title: Effects of short-term hyper- and hypo-osmotic exposure on the osmoregulatory strategy of unfed North Pacific spiny dogfish (Squalus suckleyi).
abstract: The North Pacific spiny dogfish (Squalus suckleyi) is a partially euryhaline species of elasmobranch that often enter estuaries where they experience relatively large fluctuations in environmental salinity that can affect plasma osmolality. Previous studies have investigated the effects of altered salinity on elasmobranchs over the long term, but fewer studies have conducted time courses to investigate how rapidly they can adapt to such changes. In this study, we exposed unfed (no exogenous source of nitrogen or TMAO) spiny dogfish to hyper- and hypo-osmotic conditions and measured plasma and tissue osmolytes, nitrogen excretion, and changes in enzyme activity and mRNA levels in the rectal gland over 24h. It was shown that plasma osmolality changes to approximately match the ambient seawater within 18-24h. In the hypersaline environment, significant increases in urea, sodium, and chloride were observed, whereas in the hyposaline environment, only significant decreases in TMAO and sodium were observed. Both urea and ammonia excretion increased at low salinities suggesting a reduction in urea retention and possibly urea production. qPCR and enzyme activity data for Na(+)/K(+)-ATPase did not support the idea of rectal gland activation following exposure to increased salinities. Therefore, we suggest that the rectal gland may not be a quantitatively important aspect of the dogfish osmoregulatory strategy during changes in environmental salinity, or it may be active only in the very early stages (i.e., less than 6h) of responses to altered salinity.
authors.affiliation: Department of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada; Bamfield Marine Sciences Centre, Bamfield, BC V0R 1B0, Canada. Electronic address: cdeck023@uottawa.ca.
authors.forename: Courtney A
authors.initials: CA
authors.lastname: Deck
authors.affiliation: Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA; Bamfield Marine Sciences Centre, Bamfield, BC V0R 1B0, Canada.
authors.forename: Abigail B
authors.initials: AB
authors.lastname: Bockus
authors.affiliation: Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA.
authors.forename: Brad A
authors.initials: BA
authors.lastname: Seibel
authors.affiliation: Department of Biology, University of Ottawa, Ottawa, ON K1N 6N5, Canada; Bamfield Marine Sciences Centre, Bamfield, BC V0R 1B0, Canada.
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Walsh
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D002712:Chlorides / Q000378:metabolism; D064587:Osmoregulation / Q000502:physiology*; D009995:Osmosis / Q000502:physiology*; D054712:Salinity; D012491:Salt Gland / Q000378:metabolism / Q000502:physiology; D012623:Seawater; D012964:Sodium / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D048250:Squalus / Q000378:metabolism / Q000502:physiology*; D014508:Urea / Q000378:metabolism; D014882:Water-Electrolyte Balance / Q000502:physiology
chemical_list: D002712:Chlorides; D000641:Ammonia; D014508:Urea; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Elasmobranchs; Nitrogen; Osmoregulation; Rectal gland; Salinity