FISHERY BULLETIN: VOL. 70. NO. 3 



Figure 1. — Daytime on a coral reef in Kona, Hawaii. Most of the fishes are acanthurids, 

 including Ctenochaetus strigosus, Acanthuriis leucopareiiis, and Zebrasoma flavescens. 

 Other fishes include Centropyge potteri and Zanclus canescens. 



brightest days, and by 15 min before sunset all 

 of them have dispersed among holes in the reef. 

 The progressive descent of the other plankton- 

 feeding damselfishes is treated below. 



As individuals of C. vanderbilti are taking 

 shelter, the transition to the nocturnal situation 

 is clearly underway. The numbers of smaller 

 wrasses active on the reef have been noticeably 

 declining since at least 30 min before sunset, 

 though many still remain in view. More obvi- 

 ous, an increased tendency to aggregate is 

 exhibited by some of the smaller herbivorous 

 fishes, including the surgeonfishes Acanthuriis 

 nigrofuscus (120: 100-140 mm) and Ctenochae- 

 tus strigosus (125: 110-145 mm) and also the 

 •parrotfish Scams taeyiiurus (210: 180-243 mm). 

 These aggregations continue to develop through 

 sunset and into early twilight. 



By about 5 min after sunset the last individu- 

 als of many diurnal species have taken cover, 

 including the last of the smaller wrasses. No 

 data are available on precisely when the larger 



wrasses seek cover (those exceeding a length of 

 about 350 mm are uncommon in the study areas) . 

 Nevertheless, my observations agree with those 

 of Gosline and Brock (1960) , who stated that all 

 Hawaiian labrids are inactive at night. 



Two species of smaller labrids are representa- 

 tive: Thalassoma duperrey (125: 103-146 mm) 

 and Labroides phthirophagus (63: 33-91 mm). 

 (I did not collect specimens of the latter species 

 — size data are from Youngbluth, 1968.) T. du- 

 perrey probably is the most numerous of the 

 readily observed species of fish overall in the 

 various Hawaiian reef habitats and thus serves 

 well as an indicator species. L. phthirophagus 

 is not abundant, but as a cleaner fish that centers 

 its activity around well-defined stations (Ran- 

 dall, 1958; Youngbluth, 1968), individuals can 

 be readily recognized from one evening to an- 

 other. 



Observations on Thalassoma duperrey, — On 

 five occasions I was confident that I observed 



718 



