La osmoregulación como factor potencial de la distribución diferencial de dos especies crípticas de góbido, Pomatoschistus microps y P. marmoratus, en las lagunas mediterráneas francesas

This study was aimed at the detection of potential differences in the osmoregulatory capacity of two cryptic species of gobies, Pomatoschistus microps (Krøyer, 1838) and P. marmoratus (Risso, 1810), that have different distributions in French Mediterranean lagoons characterised by different salinity regimes. Specimens of both species were experimentally exposed to different salinities, their salinity tolerance was evaluated and their blood osmolality was measured. Both species are strong osmoregulators over a wide range of salinities but P. microps showed higher performances of hyper-regulation at very low salinities (10 and 40 mosm/kg, i.e. freshwater 0.3 and 1.4) and of hypo-regulation at high salinities (1500 mosm/kg, 51). Only P. microps was able to tolerate freshwater exposure over 4 days. We conclude that the high osmoregulatory capacity found in P. microps is linked to its better survival at very low salinities and is a physiological requirement for living in areas such as the Mauguio lagoon where salinity is highly variable. In contrast, as osmoregulation of P. marmoratus is less efficient at extreme salinities, this species cannot colonise such environments and is restricted to habitats where salinity is more stable, such as the Thau lagoon.Este estudio tuvo por objeto la detección de diferencias potenciales en la capacidad osmorreguladora de dos especies crípticas de góbido, Pomatoschistus microps (Krøyer, 1838) y P. marmoratus (Risso, 1810), que presentan diferentes áreas de distribución en lagunas mediterráneas francesas caracterizadas por regímenes de salinidad distintos. Especímenes de ambas especies fueron expuestos experimentalmente a diferentes salinidades, evaluándose su tolerancia a la salinidad y midiéndose su osmolalidad sanguínea. Ambas especies tienen una amplia capacidad osmoreguladora en un amplio rango de salinidades. Sin embargo, en comparación con P. marmoratus, P. microps mostró mayores rendimientos hiper-regulatorios a salinidades muy bajas (10 y 40 mosm/kg, es decir agua dulce 0.3 y 1.4) e hipo-regulatorios a salinidades altas (1500 mosm/kg, 51). Sólo P. microps fue capaz de tolerar la exposición al agua dulce durante 4 días. Podemos concluir que la gran capacidad osmoreguladora encontrada en P. microps está ligada a su mayor supervivencia a salinidades muy bajas, siendo un requerimiento fisiológico para vivir en áreas tales como la laguna de Mauguio, donde la salinidad es muy variable. Por el contrario, puesto que la osmoregulación de P. marmoratus es menos eficiente en salinidades extremas, esta especie no puede colonizar tales ambientes y se ve restringida a hábitats donde la salinidad es más estable, como la laguna de Tha

Intestinal osmoregulatory mechanisms differ in Mediterranean and Atlantic European sea bass: A focus on hypersalinity

European sea bass (Dicentrarchus labrax) migrate towards habitats where salinity can reach levels over 60‰, notably in Mediterranean lagoons. D. labrax are genetically subdivided in Atlantic and Mediterranean lineages and have evolved in slightly different salinities. We compared Atlantic and West-Mediterranean populations regarding their capacity to tolerate hypersalinity with a focus on the involvement of the intestine in solute-driven water reabsorption. Fish were analyzed following a two-week transfer from seawater (SW, 36‰) to either SW or hypersaline water (HW, 55‰). Differences among lineages were observed in posterior intestines of fish maintained in SW regarding NKA activities and mRNA expressions of nkaα1a, aqp8b, aqp1a and aqp1b with systematic higher levels in Mediterranean sea bass. High salinity transfer triggered similar responses in both lineages but at different magnitudes which may indicate slight different physiological strategies between lineages. High salinity transfer did not significantly affect the phenotypic traits measured in the anterior intestine. In the posterior intestine however, the size of enterocytes and NKA activity were higher in HW compared to SW. In this tissue, nka-α1a, nkcc2, aqp8ab and aqp8aa mRNA levels were higher in HW compared to SW as well as relative protein expression of AQP8ab. For aqp1a, 1b, 8aa and 8b, an opposite trend was observed. The sub-apical localization of AQP8ab in enterocytes suggests its role in transepithelial water reabsorption. Strong apical NKCC2/NCC staining indicates an increased Na+ and Cl- reuptake by enterocytes which could contribute to solute-coupled water reuptake in cells where AQP8ab is expressed

