, insulin-like growth factor I and cortisol

Atlantic salmon ( Salmo salar ) parr were subjected to acute handling stresses and growth-monitored for at least 30 days. In fish stressed twice daily, growth rate in weight was 61% lower than controls after 11 days (1.00 vs. 2.57% day −1 ) and over a 30 day period it was 50% lower than controls (1.53 vs. 3.07% day −1 ). In fish stressed once daily, growth rate was 18% lower than controls after 10 days (2.17 vs. 2.63% day −1 ) and over a 30-day period it was 34% lower than controls (1.71 vs. 2.59% day −1 ). In fish stressed once daily, food consumption was reduced by 62% and 37% after 17 and 37 days, respectively. At the end of 40 days of acute stress once daily, control and stressed fish were sampled 1 h prior to, 3 and 7 h after a stress event. Plasma growth hormone levels were significantly higher in the stressed group than in the controls prior to and 7 h after stress. Plasma insulin-like growth factor I (IGF-I) levels were higher in the stressed group only 3 and 7 h after stress. Plasma cortisol levels were lower in the stressed group prior to and 3 h after stress. The results indicate that acute stressors decrease growth of Atlantic salmon parr, with increasing frequency of stress having a more rapid and greater effect.

Aquaculture↗