Shellfish relaying on longlines in the open sea: A note

Abstract

Since bivalves are filter-feeding organisms that can concentrate microorganisms and contaminants from the surrounding environment, there are strict sanitary requirements to ensure food safety. The legislation establishes a time limit of 2 months for shellfish relaying processes, but this study aims to determine whether the purification time can be reduced to make relaying an attractive activity for producers. For this purpose, mussels (Mytilus galloprovincialis) and Pacific oysters (Magallana gigas) were submerged for 6 weeks in a port near untreated urban discharges and then transferred to a relaying site located in open waters off the Basque coast (Southeastern Bay of Biscay). Salmonella spp. and Escherichia coli were analysed at 0, 2, 8, 14 and 21 days of depuration. After 2 days, Salmonella spp. was no longer detected in mussels or Pacific oysters. Geometric mean concentrations of E. coli (13068-14662 most probable number [MPN]/100 g) were high at the beginning of the experiment but decreased progressively. Pacific oysters needed 8 days to show E. coli values below the acceptable threshold for human consumption (230 MPN/100 g), while mussels needed 21 days. Under the studied conditions, the shellfish relaying period in open waters could be reduced while ensuring food safety.