Effect of cross-sectional shape of fish body on mesh selectivity of trawl codend

The conclusion given by Tokai (1998) using the relative girth, the ratio of body girth to mesh perimeter (GIP), instead of the common body length of f ish was verified by the result of 20 species' mesh selectivity in Isei pair -trawl and stern-trawl net of Japan. And, the influence of the relation bet ween the cross-sectional shape of the fish body and shape of mesh opening o n mesh selectivity was examined. The Tokai (1998)'s conclusion which says that the selectivity starts roughl y at 0.5 in GIP and attains 100% at 1.0 G/P was well applicable to the case of the most fishes except a few fish species in this study. The relation b etween the relative girth and the cross sectional coefficient give the dome -shaped curve with a mode at the aspect ratio of mesh. However the selectio n range seems related to other characteristics such as the hardness of the fish body part with the maximum body girth rather than the cross sectional coefficient. For the relation between the type of mesh and the fish body sh ape, it was suggested that the use of diamond and square mesh would be effe ctive for fish with flat bodies and round bodies, respectively, to obtain a highly selective catch.