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 phi lippinarum (Adams and Reeve)] at meiosis II. Growth rate, survival, fo od consumption, respiration rate and biochemical content of separate p loidy classes containing diploid or mainly (> 60%) triploid larvae and juveniles reared in the hatchery were compared and found to be simila r. Newly formed D-larvae were 88-95 mum in length and became pedivelig ers after 15-17 days, when they had grown to 200-220 mum. Juveniles gr ew from 0.03 mg (mean dry weight) to 15 mg in 7 wk. Larval food consum ption was described by the equation C = 0.577 x LW0.587 (where C = org anic weight of food cells consumed (mug.d-1) and LW = organic weight o f larvae (mug). Juveniles consumed 0.76 mug.d-1 of food per mug organi c weight. Lipid and carbohydrate reserves increased during larval grow th to 17.5 and 7.5% of organic content, respectively. Lipid reserves w ere 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 ind ividual clams was described by R = 15.07 x W0.638. Energy budgets for larval and juvenile Manila clams were calculated. Assimilation efficie ncy was high in the larvae (> 80%), and net growth efficiency increase d with size and declining activity of the clams. The physiological and biochemical attributes of the clams were similar to those reported fo r other bivalve mollusc species. The results are discussed in relation to the apparent absence of recruitment of Manila clams in UK coastal waters.