Pfiesteria piscicidaand Ulcerative Mycosis of Atlantic Menhaden—Current Status of Understanding

Abstract

Ulcerative lesions in estuarine finfish are associated with a variety of parasitic, bacterial, and fungal infectious agents as well as water quality and other abiotic stress factors. Atlantic menhaden Brevoortia tyrannus are a severely affected species typically exhibiting solitary, perianal, focal, deep, granulomatous lesions containing oomycete hyphae. Intense recent emphasis in the scientific literature and in the popular press has been placed on Pfiesteria-like dinoflagellates and their toxins as the causative agents for ulcerative finfish lesions in east coast estuaries of the United States. Dramatic descriptive terms for Pfiesteria, including "phantom," "ambush-predator" and "the cell from hell," capable of affecting humans, have appeared in scientific journals and the news media. However, there is no scientific evidence to date that supports a single, causal relationship between the presence of toxic Pfiesteria-like dinoflagellates and fish kills or the associated ulcerative lesions. This is due, at least in part, to the difficulty of maintaining toxic Pfiesteria-like dinoflagellates in clonal culture and, in part, to the presence of other microorganisms in laboratory culture systems. Further, there is at present no toxin-specific probe to identify Pfiesteria toxins in estuarine environments during fish kills, nor has Pfiesteria been isolated from fish lesions. Yet, based on the limited published scientific evidence and the popular press coverage, there have been river closures, notable economic losses, and public alarm due to Pfiesteria. Future research into agents infectious to menhaden, such as Aphanomyces (Oomycetes) and toxin-producing estuarine inhabitants like Pfiesteria, is needed. These organisms and the disease processes in which they are implicated may also serve as markers for overall estuarine condition. Control of microorganisms, including Pfiesteria, to improve finfish health in estuaries is unlikely. However, using the presence of these microorganisms and their Atlantic menhaden hosts as sentinels to help monitor water quality may be a viable approach to assist future estuarine management.

Molecular Assays for DetectingAphanomyces invadansin Ulcerative Mycotic Fish Lesions

“…The relationship between Pfiesteria and fish lesions, however, was based on laboratory studies that did not simulate natural conditions. Those studies were challenged by a number of researchers (10,11,(41)(42)(43)(44), and there is now a large body of research evidence that supports the primary role of A. invadans in causing UM. Repeated histological surveys of UM-affected fish have found a high number of broad aseptate hyphae in the ulcers (2,4,12,13,24,25,35).…”

Pathogenicity and oxidative stress in Nile tilapia caused by Aphanomyces laevis and Phoma herbarum isolated from farmed fish

“…*Significantly different from control (p < 0.05) Aphanomyces to induce ulceration in fish (Dykstra et al 1989, Dykstra & Kane 2000, Kiryu et al 2003, Sosa et al 2007) but data regarding oxidant or antioxidant status in response to such fungal infections are not available in literature. The present study showed that LPO level in gills of fish exposed to the 2 infection agents was strongly increased but was not affected in muscles of fish compared with the control.…”

“…Also, some species of the genus Aphanomyces induce skin and muscle lesions termed ulcerative mycosis in fish from western Atlantic estuarine waters (Dykstra & Kane 2000). Most studies of the pathological effect of fungal infection on fish have not focused on studying the oxidant or antioxidant status.…”

Scientific Opinion on Epizootic Ulcerative Syndrome

“…A variety of factors leading to skin damage appear to predispose fish to infection, including physical trauma (Kiryu et al, 2003), exposure to water of low pH (Bondad-Reantaso et al, 1992;Callinan et al, 1996;Fairweather, 1999;Choongo et al, 2009), skin lesions as a result of intra-species aggression (biting) (Fairweather, 1999;Saylor et al, 2010), or infections of fish with dinoflagellates (Dykstra and Kane, 2000). Challenge experiments with strains of A. invadans from Southeast Asia have suggested that zoospores attach to the dermis and not the epidermis before invasion .…”

“…drop in water salinity, low alkalinity and high ammonia, general poor water quality, low oxygen levels) (Callinan et al, 1989;Virgona, 1992;Pathiratne et al, 1999;Mohan et al, 1999;. Further factors that have been associated with infection are exposure to toxins (Dykstra and Kane, 2000) and infection with ectoparasites, bacteria or viruses .…”