Miyashita et al.: Morphological development and growth of Thunnus thynnus 
609 
Table 4 
myomere on which it occurs, n indicates the number of specimens examined at each size range. Melanophores were not observed on 
Myomere 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
n 
14 
36 
7 
21 
7 
7 
14 
14 
7 
14 
7 
14 
7 
14 
30 
11 
7 
15 
4 
4 
11 
11 
4 
7 
11 
7 
7 
7 
27 
14 
10 
19 
14 
5 
5 
5 
5 
19 
10 
14 
5 
10 
5 
21 
17 
8 
8 
8 
33 
8 
17 
25 
8 
8 
12 
20 
10 
10 
20 
20 
40 
10 
10 
30 
10 
10 
10 
10 
20 
10 
20 
10 
10 
11 
11 
6 
11 
17 
6 
6 
11 
6 
11 
6 
17 
11 
6 
18 
20 
10 
10 
10 
10 
20 
10 
10 
10 
10 
10 
20 
20 
10 
20 
20 
30 
10 
10 
40 
20 
10 
10 
8 
8 
15 
8 
15 
31 
31 
8 
8 
8 
13 
15 
8 
8 
31 
15 
23 
15 
23 
15 
15 
8 
8 
8 
8 
8 
13 
8 
8 
17 
17 
25 
25 
42 
58 
33 
50 
33 
50 
33 
33 
50 
42 
12 
10 
10 
20 
20 
20 
50 
60 
40 
50 
40 
30 
20 
50 
10 
Table 5 
the myomere on which it occurs, n indicates the number of specimens examined at each size range. Melanophores were not observed 
Myomere 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
n 
14 
36 
7 
21 
7 
7 
14 
14 
14 
7 
7 
14 
7 
7 
14 
4 
30 
19 
7 
15 
7 
4 
15 
4 
7 
15 
19 
7 
7 
27 
14 
10 
14 
5 
5 
19 
5 
5 
5 
21 
17 
25 
17 
17 
42 
25 
8 
17 
8 
17 
8 
12 
10 
30 
20 
20 
10 
10 
50 
30 
10 
10 
10 
10 
10 
10 
20 
10 
10 
10 
10 
10 
6 
11 
11 
11 
17 
6 
6 
11 
6 
11 
6 
17 
11 
6 
18 
10 
10 
30 
10 
10 
10 
10 
20 
20 
20 
10 
10 
10 
30 
20 
10 
10 
10 
20 
30 
30 
20 
10 
31 
8 
8 
8 
15 
15 
8 
8 
8 
13 
8 
15 
15 
54 
23 
31 
46 
46 
31 
31 
31 
8 
8 
23 
15 
13 
8 
17 
8 
8 
25 
25 
42 
50 
50 
42 
25 
42 
25 
25 
42 
25 
12 
30 
20 
20 
20 
10 
10 
30 
30 
40 
50 
50 
30 
20 
50 
10 
ratios in relation to BL at sizes smaller than other body 
parts, such as total length and body height, except for the 
caudal peduncle depth (Fig. 4). 
Another ontogenetic characteristic of growth in T. thyn- 
nus, the posterior migration of the anus (Collette et al., 
1984), was also confirmed: the anus initially positioned in 
the anterior part of the body, was located at the center 
of the body at late flexion, and thereafter in the posterior 
part of the body (Fig. 3). 
Kaji et al. (1996) examined the relative growth of lar- 
vae of the Pacific bluefin tuna at 3-14 mm BL and report- 
ed that body proportions showed constant relative growth 
values from 10 mm BL, except for preanal length. Our re- 
sults showed that at 10 mm BL, constant ratios had not 
been reached in relation to BL. This difference may be due 
to an insufficient number of larger specimens in Kaji et 
al.’s ( 1996) study. Even at the juvenile stage, ratios in rela- 
tive BL decreased gradually, except for a few cases (Fig. 3), 
suggesting that body proportions of juvenile bluefin tuna 
are different from those of adult fish. 
Early growth is rapid in T. thynnus compared with oth- 
er marine fishes cultured in Japan (e.g. red sea bream. 
