FISHERY BULLETIN: VOL. 70, NO. I 



Table 3. — Characters to separate larvae of Thunnus 

 albacares and Thunnus alalunga. 



Characters 



T. albacares 



T. alalunga 



Small larvae (4-10 mm SL): 

 Black pigmentation: 

 Upper jaw 



Lower jaw 



Red pigmentation: 



Dorsal edge body, 

 postanus 



Appears at about 5.8 

 mm SL, mostly after 

 6.0 mm SL 



Appears at 4.5-6.0 

 mm SL 



At tip on inner edge; 

 migrate to outer edge 

 with further growth 



0, 1, 2, (3) 



[mean = 0.6]; near 



caudal peduncle 



Lateral line, postanus (0), 1, 2, 3, 4, (5) 

 [mean = 2.4] 



Appears at about 5.0 

 mm SL 



Appears at 9-10 

 mm SL 



At tip on outer edge 



2, 3, (4) [mean = 

 2.6] from peduncle to 

 mid-second dorsal fin 

 base 



(2), 3, 4, (5) 

 [mean = 3.5] 



Ventral edge body, 

 postanus 



Large larvae (>10 mm SL): 



Array of ^Da 

 pterygiophores 

 between two adjacent 

 neural spines 



Position of first 

 haemal arch (vertebra 

 number) 



3-12 [mean = 7.0] 5-12 [mean 



1.0] 



1, 2, 

 1, 1 



nth 



2, 2, 3, 2, 



2, 1 



10th 



1, 2, 2, 2, 3, 



1 D2 refers to second dorsal fin. 



Other Thunnus species 



These species, which include T. thynnus {T. 

 thynnus thynnus of Atlantic and T. thynnus or- 

 ientalis of Pacific) , T. tonggol, T. maccoyii, and 

 T. obesus, have been identified mainly by black 

 pigmentation on the trunk other than that over 

 the abdominal w^all. 



In small T. thynnus of both Atlantic and Pa- 

 cific Oceans (larvae between 3 and 10 mm SL), 

 one or two large black pigment cells are present 

 on the dorsal edge of the trunk between the sec- 

 ond dorsal and caudal fins (Table 4, Fig-ures 5 

 and 6) , the anterior one usually being the larger. 

 There may also be one to four black pigment cells 

 on the ventral edge of the trunk between the 

 anus and the caudal fin. Black pigmentation in 

 T. thynnus from both oceans agrees quite well, 

 except that in 5 out of 10 Atlantic specimens 

 one or two tiny black pigment cells were noted 

 along the mid-lateral line of the body near the 

 pectoral fin, and in two instances a single tiny 

 black pigment cell was found on the mid-lateral 

 line beneath the posterior end of the second dor- 



sal fin. These pigment cells were not considered 

 reliable for identification purposes. 



Observation of red pigmentation on larvae of 

 Atlantic and Pacific T. thynnus is incomplete. 

 Only one Atlantic T. thynnus larvae was exam- 

 ined for this character, but unfortunately the 

 specimen was taken in a day tow so that the 

 pigmentation appeared as a continuous streak 

 on both the dorsal and ventral edges of the trunk 

 as well as on the ventral surface of the lower 

 jaw. In Pacific T. thynnus there were one to five 

 red pigment cells, usually three, on the dorsal 

 edge of the trunk. The number of red pigment 

 cells on the mid-lateral line and ventral edge of 

 the trunk has not been recorded, but according 

 to the Illustration by Ueyanagi (1966), the pig- 

 ment pattern may be similar to that of T. obesus. 

 On the basis of black and red pigmentation, the 

 Atlantic and Pacific T. thynnus were not sep- 

 arable. 



The identification of T. tonggol, based on size 

 series of 4.2 to 7.3 mm, has yet to be confirmed. 

 Following the description of the species by Ma- 

 tsumoto (1962), larvae similar to these having 

 the anteriormost black pigment cell on the dorsal 

 edge of the body ahead of the second dorsal fin 

 origin have been found in 1963 in the mid-South 

 Atlantic Ocean near Ascension Island. Confir- 

 mation of the species description requires the 

 finding of adults within this area and the finding 

 of additional larvae to extend the identified size 

 range. 



The identification of T. maccoyii, which was 

 first described as having black pigment pattern 

 similar to that of T. thynnus (Yabe, Ueyanagi, 

 and Watanabe, 1966) and later as having the 

 black pigment cells on the dorsal edge of the 

 trunk reduced to pinpoints (Ueyanagi, 1969), 

 also needs verification (see discussion on T. thyn- 

 nus) . The correspondence of published descrip- 

 tions based on eight specimens and observations 

 of larvae identified as this species were not con- 

 clusive. 



T. obesus was easily separated from T. thyn- 

 nus by the absence of black pigmentation on the 

 bases of the anterior dorsal finlets. Sometimes 

 a single small black pigment cell was present 

 along the ventral edge of the trunk near the 

 caudal peduncle, but more often one to three pig- 



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