Recovery from loading and transport stress in Atlantic salmon ( Salmosalar L.) smolts

Abstract

The main objective of this study was to analyse the recovery from loading and transport stress of hatchery-reared Atlantic salmon smolts. The experiment was carried out during the regular transport of fish from Eidfjord to Bondhus river (4.5 h), from Lundamo to Surna river (2.5 h) and from Eikesdal to Eira river (0.5 h). Blood samples were obtained from the smolts before transport (control), 30 min after loading and 1, 24 and 48 h after transport. Additionally, blood samples were obtained after a 24 h seawater challenge test before and after transport. Blood samples were analysed for haematocrit, plasma cortisol, lactate, glucose, chloride and sodium. Plasma cortisol concentrations increased up to 15 times from resting values, with a peak 1 h after transport. A severe discrepancy in both fresh- and seawater osmoregulatory ability was observed 24 and 48 h after transport. It is suspected that the low recapture rates and survival of the hatchery-reared salmon smolts were, in part, caused by the handling and transport of the smolts prior to the release.