THERMAL ECOLOGY AND STRESS 



349 



Red-sore disease among bass in Par Pond shows a very striking 

 seasonal periodicity. The highest incidence of infection occurs during 

 the spring months (March, April, and May), followed by lower levels 

 in summer, a decline in fall, and the lowest incidence in winter 

 (Fig. 9). Although there are differences in amplitude from year to 

 year, these seasonal variations were consistent for 36 months, 

 beginning in the fall of 1974. 



SEASON 



Fig. 9 Seasonal changes (composite for 36 consecutive months) in 

 infection percentages among large mouth bass in Par Pond. 



Since August 1975, the density of A. hydrophila has been 

 determined in vertical profile at various locations within Par Pond. 

 Temperature, dissolved oxygen, pH, redox potential, and conduc- 

 tivity were also recorded simultaneously (Hazen, manuscript in 

 preparation). As might be expected, there were seasonal changes in 

 each water-quality parameter, and A. hydrophila densities also varied 

 seasonally. The seasonal changes in A. hydrophila densities showed a 

 strong relation to the incidence of red-sore disease (Fig. 10); many of 

 the significant increases and decreases in disease among bass were 

 preceded by corresponding modulations in the density of A. 

 hydrophila in water. 



Meyer (1970) suggested that seasonal outbreaks of red-sore 

 disease may be related to depressed levels of dissolved oxygen during 

 summer months, which would lead to stress in certain fish species 

 and then to increased vulnerability to infection. Since increased 



