HOBSON: FEEDING RELATIONSHIPS OF FISHES 



invertebrates (e.g. in the tropical Atlantic by 

 Randall, 1967; and in the western Pacific by Hiatt 

 and Strasburg, 1960). Most investigators have 

 considered them diurnal. Smith and Tyler (1972) 

 described Canthigaster rostratus sleeping at night 

 on reefs in the Virgin Islands; Collette and Talbot 

 (1972) also suspected C. rostratus to be noctur- 

 nally inactive, and suggested that some they saw 

 swimming at night had been disturbed by their 

 lights. To Starck and Davis (1966), however, at 

 least some individuals of C rostratus appeared to 

 be nocturnally active in the Florida Keys; how- 

 ever, they recognized that this species is active in 

 daylight as well. 



Family Diodontidae: spiny puffers 



Diodon holocanthits Linnaeus — kokala 



This spiny puffer is numerous in Kona, where it 

 frequently swims close above the reef at night; 

 nevertheless, I never saw one there in daylight. 

 Undoubtedly, it is under shelter during the day, 

 probably deep within the coral caverns that hon- 

 eycomb much of the reef. In the Gulf of California, 

 where the rocky sea floor offers mostly ledges and 

 relatively shallow caves, one often sees the noc- 

 turnally active D. holocanthus resting in these 

 places during the day. 



All five individuals (211: 175-239 mm) that 

 were speared as they swam in exposed locations on 

 the reef after dark contained identifiable material 

 in their guts, much of it relatively fresh. Proso- 

 branch gastropods, which occurred in all five 

 specimens, were the major food item (mean per- 

 cent of diet volume and ranking index: 54.1), with 

 pagurid crabs also important prey of all five ( mean 

 percent of diet volume and ranking index: 24). 

 Other food items were: echinoids, aWEchinometra 

 mathaei, in four (mean percent of diet volume: 18; 

 ranking index: 14.4), and ophiuroids in two (mean 

 percent of diet volume: 3.9; ranking index: 1.56). 

 Although this material had been crushed by the 

 powerful jaws and beaklike dentition of the fish, it 

 was apparent that at least many of the gastropod 

 shells actually had housed pagurid crabs; thus the 

 pagurids, not the gastropods themselves, may 

 have been the major food. It remains uncertain 

 how many living gastropods are in fact taken, 

 although opercula among the gut contents showed 

 that living gastropods are important prey. 



This circumtropical species has a similar diet in 

 the Atlantic Ocean, as determined by Randall 



(1967), who also listed prosobranch gastropods as 

 the major food item. He listed pagurid crabs too, 

 but did not suggest that some of the gastropods on 

 his list may have been shells that housed these 

 crabs. 



Diodon holocanthus is nocturnal in the Florida 

 Keys, where it stays under ledges or in holes dur- 

 ing the day, but emerges at night to feed on vari- 

 ous invertebrates, particularly larger shelled 

 forms (Starck and Davis, 1966). 



CONCLUSION. — Diodon holocanthus is a noc- 

 turnal predator that feeds mostly on prosobranch 

 gastropods and pagurid crabs. 



Diodon hijstrix Linnaeus — kokala 



During the day, D. hystrix either is secreted 

 under ledges, or hovers inactively high in the 

 water column, often several together. At night, 

 solitary individuals (Figure 42) swim in exposed 

 locations close above the reef, especially among 

 basaltic boulders. 



Of the 16 individuals (263: 244-333 mm) 

 speared during day and night, only 4 had empty 

 guts, and these were collected during late after- 

 noon, either from holes under rocks, or as they 

 hovered in the water column. The only ones that 

 carried food in the anterior third of their gut were 

 taken at night — two during the hour before mid- 

 night and one 2 h before daybreak. Although the 

 anterior third of the gut was empty in the other 

 nine, all carried material posteriorly, which, com- 

 posing entirely shelled organisms, was readily 

 identifiable: two of these specimens were col- 

 lected at night — one at midnight, the other just 

 before daybreak; the remaining seven were taken 

 during the day — four of them in the morning, 

 three early in the afternoon. In all, 12 specimens 

 contained identifiable prey. 



Echinoids, including both cidarids and 

 echinometrids, occurred in 11 of the 12 specimens 

 and were the major food item (mean percent of diet 

 volume: 55; ranking index: 50.42). Prosobranch 

 gastropods, present in 11 (mean percent of diet 

 volume: 27.1; ranking index: 24.84), were ranked 

 second, and pagurid crabs, also present in 11 

 (mean percent of diet volume: 12.9; ranking index: 

 11.83), were ranked third. Thus, the diet includes 

 items similar to those taken by D. holocanthus, 

 above, but ranked in a different order As is true of 

 the material from D. holocanthus, many of the 

 gastropod shells had housed pagurid crabs, but the 



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