1 



7 

 13 





19 



(a) 



• • 



3 



8 



10 



11 



12 



13 



14 



15 



16 



17 



18 



19 



(b) 



20 



21 



22 



23 



24 



Figure 2.— Giemsa stained karyotype (a) and C-banding karyotype (b) from two different fish of the 



North Pacific albacore. 



tuna. Gibbs and Collette (1967) proposed that seven 

 species of tuna be included in the genus Thunnus 

 on the basis of external morphological and internal 

 anatomical characters. Our results demonstrate that 

 there is a genetic basis for placing the albacore, T. 

 alalunga, and the yellowfin tuna, T. albacares, in 

 one genus Thunnus and the skipjack tuna, Kat- 

 suwonus pelamis, in a separate genus. These 

 relationships are based on the assumption that 



closely related species will share certain karyotypic 

 characteristics. 



The determination that the albacore, yellowfin 

 tuna, and skipjack tuna have the same number of 

 chromosomes suggests that speciation of the genera 

 of Thunnini might have occurred by intrachromo- 

 somal rearrangement as opposed to Robertsonian 

 changes as hypothesized for the rainbow trout, 

 Salmo gairdneri (Thorgaard 1976). If speciation had 



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