title: A comparison of osmoregulatory responses in plasma and tissues of rainbow trout (Oncorhynchus mykiss) following acute salinity challenges.
abstract: Euryhaline teleosts regulate their internal osmotic and ionic status across a wide range of external salinities. Studies often rely on measurements on plasma when osmoregulatory status is perturbed, whereas tissue measurements are used for small fish with limited blood volume. However, a direct comparison is lacking for plasma and various tissues. In the present study the relationships between plasma, white muscle and carcass were examined for a range of osmoregulatory variables in rainbow trout (Oncorhynchus mykiss) following challenge with an acute (24 h) transfer from freshwater to a hyper-osmotic salinity of either 25 or 35. Significant increases in plasma osmolality, [Na+], [Cl⁻], [Ca²+], and [Mg²+] were observed when salinity was increased, but plasma [K+] was unaffected. The water content of both tissues showed reciprocal changes to plasma osmolality. The carcass content of all ions measured showed a significant increase at the highest ambient salinity. In white muscle, Na+, K+ and Mg²+ showed significant increases with external salinity, but Cl⁻ and Ca²+ were unaffected. Measurements from both tissues can provide reliable surrogates for most of the plasma osmoregulatory variables except Cl⁻ and Ca²+ when using white muscle tissue. In the case of internal regulation of K+ both tissues provide sensitive and quantitatively similar indicators of environmental salinity disturbance, whereas plasma does not.
authors.affiliation: College of Life and Environmental Sciences, Hatherly Laboratories, University of Exeter, Exeter EX44PS, United Kingdom. n.jandal@exeter.ac.uk
authors.forename: Noura J
authors.initials: NJ
authors.lastname: Al-Jandal
authors.forename: Rod W
authors.initials: RW
authors.lastname: Wilson
mesh_terms: D000818:Animals; D001834:Body Water / Q000737:chemistry; D002118:Calcium / Q000097:blood*; D002712:Chlorides / Q000097:blood*; D008274:Magnesium / Q000097:blood*; D018656:Muscle Fibers, Fast-Twitch / Q000737:chemistry; D017686:Oncorhynchus mykiss / Q000502:physiology*; D009994:Osmolar Concentration; D011188:Potassium / Q000097:blood*; D054712:Salinity; D012964:Sodium / Q000097:blood*; D014882:Water-Electrolyte Balance
chemical_list: D002712:Chlorides; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium