Saltwater Acclimation Research Articles

Does the loss of diadromy imply the loss of salinity tolerance? A gene expression study with replicate nondiadromous populations of Galaxias maculatus.

The recurrent colonization of freshwater habitats and subsequent loss of diadromy is a major ecological transition that has been reported in many ancestrally diadromous fishes. Such residency is often accompanied by a loss of tolerance to seawater. The amphidromous Galaxias maculatus has repeatedly colonized freshwater streams with evidence that freshwater-resident populations exhibit stark differences in their tolerance to higher salinities. Here, we used transcriptomics to gain insight into the mechanisms contributing to reduced tolerance to higher salinities in freshwater resident populations. We conducted an acute salinity challenge (0ppt to 23-25 ppt) and measured osmoregulatory ability (muscle water content) over 48 h in three populations: diadromous, saltwater intolerant resident (Toltén), and saltwater tolerant resident (Valdivia). RNA sequencing of the gills identified genes that were differentially expressed in association with the salinity change and associated with the loss of saltwater tolerance in the Toltén population. Key genes associated with saltwater acclimation were characterized in diadromous G. maculatus individuals, some of which were also expressed in the saltwater tolerant resident population (Valdivia). We found that some of these "saltwater acclimation" genes, including the cystic fibrosis transmembrane conductance regulator gene (CFTR), were not significantly upregulated in the saltwater intolerant resident population (Toltén), suggesting a potential mechanism for the loss of tolerance to higher salinities. As the suite of differentially expressed genes in the diadromous-resident comparison differed between freshwater populations, we hypothesize that diadromy loss results in unique evolutionary trajectories due to drift, so the loss of diadromy does not necessarily lead to a loss in upper salinity tolerance.

The effects of diazinon on the cell types and gene expression of the olfactory epithelium and whole-body hormone concentrations in the Persian sturgeon (Acipenser persicus)

The olfactory function and imprinting of odorant information of the native stream play a critical role during the homing migration in fish. Pesticides may impair olfactory imprinting by altering olfaction and hormone functions. The present study aimed to determine how diazinon impacts olfactory epithelium morphology and cell composition, as well as hormone concentrations in Persian sturgeon (Acipenser persicus) during their lifetime in freshwater and, also during diazinon-free saltwater acclimation. Fingerlings were exposed to 0, 150, 300, and 450 μg·L−1 of diazinon in freshwater for 7 days and then were transferred to diazinon-free saltwater by gradually increasing salinity up to 12 ppt. After diazinon exposure, the number of olfactory receptor cells (ORCs) and goblet cells (GCs) decreased and increased, respectively, and the expression of G-protein αolf (GPαolf) and calmodulin-dependent kinase II delta (CAMKIId) was down-regulated and up-regulated, respectively. Transferring the fish to diazinon-free saltwater (8 and 12 ppt) raised the number of ORCs, supporting cells (SCs), GCs, and GPαolf expression, and down-regulated CAMKIId without any significant differences among treatments. Exposure to diazinon increased whole-body cortisol at the high concentration, while decreased whole-body thyroxin (T4) and triiodothyronine (T3) in a dose-dependent manner. Although whole-body T4 and T3 increased in all the treatments after saltwater acclimation (8 and 12 ppt), the level of these hormones was lower in fish that had been exposed to diazinon than in the control. These results showed that diazinon can disrupt olfactory epithelium morphology and cell composition as well as hormone concentrations, which in turn may affect the olfactory imprinting in Persian sturgeon fingerlings.

Salt-water acclimation of the estuarine crocodile Crocodylus porosus involves enhanced ion transport properties of the urodaeum and rectum.

