The conclusion given by Tokai (1998) using the relative girth, the ratio of body girth to mesh perimeter (G/P), instead of the common body length of fish 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 between the cross-sectional shape of the fish body and shape of mesh opening on mesh selectivity was examined.
The Tokai (1998)'s conclusion which says that the selectivity starts roughly at 0.5 in G/P 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 between the relative girth and the cross sectional coefficient give the domeflshaped curve with a mode at the aspect ratio of mesh. However the selection 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 shape, it was suggested that the use of diamond and square mesh would be effective for fish with flat bodies and round bodies, respectively, to obtain a highly selective catch.