Harmful dinoflagellate blooms found to co-occur with high levels of organic nitrogen in hybrid striped bass aquaculture ponds. In recent years, harmful algal blooms, in particular those of the icthyotoxic dinoflagellates, Gyrodinium galatheanum and Pfiesteria piscicida , have caused massive mortality of fish in both natural riverine systems along the east coast of the United States and in cultured fish ponds. Fish ponds are typically hypereutrophic, as fertilizer or feed additions are made routinely to promote blooms or to sustain the fish. In hybrid striped bass ponds, dinoflagellate blooms, and resulting fish stress or mortality, are common. Analysis of inorganic and organic nutrients, coupled with phytoplankton community composition demonstrate that there is a striking relationship between urea concentration and dinoflagellate populations.
Many dinoflagellates use urea as a preferred nitrogen source.
By monitoring urea, and treating ponds during early bloom stages during summer 1998, losses due to these harmful bloom outbreaks were avoided. Recent algal bloom related fish kills and water quality in Delaware's Inland Bays with reference to historical Pfiesteria events. Delaware experienced two late spring fish kills in the late 1980s in mesohaline portions of Indian River that were believed to be related, but not confirmed, to some type of toxic plankton event. A large 1987 fish kill involved approximately 124,588 fish of 17 species. Water quality conditions were adequate for fish survival, although the water in the kill area was mahogany in color.