Estuarine crocodiles, Crocodylus porosus, inhabit freshwater, estuarine and marine environments. Despite being known to undertake extensive movements throughout and between hypo-osmotic and hyperosmotic environments, little is known about the role of the cloaca in coping with changes in salinity. We report here that, in addition to the well-documented functional plasticity of the lingual salt glands, the middle of the three cloacal segments (i.e. the urodaeum) responds to increased ambient salinity to enhance solute-coupled water absorption. This post-renal modification of urine serves to conserve water when exposed to hyperosmotic environments and, in conjunction with lingual salt gland secretions, enables C. porosus to maintain salt and water balance and thereby thrive in hyperosmotic environments. Isolated epithelia from the urodaeum of 70% seawater-acclimated C. porosus had a strongly enhanced short-circuit current (an indicator of active ion transport) compared with freshwater-acclimated crocodiles. This enhanced active ion absorption was driven by increased Na+/K+-ATPase activity, and possibly enhanced proton pump activity, and was facilitated by the apical epithelial Na+ channel (ENaC) and/or the apical Na+/H+ exchanger (NHE2), both of which are expressed in the urodaeum. NHE3 was expressed at very low levels in the urodaeum and probably does not contribute to solute-coupled water absorption in this cloacal segment. As C. porosus does not appear to drink water of salinities above 18ppt, observations of elevated short-circuit current in the rectum as well as a trend for increased NHE2 expression in the oesophagus, the anterior intestine and the rectum suggest that dietary salt intake may stimulate salt and possibly water absorption by the gastrointestinal tract of C. porosus living in hyperosmotic environments.

The physiology of saltwater acclimation in large juvenile Atlantic salmon Salmo salar.

The present study investigated the effects of transferring freshwater (FW) acclimated S. salar (678 g) that had been maintained under a constant photoperiod and thermal regime, into FW (salinity 0) and salt water (SW; salinity 35) on growth and physiological responses over a 28 day period. There were no mortalities observed throughout the study and no significant differences in mass or fork length between FW and SW groups after 28 days. Compared with fish transferred to FW, plasma osmolality and plasma chloride levels increased significantly in fish in SW by day 1. In the SW group, plasma chloride and osmolality had decreased significantly at day 14 when compared with day 1. Na+ -K+ -ATPase activity was significantly higher in SW compared with the FW group from day 7 and thereafter, but continued to increase until day 22. No differences in plasma cortisol and thyroxine were observed between FW and SW groups throughout the study. Plasma glucose significantly increased from day 1 to day 2 in SW but not in the FW group and levels were significantly reduced in SW compared with the FW group at day 28. Plasma cholesterol and triglyceride levels were significantly higher in FW at day 22 and day 14 to day 22, respectively, when compared with the SW group. In the SW group, plasma cholesterol and triglyceride levels did not change significantly throughout the study. The findings of this study suggest that large S. salar retained in FW maintain a high level of SW tolerance in the absence of photoperiod and thermal regimes necessary for smoltification, as demonstrated by 100% survival, unaffected growth performance, increased Na+ -K+ -ATPase activity and a capacity to regulate plasma chloride and osmolality for 28 days in the SW group.

Structural lipid changes and Na+/K+-ATPase activity of gill cells' basolateral membranes during saltwater acclimation in sea lamprey (Petromyzon marinus, L.) juveniles

Seawater acclimation is a critical period for anadromous species and a process yet to be understood in lampreys. Considering that changes in lipid composition of the gill cells' basolateral membranes may disrupt the major transporter Na+K+-ATPase, the goal of this study was to detect changes at this level during juvenile sea lamprey seawater acclimation. The results showed that saltwater acclimation has a direct effect on the fatty acid composition of gill cells basolateral membrane's phospholipids. When held in full-strength seawater, the fatty acid profile of basolateral membrane's phospholipids suffered a restructure by increasing either saturation or the ratio between oleic acid and eicosapentaenoic acid. Simultaneously, the activity of Na+K+-ATPase revealed a significant and positive correlation with basolateral membrane's cholesterol content in the presence of highest salinity. Our results pointed out for lipid adjustments involving the functional transporter present on the gill cell basolateral membranes to ensure the role played by branchial Na+K+-ATPase in ion transport during saltwater acclimation process. The responses observed contributed to the strategy adopted by gill cell's basolateral membranes to compensate for osmotic and ionic stressors, to ensure the success of the process of seawater acclimation associated with the downstream trophic migration of juvenile sea lamprey.

