INFLUENCE OF FOOD CONCENTRATION ON ENERGY-BALANCE AND GROWTH-PERFORMANCE OF VENERUPIS-PULLASTRA SEED REARED IN AN OPEN-FLOW SYSTEM

Seed of the clam Venerupis pullastra were reared with five different rations of Isochrysis galbana: 15, 30, 100, 200 and 300 cells mul-1, in an open-flow system. Physiological parameters such as clearance, ingestion and absorption rates were recorded, and energy balances calculated from these parameters were compared with the long-term growth performance of the seed. High food concentrations inhibited clearance rate but ingestion could not be regulated, being higher with higher food levels. Absorption efficiency decreased moderately at high I. galbana concentrations. Nevertheless, absorption rate was directly correlated with ingesta. Estimated metabolic rate was at a routine level for medium and high food rations and markedly lower at poor food rations. Growth performance was insignificant at 15 cells mul-1 (daily maintenance ration = 2% organic weight), optimal at 100 cells mul-1 (K1 = 46%) and maximal at 300 cells mul-1 (growth rate = 11.9 day-1), in agreement with the physiological energetics measurements. Growth rates of V pullastra seed were similar to those reported for other species, such as Ruditapes philippinarum, regarded as a fast growing member of the Veneridae.