Geology topics

Stephen D. McCormick

Publications and source records attributed to Stephen D. McCormick.

At least 55 records · Page 3Linked to original sources

USGS2020

Divergent genes encoding the putative receptors for growth hormone and prolactin in sea lamprey display distinct patterns of expression

Growth hormone receptor (GHR) and prolactin receptor (PRLR) in jawed vertebrates were thought to arise after the divergence of gnathostomes from a basal vertebrate. In this study we have identified two genes encoding putative GHR and PRLR in sea lamprey (Petromyzon marinus) and Arctic lamprey (Lethenteron camtschaticum), extant members of one of the oldest vertebrate groups, agnathans. Phylogenetic analysis revealed that lamprey GHR and PRLR cluster at the base of gnathostome GHR and PRLR clades, respectively. This indicates that distinct GHR and PRLR arose prior to the emergence of the lamprey branch of agnathans. In the sea lamprey, GHR and PRLR displayed a differential but overlapping pattern of expression; GHR had high expression in liver and heart tissues, whereas PRLR was expressed highly in the brain and moderately in osmoregulatory tissues. Branchial PRLR mRNA levels were significantly elevated by stage 5 of metamorphosis and remained elevated through stage 7, whereas levels of GHR mRNA were only elevated in the final stage (7). Branchial expression of GHR increased following seawater (SW) exposure of juveniles, but expression of PRLR was not significantly altered. The results indicate that GHR and PRLR may both participate in metamorphosis and that GHR may mediate SW acclimation.

Scientific Reports↗

USGS2020

Atlantic salmon (Salmo salar) exposed to different preparatory photoperiods during smoltification show varying responses in gill Na+/K+-ATPase, salinity-specific mRNA transcription and ionocyte differentiation

Control of the parr-smolt transformation (or smoltification) is crucial for the husbandry and successful seawater (SW) transfer of Atlantic salmon ( Salmo salar ) reared in freshwater (FW) hatcheries. Photoperiod is an important environmental signal that initiates the complex physiological, morphological and behavioural changes that coincide with marine migration. While the use of long-day photoperiods to initiate smoltification has been well studied, this study investigated how three preparatory photoperiods in FW (LD 08:16, LD 12:12, LD 16:08) preceding exposure to 24-h light (LD 24:0) may influence or enhance smolt performance and growth post-SW transfer. After the photoperiod treatment phase (8 weeks), all groups were exposed to LD 24:0 for 8 weeks (FW) and then transferred to SW for a further 8 weeks. Exposure to LD 16:08 induced rapid development of smolt-related characteristics such as increased gill NKA activity, gill NKAα1b mRNA, and plasma cortisol, and decreased gill NKAα1a mRNA levels and condition factor through the 8-week treatment phase. Subsequent exposure to a LD 24:0 photoperiod resulted in a partial reversal of several of these characteristics, suggesting these fish went through a partial desmoltification. Exposure to LD 12:12 for 8 weeks prior to LD 24:0 elicited an intermediary response in smoltification attributes compared to LD 16:08 and LD 08:16. The LD 12:12 group adapted to SW and showed no negative effects on growth or physiological responses after transfer to SW. Exposure to a shortened photoperiod (LD 08:16) did not elicit any smoltification-related changes prior to LD 24:0, however, exposure to LD 24:0 increased gill NKA activity, plasma cortisol, changes in NKAα1a and NKAα1b mRNA, and the ratio of NKAα1b: NKAα1a. These results were confirmed by the expected changes in NKAα1a and NKAα 1b-positive immuno-reactive gill ionocytes. In summary, after exposure to LD 24:0 fish in the LD 08:16 group showed similar levels of change to those of the LD 16:08 group during the initial FW phase (prior to exposure to LD 24:0). After SW transfer, all groups were able to upregulate SW-specific NKAα1b mRNA and acclimate to SW, even though no increase in cortisol was evident. By the end of the study, there was no difference in SW growth among the groups. Overall, our data indicate that LD 16:08 advanced hypoosmoregulatory characteristics prior to LD 24:0 exposure. In addition, the physiological and molecular indicators measured in this group suggest that fish could have been transferred to SW immediately after 8 weeks in LD 16:08, with no added benefit of successive exposure to LD 24:0, which is typically used by industry to induce smoltification.

Aquaculture↗

USGS2020

How repeatable is CTmax within individual brook trout over short- and long-time intervals?

