Precision farming in aquaculture: non-invasive monitoring of Atlantic salmon (Salmo salar) behaviour in response to environmental conditions in commercial sea cages for health and welfare assessment

Studies show that Atlantic salmon in captivity adjust their distribution in sea cages based on environmental gradients like temperature, waves, and photoperiod. This study used a computer vision algorithm at three marine farms to analyse fish group swimming behaviour termed "activity" (measured in percent), which includes fish abundance, speed, and shoal cohesion. The activity metric inferred the depth distribution of the main fish group and was analysed with respect to environmental conditions to explore potential behavioural drivers and used to assess changes in fish behaviour in response to a stressor, a storm event. During winter conditions, Farms A and B showed distinct thermal stratification, with fish activity demonstrating preference for the warmer lower water column (39.6 ± 15.3% and 27.5 ± 10.2%) over the upper water column (16.3 ± 5.7% and 18 ± 3.3%; p < 0.001). At Farm C, with thermally homogenous water, fish activity was similarly distributed between the upper (18.2 ± 6.9%) and lower (17.7 ± 7.6%) water column. Severe weather increased wave heights, influencing fish horizontal distribution differently at Farms B and C. At Farm B, a deeper site, fish remained in the warmer lower water column and avoided surface waves, while at Farm C, with shallower cages, they moved toward the side of the cage nearest the centre of the farm, presumably less exposed due to nearby cages. Understanding fish behavioural responses to environmental conditions can inform management practices, while using cameras with associated algorithms offers a powerful, non-invasive tool for continuously monitoring and safeguarding fish health and welfare.

European seabass, Dicentrarchus labrax, show no significant response to infrared light

Infrared (IR) light is widely accepted as a non-intrusive lighting for discreet observation but relevant studies are scarce. The response of European seabass Dicentrarchus labrax (Linnaeus 1758) towards IR light was tested during laboratory experiments alternating sequences of IR light and dark conditions. Swimming trajectories were extracted from hydroacoustic videos and behavioural metrics (e.g. speed, bearings) were quantified from the D. labrax movement patterns. D. labrax showed no preference nor deterrence towards IR light, supporting the use of discreet IR light as an alternative to visible light for monitoring unbiased D. labrax behaviour.

Early rearing of European seabass (Dicentrarchus labrax) with mild current enrichment modifies fish swimming behavior without altering their growth performance

The implementation of conditions that favor optimum swimming activity (e.g., suitable flow regimes), has been associated with enhanced growth and improved welfare in some farmed fish species. Despite the importance of European seabass in aquaculture, the potential beneficial effects of rearing flow conditions have not been sufficiently explored in this species. This study investigates how the application of fast (F, 0.01-0.20 m s-1) or slow (S, <0.01 m s-1) steady flows in rearing tanks for 75-77 days affected physiological and behavioral traits in seabass fingerlings. Growth performance, external and internal morphology, and several physiological variables, including hematocrit, plasma cortisol concentration, and osmotic and ionic balance were not affected by flow conditions during rearing. Also, behavioral tests implemented in groups or isolated individuals suggest that coping styles were not affected by the two tank-rearing conditions. On the contrary, the swimming behavior assessed in tests was modified by the flow condition experienced during rearing. Mean swimming speed, peak acceleration, swimming distance, angular velocity, and meander showed some variability across different tests and time, although consistently displaying higher values in seabass reared in the F condition, suggesting increased activity and more consistent swimming patterns in that group. However, the cumulative time in proximity between individuals measured in behavioral group tests suggested that group cohesion was variable, without displaying differences between F and S groups. These findings have particularly important implications for fish welfare and may suggest plasticity in the behavioral response to rearing conditions for this species, although not affecting the assignment of the individuals to the different coping styles. SUMMARY STATEMENT: We investigated how mild current enrichment applied during early rearing in seabass modifies physiological and behavioral responses involving swimming activity, exploring the potential associations to fish welfare.