THE PHYSIOLOGY AND BIOCHEMISTRY OF DIPLOID AND TRIPLOID MANILA CLAM (TAPES-PHILIPPINARUM ADAMS-AND-REEVE) LARVAE AND JUVENILES

Triploidy was induced in fertilised eggs of the Manila clam [Tapes philippinarum (Adams and Reeve)] at meiosis II. Growth rate, survival, food consumption, respiration rate and biochemical content of separate ploidy classes containing diploid or mainly (> 60%) triploid larvae and juveniles reared in the hatchery were compared and found to be similar. Newly formed D-larvae were 88-95 mum in length and became pediveligers after 15-17 days, when they had grown to 200-220 mum. Juveniles grew from 0.03 mg (mean dry weight) to 15 mg in 7 wk. Larval food consumption was described by the equation C = 0.577 x LW0.587 (where C = organic weight of food cells consumed (mug.d-1) and LW = organic weight of larvae (mug). Juveniles consumed 0.76 mug.d-1 of food per mug organic weight. Lipid and carbohydrate reserves increased during larval growth to 17.5 and 7.5% of organic content, respectively. Lipid reserves were utilised during metamorphosis. In the juveniles, reserves remained constant at about 11% (lipid) and 7% (carbohydrate). The relationship between dry weight (W, mg) and oxygen consumption (R, mug.d-1) of individual clams was described by R = 15.07 x W0.638. Energy budgets for larval and juvenile Manila clams were calculated. Assimilation efficiency was high in the larvae (> 80%), and net growth efficiency increased with size and declining activity of the clams. The physiological and biochemical attributes of the clams were similar to those reported for other bivalve mollusc species. The results are discussed in relation to the apparent absence of recruitment of Manila clams in UK coastal waters.