Ion uptake pathways in European sea bass Dicentrarchus labrax

Ion uptake mechanisms are diverse in fish species, certainly linked to duplication events that have led to the presence of a multitude of paralogous genes. In fish, Na+ uptake involves several ion transporters expressed in different ionocyte subtypes. In the European sea bass Dicentrarchus labrax, several key transporters potentially involved in Na+ uptake have been investigated in seawater (SW) and following a 2 weeks freshwater (FW) acclimation. Using gel electrophoresis, we have shown that the Na+/H+-exchanger 3 (nhe3, slc9a3) is expressed in gills and kidney at both salinities. Quantitative realtime PCR analysis showed a significantly higher nhe3 expression in fresh water (FW) compared to SW. Its apical localization in a subset of gill ionocytes in freshwater-acclimated fish supports the role of NHE3 in Na+ uptake. Interestingly, NHE3-immunopositive cells also express basolateral Na+/K+/2Cl− cotransporter 1 (NKCC1) and are mainly localized in gill lamella. Among the three nhe2 (slc9a2) paralogs, only nhe2c shows differential branchial expression levels with higher mRNA levels in SW than in FW. The increased branchial expression of the ammonia transporter rhcg1 (Rhesus protein), nhe3 and cytoplasmic carbonic anhydrase (cac) in FW could indicate the presence of a functional coupling between ion transporters to form a Na+/NH4+ exchange complex. Acid-sensing ion channel 4 (asic4) seems not to be expressed in sea bass gills. Na+/Cl- cotransporter (ncc2a or ncc-like) is about three times more expressed in FW compared to SW suggesting coupled Na+ and Cl− uptake in a subset of gill ionocytes. Besides the main pump Na+/K+-ATPase, branchial NCC2a and NHE3 may be key players in ion uptake in sea bass following a long-term freshwater challenge

Mechanisms of Na+ uptake from freshwater habitats in animals

Life in fresh water is osmotically and energetically challenging for living organisms, requiring increases in ion uptake from dilute environments. However, mechanisms of ion uptake from freshwater environments are still poorly understood and controversial, especially in arthropods, for which several hypothetical models have been proposed based on incomplete data. One compelling model involves the proton pump V-type H+ ATPase (VHA), which energizes the apical membrane, enabling the uptake of Na+ (and other cations) via an unknown Na+ transporter (referred to as the “Wieczorek Exchanger” in insects). What evidence exists for this model of ion uptake and what is this mystery exchanger or channel that cooperates with VHA? We present results from studies that explore this question in crustaceans, insects, and teleost fish. We argue that the Na+/H+ antiporter (NHA) is a likely candidate for the Wieczorek Exchanger in many crustaceans and insects; although, there is no evidence that this is the case for fish. NHA was discovered relatively recently in animals and its functions have not been well characterized. Teleost fish exhibit redundancy of Na+ uptake pathways at the gill level, performed by different ion transporter paralogs in diverse cell types, apparently enabling tolerance of low environmental salinity and various pH levels. We argue that much more research is needed on overall mechanisms of ion uptake from freshwater habitats, especially on NHA and other potential Wieczorek Exchangers. Such insights gained would contribute greatly to our general understanding of ionic regulation in diverse species across habitats

Effect of combined stress (salinity and temperature) in European sea bass Dicentrarchus labrax osmoregulatory processes

International audienceEuropean sea bass Dicentrarchus Iabrax undertake seasonal migrations to estuaries and lagoons that are characterized by fluctuations in environmental conditions. Their ability to cope with these unstable habitats is undeniable, but it is still not clear how and to what extent salinity acclimation mechanisms are affected at temperatures higher than in the sea. In this study, juvenile sea bass were pre-acclimated to seawater (SW) at 18 degrees C (temperate) or 24 degrees C (warm) for 2 weeks and then transferred to fresh water (FW) or SW at the respective temperature. Transfer to FW for two weeks resulted in decreased blood osmolalities and plasma Cl- at both temperatures. In FW warm conditions, plasma Na+ was similar to 15% lower and Cl- was similar to 32% higher than in the temperate-water group. Branchial Na+/K+-ATPase (NKA) activity measured at the acclimation temperature (V-apparent) did not change according to the conditions. Branchial Na+/K+-ATPase activity measured at 37 degrees C (V-max) was lower in warm conditions and increased in FW compared to SW conditions whatever the considered temperature. Mitochondrion-rich cell (MRC) density increased in FW, notably due to the appearance of lamellar MRCs, but this increase was less pronounced in warm conditions where MRC's size was lower. In SW warm conditions, pavement cell apical microridges are less developed than in other conditions. Overall gill morphometrical parameters (filament thickness, lamellar length and width) differ between fish that have been pre acclimated to different temperatures. This study shows that a thermal change affects gill plasticity affecting whole-organism ion balance two weeks after salinity transfer

