Fuiman and Ottey Temperature effects on behavior of young Sciaenops ocellatus 



27 



o 



300 



-■a -A £.__ 



— *- 



CO 



Time Since Transfer (h) 



Figure 1 



Time-course for activity of young red drum Sciaenops ocellatus 

 at two acclimation temperatures. Points represent means of 

 six observations. Upright triangles and broken lines refer to 

 control trials at 26° C. Inverted triangles and solid lines refer 

 to control trials at 21°C. Filled symbols denote periods in 

 which activity differed significantly at the two temperatures. 

 Panels show data for small (upper), medium (middle I, and 

 large (lower) fish. 



treatment, and time since transfer) had a significant 

 influence on pause frequency. Differences among the 

 size-classes were present within each of the treatments 

 (Table 2). 



Within individual fish (all sizes combined) there were 

 significant differences in pause frequency with time in 

 all treatments except the downward transfers (Table 

 2). These differences among time-periods followed lin- 

 ear trends in most temperature treatments for small 

 fish. Among medium and large fish, temporal trends 

 were less common, but curvilinear (quadratic) rela- 



tionships were significant in two combinations of tem- 

 perature treatment and size-class (Table 2). 



Controls Pause frequency differed significantly be- 

 tween the two control temperatures for small and large 

 fish (Table 2). For those sizes, pause frequency was 

 higher at 21° C (Fig. 3). 



Pause frequency generally increased with time since 

 transfer, but the amount of change during the experi- 

 ment was small for medium and large fish. Temporal 

 trends stabilized after about 2.5 h in most treatments 

 (Fig. 3). Trends for small fish were parallel, with a 

 mean difference of 13.6 (±4.1) additional pauses/5 min 

 at 21° C. Large fish had roughly parallel trends during 

 the first 3 h, with a mean difference over that period 

 of 7.5 (±3.0) pauses. Mean differences between control 

 values after behavior stabilized (3h) were -12.9 (±2.0), 

 0.2 (±2.6), and -4.0 (±2.4) pauses/5 min for small, me- 

 dium, and large fish, respectively. 



Differences between the control temperatures dur- 

 ing individual time-periods were present throughout 

 the experiments on small fish. For the two larger sizes, 

 significant differences were confined to the first 2.5 h, 

 highlighting the converging trends for those sizes. It 

 appears that an immediate effect of handling is to 

 depress pause frequency. The magnitude and duration 

 of the effect is temperature-dependent. 



Transfers Small and large fish showed qualitatively 

 similar responses to the 5°C temperature change, rela- 

 tive to control values. Pause frequency was depressed 

 by upward transfer. For the same size-classes in down- 

 ward transfers, pause frequency increased slightly at 

 first, then dropped to values below controls (Fig. 4). 

 The response of medium fish to upward transfer was 

 similar in form to the downward transfer of the other 

 size-classes. In downward transfers their response was 

 the same as that of low controls, producing a corrected 

 pause frequency of zero. Variability in these apparent 

 differences was great, and the only significant differ- 

 ence between transferred fish and their controls was 

 for small fish in upward transfers (Table 2). 



Small fish paused consistently and significantly less 

 often after experiencing a 5°C increase (Fig. 4, Table 2). 

 Large fish showed a similar, though smaller and non- 

 significant, response. Mean differences between upward 

 transfers and low controls were -6.8 (±4.3) and -4.1 

 (±2.8) s for small and large fish, respectively. Differ- 

 ences at individual time-periods were rare in upward 

 transfers, at all sizes, but the overall effect of time 

 since transfer was always significant (Table 2). 



Downward transfer did not result in a significant 

 overall effect on pause frequency, relative to controls, 

 for small, medium, or large fish (Table 2). However, 

 there were temporal trends in the differences between 



