Mechanisms of seawater acclimation in a primitive, anadromous fish, the green sturgeon

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 179; no. 7; pp. 903 - 920
• Main Authors: Allen, Peter J, Cech, Joseph J. Jr, Kültz, Dietmar
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01.10.2009; Springer-Verlag; Springer Nature B.V
• Subjects: Acclimatization; Acclimatization - physiology; Aging - physiology; Analysis of Variance; Animal Physiology; Animals; Bicarbonates - analysis; Biochemistry; Biomedical and Life Sciences; Biomedicine; Body size; Body Weight; Calcium - analysis; California; Carbon Dioxide - analysis; Cell Compartmentation; Cell Size; Fishes - growth & development; Fishes - physiology; Fresh Water; Gastrointestinal Contents - chemistry; Gills - cytology; Gills - enzymology; Homeostasis; Human Physiology; Hydrogen-Ion Concentration; Intestines - chemistry; Intestines - enzymology; Kidney - enzymology; Kidneys; Life Sciences; Localization; Magnesium - analysis; Mitochondria; Original Paper; Physiology; Relative abundance; Salinity; Seawater; Sodium-Potassium-Exchanging ATPase - metabolism; Statistics, Nonparametric; Sturgeon; Zoology; California; United States > US; Na; Pyloric caeca; Mitochondria rich cell; HCO; ATPase; Green sturgeon; Cl; exchange; K
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-009-0372-2

Relatively little is known about salinity acclimation in the primitive groups of fishes. To test whether physiological preparative changes occur and to investigate the mechanisms of salinity acclimation, anadromous green sturgeon, Acipenser medirostris (Chondrostei) of three different ages (100, 170, and 533 dph) were acclimated for 7 weeks to three different salinities (<3, 10, and 33 ppt). Gill, kidney, pyloric caeca, and spiral intestine tissues were assayed for Na⁺, K⁺-ATPase activity; and gills were analyzed for mitochondria-rich cell (MRC) size, abundance, localization and Na⁺, K⁺-ATPase content. Kidneys were analyzed for Na⁺, K⁺-ATPase localization and the gastro-intestinal tract (GIT) was assessed for changes in ion and base content. Na⁺, K⁺-ATPase activities increased in the gills and decreased in the kidneys with increasing salinity. Gill MRCs increased in size and decreased in relative abundance with fish size/age. Gill MRC Na⁺, K⁺-ATPase content (e.g., ion-pumping capacity) was proportional to MRC size, indicating greater abilities to regulate ions with size/age. Developmental/ontogenetic changes were seen in the rapid increases in gill MRC size and lamellar length between 100 and 170 dph. Na⁺, K⁺-ATPase activities increased fourfold in the pyloric caeca in 33 ppt, presumably due to increased salt and water absorption as indicated by GIT fluids, solids, and ion concentrations. In contrast to teleosts, a greater proportion of base (HCO₃ ⁻ and 2CO₃ ²⁻) was found in intestinal precipitates than fluids. Green sturgeon osmo- and ionoregulate with similar mechanisms to more-derived teleosts, indicating the importance of these mechanisms during the evolution of fishes, although salinity acclimation may be more dependent on body size.