COMPARISON OF THE SCOPE FOR GROWTH WITH THE GROWTH-PERFORMANCE OF OSTREA-EDULIS SEED REARED AT DIFFERENT FOOD CONCENTRATIONS IN AN OPEN-FLOW SYSTEM

Oyster(Ostrea edulis L.) seed was reared on five rations of Isochrysis galbana Parke: 10, 30, 100, 200 and 300 cells mu l(-1), in an open-fl ow system. Physiological parameters such as clearance, ingestion, abso rption and respiration rates were measured, and the scope for growth ( SFG) calculated from these parameters was compared with actual growth over 20 d. Actual growth was negligible at 10 cells mu l(-1) (daily ma intenance ration=2.5% organic wt) and maximum (growth rate=13.64 d(-1) ) at 200 cells mu l(-1) (daily ration=43% organic wt), which also supp orted the maximum gross and net growth efficiencies (K-1=50%, K-2=85%) . Ingestion rate was directly correlated to cell concentration up to m aximum of similar to 100 cells mu l(-1) but further increases failed t o support higher ingestions. Absorption efficiency decreased with incr easing algal concentration from 95% down to 60%. Due to the costs of g rowth, respiration rate significantly increased when food was added ab ove maintenance levels; however, metabolic costs associated with feedi ng activity were undetectable. The scope for growth calculated from th ese physiological parameters agreed with the long-term growth performa nce, validating the physiological energetics method as a valuable tool for predicting long-term growth performance under constant environmen tal conditions.