HOBSON and CHESS: TROPHIC RELATIONSHIPS AMONG FISHES 



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Figure 6. — Planktivorous fishes where currents are strong. Major species in each of the zones identified in the photo by roman 

 numerals are illustrated in the appropriate column below the photo (placement based on observations made at the scene). I. 

 Pomacentrus vaiuli; II. a, Chromis agilis, b, C. margaritifer; III. a, C. caerulea, b, C. lepidolepis; IV. Mirolabrichthys pascalus; V. 

 Pterocaesio tile. 



to 60 mm SL, x = 55.9, had longest dorsal fin spines 

 that were 20.3 to 23.4%, x = 21.0%, of their stan- 

 dard length, whereas these values for 13 individu- 

 als of Chromis spp. (4 C. agilis, 4 C. caerulea, and 5 

 C. lepidolepis ), 52 to 70 mm SL, x = 59.4, were 12.3 

 to 16.1%, x= 15.3%. The significance of these data 

 becomes clear when possible selective values of 

 both fusiform and deep-bodied morphologies in 

 planktivorous fishes are treated in the Discussion. 

 Although most diurnal planktivorous fishes fa- 

 vored conditions associated with current, the 



strongest currents observed at this site, approxi- 

 mately 1 m/s, clearly exceeded optimum veloc- 

 ities. When such currents flowed, most of the smal- 

 ler planktivores were close to the reef, many of 

 them concentrated in the lee, and their feeding 

 rates had noticeably declined. 



In comparison to the great numbers of adult 

 diurnal planktivores in these surroundings, the 

 nocturnal planktivores were sparse. Although ob- 

 servations underwater in this habitat at night 

 were limited, only a relatively few individuals of 



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