HOBSON: FEEDING RELATIONSHIPS OF FISHES 



nematocysts present, at least some coral tissue is 

 also taken (although nothing was found recogniz- 

 able as such). Presumably at least much of this 

 material had been freshly ingested, because it 

 came from individuals that were actively feeding 

 when collected. Johannes (1967) and Coles and 

 Strathman (in press) have shown there are 

 significant quantities of organic material in coral 

 mucus that could nourish a wide range of animals, 

 including fishes. A similar butterflyfish, 

 Chaetodon trifasciatus , not numerous in Kona, 

 has feeding behavior similar to C. ornatissimus. 



CONCLUSION. — Chaetodon ornatissimus is a 

 diurnal fish that feeds on coral during the day, 

 obtaining significant nourishment from coral 

 mucus. 



Chaetodon aiiriga Forskal 



In Kona this chaetodontid is less abundant than 

 many of its congeners. Generally paired, it swims 

 close to the reef in daylight, occasionally picking 

 at objects on the sea floor. At night it is alert close 

 among ledges and other reef irregularities. 



All six specimens (151: 132-160 mm) collected 

 had full stomachs including four taken during the 

 afternoon and two taken on a dark night, 3 h after 

 sunset. All these specimens contained similar 

 prey in what seemed similar condition. The data 

 are too few to draw conclusions regarding noctur- 

 nal activity, but suggest that this species may feed 

 after dark. Items in the stomachs of these six 

 specimens are listed in Table 36. 



Most of the food items were fragmented, includ- 

 ing the unidentified material, and many of them 

 were relatively fresh. Clearly, this chaetodontid 

 obtains most of its food by tearing pieces from 

 larger sessile organisms. Hiatt and Strasburg 

 (1960) found similar prey in C. auriga from the 

 Marshall Islands. 



CONCLUSION. — Chaetodon auriga preys on a 

 wide variety of benthic organisms during the day, 

 obtaining most of its food by tearing off pieces of 

 larger sessile animals. It also seems to feed to 

 some extent after dark. 



Chaetodon fremblii Bennett — 

 blue-striped butterflyfish 



This butterflyfish is most numerous where large 

 basalt boulders are interspersed with small pock- 

 ets of sand. Sometimes paired, but more often sol- 

 itary, this chaetodonid picks at objects on the 

 rocks and in the sand during the day. At night it 

 occurs close among cover, alert but seemingly in- 

 active. 



Fourteen specimens (103: 86-120 mm) were 

 speared during day and night. All eight collected 

 during the afternoon had full stomachs, whereas 

 the two taken from among rocks at night, between 

 4 and 5 h after sunset, were empty. On the other 

 hand, three others collected together among the 

 rocks during morning twilight, about 25 min be- 

 fore sunrise after a moonless night, had material 

 in their stomachs. Two of them contained only a 

 few well-digested fragments that could have been 



Table 36. — Food of Chaetodon auriga. 



975 