As stream temperatures increase due to factors such as heated runoff from impervious surfaces, deforestation, and climate change, fish species adapted to cold water streams are forced to move to more suitable habitat, acclimate or adapt to increased thermal regimes, or die. To estimate the potential for adaptation, a (within individual) repeatable metric of thermal tolerance is imperative. Critical thermal maximum (CTmax) is a dynamic test that is widely used to measure thermal tolerance across many taxa and has been used in fishes for decades, but its repeatability in most species is unknown. CTmax tests increase water temperature steadily over time until loss of equilibrium (LOE) is achieved. To determine if CTmax is a consistent metric within individual fish, we measured CTmax on the same lab-held individually-marked adult brook trout Salvelinus fontinalis at three different times (August & September 2016, September 2017). We found that CTmax is a repeatable trait (Repeatability ± S.E.: 0.48 ± 0.14). CTmax of individuals males was consistent over time, but the CTmax of females increased slightly over time. This result indicates that CTmax is a robust, repeatable estimate of thermal tolerance in a cold-water adapted fish.

Journal of Thermal Biology↗

USGS2020

Cortisol regulates insulin-like growth-factor binding protein (igfbp) gene expression in Atlantic salmon parr

The growth hormone (Gh)/insulin-like growth-factor (Igf)/Igf binding protein (Igfbp) system regulates growth and osmoregulation in salmonid fishes, but how this system interacts with other endocrine systems is largely unknown. Given the well-documented consequences of mounting a glucocorticoid stress response on growth, we hypothesized that cortisol inhibits anabolic processes by modulating the expression of hepatic igfbp mRNAs. Atlantic salmon ( Salmo salar ) parr were implanted intraperitoneally with cortisol implants (0, 10, and 40 μg g −1 body weight) and sampled after 3 or 14 days. Cortisol elicited a dose-dependent reduction in specific growth rate (SGR) after 14 days. While plasma Gh and Igf1 levels were unchanged, hepatic igf1 mRNA was diminished and hepatic igfbp1b1 and -1b2 were stimulated by the high cortisol dose. Plasma Igf1 was positively correlated with SGR at 14 days. Hepatic gh receptor ( ghr ), igfbp1a , -2a , -2b1 , and -2b2 levels were not impacted by cortisol. Muscle igf2 , but not igf1 or ghr , levels were stimulated at 3 days by the high cortisol dose. As both cortisol and the Gh/Igf axis promote seawater (SW) tolerance, and particular igfbps respond to SW exposure, we also assessed whether cortisol coordinates the expression of branchial igfbps and genes associated with ion transport. Cortisol stimulated branchial igfbp5b2 levels in parallel with Na + /K + -ATPase (NKA) activity and nka-α1b , Na + /K + / 2Cl - -cotransporter 1 ( nkcc1 ), and cystic fibrosis transmembrane regulator 1 ( cftr1 ) mRNA levels. The collective results indicate that cortisol modulates the growth of juvenile salmon via the regulation of hepatic igfbp1s whereas no clear links between cortisol and branchial igfbps previously shown to be salinity-responsive could be established.

Molecular and Cellular Endocrinology↗

USGS2020

How lipid content and temperature affect American shad (Alosa sapidissima) attempt rate and sprint swimming: Implications for overcoming migration barriers

How seasonal effects such as temperature increases and reduced lipid content affect the ability of anadromous fishes to traverse high-velocity barriers and sprint swimming is poorly understood. We evaluated American shad ( Alosa sapidissima ) swimming performance in a flume against high flow velocities (2.5–3.7 m·s −1 ) during the upstream migration period (April–May; temperatures 11.1–21.4 °C) to determine how their willingness to enter a velocity barrier (attempt rate) and their swimming endurance changed during migration. American shad did not make attempts at low temperatures, and attempt rate gradually increased throughout the migration as temperatures warmed. American shad displayed two distinct, nonsustained swimming modes (prolonged and sprint swimming), and endurance was different between sexes. At warmer temperatures, females swam at prolonged speeds more often and longer females displayed a lower endurance. Males primarily swam at sprint speeds and were affected by swimming speed, fork length, and lipid content. Our results indicate that American shad motivation and swimming endurance change over the course of the migration as conditions change, potentially limiting their ability to pass barriers.