Effects of salinity acclimation on the endocrine disruption and acute toxicity of bifenthrin in freshwater and euryhaline strains of Oncorhynchus mykiss

The pyrethroid insecticide bifenthrin is frequently detected at ng/L concentrations in tributaries of the San Francisco Bay Delta. The estuary is also experiencing increasing salinity through climate change and water redirection. To evaluate the impacts of hypersaline conditions on bifenthrin toxicity in anadromous salmonids of the San Francisco Bay Delta (CA, USA), a 14-d laboratory exposure was performed using 2 strains of Oncorhynchus mykiss (rainbow trout and steelhead) acclimated to freshwater and to 8 g/L and 17 g/L salinity. The fish were then exposed to nominal concentrations of 0 µg/L, 0.1 µg/L, and 1.5 µg/L bifenthrin. Rainbow trout exhibited significant mortality following exposure to 1.5 µg/L (1.07 ± 0.35 µg/L measured) bifenthrin in freshwater. Elevated levels of Na⁺ /K⁺ adenosine triphosphatase α1A mRNA subunit expression was observed in the gill of rainbow trout acclimated to hypersaline conditions relative to freshwater animals. No significant difference was noted in Na⁺ /K⁺ adenosine triphosphatase subunit levels in brains of either strain in freshwater or hypersaline conditions. Likewise, significant differences were not observed in plasma vitellogenin or steroid hormone concentrations in either strain whether maintained in freshwater or saltwater. Saltwater acclimation significantly reduced nicotinamide adenine dinucleotide phosphate-catalyzed biotransformation of bifenthrin in liver microsomes of rainbow trout but not of steelhead. The present study showed that, relative to steelhead, rainbow trout have different responses to bifenthrin acute toxicity as well as different rates of hepatic bifenthrin biotransformation and regulation of Na⁺ /K⁺ adenosine triphosphatase subunits in gills. These data indicate that significant differences exist between the strains and that animal life history may have important effects on the susceptibility of each strain to environmental contaminants.

The effects of the pyrethroid insecticide, bifenthrin, on steroid hormone levels and gonadal development of steelhead (Oncorhynchus mykiss) under hypersaline conditions

The San Francisco Bay Estuary and Sacramento-San Joaquin Delta (Bay-Delta) is an important breeding and nursery ground for fish. Of particular interest are salmonids that migrate through fresh and saltwater areas polluted with various contaminants including bifenthrin, a widely used pyrethroid insecticide. Male steelhead (Oncorhynchus mykiss) exposed to bifenthrin (0.1 and 1.5μg/L) for two weeks had a lower gonadosomatic index (GSI) in freshwater but were not affected by concurrent bifenthrin exposure and saltwater acclimation. Plasma estradiol-17β (E2) levels and ovarian follicle diameter of fish exposed to bifenthrin (0.1 and 1.5μg/L) in freshwater significantly increased. Under hypersaline conditions, fish exposed to bifenthrin had significantly reduced E2 levels and smaller follicles, and unhealthy ovarian follicles were observed. Given the occurrence of bifenthrin in surface waters of the Bay Delta, understanding the impact of bifenthrin on wildlife is necessary for improving risk assessments of pyrethroids in this important ecosystem.

Time course of saltwater adaptation in Spotted Scat (Scatophagus argus) (Pisces): A histomorphometric approach

Freshwater acclimatized spotted scat (Scatophagus argus) adults were adapted to 5, 10, 20 or 30 g/l seawater and observed for morphometric changes in gill and kidney histology at time points 1, 2, 10, 15 and 30 days. The overall histomorphological changes displayed by gill and kidney suggest two different phases of successful saltwater acclimation: an adaptive phase with adjustments in the abundance of gill chloride cells and renal collecting tubules, the diameter of glomerulus and collecting tubules, and the thickness of the muscular tissue of the collecting tubules; this gives way to a period with no further significant morphometric modifications.

The effects of saltwater acclimation on Na–K–2Cl and Na–K-ATPase distribution, activity and gene expression in salt glands of the estuarine crocodile

