Nofima reports

Rapport/Report 6/2015 – English summary

Espmark, Åsa Maria O.; Kolarevic, Jelena; Aas-Hansen, Øyvind; Nilsson, Jonatan

Publication details

Publisher: Nofima AS

Issue: 6/2015

Number of pages: 72

International Standard Numbers:
Printed: 978-82-8296-262-9

Open Access: green


In the project «Pumping and handling of smolt” the aim was to reduce injuries and increase welfare in smolt exposed to handling, and to prevent long term injuries caused by rough handling during early life stages. We conducted several controlled experiments and visited three commercial smolt farms where processes of sorting, vaccination and transfer to sea were studied. The controlled experiments showed that 1) It is difficult to quantify the attachment of scales to smolt because the scales are too small and loosely attached for the tested methodology. 2) Stress responses last longer and are in some occasions stronger when the fish are crowded for three hours compared to one hour. Single events of crowding also increase scale loss. 3) Long term experiments showed that crowding/pumping stress the fish, decrease the growth and impair osmoregulation while in fresh water and after sea transfer the mortality increase and end weight and skin health are impaired. Some handling, though, seems to adapt the fish to the transfer stress. Repeated sedation may increase mortality. 4) Pumping speed increase scale loss (0,9<1,4<2,3 m/s). In conclusion it appears that crowding is the handling that stress fish the most and also cause scale loss, and crowding and pumping additionally increase skin problems. Handling in commercial farms resulted in minimal injuries and stress