Growth and survival of the tropical scallop Lyropecten (Nodipecten) nodosus maintained in suspended culture at three depths

We examined growth and survival of juvenile Lyropecten (Nodipecten) nodosus, measuring 9.4 mm in shell height, which were placed in mid-December 1993 in pearl nets at 8, 21 and 34 m in depth at Turpialito in the Golfo de Cariaco, Venezuela. The mean growth rate in shell height during the first 5 months varied inversely with depth (10.0, 8.5 and 5.0 mm mon(-1) at 8, 21 and 34 m in depth, respectively). Somatic tissues also showed a progressively slower growth rate with increasing depth. The decreased growth rate with depth was not associated with the mass of total seston or its organic content but were proportional to the decrease in phytoplankton biomass with depth (chlorophyll a decreased from 4.8 to 0.7 mu g l(-1) between 8 and 34 m). Temperature also decreased with depth but the differences were likely too slight to account for differences in growth. Mortality varied markedly with depth. There was a sharp increase in mortality in July at 34 m and a total mortality in August at 8 m. In contrast, at 21 m survival was high throughout the study. After 5 months (in May), wet muscle mass of the scallops at 8 m attained the commercial size (5-6 g). A possible culture strategy for L. nodosus is to initially grow the scallops at 8 m in depth, where growth is greatest, and then transfer them to 21 m, where survival is greatest and where growth will continue at a moderate rate to a larger size. (C) 1998 Elsevier Science B.V. All rights reserved.