The time budget of Atlantic salmon (Salmo salar) held in enriched tanks

Abstract

In order to understand the impact of different experimental and husbandry procedures on fish, and ensure that the behavioural and physiological needs of fish used in research are met, it is necessary to have detailed knowledge of their behaviour. This knowledge is largely lacking for Atlantic salmon. Results from behavioural studies of rainbow trout are often extrapolated to Atlantic salmon even though this may not be correct. Pre-smolt Atlantic salmon show diurnal variation in behaviour in the wild, but there are no published descriptions of behaviour during the dark hours for salmon held in the laboratory. Thus, the first aim of this paper was to describe the time budget of singly-held salmon both during the light and dark hours on the first and seventh day after introduction to a new environment. Statistical differences in time budget between morning, afternoon and night are described. In addition, three environmental enrichments were provided, and the time spent using each resource was scored. In general, no behaviours differed in frequency between morning and afternoon registrations, but there were significant differences in the time-budget between day and night and also between day 1 and 7. Fish hid less and displayed more behaviours during the night than during the day, and also after 7 days in the tank compared to at the first day. The exceptions were bottom behaviours which were displayed with the same frequency during day and night and during day 1 and day 7, and hovering, which was unchanged at night from day 1 to day 7. Thus, different behaviours seem to be influenced by light and by the novelty of the surroundings to different degrees. Of the three enrichments included in the study, the hiding place and the inlet current were used most frequently. As far as the authors know, this is the first paper describing the daytime and night time behaviour of parr Atlantic salmon in a research facility in detail.