T.R. Emberley T.D. Singer S.E. Bryson S. D. McCormick W.S. Marshall 1999 <p><span>Freshwater-adapted killifish (</span><i>Fundulus heteroclitus</i><span>) were transferred directly from soft fresh water to full-strength sea water for periods of 1 h, 3 h, 8 h and 1, 2, 7, 14 and 30 days. Controls were transferred to fresh water for 24 h. Measured variables included: blood [Na</span>⁺<span>], osmolality, glucose and cortisol levels, basal and stimulated rates of ion transport and permeability of&nbsp;</span><i>in vitro</i><span>&nbsp;opercular epithelium, gill Na</span>⁺<span>/K</span>⁺<span>-ATPase and citrate synthase activity and chloride cell ultrastructure. These data were compared with previously published killifish cystic fibrosis transmembrane conductance regulator (kfCFTR) expression in the gills measured over a similar time course. Plasma cortisol levels peaked at 1 h, coincident with a rise in plasma [Na</span>⁺<span>]. At 8 h after transfer to sea water, a time at which previous work has shown kfCFTR expression to be elevated, blood osmolality and [Na</span>⁺<span>] were high, and cortisol levels and opercular membrane short-circuit current (</span><i>I</i>_sc<span>; a measure of Cl</span>⁻<span>&nbsp;secretion rate) were low. The 24 h group, which showed the highest level of kfCFTR expression, had the highest plasma [Na</span>⁺<span>] and osmolality, elevated plasma cortisol levels, significantly lower opercular membrane resistance, an increased opercular membrane ion secretion rate and collapsed tubule inclusions in mitochondria-rich cells, but no change in gill Na</span>⁺<span>/K</span>⁺<span>-ATPase and citrate synthase activity or plasma glucose levels. Apparently, killifish have a rapid (&lt;1 h) cortisol response to salinity coupled to subsequent (8–48 h) expression of kfCFTR anion channel proteins in existing mitochondria-rich cells that convert transport from ion uptake to ion secretion.</span></p> application/pdf 10.1242/jeb.202.11.1535 en Taylor & Francis Time course of salinity adaptation a strongly euryhaline estuarine teleost, Fundulus Heteroclitus: A multivariable approach article