MATSUMOTO ET AL. : LARVAL TUNA IDENTIFICATION 



4. 1 mm 



5.0mm 



7.0 mm 



Figure 8. — Larval stages of Thunnus alalunga, I. 

 (From Ueyanagi, 1969. Lengths have been converted 

 from total to standard.) 



only on the upper jaw tip were considered as 

 T. alalunga. Larvae of the two species from 9.0 

 to 10.8 mm SL were separated by the position 

 of black pigTnent cells on the lower jaw tip: in 

 T. albacares the pigment cells were located on 

 the inner, and sometimes outer, margins in 

 larvae up to 10.8 mm SL, but in T. alalunga they 

 were found only on the outer margin. It is 

 suspected that the black pigment cells on the 

 inner margin of the jaw in T. albacares migrate 

 to the outer margin with further growth of the 

 larvae. 



Red pigmentation was accepted as a good sup- 

 plementary character for separating T. albacares 

 from T. alalunga (Tables 1 and 2). The distinc- 



I2.0mm 



15.5 mm 



Figure 4. — Larval stages of Thunnus alalunga, II. 

 (From Ueyanagi, 1969. Lengths have been converted 

 from total to standard.) 



tive patterns were located along the dorsal mar- 

 gin of the trunk from about the midpoint of the 

 second dorsal fin base to the caudal peduncle. In 

 T. albacares there was usually none or one red 

 pigment cell at the caudal peduncle. Two pig- 

 ment cells occurred seldom and three or four 

 pigment cells occurred only rarely. Generally, 

 these pigment cells were clustered at the caudal 

 peduncle region. In T. alalunga there were usu- 

 ally two or three pigment cells, sometimes as 

 many as four. Unlike those in T. albacares, 

 these pigment cells were well spaced, extending 

 forward to the middle of the second dorsal fin 

 base. Only minor diflFerences were noted in the 

 red pigment cells along the mid-lateral line. 



In larger larvae (10-13 mm SL) differences 

 in the two species were noted in the distribution 

 of pterygiophores of the second dorsal fin on 

 cleared and stained specimens (Table 3). In 

 T. albacares the two successive single pterygio- 

 phores between two adjoining neural spines oc- 

 curred at the posterior end, whereas in T. ala- 

 lunga they were at the anterior end. Addition- 

 ally, the first haemal arch was on the 11th verte- 

 bra in T. albacares and on the 10th vertebra in 

 T. alalunga. 



