HOBSON: FEEDING RELATIONSHIPS OF FISHES 



single item greatly predominates in its diet, a 

 circumstance that may relate to its widespread 

 occurrence in a variety of habitats. 



CONCLUSION.— Sufflamen bursa is a diurnal 

 predator that feeds on a variety of benthic ani- 

 mals. 



General Remarks on Triggerfishes 



The balistids are known for their powerful jaws 

 and sharp cutting teeth, which enable them to 

 prey on a variety of armored invertebrates denied 

 as food to most other fishes (Randall, 1967). Most 

 triggerfishes seem to make full use of this equip- 

 ment: in the Virgin Islands 5a/js^es vetula preys 

 on the large echinoid Diadema (often attacking 

 this sea urchin from its oral surface, where the 

 spines are shortest) and on relatively large queen 

 conchs, Stromhus, which it crushes upon inges- 

 tion (Randall, 1967). Similarly, in the Marshall 

 Islands several triggerfishes use their powerful 

 feeding apparatus to crush mollusks and hard- 

 shelled crustaceans, as well as to break off the tips 

 of cespitose corals (Hiatt and Strasburg, 1960). 

 Rhinecanthus rectangulus and Sufflamen bursa 

 in Kona may be exceptional among bottom- 

 foraging balistids in that they feed so heavily on 

 small organisms, ingested intact. On the other 

 hand, it may be that the high proportion of 

 unidentified fragments in the guts of both species 

 are the crushed remains of larger organisms not 

 properly ranked among the data. Nevertheless, 

 the capacity to feed on tiny organisms is probably 

 well established among the balistids, as demon- 

 strated by the exclusively zooplanktivorous habits 

 o{ Xanthichthys ringens. 



Triggerfishes are well known to be active by day 

 and to rest under cover at night, usually lying on 

 their sides. Diurnal habits were reported in balis- 

 tids of the Gulf of California (Hobson, 1965, 1968a) 

 and the West Indies (Randall, 1967). Collette and 

 Talbot ( 1972) described Balistes vetula sleeping at 

 night in exposed positions on reefs in the Virgin 

 Islands, and Earle (1972) reported that in the Vir- 

 gin Islands B. vetula frequently returns nightly to 

 the same hole in the reef. There is at least some 

 activity among triggerfishes on moonlit nights, 

 however, as for example in B . polylepis in the Gulf 

 of California (Hobson, 1965), but it is unknown 

 whether this activity involves feeding. 



Family Monacanthidae: file fishes 



Cantherines dumerili (Hollard) — 'o'i7i 



During daylight, this filefish swims several 

 meters above coral-rich reefs, usually in loosely 

 associated pairs that move, often on their sides, 

 back and forth in restricted, well-defined areas. 

 Because it swims in the water column and because 

 it is relatively large, this filefish is a conspicuous 

 component of the fauna, even though relatively 

 few occur on the reef. Despite the time it spends in 

 mid-water, C. dumerili was obsei'ved feeding only 

 on the sea floor, where it bites off the tips of coral 

 branches. During evening twilight it settles into 

 holes in the reef, where it remains inactive until 

 morning. 



All eight individuals (200: 171-240 mm) 

 speared from among those hovering above the reef 

 during midday were full of food. Scleractinian cor- 

 als were the major food items, occurring in seven 

 of the eight specimens (mean percent of diet vol- 

 ume: 80; ranking index: 70), always as chunks of 

 Pocillopora and Porites. about 4 mm in diameter. 

 Other food items were: echinoids, all tips of the 

 clublike spines of Heterocentrotus mammillatus , 

 in two (mean percent of diet volume: 7.4; ranking 

 index: 1.85), a variety of bryozoans, both encrust- 

 ing and arborescent, that were almost the total 

 contents of one (mean percent of diet volume: 

 12.5; ranking index volume: 1.56), and pelecypods 

 in one (mean percent of diet volume: 0.1; ranking 

 index: 0.01). 



Hiatt and Strasburg (1960) found that of the two 

 specimens of this species (reported as Amanses 

 carolae) that they examined in the Marshall Is- 

 lands, one had fed on scleractinian corals exclu- 

 sively, whereas the other had mixed a coral diet 

 with sponges and algae. Apparently this species 

 does not feed during the considerable time that it 

 spends in the water column, as its diet seems to 

 comprise only benthic organisms. 



CONCLUSION .—Cantherines dumerili is a 

 diurnal predator that feeds mainly on scleractin- 

 ian corals. 



Cantherines sandwichiensis 

 (Quoy and Gaimard) — oili lepa 



This, the most numerous filefish in Kona, espe- 

 cially on basalt reefs in less than 10 m of water, is a 

 solitary fish that swims close over the reef during 



1009 



