COMPARISON OF GROWTH, SURVIVAL, AND REPRODUCTIVE SUCCESS OF DIPLOID AND TRIPLOID MERCENARIA-MERCENARIA

Diploid and triploid northern quahogs, Mercenaria mercenaria, were cul tured intertidally in a South Carolina estuary for about 4 y. No diffe rence in shell length was detected between quahogs identified as tripl oids and diploids at 6 and 27 mo of age; however, at 47 mo of age, tri ploid quahogs were significantly larger than diploids. The survival ra tes of diploids and triploids were similar over the field growout peri od. None of the triploids thermally induced to spawn released gametes, whereas 82% of the diploid quahogs released viable gametes. Gonads of diploid individuals were ripe, with numerous mature oocytes and radia ting bands of spermatozoa in the lumens. Gametogenesis in triploids, h owever, was severely retarded and abnormal. Although the lumen areas i n triploid and diploid quahogs were similar, the areas occupied by sex cells were significantly larger in the diploid quahogs.