DETERMINATION OF OPTIMAL THERMAL CONDITIONS FOR GROWTH OF CLAM (VENERUPIS-PULLASTRA) SEED

The energy budget of Venerupis pullastra clam seed (3 mm) fed the micr oalga, Isochrysis galbana T-ISO, was calculated after acclimation at 1 0, 15, 20 and 25 degrees C. Physiological measurements included ingest ion rate, absorption efficiency, oxygen consumption and ammonia excret ion. The effect of temperature on these rates was described. Ingestion rate was directly related to temperature up to a maximum at 20 degree s C. Further temperature increase caused a slight decrease in ingestio n. Absorption efficiency was not significantly influenced by the tempe rature, although maximum mean values were also found at 20 degrees C. Both respiration and ammonia excretion rates were directly related to temperature over the whole experimental range, reaching their maxima a t 25 degrees C. For all the physiological rates measured the higher sl opes in the rate/temperature lines occurred in the medium range of tem peratures (15-20 degrees C). The scope for growth (SFG) was positive a t all temperatures and maximum at 20 degrees C, chiefly as a consequen ce of the enhanced ingestion rate which offset the concomitant elevati on in metabolic rates. Both gross and net growth efficiencies are also expected to be maximum at 20 degrees C, which is, therefore, the ther mal optimum for this species under the experimental conditions applied in our study. An acclimation strategy for this low-shore species with in the range of thermal variation in its natural environment (10-20 de grees C), maximizing SFG at high temperatures by enhancing ingestion r ate, despite increased metabolic costs, is proposed.