Relationship between the necessary swimming power for fish passing through a mesh and the narrow fish body tightened by the mesh

In order to investigate the relationship between the girth of fish and the appropriate mesh size when the fish body passes through the mesh in case of wedged capture, a new device for measuring the maximum girth was developed. This device is capable of simultaneously measuring both the maximum girth of the fish body and the traction force as the force required to pass through the artificial mesh which is contracted by an attached load. Using the device, the maximum girth and traction force were measured for arabesque greenling Pleurogrammus azonus of about 30 cm standard length, as the contracted load was increased gradually in four steps from 0.49 N to 2.94 N. When the contracted loads were 0.98 N and 1.96 N, the mean forces of traction were 5.19 N and 10.01 N, respectively. The mean swimming power of arabesque greenling was about 6.57 N. These results suggest that arabesque greenling would not pass through a mesh contracted by a load of about 1.96 N, but would pass through a mesh contracted by a load of about 0.98 N. When the contracted load was 0.98 N, the shortening ratio of the girth was 97.3%.