Canadian Journal of Fisheries and Aquatic Sciences↗

USGS2020

Evidence of prevalent heat stress in Yukon River Chinook salmon

Migrating adult Pacific salmon ( Oncorhynchus spp.) are sensitive to warm water (>18 °C), with a range of consequences from decreased spawning success to early mortality. We examined the proportion of Yukon River Chinook salmon ( O. tshawytscha ) exhibiting evidence of heat stress to assess the potential that high temperatures contribute to freshwater adult mortality in a northern Pacific salmon population. Water temperatures greater than 18 °C have occurred almost annually in the Yukon River and correspond with low population abundance since the 1990s. Using gene transcription products and heat shock protein 70 biomarkers validated by field experiment, we identified heat stress in half of Chinook salmon examined (54%, n = 477) across three mainstem locations and three tributaries in 2016–2017. Biomarkers tracked wide variation in water temperature (14–23 °C) within a tributary. The proportion of salmon with heat stress differed between years at four of the six locations, with more prevalent heat stress in the warmer year. This work demonstrates that warming water temperatures are currently affecting northern populations of Pacific salmon.

Alaska↗

USGS2020

Osmoregulatory role of the intestine in the sea lamprey (Petromyzon marinus)

Lampreys are the most basal vertebrates with an osmoregulatory strategy. Previous research has established that salinity tolerance of sea lamprey increases dramatically during metamorphosis, but underlying changes in the gut have not been examined. In the present work, we examined changes in intestinal function during metamorphosis and seawater exposure of sea lamprey (Petromyzon marinus). Fully metamorphosed sea lamprey had 100 % survival after direct exposure to 35 ppt SW and only slight elevations in plasma chloride (Cl-) levels. Drinking rates of sea lamprey juveniles in seawater were 26-fold higher than juveniles in FW. Na+/K+-ATPase (NKA) activity in the anterior and posterior intestine increased 12- and 3-fold respectively during metamorphosis, whereas esophageal NKA activity was lower than in the intestine and did not change with development. Acclimation to SW significantly enhanced NKA activity in the posterior intestine but did not significantly change NKA activity in the anterior intestine which remained higher than that in the posterior intestine. Intestinal Cl- and water uptake, which was observed in ex vivo preparations of anterior and posterior intestine under both symmetric and asymmetric conditions, were higher in juveniles than in larvae and were similar in magnitude of those of teleost fish. Inhibition of NKA by ouabain in ex vivo preparations inhibited intestinal water absorption by 64 %. Our results suggest drinking and intestinal ion and water absorption are important to osmoregulation in SW, and that preparatory increases in intestinal NKA activity are important to the development of salinity tolerance that occurs during sea lamprey metamorphosis.

American Journal of Physiology - Regulatory, Integ↗

USGS2019

Upper thermal tolerance and heat shock protein response of juvenile American shad (Alosa sapidissima)

Juvenile American shad ( Alosa sapidissima ) experience a wide range of temperatures in rivers before migrating to the ocean. Temperatures in these freshwater environments can vary greatly spatially, seasonally, year-to-year, and can be impacted by anthropogenic factors such as power plant discharge or climate change. Currently, there is uncertainty concerning juvenile American shad thermal tolerance due to a lack of a well-controlled study. Here, we report results of laboratory experiments to establish the upper thermal tolerance and heat shock protein response of juvenile American shad exposed to gradually increasing temperatures. Upper thermal tolerance was determined to be 35 °C (median; range = 34–36 °C) when fish were acclimated to 25 °C and temperatures were raised 1 °C day −1 . Heat shock protein response was indicated by changes in branchial mRNA abundance of the inducible heat shock protein 90 alpha ( hsp90α ), which was significantly elevated (more than 5-fold increase) at 30 °C, and highest in fish that had reached their upper thermal maximum between 34 and 36 °C. Our findings indicate a higher upper thermal tolerance than previously reported for juvenile American shad, and an onset temperature of hsp90α induction at 30 °C, a temperature juvenile American shad commonly experience during summer months.

