Many people believe that red tides cause shellfish to be toxic. Most red tides are harmless . Toxin-producing organisms do not generally cause red tides. Although the presence of a red tide is a warning that shellfish may be toxic, the absence of a red tide does not mean they are safe to eat . Shellfish can consume enough toxic organisms to become toxic even when there is no visible red tide.
Toxic mussels are very dangerous because people eat the entire mussel including the viscera.
In toxic razor clams, the toxin is present in the meat. In toxic Washington clams, the toxin is present in the siphons. Remove and discard the viscera of all clams and scallops, and the siphons of Washington clams. When domoic acid may be present, remove the viscera of anchovies and crabs immediately after capture. In fish and crabs, domoic acid is confined to the internal organs.