Submergence of Atlantic salmon (Salmo salar L.) in commercial scale sea-cages: A potential short-term solution to poor surface conditions

Submergence of Atlantic salmon (Salmo salar L.) in commercial scale sea-cages (1600-2000 m3) affected their behaviour, but did not alter growth rates, food conversion ratios, appetite, condition factor or fin condition in comparison with control cages held under similar environmental conditions. Four sea-cages each held 3300-4200 Atlantic salmon of 0.45 kg; two cages acted as controls, while two were submerged for 22 days with the roof held at 3 m depth. Salmon in the control cages mainly swam at similar depths to those maintained by submerged fish, resulting in both treatments experiencing similar temperature, light, salinity and dissolved oxygen levels. Submerged fish swam an average of 1.6 times faster (0.88 BL s− 1) and in more structured schools than control fish (0.55 BL s− 1). Specific growth rates (1.1-1.3% day− 1), appetite (0.8-1.2% body weight day− 1) and condition factor (1.10-1.15) were high, while food conversion ratios (0.6-1.0) and the incidence of fin damage were low in all cages, with no significant differences between the control and submerged treatments. Our results highlight the potential for submergence of salmon in sea-cages for short periods to avoid negative surface events.