Inter-individual variability in freshwater tolerance is related to transcript level differences in gill and posterior kidney of European sea bass

Place: Amsterdam Publisher: Elsevier WOS:000526116400015Acclimation to low salinities is a vital physiological challenge for euryhaline fish as the European sea bass Dicentrarchus labrax. This species undertakes seasonal migrations towards lagoons and estuaries where a wide range of salinity variations occur along the year. We have previously reported intraspecific differences in freshwater tolerance, with an average 30% mortality rate. In this study, we bring new evidence of mechanisms underlying freshwater tolerance in sea bass at gill and kidney levels. In fresh water (FW), intraspecific differences in mRNA expression levels of several ion transporters and prolactin receptors were measured. We showed that the branchial Cl-/HCO3- anion transporter (slc26a6c) was over-expressed in freshwater intolerant fish, probably as a compensatory response to low blood chloride levels and potential metabolic alkalosis. Moreover, prolactin receptor a (prlra) and Na+/Cl- cotransporter (ncc1) but not ncc-2a expression seemed to be slightly increased and highly variable between individuals in freshwater intolerant fish. In the posterior kidney, freshwater intolerant fish exhibited differential expression levels of slc26 anion transporters and Na+/K+/2Cl(-) co-transporter 1b (nkcc1b). Lower expression levels of prolactin receptors (prlra, prlrb) were measured in posterior kidney which probably contributes to the failure in ion reuptake at the kidney level. Freshwater intolerance seems to be a consequence of renal failure of ion reabsorption, which is not sufficiently compensated at the branchial level

Transport-related enzymes and osmo-ionic regulation in a euryhaline freshwater shrimp after transfer to saline media

El conjunto de datos se obtuvieron durante el desarrollo de una beca post doctoral de CONICET realizada por la Dra. Antonela Asaro y bajo la dirección de la Dra. Romina Ituarte. Los datos corresponden a la publicación https://doi.org/10.1139/cjz-2023-0056.Fil: Asaro, Antonela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Pinoni, Silvina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Lorin Nebel, Catherine. Université Montpellier II; FranciaFil: Ituarte, Romina Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Transport-related enzymes and osmo-ionic regulation in a euryhaline freshwater shrimp after transfer to saline media

To understand the response of freshwater organisms to rising environmental salinity, it is essential to investigate their osmo-ionic regulatory physiology. Our laboratory experiment investigated the transfer of Palaemon argentinus Nobili, 1901 from 2 ‰ (control condition) to concentrated salinity (15, 25 ‰) for short (6 h), medium (48 h) and long-term (> 504 h) acclimation periods. We measured relevant parameters in the shrimp’s haemolymph, the time course of the response of branchial V-H+-ATPase (VHA), Na+, K+-ATPase (NKA), carbonic anhydrase (CA) activity, and muscle water content. Upon prolonged acclimation to 15 ‰ (hyper-regulating condition), shrimp reached a new steady-state of haemolymph osmolality by tightly adjusting ion concentrations to levels higher than the external medium. While NKA and CA activities recovered their pretransfer levels, the downregulation of VHA suggests other functions rather than ion uptake after prolonged acclimation to 15 ‰. The activity of the three transport-related enzymes remained almost unchanged at the highest salinity (isosmotic condition), leading to increasing osmotic pressure and ion concentration after prolonged acclimation to 25 ‰. Although the freshwater shrimp studied here retains a certain degree of tolerance to high salinity, a common trait in palaemonid shrimps, our results highlight that 25 ‰ represents a significant hypertonic challenge for this species

Effects of copper and parasitism on osmoregulation in the European eel Anguilla anguilla

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