Shellfish is a general term for crustaceans and fish with shells. This includes prawns (US: shrimp) crab and lobsters, as well as mussles and clams and the like. In western Europe there is general advice not to eat filter-feeding or bivalve shellfish, such as oysters, mussels and clams, unless there is an 'r' in the month. This would exclude eating them in May, June, July and August. This is generally felt to be because they may be in their breeding season and the flavour becomes milky and weak as energies are put into other things than their own meats at this time. However, Frank Evans of North Shields in a letter to the Guardian, says that the 'real reason is that filter-feeding shellfish may have consumed toxic flagellates sieved from the plankton during those months. The bivalves, when eaten, can cause paralytic shellfish poisoning. It is safe to eat lobsters, crabs and winkles, which are not filter feeders, at any time." I wonder if is something to do with increased marine temperatures at this time of year which makes the presence of toxic flagellates more prevalent, and whether this means that global warming and the subsequent warming of the oceans may make it impossible to eat such delights in the future.