Clean the shrimp, rinse in cold water and drain.
Heat the vinegar in a suace pan with about ten of the bay leaves, but do not allow to boil. Remove the bay leaves and set aside to cool.
Place in a jar a layer of shrimp, a layer of sliced onions, a few bay leaves; repeat until all the shrimp have been used.
Make a dressing using the vinegar, oil and seasonings. Pour dressing over the shrimp and allow to stand in the refrigerator at least 8 hours before serving.