HOBSON: FEEDING RELATIONSHIPS OF FISHES 



Figure 38. — Acanthurus thompsoni, a zooplanktivorous surgeonfish. In comparison with its bottom-feeding conge- 

 ners, this species carries its more upturned mouth higher on its head, its body is more fusiform, and its tail is more 

 deeply lunate. These morphological tendencies occur in many unrelated zooplanktivorous fishes. 



CONCLUSION. — Acanthurus thompsoni is a 

 diurnal planktivore that feeds mostly on semi- 

 transparent, often gelatinous, organisms — 

 especially chaetognaths, salps, siphonophores, 

 and lai'vaceans. 



Naso hexacanthus (Bleaker) — kala 



During daylight, this relatively large 

 surgeonfish swims above the outer drop-off in 



schools that periodically range farther offshore to 

 yet unknown distances. Brock and Chamberlain 

 (1968) found this species at depths below 120 m 

 when diving in the research submarine Asherah, 

 but it is not known whether these fish had mi- 

 grated from shallower water or are of deepwater 

 populations, although the latter possibility seems 

 the more probable. Generally, individuals in less 

 than 10 m of water over inshore reefs during the 

 day are relatively small, and swim in groups of 



Table 60. — Food oi Acanthurus thompsoni. 



1001 



