360 ESCH AND HAZEN 



As previously noted, red-sore disease also occurs among fish 

 species in aquatic systems that are not affected by thermal effluent. 

 In these systems the disease is associated with such conditions as 

 lowered dissolved oxygen and increased organic loading (Meyer, 

 1970; Rogers, 1971; Dean, 1974). Under these circumstances, it is 

 quite possible that bass are stressed, and this leads to increased 

 circulation of corticosteroids and then to increased susceptibility to 

 infection with red-sore disease. 



This scenario, which describes the relationships among red-sore 

 disease, body condition, and temperature in Par Pond (see Fig. 18), 

 includes the possibility that stress may be of significance in reducing 

 innate or acquired resistance of bass to infection with A. hydrophila. 

 As indicated, we have not yet generated data indicating that 

 corticosteroids are higher in bass from thermally altered areas, but 

 there is evidence in other fish species that epinephrine and 

 corticosteroids vary iii direct proportion to various types of stressors 

 (Nakano and Tomlinson, 1967; Hill and Fromm, 1968). 



CONCLUSIONS 



The aim of this discourse has been twofold. First, an effort was 

 made to describe the stress phenomenon in physiological terms and 

 to illustrate how it has application at the individual and ecosystem 

 levels of organization. Second, we attempted to represent these 

 relationships by describing the case history of red-sore disease among 

 largemouth bass in the southeastern United States. 



Hazen (manuscript in preparation) has isolated Aeromonas 

 hydrophila from lakes and streams in 34 states, from Maine in the 

 northeast, to Montana in the west, to Texas in the southwest, and to 

 Florida in the southeast. The largemouth bass, Micropterus sal- 

 moides, is present in virtually all the localities from which A. 

 hydrophila has been isolated, yet red-sore disease has been reported 

 only in the southeastern United States. On the basis of these 

 observations and of our studies in Par Pond, it seems reasonable to 

 conclude that only a unique assortment of physicochemical proper- 

 ties in a given aquatic system, an assemblage of variably susceptible 

 hosts, and the presence of virulent A. hydrophila will promote an 

 epizootic outbreak of disease. Stress and its impact at individual, 

 population, and ecosystem levels of organization would, of course, 

 temper the potential for outbreak. Thus, for red-sore disease to reach 

 epizootic proportions, a wide range of interacting biotic and abiotic 

 variables are clearly necessary. Perhaps, with additional effort, 

 conditions conducive to such outbreaks can be identified. If so, we 



