358 ESCH AND HAZEN 



As water temperature increases in an aquatic system, the 

 metabolic rates of bass will also increase (Fig. 18). With an increase 

 in metabolism, there is a concomitant rise in catabolic processes, 

 initially involving body fat but ultimately involving body protein as 

 well (Gibbons et al., in press). The body condition, or K-factor, of 

 bass affected by elevated temperature will, accordingly, decline in 

 time (assuming, of course, that caloric intake is exceeded by 

 metabolic demand). The exceedingly rapid and extensive growth of 

 luxuriant stands of the submergent, rooted, vascular macrophyte, 

 Myriophyllum spicatum, contributes to a fall in body condition in 

 summer (aside from a normal post-spawn decline). Large masses of 

 this plant provide excellent refuge for some species of forage fish. 

 Reduced foraging success among bass, coupled with increased energy 

 expenditure would exacerbate metabolic processes already conducive 

 to reducing body condition. Lowered body conditions increase the 

 probability of infection with red-sore disease. This explanation 

 certainly describes the situation that occurs during part of the spring, 

 throughout the summer, and into the fall months, before Myrio- 

 phyllum dies back and disappears. It does not explain the high 

 infection percentages that develop early in spring, however. During 

 early spring, sexually mature bass are involved with activities 

 associated with spawning and levels of circulating sex hormones (all 

 steroids) are highest. These hormones function primarily to promote 

 sexual behavior and develop secondary sexual characteristics, but 

 they are also known to enhance the establishment, maintenance, 

 and/or growth of numerous species of parasitic organisms (see Esch, 

 Gibbons, and Bourque, 1975, for review). It is, thus, conceivable that 

 elevated levels of circulating sex hormones also increase vulnerability 

 to infection with A. hydrophila. 



We believe that persistent, elevated temperature in thermally 

 altered areas of the reservoir during most seasons of the year and 

 during summer in ambient locations also promotes stress in bass. 

 Stress, in the classical sense (Selye, 1950), necessarily implies the 

 production and release of excess levels of adrenocorticosteroids, 

 some of which have a striking anti-inflammatory action that 

 promotes increased susceptibility to invasion by pathogenic organ- 

 isms. We must point out that we have no evidence for increased 

 production of corticosteroids during periods when there are high 

 levels of red-sore disease among Par Pond bass, but this line of study 

 is being pursued. We do know, however, that thyroxine levels are 

 highest in bass during the summer months (Hazen et al., 1978) and 

 that an increased level of circulating thyroxine is an indication of 

 stress among mammals. 



