THERMAL ECOLOGY AND STRESS 341 



affected. Recently we have begun to deal with a disease in fish which 

 we know to be related not only to thermal effluent but also to 

 organic loading. Indeed, we now believe it to be basically a problem 

 of stress, induced by a series of etiologies with which we can 

 associate a number of environmental variables. 



RED-SORE DISEASE, TEMPERATURE, AND STRESS 



Description of Problem 



Epistylis, a stalked, colonial ciliate, has been identified as the 

 causative agent for red-sore disease, which affects several fish species 

 in various aquatic systems throughout the southeastern United States 

 (Rogers, 1971). The protozoan has a motile telotroch stage that 

 attaches to a substrate, forms a stalk, and produces feeding bodies 

 called zooids. When attached to the surface of a fish, it is said to 

 cause scale erosion, producing pit-like lesions. The gram-negative 

 bacterium Aeromonas hydrophila enters the tissues via these lesions 

 and in time produces hemorrhagic septicemia and death. 



Because of the heavy mortality from the disease, it has drawn 

 considerable attention over the past few years. For example, more 

 than 37,500 fish were killed in a few weeks in 1973 in Badin Lake, 

 on the Yadkin River in North Carolina (Dean, 1974). During the fall 

 of 1976, approximately 95% of the white perch population in 

 Albemarle Sound, North Carolina, was killed by an epizootic of 

 red-sore disease (Cook, 1976). During the same outbreak, 50% of the 

 commercial catch of all species was discarded because of the presence 

 of unsightly surface lesions associated with red-sore. 



Despite the widespread nature of red-sore disease in the 

 southeast, its epizootiology has not been extensively studied. Indeed, 

 some literature on the problem is confusing, if not actually 

 contradictory. For example, Rogers (1971) stated that Epistylis is 

 the primary invader, with A. hydrophila then producing the second- 

 ary infection. On the other hand, Lom (1973) emphatically stated 

 that Epistylis is incapable of producing lesions and that, as a 

 bacterivore, it only secondarily associates with fish. Earlier Lom 

 (1966) reported that heavy infections of fish with Epistylis were 

 seasonal (occurring mostly in winter) and were independent of the 

 amount of organic solids and the density of bacteria in the water. 

 Bullock and McLaughlin (1970) and Meyer (1970) reported the most 

 severe outbresiks to occur during summer when temperature is high 

 and dissolved oxygen is low. During winter of 1973, Esch and 

 Gibbons (unpublished observations), noting the presence of red-sore 

 disease among several species of centrarchids in a South Carolina 



