Miyashita et al.: Morphological development and growth of Thunnus thynnus 
613 
FLS 
Mpc 
CZJ 
c 
Relative growth 
Preanal 
Caudal peduncle depth _ 
□ 
Snout _ 
□ 
Eye diameter J 
□ 
Head height 
□ 
Upper jaw 
□ 
Head 
□ 
Body height 
□ 
Total 
T 1 1 1 
— 1 — 1 — 1 — 1 — 
1 1 1 T 
— ^ 
1 1 1 1 
t " ■ ■ i ' ■ ■ ■ i ■ ' ■ . i ■ . i ■ ~r ■ ■ -t ■ | ■ , i i | ■ i i | 
0 5 10 15 20 25 30 35 
Body length (mm, BL) 
Figure 4 
Schematic representation of the relative growth (length of body parts in relation to body length) in 
hatchery-reared bluefin tuna, Thunnus thynnus. Flexion larva subdivision (FLS) and numerical com- 
plement of fin rays (NCF) are also shown. In relative growth, □ = the peak value of body part proportion 
(in relation to BL) and ■ = the attainment of a constant value of body part proportion (in relation to 
BL). 
will allow further study of the structure and development 
of feeding-related bony elements for T. thynnus, as has 
been the case for S. japonicus (Kohno et al., 1984) and 
Lates calearifer (Kohno et al., 1996). 
Pigmentation 
Accurate identification of Thunnus larvae requires an 
extensive knowledge of individual, growth-associated, and 
geographic variations in melanophore and erythrophore 
patterns. We obtained information on the individual and 
growth-associated variations of these patterns from labo- 
ratory-reared specimens. 
The melanophore distribution pattern of T. thynnus lar- 
vae and juveniles showed four distinct characteristic peri- 
ods of development: newly hatched, 1-3 days after hatch- 
ing, preflexion to postflexion, and juvenile. 
T. thynnus thynnus larvae <3.99 mm BL from the Med- 
iterranean had embedded melanophores (Kohno et al., 
1982); but we did not observe these in our specimens until 
4.49 mm BL. This difference may be a subspecific differ- 
ence between T. thynnus orientalis and T. thynnus thyn- 
nus, or it may be due to insufficient numbers of specimens 
larger than 6.0 mm BL in Kohno et al.’s study, or to the 
experimental culture product as mentioned later. 
Wild-caught T. thynnus orientalis larvae (3.15-8.20 mm 
BL) most frequently had two melanophores both on the 
dorsal and ventral edges of the trunk and tail (Nishikawa, 
1985). This pattern resembles that of T. thynnus thynnus 
larvae from the Mediterranean (2.53-5.25 mm BL, Kohno 
et al., 1982). But our cultured specimens in the same size 
range had greater numbers of these melanophores (Tables 
2 and 3). Nishikawa (1985) reported the appearance of 
melanophores at the dorsal fin somewhat earlier than we 
observed their appearance, but their appearance on the 
lower and upper jaws occurred in the same size range in 
both studies where specimens were examined from the 
same population. Laboratory-reared fish larvae have been 
40 r 
Figure 5 
Growth of bluefin tuna (Thunnus thynnus ), red sea bream 
(Pagrus major), and white trevally ( Pseudocaranx dentex). 
Red sea bream and white trevally were reared at the same 
temperature range (24-27°C) as bluefin tuna (Sawada, 
unpubl. data). 
shown to have greater pigmentation than wild-caught lar- 
vae (e.g. Pagrus major [Fukuhara and Kuniyuki, 1978], 
Sparus sarba [Kinoshita, 1986], Parapristipotna trilinea- 
tum [Kimura and Aritaki, 1985], and Nibea mitsukurii 
[Kinoshita and Fujita, 1988]). Thus, the source of speci- 
mens, wild-caught or laboratory-reared, may account for 
observed differences in larval pigmentation between our 
study and Nishikawa’s study ( 1985). 
A slight difference in the occurrence of lower jaw, trunk, 
and tail melanophores has been reported among T. thyn- 
nus from the Mediterranean (Kohno et al., 1982), the At- 
lantic (Richards and Potthoff, 1974), and the Pacific (Mat- 
sumoto et al., 1972). Lower jaw melanophores appeared 
in all specimens larger than 3.0 mm BL from the Atlantic 
