Forsøksdyr: Refilling behaviour of salmon with different air dome heights

Godkjenningsdato 07.04.2020

Godkjenningsperiode 01.05.2020-31.12.2020

By lowering sea based net cages to lie under the "lice belt", the sea lice infection pressure on farmed fish will be reduced. For this to be possible, salmon in the submerged net pens must have air available at all times through an air dome. The purpose for this study is to find the optimal height of the air dome that is sufficient for the salmon to refill their swimbladders but minimises dome size overall (of which can influence logistical functionality at commercial scale). Salmon lice have been shown to promote stress in salmon, which is expressed through increased surface activity. Natural stress behavior is an important factor that must be taken into account when determining the height of the dome. This study will test three different heights of air dome (1, 10, 100 cm), and refilling/surface behaviours will be monitored in salmon for 3 weeks, followed by exposure to sea lice, both Lepeoptheirus salmonis and Caligus elongatus. Fish will be exposed to L. salmonis first, to characterise the behavioural change during infection but also when lice moult into the preadult stage. Once lice are mobile (3 weeks later), behaviours are expected to reach an equilibrium. Then, fish will be exposed to C. elongatus to investigate behavioural changes in the same way. Benefits include practical implications for the use of dome technology and increased understanding to be applied in commercial farming, ensuring fish welfare. It can also facilitate advise to authorities on the positive and negative aspects of dome use, relating to behaviour and infections.

The lice infection is considered to be mild severe, but the ability for the salmon to jump is limited throughout the study period, and thus due to this, the experiment considered to be moderate severe. Fish will be held for a total of 9 weeks. Throughout the trial, surface activity will be observed, and fish will be sampled periodically for welfare assessments. Results from this trial will provide a recommended height of the air dome in submerged cages to minimize damage to the fish when filling air. This can benefit the commercial aquaculture industry if the sea lice levels are reduced and at the same time fish welfare is promoted.

The trial will include 3600 Atlantic salmon divided into three different treatment groups (different heights of the dome) and 3 replicate tanks per group. The number of fish for this trial is determined from previously observed surface activity in sea-based net pens. Throughout the trial, surface activity will be recorded, health status will be evaluated (SWIM) and lice will counted.

Replacement: Since the trial is considering species- specific response, replacement can not be applied.
Reduction: The number of salmon is minimized and put into the tanks of the smallest size that will still provide relevant data.
Refinement: Minimal movement and handling of fish. All handling is done by experienced technicians. Lice infection pressures will be lower, to mitigate combined stress of restricted surface access and infection.