FIELD-EVALUATION OF THE EFFECT OF CURRENT VELOCITY AND DIRECTION OF THE GROWTH OF THE GIANT SCALLOP, PLACOPECTEN-MAGELLANICUS, IN SUSPENDED CULTURE

We measured the growth of juvenile giant scallops Placopecten magellanicus glued to panels and placed inside or outside of pearl nets in the water column at two sites where environmental conditions were similar except for a twofold differences in the current velocity (mean velocity < 0.9 and > 0.16 m . s-1, respectively). We did not detect differences in growth related to the orientation of scallops relative to current direction and this contrasts with several studies examining the effect of steady current velocities in flumes. For scallops outside of pearl nets, daily specific growth rate of the shell was similar at the two sites, however, the mass of the shell, muscle and remaining viscera, scaled to shell height, was greater under weak than strong current. Pearl nets decreased water flow by 46-61%. At the strong current site, tissue masses were greater for scallops inside than outside the pearl net, probably because the net reduced the frequency of velocities which inhibit feeding. In contrast, at the weak current site, tissue masses were less inside the pearl net, probably because flow was slowed to the extent that seston depletion limited growth. Aquaculture methods must be adapted to hydrodynamic conditions to optimize growth.