OBJECTIVES: Objective 1) Assess the effects of Microcystis toxins on blue crab immune functions. Using crabs fed defined amounts of toxic Microcystis for prescribed periods of time, we will measure: A. histological appearance of hematopoietic tissue and hemocytes, B. hemocyte number and hemolymph clotting time C. reactive oxygen production by hemocytes D. phenoloxidase activity in hemocytes METHODOLOGY: Hatchery-reared blue crabs will be exposed to defined amounts of Microcystis toxin (MC) by incorporating Microcystis of defined toxin content into crab food. Groups of crabs will be fed 1, 10, or 100 microgram/kg MC each day. At days 0, 2, 4, 8, 12 and 24, crabs will be sacrificed for analyses.