Ecophysiologie et bilan énergétique de la palourde japonaise d'élevage Ruditapes philippinarum

Rates of filtration and respiration both follow a nonlinear model based on temperature of the form: Y = a × (T−T0)c × e −b(T−T0 with maximal values at 15 and 20°C, respectively. Quantities of seston varying from 0 to 30 mg · 1−1 have no effect in reducing the filtration rate. > 8 mg · 1−1, ingestion is regulated by the production of pseudofaeces. Maximal assimilation efficiency is ≈ 78%, but this is considerably reduced when the mineral content of the water increases. Assimilation efficiency for the Manila clam is reduced at both high (> 10 mm3· h−1) or low (< 2 mm3· h−1) values of ingested ration. The estimated value of growth efficiency (75%) and values of growth efficiency derived from the model k1 = 33%, K2 = 51% are optimized when ingested volumes are between 1 and 2 mm3. Standard metabolism is estimated as 0.11 ml O2 · h−1. Zero growth efficiency occurs at a ration level of 2 J · h−1 for an adult. The individual energy budget shows that production is dependent more on temperature than on the energy value of the food. Comparison of calculated and measured production reveals differences resulting from the higher levels of seston found in the field. In particular, during the winter when the mineral content of the seston is high (90 mg · 1−1), there is a continuous loss of weight. This results from a lower assimilation efficiency together with production of pseudofaeces. Excretion of organic nitrogen varies throughout the year, ammonia representing no more than a mean of 29.8% of the total nitrogen excretion.