Fjordranching with conditioned cod

In June 1986, 1600 pond-reared one-year old cod were released into a fjord after being conditioned with a pulsed 160 Hz sound signal to search for food at a feeding location. Echosounders, UW-video and ultrasonic transmitter tags were used to monitor the fish behaviour. The fish were fed four times a day (09:00, 12:00, 15:00 and 19:00) in the current lobe from a propeller.

A majority of the trained fish returned to the stimulus loeation, and also some "wild" cod and other species adapted the same behaviour. The ultrasonic tagged fish were distributed within 400 m from the stimulus location between the feeding periods. The experiment was terminated after three months. In this period the mean daily length increment was 0.6 mm/day.