Control of feed dispensation in seacages using underwater video monitoring: Effects on growth and food conversion

Two feeding trials were conducted on Atlantic salmon (Salmo salar) farms to judge the efficacy of using subsurface-feeding activities and pellet loss as a basis for judging satiation and determining feed dispensation rate. Salmon were fed using mechanical feeders while viewing a monitor connected to an underwater video camera placed below the feeding zone. As controls, fish in similar cages were fed using only declining visually perceived surface activities as an indicator of satiation. Fish in camera-monitored cages (CMCs) achieved significantly better feed conversions and lower mortality rates in both experiments, and under summer conditions they achieved higher growth rates. During periods of poor water clarity, fish apparently had difficulty detecting pellets. In CMCs, feed dispensation rate (kg kg(-1) of fish min(-1)) varied depending on lighting conditions and broadcast method, and ration level changed constantly. Subsurface-feeding activities and pellet loss constituted a better indicator of satiety in Atlantic salmon than did surface feeding activities. (C) 1997 Elsevier Science B.V.