Shell characterization and effects on cavity volume of wild Jinjiang oyster Crassostrea ariakensis in different estuaries of China

Jinjiang oyster Crassostrea ariakensis , a species with economic and ecological value, is distributed along the estuaries and coasts of East Asia. With the decline in natural resources, the conservation and aquaculture of this species is urgent. However, studies characterizing their shell shape remain scarce. We investigated the morphological differences in the shells of wild Jinjiang oysters from six populations (Qinzhou, Shanghai, Nantong, Qingdao, and Binzhou hard or muddy bottom) along the coast of China. The color of the shell and adductor muscle scar showed associations with temperature gradient along its geographical distribution. Oyster shape was defined by shell height to shell length ratio, and the ratio varies among geographic locations of the populations. They were found nearly round (Qinzhou and Nantong populations), oval (Qingdao and Binzhou populations), or water-droplet-shaped (Shanghai population). Binzhou populations living on muddy substrates are more elongated than those on hard substrate. In addition, we developed a method to measure the cavity volume in oysters. Correlation and path analysis showed that shell height significantly influenced cavity volume. The synergistic effect of the two factors (the height, length, and width of the shell in pairs) on the cavity volume resulted in differences between northern and southern groups: samples from the southern group (Qinzhou and Shanghai) showed correlation between shell height and shell width, while those from the northern group (Nantong, Qingdao, and Binzhou) showed correlation between shell height and shell length. All populations showed significant correlation between shell height and cavity height, and shell length and cavity length, while the correlation between shell width and cavity width was minimal, which may have been resulted from uneven shell thickness. The linear equation for shell height and cavity volume under different ratios of shell height to length was obtained. In this study, we determined that shell height has the most influence on cavity volume, and specific cavity volume fitting linear equations are given for different shell types, which may provide a reference for future oyster breeding for shell shaping.