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°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°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°C. Both respiration and ammonia excretion rates were directly related to temperature over the whole experimental range, reaching their maxima at 25°C. For all the physiological rates measured the higher slopes in the rate/temperature lines occurred in the medium range of temperatures (15–20°C). The scope for growth (SFG) was positive at all temperatures and maximum at 20°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°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°C), maximizing SFG at high temperatures by enhancing ingestion rate, despite increased metabolic costs, is proposed.