Lesions on menhaden caused by the dinoflagellate Pfiesteria
Unknown substances freshly secreted by finfish and shellfish stimulate Pfiesteria piscicida to
transform from benthic cysts or amoebae, or non-toxic flagellated stages to toxic zoospores.
Planktivorous schools of menhaden are particularly susceptible to the toxins which are released to the
water and narcotize finfish, slough fish epidermis, and cause formation of open bleeding sores such as those shown in the photo. Photo by J.
Burkholder