ACTIVITY PATTERNS OF CORAL REEF FISHES WitH EMPHASIS ON 

 NOCTURNAL- DIURNAL CHANGEOVER 



Bruce B. Collette 



National Marine Fisheries Service 



Systematics Laboratory 



and 



Frank H. Talbot 



Australian Museum 



ABSTRACT 



Two hour dives were made at morning and evening changeovers for 

 17 days. Fish activity was recorded at 5 minute intervals on two 

 reefs. The first appearance of diurnal species was as early as 

 0540 hours and all were usually active before 0645 hours. 

 Damselfishes became active earlier and stayed out longer than 

 parrotfishes and wrasses. The sparse nocturnal fish fauna, pri- 

 marily cardinalfishes and squirrelf ishes , became active between 

 1812 and 1835 hours, after most diurnal fishes had disappeared 

 (1732-1812 hours). Delay and extension of changeover in several 

 species of fishes correlated with storm-caused turbidity one 

 morning indicates that these fishes may have a primarily 

 exogenous clock. 



OBJECTIVE 



Our objective was to describe in detail rhythms of activity that are 

 correlated with the daily light-dark cycle in coral reef fishes. Pre- 

 vious work has demonstrated general patterns of day and night behavior; 

 however, earlier workers found it difficult to directly observe the 

 complete changeover. We tried to find out when each species became 

 active and when it became quiescent relative to ambient light levels. 



EQUIPMENT 



Equipment consisted of underwater light, pencils, and plastic slates 

 upon which to record our observations. The use of the rebreather 

 permitted us to gather observations much more quickly than standard 

 SCUBA because of the absence of bubbles. Additional work along these 

 lines should have a recording photometer available to record the 

 amount of light throughout the observations. 



PROCEDURES 



Two reefs were selected for study. "Habitat Reef," lay immediately 

 adjacent to the Habitat at a depth of 15 m and was selected because 

 of its proximity and because we could watch the changeover while on 

 hookah from the habitat. The presence of the habitat, diver activity, 



VI-257 



