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Bjorn Thrandur Bjornsson

Publications and source records attributed to Bjorn Thrandur Bjornsson.

At least 19 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↗
USGS2017

Variation in branchial expression among insulin-like growth-factor binding proteins (igfbps) during Atlantic salmon smoltification and seawater exposure

Background In preparation for migration from freshwater to marine habitats, Atlantic salmon ( Salmo salar L.) undergo smoltification, a transformation that includes the acquisition of hyposmoregulatory capacity. The growth hormone (Gh)/insulin-like growth-factor (Igf) axis promotes the development of branchial ionoregulatory functions that underlie ion secretion. Igfs interact with a suite of Igf binding proteins (Igfbps) that modulate hormone activity. In Atlantic salmon smolts, igfbp4 ,− 5a ,− 5b1 ,− 5b2 ,− 6b1 and −6b2 transcripts are highly expressed in gill. We measured mRNA levels of branchial and hepatic igfbps during smoltification (March, April, and May), desmoltification (July) and following seawater (SW) exposure in March and May. We also characterized parallel changes in a broad suite of osmoregulatory (branchial Na + /K + -ATPase (Nka) activity, Na + /K + /2Cl − cotransporter 1 ( nkcc1 ) and cystic fibrosis transmembrane regulator 1 ( cftr1 ) transcription) and endocrine (plasma Gh and Igf1) parameters. Results Indicative of smoltification, we observed increased branchial Nka activity, nkcc1 and cftr1 transcription in May. Branchial igfbp6b1 and -6b2 expression increased coincidentally with smoltification. Following a SW challenge in March, igfbp6b1 showed increased expression while igfbp6b2 exhibited diminished expression. igfbp5a,−5b1 and −5b2 mRNA levels did not change during smolting, but each had lower levels following a SW exposure in March. Conclusions Salmonids express an especially large suite of igfbps . Our data suggest that dynamic expression of particular igfbps accompanies smoltification and SW challenges; thus, transcriptional control of igfbps may provide a mechanism for the local modulation of Igf activity in salmon gill.

BMC Physiology↗
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

Aqueous exposure to 4-nonylphenol and 17β-estradiol increases stress sensitivity and disrupts ion regulatory ability of juvenile atlantic salmon

Population declines of wild Atlantic salmon have been attributed to an array of anthropogenic disturbances, including dams, commercial and recreational fishing, habitat loss, and pollution. Environmental contaminants in particular, can act as environmental stressors on fish, typically causing disruption of ion homeostasis due to their close association with the aquatic environment. To examine the effects of the xenoestrogen 4-nonylphenol (NP) or 17&beta;-estradiol (E 2 ) on stress sensitivity and ion regulation, we exposed juvenile Atlantic salmon continuously for 21 d to either 10 or 100 &mu;g/L NP (NP-L or NP-H), 2 &mu;g/L E 2 (positive control), or vehicle control during the parr-smolt transformation in April. After treatment, fish were sampled in freshwater (FW), transferred to 30&permil; seawater (SW) for 24 h, or subjected to a handling stress. Estradiol and NP-H increased plasma vitellogenin in males and females, and E 2 increased gonadosomatic index only in males. In FW, E 2 reduced sodium potassium&ndash;activated adenosine triphosphatase activity as well as plasma levels of growth hormone, insulin-like growth factor I, and triiodothyronine. Both E 2 and NP-H reduced plasma sodium in FW and increased plasma chloride in SW. Plasma Cortisol levels pre- and poststressor were significantly elevated by all treatments relative to controls, but only E 2 increased plasma glucose before and after the stressor. These results indicate that exposure of anadromous salmonids to environmental estrogens heightens sensitivity to external stressors, impairs ion regulation in both FW and SW, and disrupts endocrine pathways critical for smolt development.

Environmental Toxicology and Chemistry↗
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↗
USGS2005

Endocrine disruption of parr-smolt transformation and seawater tolerance of Atlantic salmon by 4-nonylphenol and 17β-estradiol

