REPRODUCTIVE STAGE AND OSMOREGULATION ABILITY OF THE ESTUARINE CLAM RANGIA-CUNEATA (BIVALVIA, MACTRIDAE)

Osmoregulation experiments were conducted on Rangia cuneata, over a ra nge of salinities from < 0.5 ppt to 20 ppt, to determine if the reprod uctive stage and high gonadal biomass affected osmoregulation ability and survival. Clams in the ripe and partially spent stages with 27% go nadal biomass and in the ripe stage with 39% gonadal biomass were not able to osmoregulate at <0.5 and ppt salinities, with 100k mortality a fter 48 and 72 hours,respectively. Clams in the partially spent stage, in the process of cytolyzing unspawned gametas, with 30% gonadal biom ass survived the entire 360-hour experiment. These data indicate the e nergy cost of being iteroparous, resulting in high gonadal biomass, an d of osmoregulation, in combination, resulted in the observed mortalit ies.