INFLUENCE OF FOOD CONCENTRATION ON THE PHYSIOLOGICAL ENERGETICS AND GROWTH OF OSTREA-EDULIS LARVAE

Feeding, respiration and growth rates of oyster (Ostrea edulis L.) larvae reared at five food levels were measured throughout the entire larval period. Energy budgets were derived as a function of algal (Isochrysis galbana Parke) food concentration. Ingestion rate (IR, cells h(-1)) and oxygen consumption rate (V-O2, nl h(-1)) were almost isometric functions of larval size [ash-free dry weight, (AFDW, mu g)], characterized by the equations: IR = 803.9 AFDW(1.13) and V-O2 = 4.85 AFDW(1.09). Ingested ration was directly correlated to cell concentration up to a maximum at 200 cells mu l(-1), with further increases failing to support higher ingestion rates. Likewise, growth rate linearly increased with food ration up to 100 cells mu l(-1) (max. growth efficiency, K-1 = 25%) and reached a maximum at 200 cells mu l(-1) (growth rate = 5.6 mu m d(-1)), with further increases in food not supporting significantly faster growth. Maintenance ration was 2 to 3% daily dry weight (DW); optimum ration increased during larval development from 5 to 20% DW; maximum ration was 20% DW. During larval rearing, an increasing feeding schedule of 50, 100 and 200 cells mu l(-1)from Days 0, 5 and 10, respectively, is recommended.