Seawater tolerance in Atlantic salmon, Salmo salar L., brown trout, Salmo trutta L., and S. salar × S. trutta hybrids smolt
High levels of hybridization between Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) have been reported in the Gyrodactylus salaris infected Rivers Vefsna and Driva in Norway. The survival and behaviour during the sea phase of such hybrids is unknown. The reported work documents ionoregulatory status after 24 h seawater challenge tests (24hSW) and gill Na+/K+-ATPase (NKA) activity of migrating wild smolts of Atlantic salmon, brown trout and hybrids at two sampling dates during the 2006 smolt run in River Driva. Salmon, trout and hybrids contributed to 27, 52 and 21% of the catches, respectively. The large contribution of hybrids suggests both a high hybridization rate and a high survival rate from fry to smolt. Both salmon and hybrids had a well-developed seawater tolerance at the time of downstream migration, revealed by small ionoregulatory effects and no or low mortality rates during the 24hSW tests. The trout were not fully adapted to seawater, and high mortality rates were observed (71 and 92%) during the 24hSW tests. The NKA activity was not significantly different between salmon and hybrids. Most of the hybrids were physiologically capable of direct entry to full strength seawater. The incomplete seawater tolerance in trout compared to salmon corresponds well with differences in life-history patterns between these two species. The life history strategy of the hybrids during the sea phase is not known, and further investigations on the marine behaviour and survival is needed to evaluate the role of hybrids in the risk of spreading G. salaris to nearby river systems.
KeywordsSmoltification Seawater tolerance Salmo salar Salmo trutta Hybrids
We are grateful for the field assistance given by Lars Rønning and Gaute Kjærstad at the Norwegian University of Science and Technology, Prof. Sigurd Stefansson and Dr. Tom Ole Nilsen University of Bergen, Department of Biology for conducting the NKA analyses and Dr. Carolyn Knight and Dr. Thrond Oddvar Haugen, Norwegian Institute of Water Research for improving the manuscript. The reported work was financed by the county of Møre and Romsdal through project no (43/2006). This study was conducted as a part of a long-term study in salmonid smolts financed by the TrønderEnergi power company. Funding of manuscript preparation was kindly provided by Norwegian Institute of Water Research and Norwegian University of Science and Technology.
- Arnekleiv JV, Koksvik J, Hindar K, Rønning L, Kjærstad G (2006) Smoltundersøkelser i Driva i 2005 i forbindelse med endring av manøvreringsreglement for Driva kraftverk. NTNU Vitenskapsmuseet Zoologisk notat 2006 2:1–23 (in Norwegian)Google Scholar
- Brown AJ (1993) Endocrine responses to environmental pollutants. In: Rankin JC, Jensen FB (eds) Fish Ecophysiology. Chapman & Hall, London, pp 276–295Google Scholar
- Hoar WS (1988) The physiology of smolting salmonides. In: Hoar WS, Randall DJ (eds) Fish Physiology: The Physiology of Developing Fish, vol XIB. Academic Press, New York, pp 275–343Google Scholar
- Johnsen BO (2007) Økologiske undersøkelser av Gyrodactylus salaris og fisk i norske vassdrag. Årsrapport 2006 NINA Minirapport 183:1–56 (in Norwegian)Google Scholar
- Johnsen BO, Hindar K, Balstad T, Hvidsten NA, Jensen AJ, Jensås JG, Syversveen M, Østborg GM (2005) Laks og Gyrodactylus i Vefsna og Driva. Årsrapport 2004. NINA Rapport 34. 33 p (in Norwegian, abstract in English)Google Scholar
- Kroglund F, Finstad B, Stefansson SO, Nilsen TO, Kristensen T, Rosseland BO, Teien HC, Salbu B (2008) Exposure to moderate acid water and aluminum reduces Atlantic salmon post-smolt survival. Aquaculture 273(2–3):360–373Google Scholar
- McCormick SD, Saunders RL (1987) Preparatory physiological adaptions for marine life of salmonids; osmoregulation, growth and metabolisme. Trans Am Fish Soc 1:211–229Google Scholar
- Molvær J (1990) Tiltaksorientert overvaking av Sunndalsfjorden. Delrapport 6, Vannutskifting og vannkvalitet. NIVA rapport. ISBN82-577-1221-5 (in Norwegian)Google Scholar
- Soleng A, Jansen PA, Bakke TA (1999) Transmission of the monogenean Gyrodactylus salaris. Folia Parasitol 46:179–184Google Scholar
- Wedemeyer GA (1996) Physiology of Fish in Intensive Culture Systems. Chapman and Hall, New York, 232 pGoogle Scholar