FISHERY BULLETIN: VOL. 72, NO. 2 



Table 8. — Distribution of gillrakers over the branchial bones of the first gill arch for various size groups in Thunnus atlanticus 



juveniles, n =104. 



(Total gillraker counts for western Atlantic adults from Gibbs and Collette, 1967, Table 2*.) 



N 



SL 

 (mm) 



1 



Epibi'anchlal 



Ceratobranchial 



10 11 12 13 



Hypobranchial 



6 7 



1 — 



Total gillraker coun 



9 10 11 12 13 14 15 16 17 If 



1 



3 



15 



20 



8 



10 



1 



6 



2 



1 

 2 



1 

 1 



7 



14 



4 



8 1 



8 4 



1 



— 5 

 2 

 1 

 1 



1 — 

 1 

 1 



1 1 



9 20 21 22 23 24 25 26 27 



1 2 5 



3 — 1 



— 1 



— 1 



1 7 29 59 21 



T. atlanticus may actually not fully develop 

 or may lose some rakers during its later life. 

 Potthoff and Richards (1970) already mentioned 

 this possibility. 

 Thunnus alalunga (Table 9; Figures 11, 12). The 

 maximum gillraker count over the epibranchial 

 bone of 7 to 8 rakers was first obtained in a 

 61-mm-SL specimen. Most likely, however, 

 maximum counts over the epibranchial would 

 first show in the 55- to 59-mm-SL size range, 

 but the lack of specimens for those sizes pre- 

 cludes a definite statement. Bullis and Mather 

 (1956) counted 7 to 9 rakers on four adult 

 specimens. The diagnostic maximum count of 

 14 to 16 rakers over the ceratobranchial bone 

 was first present in a few 17-mm-SL specimens. 

 At 20 mm SL, all specimens had the diagnostic 

 maximum count. This count overlaps with the 

 Thunnus spp. complex. Maximum counts over 



the hypobranchial bone (including the cerato- 

 hypobranchial cartilage) of 5 to 6 rakers were 

 first observed on a 34-mm-SL specimen; all 

 specimens larger than 35 mm SL had the maxi- 

 mum count. The maximum total count for the 

 first gill arch of 27 to 29 rakers is attained 

 at 53 mm SL. Gibbs and Collette (1967) give 

 25 to 31 rakers as the total number over the 

 first gill arch for adult T. alalunga from the 

 western Atlantic. Our difference is due to my 

 smaller sample size and population variance. 

 Thunnus thynnus (Table 10; Figures 11, 12). The 

 maximum total gillraker count over the epi- 

 branchial bone of 12 to 13 rakers was first 

 present in one 79-mm-.SL specimen. Because I 

 lack data in the larger size ranges, I can only 

 estimate that all T. thynnus have a full epi- 

 branchial after they have reached 90 mm SL. 

 The diagnostic maximum counts of 17 to 20 



580 



