GROWTH AND SURVIVAL OF THE TROPICAL SCALLOP LYROPECTEN (NODIPECTEN) NODOSUS MAINTAINED IN SUSPENDED CULTURE AT 3 DEPTHS

We examined growth and survival of juvenile Lyropecten (Nodipecten) no dosus, measuring 9.4 mm in shell height, which were placed in mid-Dece mber 1993 in pearl nets at 8, 21 and 34 m in depth at Turpialito in th e Golfo de Cariaco, Venezuela. The mean growth rate in shell height du ring 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 d ecrease in phytoplankton biomass with depth (chlorophyll a decreased f rom 4.8 to 0.7 mu g l(-1) between 8 and 34 m). Temperature also decrea sed with depth but the differences were likely too slight to account f or differences in growth. Mortality varied markedly with depth. There was a sharp increase in mortality in July at 34 m and a total mortalit y 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, whe re 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 lar ger size. (C) 1998 Elsevier Science B.V. All rights reserved.