The ontogeny of Na + balance during rapid smoltification in pink salmon ( Oncorhynchus gorbuscha )
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ORIGINAL PAPER
The ontogeny of Na+ balance during rapid smoltification in pink salmon (Oncorhynchus gorbuscha) Emily J. Gallagher1 · Till S. Harter1,2 · Colin J. Brauner1 Received: 15 May 2020 / Revised: 2 August 2020 / Accepted: 9 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Pink salmon hatch in fresh water, but their highly anadromous life history requires them to migrate into the ocean immediately after gravel-emergence, at a very small size. During their down-river migration these larvae undergo rapid smoltification that completely remodels their osmoregulatory physiology. At this time, the larvae reportedly have high whole-body Na+ contents and we hypothesised that the active accumulation of internal Na+ occurs in preparation for ocean entry. Using a comparative approach, the present study characterised the ontogeny of Na+ regulation in larvae of the anadromous pink salmon and the fresh-water rainbow trout. Our results indicate that larvae from both species actively accumulated Na+; however, whole-body Na+ content was higher in rainbow trout larvae compared to pink salmon. The time-course of this response in was similar in the two species, with highest N a+-uptake rates ( JNa + ) shortly after yolk sac absorption, but the mechanism of + in Na accumulation differed between the species. Rainbow trout larvae greatly increased JNa + to overcompensate for a large + out in simultaneous increase in Na -efflux rate ( JNa+ ), whereas pink salmon mounted a smaller increase in JNa + while maintaining out tight control over JNa , which is supported by a significantly lower paracellular permeability. Our results indicate that the + + transient accumulation of internal N a is not a unique feature of the highly anadromous life history in pink salmon and may be a common ontogenetic pattern during larval development in salmonids; and perhaps it is associated with the development of the cardiovascular system during the larvae’s transition to a more active lifestyle. Keywords Teleost · Sodium · Rainbow trout · Ocean migration · Anadromy · Ion balance · Osmoregulation
Introduction Pacific salmon (genus Oncorhynchus) in North America represent a clade of five species with an anadromous life cycle that sets them apart from the closely related, sympatric Pacific trout (Smith and Stearley 1989). Salmon spend most of their adult lives in the ocean taking advantage of abundant marine food resources and eventually return to freshwater where their life cycle culminates in iconic spawning migrations up their native rivers (Gross et al. 1988). Most salmon Communicated by Bernd Pelster. * Till S. Harter [email protected] 1
Department of Zoology, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, USA
2
die after spawning, leaving behind fertilized eggs that hatch and develop in freshwater for 1–2 years, before starting their down-riv
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