The invention relates to a method of preserving shellfish using a modified atmosphere which is rich in oxygen and which contains a second main nitrogen component, such as to preserve the live bivalve shellfish and safeguard the quality of said food for as long as possible throughout the marketing and sales process. The shellfish sales packaging must be full and well compacted, for which purpose, the units must be perfectly inserted during the filling operation using a vibrator, such that the bivalve shellfish cannot open their valves and lose intervalvular liquid throughout the sales process. The invention relates to the most popular bivalve on the market in terms of sales and price and, as a result, is of particular interest to the mussel industry.