OPTIMUM CONCENTRATIONS OF ISOCHRYSIS-GALBANA FOR GROWTH OF LARVAL ANDJUVENILE BAY SCALLOPS, ARGOPECTEN IRRADIANS CONCENTRICUS (SAY)

Bay scallops from Homosassa, FL, were spawned at the Department of Mar ine Science, University of South Florida at St. Petersburg, FL. Total dry weight (DW) and ash free dry weight (AFDW) were determined for lar vae and juveniles. DW and AFDW (in milligrams) increased with increasi ng shell length (L, in millimeters, for larvae) or shell height (H, in millimeters, for juveniles), according to the following allometric eq uations: DW = 0.0693L(2.715) and AFDW = 0.0459L(2.984) in larvae and D W = 0.0715H(3.069) and AFDW = 0.0138H(2.664) in juveniles. Growth was determined for larvae and juveniles at 25 degrees C under six algal co ncentrations of Isochrysis galbana (1-30 cells/mu L for larvae and 1-5 0 cells/mu L for juveniles). Growth rates increased as algal concentra tion increased. The maximum larval growth rate ranged from 7-23 mu m/d ay. The development of eyespots and metamorphosis started earlier at h igher algal concentrations. The optimal algal concentration for growth was 20 cells/mu L for larvae and 10 cells/mu L for juveniles. In juve niles, the growth rate was higher and increased with increasing body s ize. The relative growth rate (daily percent increase in AFDW) was hig her in larvae than in juveniles and decreased with increasing body siz e in juveniles.