Phycotoxins are toxins produced by various saltwater and fresh water plants, such as seaweeds and algae, under certain conditions. Many phycotoxins target the nervous systems of animals and fish that ingest them. The major source of human episodes is by eating filter-feeding shellfish (molluscs) which have fed on toxigenic algae, thereby accumulating large amounts of the toxins. HPLC is commonly used to screen for the presence of phycotoxins.