AJP - Regulatory, Integrative and Comparative Physiology, Vol 272, Issue 3 743-R749, Copyright © 1997 by American Physiological Society
Summer osmoregulatory capacity of the world's northernmost living salmonid
K. J. Nilssen, O. A. Gulseth, M. Iversen and R. Kjol
Department of Zoology, Norwegian University of Science and Technology, Trondheim.
Anadromous Arctic charr (Salvelinus alpinus L.) were caught on their way to
and from the sea with the use of a fish trap placed in the Dieset
watercourse located on the Spitsbergen Island (79 degrees 10' Northern
latitude) within the high-Arctic Svalbard archipelago. When subjected to a
seawater challenge test (34 parts/thousand at 4-5 degrees C), charr on
their way to the sea showed only minor and temporary changes in blood
plasma osmolality and Na+ and Mg2+ concentrations. The seawater tests also
revealed good hypoosmoregulatory capacity for Arctic charr returning from
the marine environment 4 wk later. A progressive decrease in seawater
tolerance was first documented 7-11 days after their return to the
freshwater habitat. Thus the Svalbard charr, being the northernmost
anadromous salmonid and probably a direct descendant from the first
Salvelinus immigrants to freshwater systems, undergoes a preparatory
increase of hypoosmoregulatory capacity (smoltification) before entering
the oceanic water bodies. Furthermore, the termination of their short
annual seawater stay is probably elicited by factors controlling body
systems other than osmoregulation.
