Development of seawater tolerance and concurrent hormonal changes in fed and fasted artic charr at two temperature regimes

Aquaculture 222 (2003) 135 – 148 www.elsevier.com/locate/aqua-online

Development of seawater tolerance and concurrent hormonal changes in fed and fasted Arctic charr at two temperature regimes
Øyvind Aas-Hansen a,b,*, Helge K. Johnsen b, Mathilakath M. Vijayan c, Even H. Jørgensen a
a

Norwegian Institute for Nature Research (NINA), Polar Environmental Centre, N-9296 Tromsø, Norway bNorwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway c Department of Biology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1 Received 31 October 2002; accepted 15 December 2002

Abstract Anadromous Arctic charr cease feeding and rely on endogenous energy stores during overwintering in fresh water. During spring, they undergo seasonal development of seawater(SW) tolerance (hypoosmoregulatory capacity) and seaward migratory behaviour. As hormones known to be involved in smoltification are also prime regulators of growth and metabolism, the present study set out to investigate whether the seasonal development of hypoosmoregulatory capacity and accompanying changes in cortisol, thyroid hormones and insulin-like growth factor-I (IGF-I) levels are influencedby metabolic and nutritional status. In addition, the present study also investigated the effect of early spring water temperatures (1.5-month advance) on the above parameters. Hatcheryreared offspring of anadromous Arctic charr were either fed or fasted from October 1998 to July 1999. In fish held at ambient water temperature, hypoosmoregulatory capacity improved from March, and reached a levelindicating prime SW tolerance in late June. Hypoosmoregulatory development was accompanied by significantly higher gill Na+,K+-ATPase activity, and low levels of thyroid hormones and total IGF-I in the fed and fasted groups. Of the hormones investigated, only plasma cortisol levels in fasted fish resembled the pattern typically seen in smolting salmonids, with peak levels coinciding withdevelopment of SW tolerance and increased gill Na+,K+-ATPase activity. Elevation of water temperature in early spring seemed to impair the development of hypoosmoregulatory capacity in this high-Arctic species. It is concluded that long-term fasting associated with overwintering does not impair seasonal development of SW tolerance in Arctic charr, but elevated temperatures in early spring may compromisethis developmental process. The lack of hormonal changes regarded as

* Corresponding author. Norwegian College of Fishery Science, University of Tromsø, N-9037 Tromsø, Norway. Tel.: +47-77-64-60-00; fax: +47-77-64-60-20. E-mail address: oyvindah@nfh.uit.no (Ø. Aas-Hansen). 0044-8486/03/$ - see front matter D 2003 Published by Elsevier Science B.V. doi:10.1016/S0044-8486(03)00107-8

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typical for parr – smolt-transforming salmonids may reflect regulatory adjustments at other levels (receptor concentration/affinity, hormone turnover and binding proteins). Furthermore, the hormonal changes seen in the present study may resemble a seasonal resmoltification typical of repeat migrants of this species, rather than parr –smolt-transforming first-time migrants. D 2003 Published by Elsevier Science B.V.
Keywords: Parr – smolt transformation; Salvelinus alpinus; Nutritional status; Hypoosmoregulation; Cortisol; Thyroid hormones; Insulin-like growth factor-I

1. Introduction The life strategy of anadromous Arctic charr, Salvelinus alpinus (L.), involves a transformation from a freshwater (FW)-dwelling parr to aseawater-adapted, downstreammigrating smolt. Studies examining both wild and captive Arctic charr have demonstrated seasonal development of seawater (SW) tolerance during the spring, when the fish reside in freshwater environments (Finstad et al., 1989; Arnesen et al., 1992; Halvorsen et al., 1993; Finstad and Heggberget, 1995; Nilssen et al., 1997; Eliassen et al., 1998; Johnsen et al., 2000; Gulseth et...