Environmental drivers of Atlantic salmon behaviour in sea-cages: A review

High host densities dilute sea lice Lepeophtheirus salmonis loads on individual Atlantic salmon, but do not reduce lice infection success

“…Moreover, studies generally use absolute stocking densities (i.e. based on total biomass), which seldom reflect the actual fish density inside the cage as fish choose to congregate at specific depths depending on environmental conditions (Oppedal et al 2011a). For farmed Atlantic salmon, swimming densities typically exceed stocking densities by 1.5 to 5 times, and up to 17 times in specific environments (Oppedal et al 2011a,b), and this has to be considered when planning strategic procedures to improve welfare at the farm level.…”

“…These densities reflect realistic swimming densities experienced by farmed salmon in sea-cages (Oppedal et al 2011a,b). While stocking density (total biomass of fish divided by cage volume) is typically 5 to 25 kg m −3 , swimming density is driven by fish actively choosing specific depths based on environmental preferences (Oppedal et al 2011a). Swimming densities are typically 1.5 to 5 times the stocking densities, thus our 2 densities sit well within the lower and upper bounds of known swimming densities (0 to 190 kg m −3 ; Oppedal et al 2011b).…”

“…A laminar current speed of 16.2 ± 0.5 cm s −1 (mean ± SE), equivalent to a swimming speed of 0.7 body lengths (BL) s −1 , was generated in the raceways by a propeller (Minn Kota RT80/EM, Johnson Outdoors Marine Electronics) with adjustable speed followed by a honeycomb (5 mm opening, 102 mm thick, PC 5.0 G4, Plascore). Current speed was measured with a Vectrino velocimeter (Nortek) and was set at this level to reflect typical daytime swimming speeds of salmon (Oppedal et al 2011a, Thorstad et al 2012. Underwater video cameras (SeaVision SV27) were mounted in the middle of each raceway, with the field of view covering the back of the raceway.…”

“…The static water conditions during artificial infections or immobile fish contrast with natural infection settings for both farmed and wild salmon, where water currents may change infection dynamics (Revie et al 2003). Here, we used swimming chambers with a fixed current speed that reflected the normal swimming speeds of salmon in farmed (Oppedal et al 2011a) and wild environments (Thorstad et al 2012). This enabled more realistic swimming behaviours during infection to test how host density influences infection intensity, infection success, prevalence and degree of aggregation of sea lice L. salmonis on Atlantic salmon (Fig.…”

Improving aeration for efficient oxygenation in sea bass sea cages. Blood, brain and gill histology

“…Diffuser aerators use air produced by an air-compressor to inject air through diffusers located at the bottom of a pond or suspended in a water column. Understanding the spatial and temporal variability of key environmental variables within sea cages and how fish respond to them may enable modifications to sea cage environments and adjustments to management practices for improving production efficiency and fish welfare [5].…”