Measurement of swimming pattern and body length of cultured Chinese sturgeon by use of imaging sonar

• An acoustic camera was used to record the swimming pattern of Chinese sturgeon and their length.
• The target length by DIDSON was 35.6% shorter than that from manual measurements. Overall, the maximum lengths from both measurements were very close.
• Swimming pattern hada significant influence on the target length accuracy.

Measurement of fish length and assessment of behavior are important to fish farming, but it can be a practical challenge. In this study, an acoustic camera (Dual-frequency Identification Sonar, DIDSON) was used to observe the swimming pattern of 10 cultured Chinese sturgeon (Acipenser sinensis) in a net cage, and to estimate their length. In total, 2743 targets were identified from DIDSON data collected over 12 h. Target tracking indicated that most fish swam close to the net in a circular motion, at mean speed of 0.7 ± 0.3 m s− 1. The length (95.2 ± 25.0 cm) of the targets measured through the DIDSON was 35.6% shorter than the total length from manual measurements (147.9 ± 9.3 cm), although the maximum lengths found by both methods were similar. Swimming pattern had a considerable influence on the accuracy of target length estimation. Accordingly, it was essential to select the targets based on swimming behavior to achieve more accurate length estimates. This study proposes that the acoustic camera is a valuable tool for investigating the behavior of the cultured fish and for estimating their length. However, designs for system installation and the net cage should be enhanced.