Sex steroids are known to interfere with the parr-smolt transformation of anadromous salmonids, and environmental estrogens such as nonylphenol have recently been implicated in reduced returns of Atlantic salmon in the wild. To determine the endocrine pathways by which estrogenic compounds affect smolt development and seawater tolerance, groups of juvenile Atlantic salmon were injected with one of five doses (0.5, 2, 10, 40 or 150 &mu;g g &minus;1 ) of branched 4-nonylphenol (NP), 2 &mu;g g &minus;1 of 17&beta;- estradiol (E 2 ), or vehicle, during the parr-smolt transformation in April, and the treatment was repeated 4, 8, and 11 days after the first injection. Plasma was obtained for biochemical analysis 7 and 14 days after initiation of treatment. After 14 days of treatment, additional fish from each treatment group were exposed to seawater for 24 h to assess salinity tolerance. The E 2 treatment and the highest NP dose resulted in lower salinity tolerance and decreased plasma insulin-like growth factor I (IGF-I) levels, along with elevated levels of plasma vitellogenin and total calcium. Plasma growth hormone levels were elevated at intermediate NP doses only, and not affected by E 2 . After 7 days, plasma thyroxine (T 4 ) levels decreased in a strong, dose-dependent manner in response to nonylphenol, but after 14 days, this suppressive effect of T 4 occurred at the highest NP dose only. Similarly, E 2 decreased plasma T 4 levels at 7, but not 14 days. Plasma 3,3&prime;,5-triodo- l -thyronine was reduced by E 2 and the highest NP dose after 7 and 14 days of treatment. Plasma cortisol levels were not affected by any of the treatments. The results indicate that the parr-smolt transformation and salinity tolerance can be compromised by exposure to estrogenic compounds. Suppression of plasma IGF-I levels is a likely endocrine pathway for the effects of estrogenic compounds on hypo-osmoregulatory capacity, and the detrimental effects of E 2 and NP on thyroid hormone levels are also likely to compromise the normal parr-smolt transformation of Atlantic salmon.

General and Comparative Endocrinology↗
USGS2003

Endocrine and physiological changes in Atlantic salmon smolts following hatchery release

Physiological and endocrine changes during smolt development were examined in Atlantic salmon (Salmo salar) reared and released as part of a restoration program on the Connecticut River and its tributaries. Fish were reared in a cold water hatchery in Pittsford, VT and released into the Farmington River, CT (a major tributary of the Connecticut River) or into 'imprint ponds' fed by the Farmington River. Smelts were recaptured 10-20 days after their release at a smolt bypass facility 16 km downstream of their release site. Fish sampled at the hatchery from January to May had only moderate smolt development based on salinity tolerance, gill Na+,K+-ATPase activity and hormone profiles. In contrast, smolts released into the river or imprint ponds had higher salinity tolerance, gill Na+,K+-ATPase activity, plasma growth hormone, insulin-like growth factor I (IGF-I) and thyroxine than smolts that remained in the hatchery. These physiological and endocrine changes were nearly identical to those of smolts that had been released into the river 2 years earlier as fry and were captured as active migrants at the same bypass facility (stream-reared smolts). The stomach contents as a percent of body weight (primarily aquatic insects) varied greatly among individuals and were greater in hatchery-reared fish than stream-reared smolts. Results from the rearing of hatchery fish at temperatures similar to that of the Farmington River indicate that some of the physiological changes may be due to increased temperature after release, though other factors may also be involved. The results indicate that substantial physiological smolt development can occur after hatchery release, coincident with downstream migration. ?? 2003 Published by Elsevier Science B.V.

Aquaculture↗
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↗
USGS2002

Effects of an advanced temperature cycle on smolt development and endocrinology indicate that temperature is not a zeitgeber for smolting in Atlantic salmon

Atlantic salmon ( Salmo salar ) juveniles were reared under simulated conditions of normal photoperiod (LDN) or short days (LD 9:15) and ambient temperature (AMB: normal temperature increases in April) or an advanced temperature cycle (ADV: temperature increases in February). Under both photoperiod conditions, the timing of increased and peak levels of gill Na + ,K + -ATPase activity were not altered by temperature,although the rate of increase was initially greater under ADV. ADV/LD 9:15 resulted in peak gill Na + ,K + -ATPase activity that was half of that seen under normal photoperiod and temperature conditions. Plasma growth hormone (GH) levels increased threefold in late March under ADV/LDN,but not under ADV/LD 9:15, indicating that there is a photoperiod-dependent effect of temperature on levels of this hormone. Plasma insulin-like growth factor I (IGF-I) increased in spring in all groups, with increases occurring significantly earlier in the ADV/LDN group. In each photoperiod condition, the advanced temperature cycle resulted in large decreases in plasma thyroxine(T 4 ) levels in March, which subsequently recovered, whereas plasma 3,5,3′-triiodo-L-thyronine (T 3 ) levels were not substantially affected by either photoperiod or temperature. There was no consistent pattern of change in plasma cortisol levels. The results do not provide support for the role of temperature as a zeitgeber, but do indicate that temperature has a role in the timing of smolting by affecting the rate of development and interacting with the photoperiod.

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↗