DEMAND FEEDING IN SALMON FARMING BY HYDROACOUSTIC FOOD DETECTION

A new method for demand feeding of salmon in sea cages where automatic feeders are controlled by a 'food detector' is described Hydroacousti c detection of food pellets at 2.5 m depth was used as an indicator of reduced appetite. Feeding was terminated when echo energy from food p ellets sinking through a 360-degrees acoustic beam exceeded a preset t hreshold. In an 83-day full-scale test, the food intake and growth of salmon whose feeding was controlled by this method (detector group) we re compared with those of fish fed in accordance with growth rate esti mates (control group). The specific growth rates (% wet weight/day) we re 1.01 and 0.71 in the detector and control groups respectively. This difference in growth was mainly explained by a considerable higher fo od intake in the detector group. The results indicate that demand feed ing by hydroacoustic food detection automatically adjusts food ration to fish appetite, so that food waste is avoided and the growth potenti al of the fish is utilized