56 W. W. Reynolds, M. E. Casterlin, D. G. Lindquist 



MATERIALS AND METHODS 



The fishes (38-60 mm standard length) were captured by seine or hand 

 net, either in the lake or in backwaters of the Big Creek tributary, and 

 tested individually in Ichthyotron electronic shuttleboxes as described by 

 Reynolds (1977). These devices permit a fish, by passing through an 

 electronic gate (light beam), to control water temperatures by normal 

 swimming movements, which are monitored automatically via photo- 

 transistors. The fish were tested during the first half of August 1981, 

 under a natural photoperiod of 14 h light: 10 h dark (LD 14:10). Final 

 thermal preferenda, which are independent of thermal acclimation (Rey- 

 nolds & Casterlin 1979, 1980), were measured, and hourly activity as 

 registered by the phototransistors (mean light beam interruptions per 

 hour) were used to characterize diel activity patterns (Table 1). In gen- 

 eral, more precise behavioral thermoregulators will show greater activity. 

 The relative amount of activity (light beam interruptions) during day, 

 night, and crepuscular periods is used to determine the diel patterns. 



RESULTS 



All species exhibited mean final thermal preferenda between 25 ° and 

 30° C (Table 1). Various measures of central tendency failed to coincide 

 for each species because of skewness in the distributions of occupied 

 temperatures. Of these species, Lepomis marginatus was the most precise 

 behavioral thermoregulator, exhibiting the smallest range and standard 

 deviation, while Menidia extensa was the least precise. Thus, the former 

 species also exhibited the highest hourly activity rate, while the latter was 

 the least active. Noturus gyrinus preferred the warmest temperatures, and 

 Enne acanthus chaetodon the coolest, in terms of mean value. 



Fundulus waccamensis was the only diurnal species as determined by 

 maximal activity, while Etheostoma perlongum and Noturus sp. were 

 nocturnally most active (Table 1). The other species were crepuscular, 

 being most active around dawn and/ or dusk. Here there was a marked 

 behavioral difference between the two Noturus species, which often share 

 the same microhabitats and nesting sites (Lindquist, unpubl.). 



During the first half of August 198 1 , normally a time of warmest water, 

 the temperatures in the lake ranged from 27.4 ° to 3 1 .0 ° C over all areas 

 and depths. Warmest temperatures occurred near the mouth of Big 

 Creek, the major tributary. In the creek and associated canals, tempera- 

 tures ranged from 24.8 ° to 30.9 ° C during the same period. 



DISCUSSION 



Lake Waccamaw does not normally freeze completely over in winter, 

 nor does it stratify thermally to any significant extent in summer, as its 

 maximum depth is only about 3 m. The temperatures preferred by the 



