FISHERY BULLETIN; VOL. 72, NO. 4 



Hiatt and Strasburg (1960) noted only tips of 

 coral polyps in one C. lunula from the Marshall 

 Islands. Although the diet of this individual di- 

 verges sharply from that of representatives in 

 Kona, one cannot speculate on its significance 

 from one specimen. 



CONCLUSION. — Chaetodon lunula preys on 

 benthic invertebrates, especially opisthobranchs, 

 at night. 



General Remarks on Angelfishes 

 and Butterflyfishes 



The two Hawaiian angelfishes, Holacanthus ar- 

 cuatus and C entropy ge potter i, have feeding habits 

 that set them apart from the butterflyfishes. 

 Holacanthus arcuatus is the only chaetodontid 

 that feeds strictly on sponges, and C. potteri is the 

 only one that takes just algae and detritus. Thus 

 the Hawaiian situation parallels that in the tropi- 

 cal Atlantic, where species o^ Holacanthus and of 

 Pomacanthus (another genus of angelfish) feed 

 mostly on sponges and where species of 

 Centropyge feed almost exclusively on algae and 

 detritus (Randall, 1967). Similarly, Hiatt and 

 Strasburg (1960) reported a strictly herbivorous 

 diet for C. flavissimus in the Marshall Islands. 



Although butterflyfishes in Kona are more 

 strictly predators in the conventional sense than 

 are the angelfishes, Hiatt and Strasburg (1960) 

 reported Chaetodon reticulatus in the Marshall 

 Islands to be strictly herbivorous. That species is 

 seen only occasionally in Kona, and so was not 

 included in the present study. Otherwise, Hiatt 

 and Strasburg found scleractinian corals and 

 polychaetes to be the major food of butterflyfishes 

 in the Marshall Islands, and this is in broad accord 

 with the habits of certain species in Kona. Randall 

 (1967) reported that West Indian butterflyfishes 

 feed primarily on anthozoans and the tentacles of 

 polychaetes, again paralleling the habits of cer- 

 tain Kona species. On the other hand, the number 

 of planktivorous butterflyfishes in Kona seems on 

 a scale without parallel in published accounts of 

 other reef areas. 



Chaetodontids have been widely described as 

 diurnal fishes, e.g. in the tropical Atlantic (Starck 

 and Davis, 1966; Collette and Talbot, 1972), and in 

 the Gulf of California (Hobson, 1965, 1968a). Al- 

 though diurnal habits are generally characteristic 

 of chaetodontids in Kona, the fact that at least one, 

 Chaetodon lunula, is nocturnal and that several 



others feed at least somewhat after dark may 

 reflect increased interspecific pressures associated 

 with the large number of Chaetodon species on 

 Kona reefs. I treat the nine most numerous species 

 of Chaetodon here, but also saw five others during 

 this study. 



Family Pomacentridae: damselfishes 



Plectroglyphidodon johnstonianiis 

 Fowler and Ball 



This solitary species is most numerous where 

 stony corals abound. During the day it swims close 

 to the reef, each individual seemingly associated 

 with a particular location, and here it picks fre- 

 quently at the substratum, especially around 

 coral. At night it is secreted deep among the coral, 

 relatively inactive, but alert. 



Of the eight specimens (60: 39-70 mm) ex- 

 amined, the stomachs of two that were speared 

 among the coral shortly before dawn contained 

 only a few well-digested fragments (probably 

 material that had been ingested during the previ- 

 ous day), whereas the stomachs of all six taken 

 during midday were full of food, much of it fresh. 



The major food item in all six was anthozoans: 

 nematocysts and zooxanthellae, with tissue 

 fragments and mucus, but no skeletal material 

 (mean percent of diet volume and ranking index: 

 94.3). All other items made up only a minor part of 

 the diet: algal fragments in three (mean percent of 

 diet volume: 2; ranking index: 1), sipunculid in- 

 troverts in one (mean percent of diet volume: 0.2; 

 ranking index: 0.03), and unidentified fragments 

 in four (mean percent of diet volume: 3.5; ranking 

 index: 2.33). Because P . johnstonianus is closely 

 associated with scleractinian corals, these proba- 

 bly are the anthozoans so prominent in its diet. 

 However, specific identifications of the frag- 

 mented gut contents remain uncertain, and be- 

 cause direct observations of feeding are limited, 

 other anthozoans may also be involved. In any 

 event, the observations indicate that this fish is 

 adept at snipping off pieces of anthozoan tissue 

 and mucus without taking any of the surrounding 

 skeletal material. 



CONCLUSION.— P/ec^ro^/jp^irforfon john- 

 stonianus is a diurnal predator that feeds chiefly 

 on anthozoans. 



978 



