614 
Fishery Bulletin 99(4) 
Erythrophores 
Ventral notochord 
Dorsal notochord 
Lateral notochord 
Lower jaw 
Melanophores 
Gut 
Ventral tail 
Midbrain 
Forebrain 
Low. jaw tip 
Internal 
Upp. jaw tip 
First dorsal fin 
Anal fin base 
Dorsal fin base 
p ectoral fin 
Spines 
Inner preopercular spine 
Preopercular spine 
Posttemporal spine 
Jaw teeth 
Upper jaw teeth 
Lower jaw teeth 
Squamation 
Lateral line scale 
Postorbital scale 
Corselet scale 
0 5 10 15 20 25 30 35 
Body length (mm, BL) 
Figure 6 
Schematic representation of the development of pigment, spines, jaw teeth, and squamation in hatch- 
ery-reared bluefin tuna (Thunnus thynnus). □ = appearance of pigment and spines was subject to indi- 
vidual variation; ■ = pigment and spines were present in all specimens examined. 
and larger than 4.0 mm BL from the Pacific. In our speci- 
mens, the incidence of these melanophores was 7.1% at 
3.50- 3.99 mm BL, 29.6% at 4.00-4.49 mm BL, 57.1% at 
4.50 — 4.99 mm BL, 83.3% at 5.00-5.49 mm BL, and more 
than 90% in specimens >5.50 mm BL. The largest speci- 
men we observed lacking these melanophores was 9.46 
mm BL. Our data are similar to those for specimens from 
the Mediterranean. The difference in lower jaw melano- 
phore distribution between our specimens and those of 
Matsumoto et al. (1972) might be explained by geographic 
variation of the melanophore pattern in the Pacific bluefin 
tuna. Further study is needed to confirm this hypothesis. 
Ueyanagi (1966) reported species-specific characteris- 
tics of the erythrophore distribution pattern of Thunni- 
nae larvae from the Pacific Ocean: T. alalunga consis- 
tently had more erythrophores on the dorsal edge of the 
trunk and tail in front of the caudal peduncle than did 
T. albacares , which had only one or two erythrophores at 
the caudal peduncle; T. thynnus and T. obesus had pat- 
terns transitional between those of T. alalunga and T. al- 
bacares. Our data for T. thynnus generally agreed with 
those of Ueyanagi (1966); however, the number of dorsal 
erythrophores in one individual ranged more (0—8) than 
in Ueyanagi’s study (1-5). In addition, ventral erythro- 
phores appeared in large numbers (more than 20) at the 
preflexion stage (4.63-6.10 mm BL). From examinations 
of tuna larvae taken in Hawaiian waters, Matsumoto et 
al. (1972) considered the erythrophore pattern useful as a 
morphological characteristic for identifying tuna larvae. 
At present, however, information is limited on erythro- 
phore patterns of other Thunninae larvae and juveniles 
and on the difference of these patterns in wild-caught and 
laboratory-reared specimens. Thus collection of such in- 
formation is needed to establish the erythrophore pattern 
as a species-identifying characteristic of Thunninae lar- 
vae and juveniles. 
Thunnus thynnus did not have xanthophores from 
hatching to the preflexion stage. However, T. albacares 
(Harada et al., 1971b; Mori et al., 1971) and T. obesus (Ya- 
sutake et al., 1973) have clusters of xanthophores in the 
Unfolds of both the dorsal and ventral fins, and on the dor- 
sal body, respectively. Thus, the xanthophore pattern can 
be used for distinguishing these Thunnus species at the 
preflexion stage. 
Much additional work on development of tunas under 
controlled conditions, as well as the study on wild-caught 
materials, is needed to understand their early life history. 
We believe recent progress in the technology of rearing tu- 
nas will yield important information on the early life his- 
tory of Thunnus spp. 
