FISHERY BULLETIN: VOL. 72, NO. 4 



Table 63. — Food of Melichthys niger. 



proportion of coralline algae in its diet and also by 

 the stony coral, bitten off in chunks, in one indi- 

 vidual; nevertheless, most of its food is planktonic. 

 Certainly the relatively minor status of the many 

 zooplankters in the above list far understates 

 their relative significance to this fish. The ranking 

 is biased toward the more bulky items; thus, one 

 algal fragment, in terms of volume, may be equiv- 

 alent to a hundred or more copepods. And yet the 

 effort expended in taking the algal fragment 

 may have been no greater than that expended in 

 taking a single copepod. A given volume of 

 copepods (and many other zooplankters) probably 

 is far more nutritious than the same volume 

 of algae. 



In the West Indies, this circumtropical trigger- 

 fish similarly feeds on algae and zooplank- 

 ton in the mid-waters, taking the algae from the 

 benthos, or as drifting fragments (Randall, 1967). 



CONCLUSION.— Melichthys niger is a diurnal 

 omnivore that feeds mostly on drifting algal frag- 

 ments and zooplankton, along with some benthic 

 vegetation. 



Xanthichthys ringens (Linnaeus) 



This triggerfish (Figure 40) is one of the most 

 numerous fishes at depths below 25 m along the 

 outer drop-off Like so many fishes that concen- 

 trate in this location, it aggregates in the water 

 column and picks plankton, an activity that is 

 limited to daylight; at nightfall, it shelters in reef 

 crevices, where it rests on its side until morning. 



Of the 11 specimens ( 125: 98-145 mm) speared 

 during day and night, 2 that were collected from 

 reef crevices during the last hour before daybreak 

 were empty, whereas all 9 that were taken from 

 mid-water aggregations at various times during 

 the day were full of food, as listed in Table 64. 



I found no evidence that this triggerfish takes 

 food from the sea floor. Like Melichthys niger, X. 

 ringens is circumtropical (Bohlke and Chaplin, 

 1968); perhaps the planktivorous habits of 

 these two triggerfishes permit survival over long 

 periods in the open sea where their bottom-feeding 

 relatives would perish. Gosline and Brock (1960), 

 whose data were mostly from relatively shallow 

 water, reported X. ringens uncommon in Hawaii. 

 The large numbers of this species occurring along 

 the outer drop-off in Kona, however, indicates a 

 habitat in Hawaii similar to that in the West In- 

 dies, where it rarely occurs in less than 35 m of 

 water, but is one of the most numerous fishes 

 below that depth (Randall, 1968). 



CONCLUSION .—Xanthichthys ringens is a 

 diurnal planktivore that feeds mostly on calanoid 

 copepods. 



Rhinecanthus rectangtilus (Bloch and 

 Schneider) — humithumu nukuniiku a piiaa 



This triggerfish is most common on shallow, 

 surge-swept, basalt reefs. It is a solitary fish that 

 swims close to the reef top during the day, picking 

 at organisms on the bottom. A wary animal, it 

 quickly takes refuge in the reef when threatened. 



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