FISHERY BULLETIN: VOL. 72, NO. 4 



Figure 42. — Diodon hystrix, a spiny puffer, swimming above the reef at night. With its heavy, beaklike dentition, this 



fish crushes its shelled prey. 



number remains unknown. Nevertheless, the 

 pagurids may actually rank second as prey even 

 though the opercula among this material show 

 that living gastropods are important prey. One D. 

 hystrix also contained ostreid pelecypods (mean 

 percent of diet volume: 0.8; ranking index: 0.07), 

 and one contained unidentified fragments (mean 

 percent of diet volume: 4.2; ranking index: 0.35). 



Randall (1967) similarly found echinoids the 

 major food of this circumtropical species in the 

 West Indies. For this species as well as D. holocan- 

 thus, Randall listed gastropods and pagurids 

 separately, without suggesting that some of the 

 gastropods may have been only shells which 

 housed pagurids. Randall recognized that D. hys- 

 trix feeds partly by night, but believed it to be 

 primarily diurnal. Starck and Davis (1966), how- 

 ever, reported strictly nocturnal habits for D. hys- 

 trix in the Florida Keys. 



The strong, sharp spines that cover D. hystrix 

 and D. holocanthus are perhaps their most dis- 

 tinctive morphological characteristic. These 

 spines lie flat against their bodies most of the time, 

 but when the bodies inflate with water — a regular 

 response to threats — the spines stand straight out. 

 Although this formidable defense probably deters 



most predators, the slow-moving Diodon would be 

 ready prey for those predators able to tolerate the 

 spines and inflated body. In Hawaii, the tiger 

 shark, Galeocerdo cuvieri, regularly preys on 

 full-grown adults of D. hystrix (Tester, 1963). 



CONCLUSION. — Diodon hystrix is a nocturnal 

 predator that feeds mostly on echinoids, and to a 

 lesser extent on prosobranch gastropods and 

 pagurid crabs. 



General Remarks on Spiny Puffers 



The teeth in both upper and lower jaws of the 

 diodontids are fused together to produce a solid, 

 heavy beak, and this apparatus enables them to 

 crush some of the larger, heavily shelled prey that 

 are beyond the capacity of other fishes — even their 

 relatives the balloonfishes. 



The nocturnal habits of the two species of 

 Diodon, described above, may be a family charac- 

 teristic. Starck and Davis ( 1966) reported that two 

 species of Chilomycterus in Florida — antillarum 

 and schoepfi — are active at night and inactive 

 during the day. 



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