348 ESCH AND HAZEN 



muscle, there is also substantial infiltration of bacterial cells, 

 presumably A. hydrophila (Huizinga, Esch, and Hazen, manuscript in 

 preparation; Hazen, Raker, and Esch, 1977). 



A second line of evidence is provided by collaborative studies 

 conducted by Robert Gorden and colleagues at the Savannali River 

 Laboratory, Savannali River Ecology Laboratory, University of 

 South Carolina Medical School, South Carolina Wildlife and Marine 

 Resources Department, and Wake Forest University. During the 

 spring and summer of 1975, a series of unexpected alligator 

 mortalities occurred in Par Pond. In virtually all cases, A. hydrophila 

 was cultured from lungs and other internal organs at the time of 

 necropsy. This suggests that, in some manner, mortality may have 

 been related to the presence of the bacteria. A review of available 

 literature indicated that in 1971 red-sore disease induced by A. 

 hydrophila was responsible for mortality of approximately 120,000 

 fish of several species in Lake Apopka, Florida (Shotts et al., 1972). 

 In addition, 16 alligators died suddenly during the same period of 

 time, all with symptoms of red-sore disease. During the fall and 

 winter of 1976—1977, Gorden and his colleagues were able to 

 generate substantial experimental evidence to show that A. hydroph- 

 ila was capable of producing skin lesions on the surface of 

 alligators aiid that A. hydrophila could be isolated from the tissues of 

 dead and/or dying alligators. Furthermore, it was shown that surface 

 lesions and mortality in alligators could be induced without a 

 primary infection by Epistylis. Indeed, Epistylis was not present in 

 50 alligators with experimentally induced red-sore disease. 



Finally, for A. hydrophila to be the primary invader, it is 

 essential that the bacteria be capable of producing an extracellular 

 toxin. Liu (1961) and others reported that A. hydrophila produces a 

 number of potent exotoxins capable of inducing lesions such as those 

 typically associated with red-sore disease. 



On the basis of these observations, we feel confident in stating 

 that the etiological agent for red-sore disease is A. hydrophila. 

 Therefore, our further discussion is directed toward understanding 

 the biology of the bacterium and its relation to the disease in fish. 



Seasonal and Other Factors Associated with Red-Sore Disease 



Previous studies have shown that red-sore disease differentially 

 affects five species of centrarchid fish in Par Pond (Esch et al., 1976); 

 infection percentages were consistently highest for largemouth bass 

 (Micropterus salmoides). Since this trend has been the same since 

 1974, efforts have focused on this species of fish. 



