HOBSON: FEEDING RELATIONSHIPS OF FISHES 



CONCLUSION. — Hemitaurichthys thompsoni 

 is a diurnal planktivore that takes mostly 

 copepods. 



Hemitaurichthys zoster (Bennett) — 

 blackface butterflyfish 



Gosline and Brock ( 1960) stated that the color- 

 ful H. zoster (Figure 28a) and H. thompsoni attain 

 a similar size (about 175 mm), but of those seen 

 during this project, H. zoster was consistently 

 smaller. Of the two, H. zoster also was by far the 

 more numerous and more widespread. During the 

 day H. zoster aggregates much like H. thompsoni, 

 especially where the reefs drop abruptly into 

 water deeper than about 10 m. Where H. thomp- 

 soni occurred, H. zoster was always nearby, but 

 mixed aggregations of the two species were never 

 seen. Unlike H. thompsoni, which was seen feed- 

 ing only in mid-water, H. zoster sometimes is ac- 

 tive in small groups close to the reef. At night H. 

 zoster is generally solitary, close among cover in 

 the same areas where it is active in daylight. Al- 

 though H. thompsoni has the same coloration day 

 and night, H. zoster displays a color pattern at 

 night that differs strikingly from its daytime 

 coloration (Figure 28a and b). 



Twelve specimens (119: 100-128 mm) were 

 collected during day and night. Four were speared 

 during morning twilight from a group milling 

 about close above the reef just prior to rising into 

 mid-water. Two of these, taken 18 and 20 min 

 before sunrise, respectively, both had empty 

 stomachs; the third, taken 15 min before sunrise, 

 contained calanoid copepods in varied stages of 

 digestion; the fourth, taken 10 min before sunrise, 

 contained more than 100 calanoid copepods and 

 assorted other prey in varied stages of digestion. I 

 cannot believe that all these prey had been taken 

 since first light that morning, especially as no 

 feeding was observed, and these fish had not yet 

 risen to their customary plankton-feeding levels. 

 And yet H. zoster was never seen above the reef at 

 night. Until additional data are available, these 

 two specimens remain anomalous. The other eight 

 specimens, taken at various times during daylight 

 from small aggregations above the reef, all had 

 full stomachs. Items in the 10 individuals contain- 

 ing identifiable prey are listed in Table 30. 



These data indicate that H. zoster has feeding 

 habits that are less specialized than those of H. 

 thompsoni. Planktonic copepods, constituting al- 

 most 62% of its diet, are still the major prey. 



but are less dominant than in H. thompsoni. 

 Furthermore, H. zoster appears to feed signif- 

 icantly on benthic prey: the alcyonarian Sarco- 

 thelia edmondsoni constituted over 60% of the 

 material in each of the three specimens in which 

 it occurred. 



CONCLUSION. — Hemitaurichthys zoster is 

 chiefly a diurnal planktivore that takes primarily 

 copepods, but also feeds on benthic organisms, 

 especially alcyonarians. 



Chaetodon corallicola Snyder 



Observations in the western Pacific have indi- 

 cated that the Hawaiian C. corallicola is closely 

 related to, if not conspecific with, the widespread 

 Indo-Pacific C. kleini. In Kona, this species is rela- 

 tively numerous at depths below 20 m along the 

 edge of the outer drop-off In daylight it generally 

 swims in loosely associated pairs that pick free- 

 swimming organisms from the water column 

 within a meter or so of the reef. At night it remains 

 close among the coral — alert, but apparently inac- 

 tive. 



All 11 specimens (89: 75-96 mm) collected for 

 study during afternoons had full stomachs (in- 

 cluding fresh material), as listed in Table 31. The 

 only evidence of bottom feeding among this mate- 

 rial is the capreUid amphipods and hydroids, both 

 taken from the same individual. 



CONCLUSION .—Chaetodon corallicola is 

 primarily a diurnal planktivore that feeds largely 

 on copepods. 



Chaetodon miliaris Quoy and Gaimard 



Gosline and Brock (1960) noted that C. miliaris 

 is one of the commonest inshore fishes. Although it 

 is numerous in shallow water around Oahu, Brock 

 and Chamberlain (1968), using a submarine off 

 that island, found it even more abundant in deeper 

 water. They discovered it to be a dominant form at 

 depths below 120 m, where it hovered in aggrega- 

 tions 15 to 40 m above the sea floor, apparently 

 feeding on plankton. In the Kona study area, this 

 species rarely occurs in water shallower than 20 

 m, but is numerous along the outer drop-off at 30 

 m and deeper. During the day it aggregates 2 to 3 

 m above the reef, where it picks organisms from 

 the plankton. At night it is scattered among the 

 rocks and ledges, alert but apparently inactive. 



969 