The estuarine crocodile, Crocodylus porosus utilises lingual salt glands to excrete excess NaCl accumulated whilst living in saline environments. In avian salt gland models, Na–K-ATPase (NKA) is essential for the maintenance of the electrochemical gradients which facilitate the secretory activity of other ion pumps, while Na–K–2Cl (NKCC) functions to pump Na+ and K+ into the paracellular space, in exchange for Cl− which is transported into the cell. We have investigated the effects of chronic saltwater acclimation on the distribution, activity and gene expression patterns of both NKA and NKCC in the crocodilian salt gland. Using immunohistochemistry, both NKA and NKCC were localized to the basolateral membranes of salt gland secretory cells in both freshwater (fw) and saltwater (sw) acclimated salt gland tissues. The intensity of staining was slightly, but significantly, higher in tissues from SW-acclimated animals. Western blotting indicated that there was an increase in NKA and NKCC abundances in SW-acclimated tissues. The relative metabolic costs associated with these two pumps were investigated in vitro. While there were no differences between fw- and sw-acclimated tissues in the relative costs associated with NKA activity, NKCC activity was almost 50% higher in SW-acclimated tissues. We are currently exploring patterns of NKA and NKCC gene expression in sw- and fw-acclimated animals. This study has demonstrated the presence of NKA and NKCC in the salt glands of C. porosus and has shown that the activity and abundance of these transporters can be influenced by prolonged saltwater acclimation. Copyright © 2008 Published by Elsevier Inc.

Effect of cortisol on some osmoregulatory parameters of the teleost, Oreochromis niloticus L., after transference from freshwater to seawater

This trial was conducted in order to determine the effects of cortisol on salt water acclimation of tilapia Oreochromis niloticus (L.). Tilapia (n=42) were injected intraperitoneally with cortisol and then were directly transferred from freshwater (FW) to 15‰ salt water (SW). Changes in plasma osmolality, chloride ion concentration (Cl-), plasma level of cortisol and gill Na+, K+-ATPase activity were measured at 6, 12, 24, 48, 72 and 168 hours after transference to 15‰ SW. Plasma osmolality and Cl- increased immediately after transference until 12-24 h. The fish injected with cortisol (F) showed higher plasma levels of cortisol than those from control group (C) that maintained the initial levels during the experiment. Gill Na+, K+-ATPase activity of C fish began to increase at first hours after transference and peak at 48h. The differences between gill Na+, K+-ATPase activity of F and C groups were significant (P<0.05) in FW, which confirm the effect of exogenous cortisol.

Ammonia excretion and urea handling by fish gills: present understanding and future research challenges.

In fresh water fishes, ammonia is excreted across the branchial epithelium via passive NH(3) diffusion. This NH(3) is subsequently trapped as NH(4)(+) in an acidic unstirred boundary layer lying next to the gill, which maintains the blood-to-gill water NH(3) partial pressure gradient. Whole animal, in situ, ultrastructural and molecular approaches suggest that boundary layer acidification results from the hydration of CO(2) in the expired gill water, and to a lesser extent H(+) excretion mediated by apical H(+)-ATPases. Boundary layer acidification is insignificant in highly buffered sea water, where ammonia excretion proceeds via NH(3) diffusion, as well as passive NH(4)(+) diffusion due to the greater ionic permeability of marine fish gills. Although Na(+)/H(+) exchangers (NHE) have been isolated in marine fish gills, possible Na(+)/NH(4)(+) exchange via these proteins awaits evaluation using modern electrophysiological and molecular techniques. Although urea excretion (J(Urea)) was thought to be via passive diffusion, it is now clear that branchial urea handling requires specialized urea transporters. Four urea transporters have been cloned in fishes, including the shark kidney urea transporter (shUT), which is a facilitated urea transporter similar to the mammalian renal UT-A2 transporter. Another urea transporter, characterized but not yet cloned, is the basolateral, Na(+) dependent urea antiporter of the dogfish gill, which is essential for urea retention in ureosmotic elasmobranchs. In ureotelic teleosts such as the Lake Magadi tilapia and the gulf toadfish, the cloned mtUT and tUT are facilitated urea transporters involved in J(Urea). A basolateral urea transporter recently cloned from the gill of the Japanese eel (eUT) may actually be important for urea retention during salt water acclimation. A multi-faceted approach, incorporating whole animal, histological, biochemical, pharmacological, and molecular techniques is required to learn more about the location, mechanism of action, and functional significance of urea transporters in fishes.

