The role of grazing fish in the phytoplankton dynamics of solar silo microcosms was examined by following the quantitative effects of grazing as measured by chlorophyll a (chla), total protein (TP), and phytoplankton cell counts for 15 weeks. Qualitative effects during this period were measured by recording phytoplankton community composition changes. Three treatments were used: a control silo with no fish, two “low” density silos containingOreochromis aureusat 8 m−3, and two “high” density silos containingO. aureusat 17 m−3.