title: Hypo-osmotic stress-induced physiological and ion-osmoregulatory responses in European sea bass (Dicentrarchus labrax) are modulated differentially by nutritional status.
abstract: We investigated the impact of nutritional status on the physiological, metabolic and ion-osmoregulatory performance of European sea bass (Dicentrarchus labrax) when acclimated to seawater (32 ppt), brackish water (20 and 10 ppt) and hyposaline water (2.5 ppt) for 2 weeks. Following acclimation to different salinities, fish were either fed or fasted (unfed for 14 days). Plasma osmolality, [Na(+)], [Cl(-)] and muscle water content were severely altered in fasted fish acclimated to 10 and 2.5 ppt in comparison to normal seawater-acclimated fish, suggesting ion regulation and acid-base balance disturbances. In contrast to feed-deprived fish, fed fish were able to avoid osmotic perturbation more effectively. This was accompanied by an increase in Na(+)/K(+)-ATPase expression and activity, transitory activation of H(+)-ATPase (only at 2.5 ppt) and down-regulation of Na(+)/K(+)/2Cl(-) gene expression. Ammonia excretion rate was inhibited to a larger extent in fasted fish acclimated to low salinities while fed fish were able to excrete efficiently. Consequently, the build-up of ammonia in the plasma of fed fish was relatively lower. Energy stores, especially glycogen and lipid, dropped in the fasted fish at low salinities and progression towards the anaerobic metabolic pathway became evident by an increase in plasma lactate level. Overall, the results indicate no osmotic stress in both feeding treatments within the salinity range of 32 to 20 ppt. However, at lower salinities (10-2.5 ppt) feed deprivation tends to reduce physiological, metabolic, ion-osmo-regulatory and molecular compensatory mechanisms and thus limits the fish's abilities to adapt to a hypo-osmotic environment.
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, Antwerp BE-2020, Belgium. Electronic address: sinha_cife@rediffmail.com.
authors.forename: Amit Kumar
authors.initials: AK
authors.lastname: Sinha
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, Antwerp BE-2020, Belgium.
authors.forename: Antony Franklin
authors.initials: AF
authors.lastname: Dasan
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, Antwerp BE-2020, Belgium.
authors.forename: Rindra
authors.initials: R
authors.lastname: Rasoloniriana
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, Antwerp BE-2020, Belgium.
authors.forename: Nitin
authors.initials: N
authors.lastname: Pipralia
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, Antwerp BE-2020, Belgium.
authors.forename: Ronny
authors.initials: R
authors.lastname: Blust
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, Antwerp BE-2020, Belgium.
authors.forename: Gudrun
authors.initials: G
authors.lastname: De Boeck
mesh_terms: D000222:Adaptation, Physiological; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001492:Bass / Q000502:physiology*; D004734:Energy Metabolism; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D005880:Gills / Q000378:metabolism; D019344:Lactic Acid / Q000097:blood; D018482:Muscle, Skeletal / Q000378:metabolism; D009752:Nutritional Status; D064587:Osmoregulation; D009997:Osmotic Pressure; D013312:Stress, Physiological; D014508:Urea / Q000378:metabolism
chemical_list: D029941:Fish Proteins; D019344:Lactic Acid; D000641:Ammonia; D014508:Urea
keywords: Ammonia excretion; Fasting; Na(+)/K(+)-ATPase; Na(+)/K(+)/2Cl(−); Osmoregulation; Salinity acclimation