Estuaries and Coasts↗

USGS2019

Energy depletion and stress levels of Sockeye Salmon migrating at the northern edge of their distribution

The physiological challenge for anadromous fish to migrate upriver is influenced by river temperature, but the impacts of river temperature can be difficult to predict due to an incomplete understanding of how temperature influences migration costs, especially in high‐latitude (>60°N) ecosystems. To assess temperature influences on migrating Pacific salmon Oncorhynchus spp., we measured heat shock protein 70 (HSP70), as an indicator of cellular stress, and energy content of Sockeye Salmon Oncorhynchus nerka throughout their upriver migration in the Pilgrim River, Alaska. Although HSP70 was elevated as fish moved to the spawning grounds and was higher in fish with low energy content, HSP70 did not increase with warmer river temperatures. We verified in an experiment that HSP70 abundance in Sockeye Salmon does respond to temperatures above 20.5°C. Over the 4 years of sampling, energy content decreased at similar rates as Sockeye Salmon moved upstream. We expected Sockeye Salmon energy levels would be lower when migrating in warmer river temperatures; however, we found higher energy levels occurred with higher temperatures in the Pilgrim River. We hypothesize that the relationship between temperature and energy content is due to river temperatures often occurring below optimal temperatures for migration. Lower temperatures could be energetically costly or reduce migration rates, both of which would result in lower energy content with cooler temperature. Understanding interactions between environmental drivers and physiological responses will help managers anticipate future changes for Sockeye Salmon at the northern edge of their distribution.

Alaska↗

USGS2019

Functional divergence of thyrotropin beta-subunit paralogs gives new insights into salmon smoltification metamorphosis

Smoltification is a metamorphic event in salmon life history, which initiates downstream migration and pre-adapts juvenile salmon for seawater entry. While a number of reports concern thyroid hormones and smoltification, few and inconclusive studies have addressed the potential role of thyrotropin (TSH). TSH is composed of a α-subunit common to gonadotropins, and a β-subunit conferring hormone specificity. We report the presence and functional divergence of duplicated TSH β-subunit paralogs (tshβa and tshβb) in Atlantic salmon. Phylogeny and synteny analyses allowed us to infer that they originated from teleost-specific whole genome duplication. Expression profiles of both paralogs in the pituitary were measured by qPCR throughout smoltification in Atlantic salmon from the endangered Loire-Allier population raised at the Conservatoire National du Saumon Sauvage. This revealed a striking peak of tshβb expression in April, concomitant with downstream migration initiation, while tshβa expression remained relatively constant. In situ hybridization showed two distinct pituitary cell populations, tshβa cells in the anterior adenohypophysis, and tshβb cells near to the pituitary stalk, a location comparable to the pars tuberalis TSH cells involved in seasonal physiology and behaviour in birds and mammals. Functional divergence of tshβ paralogs in Atlantic salmon supports a specific role of tshβb in smoltification.

Scientific Reports↗

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

Characterization of smoltification in the Tasmanian strain of Atlantic salmon (Salmo salar) in recirculation and flowthrough systems

This study examined morphological, physiological and molecular indicators of smoltification in Atlantic salmon (Salmo salar) juveniles in a flow-through (FT) and recirculating aquaculture system (RAS). Fish were exposed to 24-h light to initiate smoltification, for 5 (FT) and 7 (RAS) weeks prior to transfer from freshwater (FW) to seawater (SW) and were sampled weekly preceding and following SW transfer. Mass, length, condition factor, plasma chloride, gill Na+/K+-ATPase (NKA) activity and expression of salinity-specific isoforms of NKA mRNA transcripts were monitored. Fish raised in FT had significantly lower specific growth rate (SGR) in FW than in SW and showed a significant 5-6-fold increase in gill NKA activity, and high plasma chloride levels after transfer to SW. These fish also exhibited no significant reduction in relative mRNA expression of NKAα-1a in FW but a sharp significant downregulation post-SW transfer. No significant increase in NKAα-1b was seen until week 8 (3 weeks post-SW transfer). The log2 ratio of NKAα-1b to NKAα-1a showed a significant 8-fold increase throughout the experiment. Fish raised in the RAS had significantly higher SGR in FW than SW, and showed significantly higher plasma chloride in saltwater challenged fish compared to the freshwater control at all weeks during the FW phase. Fish had a 50% higher initial NKA activity than in FT, increasing significantly 2-3-fold and showed an immediate down-regulation of NKAα-1a after exposure to 24-hr light in FW, and a further reduction after SW-transfer. There was no significant increase in NKAα-1b in the RAS-raised fish for the duration of the experiment, and there was a significant 8-fold increase in log2 ratio of NKAα-1b to NKAα-1a. Whilst there were too many varying factors to statistically compare hatchery type in this study, it’s evident that there are potentially system-related effects worthy of future investigation.