Morphology and innervation of the buccal glands of the southern hemisphere lamprey, Geotria australis

The buccal glands of adults of the Southern Hemisphere lamprey Geotria australis consist of a pair of small, bean-shaped, hollow sacs, embedded within the basilaris muscle in the region below the eyes and to either side of the piston cartilage. Each gland, which is lined by a simple columnar epithelium and surrounded by an incomplete layer of skeletal muscle, discharges its contents into the oral cavity via a long, narrow duct. In downstream migrating young adults, the epithelial cells are low columnar, intermediate in electron density, and contain dark-staining inclusions and numerous lipid-like droplets. After saltwater acclimation, the epithelial cells become taller and the numbers of dark-staining inclusions increase whereas those of lipid-like droplets decline. By the end of the marine phase, the epithelium is more folded and now also contains dark and light cells. The ultrastructure of the epithelium shows the characteristics of both apocrine and merocrine secretion. Although intra-epithelial nerve endings were not observed, axons and occasional neurons are present in the lamina propria. Since the skeletal muscle capsule is also well innervated and contains neurons, a local feed-back mechanism may regulate the release of buccal gland fluid by monitoring the luminal pressure. Contractions of the skeletal muscle capsule and movements of the basilaris muscle during feeding would presumably assist the movement of secretion along the duct. The secretion possesses anticoagulating and haemolytic properties.

Role of the Lower Intestine in the Adaptation of Gulls (Larus Glaucescens) to Sea Water

ABSTRACT We used in vivo perfusion of the lower intestine (colon plus coprodeum) to examine the osmoregulatory role of that organ in glaucous-winged gulls (Larus glaucescens Naum.) drinking sea water and fresh water. The area of the lower intestine was small, 0·59 cm2 100g-1 body mass. Its electrolyte and water transport rates were unaffected by salt water acclimation. Sodium and chloride were always reabsorbed from the intestinal lumen to the plasma. The maximum sodium transport rate we measured was 37μlequivcm-2h-1, from a sodium concentration of 200 mequiv l-1. Potassium transport from the different perfusion fluids differed, and was generally negatively correlated with sodium transport, suggesting some form of sodium-potassium exchange. Solute-linked water was reabsorbed at a rate of 3·5 μlμequiv-1 Na+, permitting the lower intestinal epithelium to maintain a luminal fluid up to 130mosmolkg-1 hyperosmotic to plasma. The serosal-to-mucosal osmotic permeability coefficient of the lower intestinal epithelium was 0·21 μlcm-2h-1 (mosmolkg-1)-1. Ureteral urine from birds in both groups was usually strongly (up to 250mosmolkg-1) hypertonic to plasma, but sodium, potassium and chloride concentrations were low and constituted less than 25 % of total osmolytes. We suggest that the lower intestine of L. glaucescens does not play a major role in reclaiming urinary water and electrolytes for recycling to the salt glands.

The biokinetic behavior of 95mTc in juvenile Coho Salmon, Oncorhynchus kisutch (Walbaum)

Juvenile coho salmon, Onchorynchus kisutch, were exposed to 95mTc in both saltwater and freshwater to study the biokinetic behavior of this element in an anadromous fish. In freshwater, equilibrium whole-body concentration factors (CF 5) ranged from 28 to 32 in two separate experiments, in sharp contrast to an equilibriumCF of < 5 in saltwater. While the uptake kinetics were unimodal in saltwater, in freshwater, biomodal uptake kinetics were observed. Technetium-95m retention was biphasic in freshwater depuration experiments, an initial rapid loss of 21% to 26% of the steady-state activity with an elimination half-life of 3 to 5 days was followed by a slower loss rate, with a whole-body elimination half-life ranging from 23 to 33 days. In saltwater, retention was monophasic with an elimination half-life of 5–16 days. Dramatic decreases in 95mTc body burdens when freshwater-labeled fish are transferred to Tc-labeled saltwater indicate that the changes in physiology accompanying saltwater acclimation lead to the loss of 95mTc.

Electrolyte excretion by the salt gland of the Galapagos marine iguana

Electrolyte excretion by the salt gland of the Galapagos marine iguana

Salt gland secretion in the pelagic sea snake Pelamis.

