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Fishery Bulletin 99(4) 
approximately 2200 h on 1 1 July. The first 24 hours after 
hatching were counted as day 0 (day-0) after hatching. 
Water temperature ranged from 24.5 to 27.7°C during the 
rearing period (x=25.5°C, Fig. 1). The feeding scheme for 
larvae and juveniles was as follows: rotifers, Brachionus 
rotundiformis, from day 2 to day 22 after hatching, Arte- 
mia nauplii from day 10 to day 25, and other live fish 
larvae ( Oplegnatlius fasciatus) from day 12 to day 30. 
At 1000 h daily from day 0 (12 July) to day 30 (11 Au- 
gust), 20 tuna were sampled. Before preservation in 5% 
formalin, individual computer-captured video images were 
made with a video camera attached to a binocular micro- 
scope while all specimens were under MS-222 anesthesia. 
Ten body parts were measured from these images: total 
length (TL), body length (BL), preanal length, body height 
at the base of the first dorsal spine, head length, head 
height, snout length, eye diameter, caudal peduncle depth, 
and upper jaw length. Video image measurements to 1/10 2 
mm with an accuracy of ±1% were obtained from NIH Im- 
age (version 1.61) image analysis software (NIH, 1997). 
Before and during notochord flexion, BL was measured 
from the tip of the upper jaw to the end of the notochord. 
After notochord flexion, BL was measured from the tip of 
the upper jaw to the posterior margin of the hypurals. All 
specimens (/? =620, 3.49-37.78 mm BL) were used to de- 
termine growth estimates and to record pigmentation pat- 
terns and spine and fin development. 
Sixty-nine specimens (5.26-33.68 mm BL) were stained 
with alizarin red-S to describe spine development, and 
squamation. Pigment patterns, especially the position of 
body melanophores in relation to myomeres, were deter- 
mined for specimens from 3 to 16 days after hatching 
(n=180, 3.63-9.96 mm BL). At irregular intervals from 
day 0 to day 22, one to five fish (a total of 53 specimens, 
3.38-26.76 mm BL) were examined while anesthetized 
with MS-222 to determine erythrophore distribution. Ad- 
ditional samples were examined at irregular intervals 
from hatching to day 2. 
A representative series of specimens from this study 
was deposited in the Aquatic Natural History Museum of 
the Fisheries Research Station, Kyoto University (FAKU 
129041-129075). 
Results 
Structural characteristics and growth 
Eggs, having a mean diameter of 1.02 mm (SD=0.02; 
n= 20), were spherical and pelagic and had a single oil 
globule of 0.26 ±0.05 (mean ±SD) mm in diameter. 
Newly hatched larvae measured 2.83 ±0.16 mm in BL 
(mean ±SD, n= 20; Fig. 2A). At 3 days after hatching (3.81 
±0.14 mm BL), the mouth was developed and larvae began 
feeding. Yolk was present until day 5 (4.32 ±0.13 mm BL). 
Larvae grew to 5.58 ±0.35 mm by day 10, 9.34 ±1.36 mm 
by day 20 and 30.36 ±4.34 mm by day 30 after hatching 
(Fig.l). From hatching to day 20, growth rate was 0.33 
mm/day, then increased to 2.10 mm/day from day 20 to 
day 30. 
Notochord flexion began as early as 5.76 mm BL, and 
the largest preflexion larva was 5.83 mm BL. The small- 
est postflexion larva was 7.46 mm BL; the largest flexion 
larva, 8.65 mm BL. Thus, the flexion stage occurred from 
6 to 8 mm BL (Fig. 2E). 
The relative values of the nine body parts, except preanal 
length, increased during larval development, then subse- 
quently declined (Fig. 3). The ratio of head length, head 
height, eye diameter, snout length, and upper jaw length to 
BL reached a maximum at 11-13 mm BL. Head length in- 
creased rapidly from 10% BL at hatching to 40% at 13 mm 
BL and then decreased slowly to 34 % BL at 40 mm BL. 
Head height also increased rapidly from 10% BL at hatch- 
ing to 27% at 11 mm BL and decreased slowly to 23% BL at 
40 mm BL. Eye diameter increased from 10% BL at hatch- 
ing to 15% at 11 mm BL and then decreased slowly to 9% 
BL at 40 mm BL. Snout length rapidly increased from 2% 
BL at hatching to 14% at 12 mm BL and then decreased 
slowly to 9% BL at 40 mm BL. Upper jaw length increased 
rapidly from 5% BL at hatching to 20-30% at 12 mm BL 
and then decreased slowly to 14% BL at 40 mm BL. The 
