HOBSON: FEEDING RELATIONSHIPS OF FISHES 



13. Characteristics developed in feeding on ses- 

 sile benthic invertebrates have been modified in 

 some fishes for grazing on benthic vegetation. 

 Thus, many families, for example the Chaetodon- 

 tidae, Pomacentridae, Balistidae, and Monacan- 

 thidae, include some strictly carnivorous forms 

 that prey on benthic invertebrates, other forms 

 that feed on both benthic invertebrates and vege- 

 tation, and still others, strictly herbivorous, that 

 only graze on benthic vegetation. 



14. On coral reefs there is no sharp distinction 

 between fishes that feed on sessile invertebrates 

 and those that graze on benthic vegetation: 

 species in both categories tend to be colorful diur- 

 nal fishes with a small mouth that is part of a 

 highly evolved digestive apparatus. 



15. The plasticity in feeding habits and struc- 

 tures characteristic of higher teleosts that feed on 

 benthic organisms has led to the multiplicity of 

 closely related, and morphologically similar 

 species that live together on coral reefs. This situ- 

 ation could not have evolved without effective 

 barriers to interbreeding, which in turn requires 

 that individuals recognize others of their own kind 

 from among many very similar forms. This re- 

 quirement has been met by having developed 

 highly visible, species-specific color patterns. The 

 distinctive nocturnal color patterns of some forms, 

 for example Zanclus and certain chaetodontids, 

 indicate that, although they are diurnal, certain of 

 them need identifying features at night, as well as 

 during the day. 



16. The small mouth of higher teleosts is adap- 

 tive for feeding on the smaller plankters, like 

 calanoid copepods, that compose the vast majority 

 of organisms in the water column. This charac- 

 teristic distinguishes diurnal planktivores, in- 

 cluding certain pomacentrids, chaetodontids, and 

 balistids, from the nocturnal planktivores, which 

 include certain holocentrids and apogonids. Most 

 nocturnal planktivores have the larger mouth of 

 the generalized predators, and most of them feed 

 primarily on the larger plankters, like crab 

 megalops and mysids, that are most numerous in 

 the water column over the reef at night. 



ACKNOWLEDGMENTS 



Lloyd D. Richards assisted in all phases of the 

 field work, and James R. Chess made many of the 

 identifications of items in the gut contents, espe- 

 cially from the chaetodontids and pomacentrids. I 

 am grateful to John A. Maciolek, U.S. Bureau of 



Sport Fisheries and Wildlife, and Maxwell S. 

 Doty, University of Hawaii, for their help in mak- 

 ing preliminary arrangements for our stay in 

 Kona. William A. Gosline, University of Hawaii, 

 and John E. Randall, B. P. Bishop Museum, Hono- 

 lulu, provided taxonomic information on various 

 fishes. Kenneth Raymond, National Marine 

 Fisheries Service, made the drawings that appear 

 as Figures 1, 26, and 27a and b. Finally, I thank 

 Carl L. Hubbs and Richard H. Rosenblatt, Scripps 

 Institution of Oceanography, for helpful com- 

 ments on the manuscript. 



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