title: Osmoregulatory response to low salinities in the European sea bass embryos: a multi-site approach.
abstract: Embryonic osmoregulation effected by embryonic ionocytes in the European sea bass Dicentrarchus labrax has been studied at several sites, including the yolk sac membrane, the first gill slits and the gut ionocytes. D. labrax embryos, spawned in seawater (SW) (39 ‰), were exposed to dilute seawater (DSW) (5 ‰) during 48 h, from stage 10 pairs of somites (10S) to hatching time (HT). Control embryos originating from the same spawn were maintained in SW. Both SW and DSW embryos were examined after 24- and 48-h exposure. Nanoosmometric measurements of the embryonic fluids osmolality suggest that late embryos are confronted with the variations in external salinity and that they were able to slightly regulate their osmolality. Immunolocalization of Na⁺/K⁺ ATPase, NKCC and CFTR has shown that DSW-exposed embryos can limit ion losses due to compensatory physiological mechanisms. CFTR and NKCC were not observed in DSW embryos in the yolk sac ionocytes and in the tegumentary ionocytes of the gill slits. The quantification of mRNA indicated that NKA, NKCC1 and CFTR transcript levels increased from stage 10S to stage HT. At stage HT, following 48 h of DSW- or SW-exposure, different responses were observed according to salinity. These results, when compared to those obtained in D. labrax juveniles and adults long-term exposed to fresh water (FW), show that in embryos the physiological response following a short-term DSW exposure is different. The mechanisms of hyper-osmoregulation observed in D. labrax embryos, although not fully efficient, allow their survival for several days in DSW.
authors: AEO Team (Adaptation Ecophysiologique et Ontogenèse), UMR 5119 Ecosym UM2, CNRS, IRD, Ifremer, Université Montpellier 2, Montpellier, France. elliott.sucre@univ-montp2.fr
authors: Elliott
authors: E
authors: Sucré
authors: Maryline
authors: M
authors: Bossus
authors: Charlotte
authors: C
authors: Bodinier
authors: Viviane
authors: V
authors: Boulo
authors: Guy
authors: G
authors: Charmantier
authors: Mireille
authors: M
authors: Charmantier-Daures
authors: Patricia
authors: P
authors: Cucchi
mesh_terms: D000818:Animals; D017756:Aquaculture; D001492:Bass / Q000196:embryology* / Q000502:physiology; D001826:Body Fluids / Q000737:chemistry; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism; D005060:Europe; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D041981:Gastrointestinal Tract / Q000196:embryology / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D005880:Gills / Q000196:embryology / Q000378:metabolism; D008522:Mediterranean Sea; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D054712:Salinity; D012623:Seawater; D028021:Sodium-Potassium-Chloride Symporters / Q000235:genetics / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism; D019170:Somites / Q000196:embryology / Q000502:physiology; D014882:Water-Electrolyte Balance; D015017:Yolk Sac / Q000196:embryology / Q000378:metabolism
chemical_list: D029941:Fish Proteins; D020033:Protein Isoforms; D012333:RNA, Messenger; D028021:Sodium-Potassium-Chloride Symporters; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000254:Sodium-Potassium-Exchanging ATPase