The Osmorespiratory Compromise in Sculpins: Impaired Gas Exchange Is Associated with Freshwater Tolerance

• Published in: Physiological and biochemical zoology 2008-05, Vol.81 (3), p.310-319
• Main Authors: Henriksson, Patrik, Mandic, Milica, Richards, Jeffrey G.
• Format: Article
• Language: English
• Subjects: Acclimatization; Acclimatization - physiology; Animals; Biologi; Biological Sciences; Body Weight - physiology; Brackish water; Ecology; Ekologi; Fishes - blood; Fishes - physiology; Fresh Water; Freshwater fishes; Gills; Gills - anatomy & histology; Gills - physiology; Hematocrit; Marine fishes; Natural Sciences; Naturvetenskap; Oxygen Consumption; Salinity; Sculpin; Sea water; Seawater; Water-Electrolyte Balance - physiology
• ISSN: 1522-2152; 1537-5293
• DOI: 10.1086/587092

We acclimated two species of sculpin, the freshwater prickly sculpin (Cottus asper) and the closely related marine Pacific staghorn sculpin (Leptocottus armatus) to freshwater (∼0 g/L), brackish water (15 g/L), and seawater (30 g/L) for at least 4 wk and examined the relationships between respiration, ion regulation, gill morphology, and freshwater tolerance. The prickly sculpin successfully acclimated to all three salinities and did not experience appreciable changes in plasma osmolality, [Cl−], or mortality. Gill Na+/K+‐ATPase activity was lowest in prickly sculpins acclimated to freshwater, their native salinity, and increased during acclimation to seawater. Furthermore, prickly sculpins acclimated to freshwater had a 30% higherP critthan fish acclimated to brackish water or seawater;P critis the environmental Po 2below which an animal can no longer maintain a routine \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\dot{\mathrm{M}}\textsc{$o$}_{2}$ \end{document} , and an increase inP critrepresents a compromise of respiratory gas exchange. The higherP critobserved in prickly sculpins acclimated to freshwater is likely a consequence of their having small, relatively thick gills that increase in thickness (by ∼1 μm) during freshwater exposure. In contrast, the marine Pacific staghorn sculpin successfully acclimated to brackish water and seawater, but high mortality (25%) was observed after 3 wk of exposure to freshwater. Pacific staghorn sculpins exposed to freshwater suffered significant, 15%–20%, reductions in plasma osmolality and [Cl−], and these losses in plasma ions resulted in a 1.4‐fold increase in gill Na+/K+‐ATPase activity. Pacific staghorn sculpins have large, thin gills that are not modified in response to salinity acclimation, and as a result, these animals show no respiratory compromise during freshwater acclimation, as evidenced by the lack of change inP crit, but show significant ion regulatory disturbance. Overall, this study suggests that gill thickening and