Aquaculture↗

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↗

USGS2019

The emerging contaminant 3,3’-dichlorobiphenyl (PCB-11) impedes Ahr activation and Cyp1a activity to modify embryotoxicity of Ahr ligands in the zebrafish embryo model (Danio rerio)

Background: 3,3’-Dichlorobiphenyl (PCB-11) is a non-legacy PCB congener widely detected in environmental samples and has been detected in human serum, but its toxicity potential is poorly understood. Objectives: We measured PCB-11 in wild caught fish and assessed its embryotoxicity and interactions with the aryl hydrocarbon receptor (Ahr) pathway in developing zebrafish (Danio rerio). Methods: PCB-11 was measured in wild freshwater fish from a river in Western Massachusetts. In the laboratory, zebrafish embryos were exposed to 45 µg/L, 450 µg/L, or 4,500 µg/L PCB-11 from 24-96 hours post fertilization (hpf), when they were assessed for gross morphology and Cyp1a activity using the in vivo EROD bioassay. Ahr pathway interactions were probed by co-exposing zebrafish to the Ahr agonists PCB-126 and the model PAH beta-naphthoflavone (BNF). Liver development was assessed using the Tg(gut:GFP) zebrafish line. Zebrafish exposed to 4,500 µg/L PCB-11 were also collected at 96 hpf for qRT-PCR, RNAseq, and histology. Results: Environmental concentrations of PCB-11 ranged from 103.0-136.0 ng/kg wet weight in wild fish tissue. Exposure to PCB-11 alone mildly affected EROD activity but did not affect gross morphology. However, 4,500 µg/L PCB-11 alone altered the expression of xenobiotic metabolism and liver development genes, impeded liver development, and increased vacuole formation in histology sections. In co-exposures, 4,500 µg/L PCB-11 prevented deformities caused by PCB-126 but exacerbated deformities in co-exposures with BNF. Discussion: PCB-11 is present in wild fish caught near a paper recycling facility in Western Massachusetts. Higher concentrations that may be present elsewhere such as the 4,500 µg/L PCB-11 concentration tested in zebrafish, can affect liver development, act as both a partial agonist/antagonist of the Ahr pathway, and act as an antagonist of Cyp1a activity to modify the toxicity of compounds that interact with the Ahr pathway.

Environmental Pollution↗

USGS2019

Functional characterization and osmoregulatory role of the Na+/K+/2Cl--cotransporter (NKCC1) in the gill of sea lamprey (Petromyzon marinus), a basal vertebrate

The present study provides molecular and functional characterization of Na+/K+/2Cl- cotransporter (nkcc1/NKCC1) in the gills of sea lamprey, the most basal extant vertebrate with an osmoregulatory strategy. We report the full-length peptide sequence for the lamprey NKCC1, which we show to group strongly with and occupy a basal position among other vertebrate NKCC1 sequences. Lamprey nkcc1 mRNA were present in many tissues but was 5-fold higher in the gill than any other tissue. NKCC1 protein was only detected in the gill. Gill mRNA and protein abundances of NKCC1 and Na+/K+-ATPase (NKA) were significantly upregulated (20- to 200-fold) in late metamorphosis in freshwater, coinciding with the development of salinity tolerance, and were upregulated an additional 2-fold after acclimation to seawater. Immunohistochemistry revealed that NKCC1 in the gill is found in filamental ionocytes that develop during metamorphosis. Lamprey treated with bumetanide, a widely used pharmacological inhibitor of NKCC1, exhibited higher plasma Cl- and osmolality and reduced muscle water content after 24 h in seawater, but had no effect in FW. This work provides the first functional characterization of NKCC1 as having a functional role mechanism for branchial salt secretion in lampreys, providing evidence that this mode of Cl- secretion has been present among vertebrates for ~550 million years.

American Journal of Physiology - Regulatory, Integ↗

USGS2019

Evidence for a role of arginine vasotocin (AVT) receptors in the gill during salinity acclimation by a euryhaline teleost fish

