FISHERY BULLETIN: VOL. 70. NO. 1 



Ueyanagi examined 350 larvae and concluded 

 that T. albacares and T. alalunga, which are 

 difficult to identify by the usual diagnostic char- 

 acters, could be distinguished by differences in 

 red pigment patterns: larvae of T. alalunga 

 consistently had more red pigment spots on the 

 dorsal and ventral edges of the body and along 

 the mid-lateral line forward of the caudal pe- 

 duncle than larvae of T. albacares; red pigment 

 patterns in larvae of T. thynnus and T. obesus 

 were intermediate between those of T. alalunga 

 and T. albacares; the red pigment pattern in 

 Allothunnus fallal was similar to that in Thun- 

 nus; and the pattern in K. pelaniis resembled 

 that in Auxis spp. and E. affinis but differed 

 from that in Thunnus. 



To confirm these results and to provide addi- 

 tional information on red pigmentation in tuna 

 larvae, the results of observations made on 432 

 larvae taken in Hawaiian waters during August 

 and September 1967 were presented. Tables 1 

 and 2 give the number of red pigment cells along 

 the dorsal, ventral, and lateral lines on the pos- 

 terior half of the trunk and a summary of the 

 number of larvae examined, the number of larvae 

 observed with red pigmentation, and the mean 

 numbers of red pigment cells at the three sites. 

 In Table 2, the number of red pigment cells ob- 

 served most frequently are given in bold face 

 type and those observed occasionally or seldom 

 are enclosed in parentheses. 



The pigment patterns agreed generally with 

 those reported by Ueyanagi for the species listed 

 in the tables. Differences in the patterns were 

 noticeable mainly in the dorsal edge of the trunk 

 and, to a lesser extent, in the mid-lateral line. 

 There was no significant difference in the num- 

 ber of pigment cells t)etween the left and right 

 sides of the body. 



The appearance and extent of red pigment 

 cells varied in larvae taken in night and day 

 tows. In larvae taken at night the pigment cells 

 were numerous, distinct, and brightly colored, 

 whereas in larvae taken during the day the pig- 

 ment cells were faintly colored, often not visible, 

 and in many instances the pigment spots were 

 united, forming single continuous lines. Of the 

 species taken in both day and night tows {T. al- 

 bacares, T. obesus, and K. pelamis) , red pigmen- 



tation was not visible in 41.5% of the larvae 

 taken during the day, compared with only 3.6% 

 of the larvae taken at night. Thus, observations 

 of red pigment cells must be made largely on 

 larvae taken at night to reduce the effects of 

 diel variations. 



Despite the variations, red pigmentation is a 

 useful supplementary character to either sepa- 

 rate certain species or verify the identification 

 made on the basis of other characters. That the 

 red pigment pattern is not species specific is 

 clearly seen in the similarity among K. pelamis, 

 Auxis spp., and E. affinis and between T. obesus 

 and T. albacares; however, it is useful in sepa- 

 rating T. alalunga from the other kinds of 

 Thimnus. 



EXAMINATION AND DISCUSSION 

 OF SPECIES 



Thunnus alalunga and T. albacares 



Larvae of these two species were examined 

 together because they are the only species lack- 

 ing black pigment cells on the trunk, exclusive 

 of the caudal fin and abdomen (Yabe and Ueya- 

 nagi, 1962), Characters, including some that 

 have not been used in the past, for separating 

 the two species are summarized in Table 3. The 

 larval stage was divided into two size categories, 

 small larvae less than 10 mm SL and larger lar- 

 vae 10 to 13 mm SL, because the characters used 

 in differentiating small larvae became ineffective 

 or obscured with growth. As mentioned earlier, 

 pigmentation, particularly the presence of black 

 pigment cells at the tips of the upper and lower 

 jaws and the amount of red pigment cells on the 

 trunk, was the most reliable character in sepa- 

 rating larvae of the two species. 



In small larvae, black pigment cells on the 

 lower jaw tip were first observed in larvae of T. 

 albacares about 4.5 to 6.0 mm SL, and often as 

 small as 3.8 mm SL; those on the upper jaw tip 

 were first observed in larvae about 7.0 mm SL 

 (Figures 1 and 2, reproduced from Matsumoto, 

 1958') . In T. alalunga these pigment cells were 



' The difference in developmental stages per given 

 size in the figures by Matsumoto (1958) and Ueyanagi 

 (1969) is due to method of preservation: Matsumoto's 

 figures are of larvae preserved in 10% Formalin; Ueya- 

 nagi's figures are of larvae preserved in 70% alcohol. 



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