Abstract— Spontaneous behavior 

 of young red drum Sciaenops ocella- 

 tus was examined over a period of 

 8h at two acclimation temperatures 

 (21° and 26° C) and after acute tem- 

 perature changes between these lev- 

 els. Three sizes of fish were used 

 (jc=9, 23, and 34mmTL). Activity of 

 fish acclimated to 26° C was greater 

 than that at 21°C for fish of all sizes. 

 Duration of pauses in spontaneous 

 activity was generally lower at the 

 warmer temperature. Effects of han- 

 dling stabilized after 2-5 h. The time 

 course for activity after an acute 

 thermal change followed the tradi- 

 tional model for thermal stress, with 

 an early overshoot followed by a sta- 

 bilized period. The overshoot was 

 positive for upward transfers (21- 

 26° C) and negative for downward 

 transfers (26-21° C). Pause duration 

 showed a time course roughly in- 

 verse of the trend for activity, but 

 pause frequency was inconsistent. 

 Effects of 5° C changes stabilized af- 

 ter about 2 h. Results indicate that 

 a minimum adjustment period of 

 2-5 h is advisable when handling 

 young red drum for research or for 

 stocking into natural waters. The be- 

 havior of young red drum deprived 

 of food at acclimation temperatures 

 suggests they are sweep, rather than 

 saltatory, searchers. 



Temperature effects on 

 spontaneous behavior of larval 

 and juvenile red drum Sciaenops 

 oce/fatus, and implications 

 for foraging* 



Lee A. Fuiman 

 David R. Ottey 



The University of Texas at Austin. Marine Science Institute 

 PO. Box 1267, Port Aransas. Texas 78373-1267 



Searching for food is critical to sur- 

 vival, and any factor that influences 

 foraging behavior may have vital con- 

 sequences, especially early in life 

 when starvation is a serious threat. 

 Temperature is one of the most po- 

 tent natural factors affecting fishes, 

 and substantial thermal variability 

 may be experienced routinely. Such 

 variability can span a wide range of 

 time scales. Annual and seasonal dif- 

 ferences in water temperature are 

 common. Measurements of thermal 

 effects on this scale probably reflect 

 differences between physiologically 

 stable (acclimated) states with re- 

 spect to temperature. Differences in 

 swimming performance due to accli- 

 mation temperature are well docu- 

 mented (Beamish 1978). Shorter- 

 term temperature variations are also 

 common in nature (summarized by 

 Montgomery & MacDonald 1990). 

 Fishes residing in shallow, lentic wa- 

 ters can experience large amplitude, 

 diel temperature cycles (Bamforth 

 1962, Smid & Priban 1978). Move- 

 ment across a thermocline imposes 

 an even more rapid temperature 

 change, as does inundation of tidal 

 marshes and pools and the act of 

 stocking hatchery fish into surface 

 waters. Under these circumstances, 



Manuscript accepted 14 September 1992. 

 Fishery Bulletin, U.S. 91:23-35(1993). 



* Contribution 847 of The University of 

 Texas at Austin Marine Science Institute. 



the dynamic processes of physiologi- 

 cal adaptation to the temperature 

 change also contribute to the overall 

 thermal effect. 



Our goal was to examine the 

 effects of temperature on spontane- 

 ous behavior of young red drum 

 Sciaenops ocellatus. Here, we con- 

 strue spontaneous behavior of soli- 

 tary young fishes deprived of food as 

 that typically used in foraging. We 

 designed experiments to evaluate dif- 

 ferences in behavior at two constant 

 temperatures and after acute in- 

 crease or decrease in temperature. 

 Our measures of behavior are useful 

 for quantifying foraging effort. 



Materials and methods 



All fish were reared from eggs 

 spawned at the Fisheries and Mari- 

 culture Laboratory of the University 

 of Texas Marine Science Institute. 

 Spawning occurred in the evening at 

 27-28° C. Eggs were collected the 

 following morning and placed in 

 150 L rearing tanks maintained at 

 two nominal acclimation tempera- 

 tures (21° and 26° C), where they 

 hatched within 24 h of spawning. Lar- 

 vae were fed rotifers {Brachionus) at 

 3-4 d after hatching (3mmTL); 

 Artemia nauplii were added to the 

 diet at 10-11 d after hatching. Roti- 



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