SWIMMING SPEED AND SWIMMING METABOLISM OF ATLANTIC COD (GADUS-MORHUA)IN RELATION TO AVAILABLE FOOD - A LABORATORY STUDY

A laboratory study was performed on how young Atlantic cod (Gadus morh ua) regulate their swimming speed according to available food. A circu lar tank 15 m in diameter was divided into six sectors, each containin g two cod ranging in length from 29 to 42 cm. Live fish 5 cm long on a verage were used as prey. For the first 48 d food intake was changed e very 1 or 2 wk equally for all six groups. During the last 31 d each g roup received different amounts of food. The mean swimming speed was h ighest (0.6 bl/s) when food intake was about half the maximum intake a nd lowest (0.2 bl/s) when food was unlimited or not available. Swimmin g metabolism was related to food intake in a similar way, but with a l arger difference between the most active (50 mg O2 . kg-1 . h-1) and t he least active group (10 mg O2 . kg-1 . h-1). Maximum sustained swimm ing metabolism was estimated to be about 0.6 times the standard metabo lism. The estimated energetic cost of swimming as a percentage of ener gy obtained from the food decreased with food intake from 24% at maint enance ration to 2% at maximum food intake. On a log-log plot swimming speed decreased linearly with time after encounter of prey.