The neurohypophysial nonapeptide arginine vasotocin (AVT) plays a role in regulation of osmotic balance in teleost fishes, but its mechanisms of action are not fully understood. Recently, is was discovered that nonapeptide receptors differentiated into V1a-type, several V2-type, and two isotocin (IT) receptor paralogs in teleost fishes, and it remains unclear which of these nonapeptide receptors mediate AVT’s action on gill osmoregulation. Here, we examine the role of nonapeptide receptors in gill osmoregulation by examining the transcriptional responses of gill nonapeptide receptors in euryhaline Amargosa pupfish (Cyprinodon nevadensis) acclimated to 7.5 ppt salinity, and then transferred to fresh water (0.3 ppt), seawater (35 ppt), or hypersaline (55 ppt) conditions. Transcript abundance of the teleost V1a-type receptor v1a2 was up-regulated over 4-fold in gill 24 h after transfer of fish from 7.5 ppt to 35 ppt or 55 ppt, and down-regulated upon transfer to 0.3 ppt, but returned to baseline levels by 14 d after transfer when fish had re-established osmolality. Transcripts for the nonapeptide degradation enzyme leucyl-cystinyl aminopeptidase (LNPEP) also increased in the gill of fish acclimating to 35 ppt, but returned to baseline levels by 14 d. To test whether AVT’s effects on the gill might be mediated by a V1a-type receptor, we also administered exogenous AVT or a V1-type receptor antagonist (Manning compound) to pupfish acclimated to 7.5 ppt prior to transfer of fish to 0.4 ppt or 35 ppt. AVT inhibited the increase in gill Na+/Cl- cotransporter 2 (ncc2) mRNA abundance that occurs when fish are transferred to hypo-osmotic environments, and V1-type receptor antagonism increased mRNA levels for ncc2 even without a change in salinity. Pupfish transferred to 35 ppt also exhibited elevated gill mRNA abundance for cystic fibrosis transmembrane conductance regulator (cftr), which diminished under V1-receptor inhibition. Taken together, these findings provide evidence for AVT acting via a V1-type receptor to regulate gill Cl- transport by inhibiting Cl- uptake and facilitating Cl- secretion during seawater acclimation.

American Journal of Physiology - Regulatory, Integ↗

USGS2018

Effects of ocean acidification on salinity tolerance and seawater growth of Atlantic salmon Salmo salar smolts

Human activity has resulted in increasing atmospheric carbon dioxide (CO 2 ), which will result in reduced pH and higher levels of CO 2 in the ocean, a process known as ocean acidification. Understanding the effects of ocean acidification (OA) on fishes will be important to predicting and mitigating its consequences. Anadromous species such as salmonids may be especially at risk because of their rapid movements between fresh water and seawater, which could minimize their ability to acclimate. In the present study, we examine the effect of future OA on the salinity tolerance and early seawater growth of Atlantic salmon Salmo salar smolts. Exposure to 610 and 1010 μatm CO 2 did not alter salinity tolerance but did result in slightly lower plasma chloride levels in smolts exposed to seawater compared with controls (390 μatm). Gill Na + –K + ‐ATPase activity, plasma cortisol, glucose and haematocrit after seawater exposure were not altered by elevated CO 2 . Growth rate in the first 2 weeks of seawater exposure was greater at 1010 μatm CO 2 than under control conditions. This study of the effects of OA on S. salar during the transition from fresh water to seawater indicates that elevated CO 2 is not likely to affect osmoregulation negatively and may improve early growth in seawater.

Journal of Fish Biology↗

USGS2018

Effects of elevated temperature on osmoregulation and stress responses in Atlantic salmon (Salmo salar) smolts in freshwater and seawater

Smolting in Atlantic salmon Salmo salar is a critical life‐history stage that is preparatory for downstream migration and entry to seawater that is regulated by abiotic variables including photoperiod and temperature. The present study was undertaken to determine the interaction of temperature and salinity on salinity tolerance, gill osmoregulatory proteins and cellular and endocrine stress in S. salar smolts. Fish were exposed to rapid changes in temperature (from 14 to 17, 20 and 24°C) in fresh water (FW) and seawater (SW), with and without prior acclimation and sampled after 2 and 8 days. Fish exposed simultaneously to SW and 24°C experienced 100% mortality, whereas no mortality occurred in any of the other groups. The highest temperature also resulted in poor ion regulation in SW with or without prior SW acclimation, whereas no substantial effect was observed in FW. Gill Na + –K + ‐ATPase (NKA) activity increased in SW fish compared to FW fish and decreased with high temperature in both FW and SW. Gill Nkaα1a abundance was high in FW and Nkaα1b and Na + –K + ‐2Cl‐ cotransporter high in SW, but all three were lower at the highest temperature. Gill Hsp70 levels were elevated in FW and SW at the highest temperature and increased with increasing temperature 2 days following direct transfer to SW. Plasma cortisol levels were elevated in SW at the highest temperature. Our results indicate that there is an important interaction of salinity and elevated temperature on osmoregulatory performance and the cellular stress response in S. salar , with an apparent threshold for osmoregulatory failure in SW above 20°C.

Journal of Fish Biology↗