Ecohab: Pfiesteria Or Fungus? Etiology Of Lesions In MenhadenEPA Grant Number: R828225
Title: Ecohab: Pfiesteria Or Fungus? Etiology Of Lesions In Menhaden
Investigators: Shields, Jeffrey , Haas, Larry , Kator, Howard , Vogelbein, Wolfgang K.
Current Investigators: Shields, Jeffrey , Blazer, Vicki , Haas, Larry , Kator, Howard , Kiryu, Yasunari , Vogelbein, Wolfgang K.
Institution: Virginia Institute of Marine Science
Current Institution: Virginia Institute of Marine Science , College of William and Mary-VA
EPA Project Officer: Hiscock, Michael
Project Period: June 16, 2000 through June 15, 2003
Project Amount: $508,937
RFA: Ecology and Oceanography of Harmful Algal Blooms (1999) RFA Text | Recipients Lists
Research Category: Aquatic Ecosystems , Water Quality , Water , Ecosystems
Description:Menhaden, Brevoortia tyrannus, develop ulcerous skin lesions that have been attributed to exposure to Pfiesteria piscicida toxins. The characteristic lesions present as deep penetrating circular ulcers with intense granulomatous inflammation. There, however, is controversial evidence that the lesions are caused by an oomycete fungus, Aphanomyces sp., either as a primary or secondary invader. The fungus is almost always associated with the lesions, with hyphae penetrating the tissues and organs of the infected fish.
Biological and environmental stressors appear central to the etiology of ulcers on menhaden. We hypothesize that the development of the disease requires some initiating stressor(s) that erode, damage or penetrate the epidermis and expose the underlying dermis. Recent experiments with striped bass and tilapia exposed to sublethal levels of P. piscicida indicate that fish experience an initial loss of the epidermis. The goal of the project is to identify the interrelationships between menhaden, Pfiesteria, and Aphanomyces, and the environmental conditions that may modulate or contribute to the epizootics of ulcers on the fish. The objectives are to conduct controlled laboratory exposure studies with menhaden to (1) identify the causal agents responsible for the ulcerous lesions, and (2) identify contributory environmental and biological conditions that are required for the development and progression of the lesions.
Approach:We want to understand the time course of the disease in menhaden and what specific biotic and abiotic stressors result in epidermal lesions. We will undertake controlled aquarium challenge studies to examine the effect of individual stressors (P. piscicida, Aphanomyces sp., trauma, dissolved oxygen, and pH) on the skin and fins of menhaden. Standardized exposures consist of placing fish in bath cultures of Pfiesteria piscicida or Aphanomyces sp., or housing fish in aquaria adapted to strictly regulate environmental conditions over controlled periods. Fish are then moved to aquaria and monitored for the development of lesions.
Single factor and two factor experiments are planned. For example, the Pfiesteria-Aphanomyces series of combination experiments will consist of an experimental group of fish exposed to sublethal levels of a toxic Pfiestiera culture (8-12 hr), an experimental group of fish exposed to a known quantity of fungal zoospores, an experimental group of fish pre-exposed to cultures of Pfiesteria (8-12 hr), then exposed to a known quantity of fungal zoospores, and control groups of unexposed fish. After four weeks, any sample not resulting in overt toxic pathology will be assessed as not contributing to the formation of lesions. Each combination of stressors and organisms will be tested as outlined above. During exposure studies, cell densities of dinoflagellates will be monitored using a hemacytometer. Critical water quality parameters (dO, nitrite, ammonia, pH) will be monitored and maintained within acceptable levels. Pathological effects will be examined histologically and ultrastructurally using well described methods.