ARTICLESSalt gland secretion in the pelagic sea snake PelamisW DunsonW DunsonPublished Online:01 Dec 1968https://doi.org/10.1152/ajplegacy.1968.215.6.1512MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Download PDF FiguresReferencesRelatedInformationCited ByEcophysiological steps of marine adaptation in extant and extinct non‐avian tetrapods26 April 2021 | Biological Reviews, Vol. 96, No. 5Biocomposites and Mineralized Tissues27 October 2014Hypernatremia in Dice Snakes (Natrix tessellata) from a Coastal Population: Implications for Osmoregulation in Marine Snake Prototypes21 March 2014 | PLoS ONE, Vol. 9, No. 3Variations of natremia in sea kraits (Laticauda spp.) kept in seawater and fresh waterComparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, Vol. 166, No. 2Salinity influences the distribution of marine snakes: implications for evolutionary transitions to marine life16 April 2012 | Ecography, Vol. 35, No. 11Dehydration and Drinking Responses in a Pelagic Sea Snake17 April 2012 | Integrative and Comparative Biology, Vol. 52, No. 2Activity, abundance, distribution and expression of Na+/K+-ATPase in the salt glands of Crocodylus porosus following chronic saltwater acclimationJournal of Experimental Biology, Vol. 213, No. 8Osmotic and Ionic Regulation in Reptiles5 February 2014Thirsty sea snakes forsake refuge during rainfallAustral Ecology, Vol. 33, No. 7The effects of saltwater acclimation on neurotransmitters in the lingual salt glands of the estuarine crocodile, Crocodylus porosusRegulatory Peptides, Vol. 140, No. 1-2Nitrogen metabolism and excretion in the aquatic chinese soft-shelled turtle,Pelodiscus sinensis, exposed to a progressive increase in ambient salinity1 January 2006 | Journal of Experimental Zoology Part A: Comparative Experimental Biology, Vol. 305A, No. 12Extrarenal Mechanisms in Hydromineral and Acid‐Base Regulation in Aquatic Vertebrates1 January 2011Fine Structure, Innervation, and Functional Control of Avian Salt GlandsCONTROL OF SECRETION IN REPTILIAN SALT GLANDSAdaptation to fresh water in the sea snake Hydrophis cyanocinctus: Tissue electrolytes and peripheral corticosteroidsGeneral and Comparative Endocrinology, Vol. 36, No. 4The venom and venom apparatus of the sea snake Lapemis hardwicki Gray28 June 2008 | Zoological Journal of the Linnean Society, Vol. 63, No. 4PHYSIOLOGYSodium balance in the green turtle,Chelonia mydas, in seawater and freshwaterJournal of Comparative Physiology ? B, Vol. 107, No. 2Sea snake skin: Permeable to water but not to sodiumJournal of Comparative Physiology ? B, Vol. 108, No. 3Osmoregulation and pituitary-adrenal function in desert reptilesGeneral and Comparative Endocrinology, Vol. 25, No. 2The Supraorbital Glands of Pygoscelid PenguinsThe relation between plasma Na concentration and salt gland Na?K ATPase content in the diamondback terrapin and the yellow-bellied sea snakeJournal of Comparative Physiology ? B, Vol. 101, No. 2Convergent evolution of sublingual salt glands in the marine file snake and the true sea snakesJournal of Comparative Physiology, Vol. 86, No. 3Studies on the control of electrolyte excretion by the nasal gland of the lizard Dipsosaurus dorsalisComparative Biochemistry and Physiology Part A: Physiology, Vol. 42, No. 3Excretion of urate salts by reptilesComparative Biochemistry and Physiology Part A: Physiology, Vol. 41, No. 3The endocrine control of water and electrolyte metabolism in desert reptilesGeneral and Comparative Endocrinology, Vol. 3Sea Snakes: An Unusual Salt Gland under the TongueScience, Vol. 173, No. 3995Water and electrolyte balance of the desert iguana, dipsosaurus dorsalis, in its natural habitatComparative Biochemistry and Physiology, Vol. 35, No. 4Some aspects of electrolyte and water balance in three estuarine reptiles, the diamondback terrapin, American and “salt water” crocodilesComparative Biochemistry and Physiology, Vol. 32, No. 2 More from this issue > Volume 215Issue 6December 1968Pages 1512-1517 Copyright & PermissionsCopyright © 1968 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1968.215.6.1512PubMed5723013History Published online 1 December 1968 Published in print 1 December 1968 Metrics