FISHERY BULLETIN. VOL. 76, NO. 3 



Ventrally, however, a number of distinct spots 

 have formed that cover the belly (Figure 23). 

 The spots (pelagic spotting) are at first close 

 together but become less numerous and propor- 

 tionately larger, aligning in rows with growth 

 (Figure 19). Dorsal spotting (always more dif- 

 fuse than ventral spotting) begins to form at 

 around 10 mm and the characteristic dorsal 

 blotch pattern is generally visible by 30 mm, 

 although in pelagic specimens the contrast with 

 the background color is not great. The pelagic 

 spotting is retained in all pelagic individuals 

 examined (to 86 mm) and in some specimens 

 collected inshore. The fins remain unpigmented 

 except for a few melanophores along the fin rays 

 of the dorsal fin. 



Identification of Larvae and Juveniles: Diodon- 

 tid larvae are likely to be confused only with the 

 rotund, heavily pigmented, sac enclosed 

 ceratioid larvae and other tetraodontiform lar- 

 vae. Reference to Bertelsen's (1 95 1 ) work should 

 allow ceratioid larvae to be distinguished as 

 such. Rotund tetraodontiform larvae may be 

 distinguished from diodontid larvae as follows: 

 molids by their body spination and early form- 

 ing pectoral rays; ostraciids by their pigmenta- 

 tion and early forming pectoral rays; tetraodon- 

 tids by their relatively more elongate body 

 shape and early forming fin rays. Diodon larvae 

 are heavily pigmented only on dorsal surfaces, 

 do not develop fin rays until near or at 

 metamorphosis, have very wide heads and 

 bodies ( >body depth), and have very wide 

 mouths. 



The larvae of D. hnlocanthus can be distin- 

 guished from the putative D. hystrix larvae, the 

 only other larval diodontid known, by the less 



Figure 23.— Reared juvenile of 

 Diodon holocanthus, 4.8 mm SL, 25 

 days old. Note pelagic spotting. 

 Hawaiian material. 



well-developed condition at hatching of the lat- 

 ter (see section on D. hystrix). In addition, D. 

 hystrix larvae are predominantly orange upon 

 hatching while those of D. holocanthus are yel- 

 low. Melanophores of D. holocanthus do not 

 extend onto the postanal myomeres past the 

 middle of the dorsal and anal fin anlagen; the 

 postanal myomeres of D. hystrix are moderately 

 pigmented. Lastly, the eyes of Z). hystrix larvae 

 are smaller than those of D. holocanthus larvae 

 (Tables 2,3). 



Once the spines form, the lack of caudal 

 peduncle spination, fin ray counts and spine 

 placement serve to distinguish D. holocanthus 

 from all other Diodon species (see Key). 



The duration of the pelagic stage is unknown, 

 but judging from reared specimens, metamor- 

 phosis occurs about 3 wk after hatching at about 

 4 mm SL. The largest individual captured pelag- 

 ically was 86 mm while the smallest captured 

 inshore was 60 mm. A certain amount of plastic- 

 ity in the duration of the pelagic stage is indi- 

 cated, but its length clearly must be measured 

 in terms of months. No special adaptations for 

 pelagic life are evident in these juvenile stages 

 except, perhaps, in color. In the tetraodontiform 

 fishes (except the molids) the larval stage is 

 short and relatively unspecialized, while a rela- 

 tively unmodified pelagic juvenile stage may be 

 quite long (see Remarks under D. eydouxii). 

 This strategy (for dispersal?) is in marked con- 

 trast to that in many advanced perciform 

 shorefishes (e.g., Acanthuridae, Chaetodon- 

 tidae) where bizarrely modified and long-lived 

 larval and pelagic prejuvenile stages are de- 

 veloped which subsequently undergo marked 

 (and rapid) metamorphosis upon becoming 

 benthic. 



562 



