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

The energy budget of Venerupis pullastra clam seed (3 mm) fed the microalga, Isochrysis galbana T-ISO, was calculated after acclimation at 10, 15, 20 and 25 degrees C. Physiological measurements included ingestion rate, absorption efficiency, oxygen consumption and ammonia excretion. The effect of temperature on these rates was described. Ingestion rate was directly related to temperature up to a maximum at 20 degrees C. Further temperature increase caused a slight decrease in ingestion. Absorption efficiency was not significantly influenced by the temperature, 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 at 25 degrees C. For all the physiological rates measured the higher slopes in the rate/temperature lines occurred in the medium range of temperatures (15-20 degrees C). The scope for growth (SFG) was positive at all temperatures and maximum at 20 degrees C, chiefly as a consequence of the enhanced ingestion rate which offset the concomitant elevation in metabolic rates. Both gross and net growth efficiencies are also expected to be maximum at 20 degrees C, which is, therefore, the thermal optimum for this species under the experimental conditions applied in our study. An acclimation strategy for this low-shore species within the range of thermal variation in its natural environment (10-20 degrees C), maximizing SFG at high temperatures by enhancing ingestion rate, despite increased metabolic costs, is proposed.