Forced sustained swimming exercise at optimal speed to enhance growth performance of yellotail kingfish (Seriola lalandi)

Juvenile yellowtail kingfish were either forced to perform sustained swimming exercise at an optimal speed of 2.46 body-lengths per second (‘swimmers’) or allowed to perform spontaneous activity at low water flow (‘resters’) in a 3,600 L oval-shaped flume with flow created by an impeller driven by an electric motor. At the start of the experiment, ten fish were sampled as controls (346±6mm, 504±27g). After 18 days, swimmers (n=23; 385±4mm, 735±23g) showed a 92% greater increase in body-length and 46% greater increase in body-weight as compared to resters (n=23; 367±5mm, 661±32g). As both groups were fed equal portions, the feed conversion ratio (FCR) for swimmers was 1.21 and lower than 1.74 for resters. Using Doppler ultrasound imaging, we found a 31% higher blood flow in the ventral aorta of swimmers vs. resters (respect. 44±3 ml/min vs. 34±3 ml/min, under anaesthesia). This study shows that growth performance can be rapidly improved by optimal swimming, even without larger feed investments.