Skin ulcers in fish: Pfiesteria and other etiologies

Skin ulcers on fish are one of the most well-recognized indicators of pollu ted or otherwise stressed aquatic environments. In recent years, skin ulcer epidemics have been either experimentally or epidemiologically linked to e xposure to a number of xenobiotic chemicals as well as to biotoxins. Some o f these agents, such as toxins produced by the dinoflagellate alga Pfiester ia, have led to serious concerns about the health of aquatic ecosystems, su ch as estuaries along the east coast of the United States. However, a numbe r of other risk factors besides Pfiesteria have been shown to damage epithe lium and may also play important roles in skin ulcer pathogenesis. In addit ion, increasing evidence indicates that not only may skin damage occur via direct contact with toxins, but it may also be induced indirectly from phys iological changes that result from exposure not only to toxins but also to other environmental stressors, such as pH and temperature extremes. The mul tifactorial pathways that operate at both the ecological and the organismal levels as well as the nonspecific response of the skin to insults make it very challenging to link epidemic skin ulcers to any single cause in natura l aquatic populations. Consequently, using pathology to unequivocally ident ify the specific cause of a lesion (eg, Pfiesteria exposure) is not a valid approach. Only with an increased understanding of the basic mechanisms lea ding to skin damage (including development of specific biomarkers for speci fic toxins), along with a better understanding of ecological processes oper ating in these environments, will we be able to discern the relative import ance of various risk factors in skin ulcer development.