Fjordranching with conditioned cod

Abstract

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 (0900, 1200, 1500 and 1900) in the current lobe from a propeller. A majority of the trained fish returned to the stimulus location, 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.