||Pommepuy Monique, Caprais Marie-Paule, Le Saux Jean-Claude, Le Mennec Cecile, Parnaudeau Sylvain, Madec Yvon, Monier Martial, Brest Goulven, Le Guyader Francoise
||4th International Conference on Molluscan Shellfish Safety, June 4-8 2002, Santiago de Compostella (
||4th International Conference on Molluscan Shellfish Safety, pp. 485-499
||Bacteriophage FRNA, Depuration, Shellfish
||Depuration processes try to eliminate microorganisms using seawater to allow living, filter-feeding shellfish to naturally purge themselves from agents they accumulated from the environment. Until now the only parameter to evaluate depuration was the decrease in E. coli counts. Studies have shown that viruses can persist in the environment longer than E. coli and that shellfish meeting the endstandard (< 230 E.colil /100g) have been involved in viral outbreaks. Starting in February 2000, the European Commission has been funding (Fifth Framework Programme), a 3-year project entitled "Virus Safe Seafood". One of the specific objectives of this project is to innovate technology for shellfish depuration. For this purpose a depuration system was designed and built: a four-tank pilot was selected allowing different parameters (temperature, aeration, nutrition..) to be tested simultaneously and on the same shellfish group. The nominal capacity of each tank (960 kg of oysters) was a compromise between scientific experiments and producer needs. After tank calibration (hydraulic, water stability, water desinfection), assays were carried out with artificially-or naturally-contaminated oysters (Crassostreas gigas). The bacteriophage F+RNA specific was used as a viral indicator model. Eleven experiments, four with naturally-contaminated shellfish, have been performed in the pilot with continuous aeration, different water temperatures (from 8°C to 25°C) and, in two experiments, phytoplancton (Chaetoceros calcitrans and Isochrysis affinis galbana) feeding. The results indicate the major effect of temperature on shellfish depuration, while feeding seems to increase the decontamination only when active physiology is observed (22°C). Viral depuration rates (T90D : times for 90% i.e. 1 log10 reduction) were found to vary between 3-4 days (T>20°C) to 7-11 days (T<16°C). The lower T90D -2 days- was found at 22°C with algae feeding. Mortality rate and oyster flesh weight recorded after each - 485 - experiment indicated no effect of any treatment (even high temperature) on these parameters. The same results were obtained on naturally-contaminated shellfish. These data show that the pilot provides all facilities to assess shellfish depuration according to the professional practices.