uncertain. However, the occurrence of terminal C- 

 bands on chromosome 1 of the albacore and chromo- 

 somes 1 and 3 of the yellowfin tuna is consistent with 

 the hypothesis that these biarmed chromosomes 

 were derived from a uniarmed condition. Indeed, 

 White (1951) believed that, in grasshoppers, telo- 

 centric chromosomes are more primitive than the 

 metacentric condition. Absence of terminal bands 

 on chromosomes 2 and 3 of the albacore and chromo- 

 some 2 of the yellowfin tuna does not preclude the 

 suggested derivation of metacentric chromosomes. 

 It is possible that in the metacentric chromosomes 

 lacking terminal bands, centrometric heterochroma- 

 tin either was not moved or was lost. It is also possi- 

 ble that chromosome rearrangement in the specia- 

 tion of the albacore and yellowfin occurred through 

 changes in the euchromatic portions of chromo- 

 somes. To test this hypothesis it will be necessary 

 to use G-banding techniques (Rishi 1978) to conduct 

 analysis of these portions of the chromosomes. 



In contrast to the albacore and yellowfin tuna, the 

 telocentric chromosomes of the skipjack tuna 

 showed a variety of intercalary and terminal C-band- 

 ing in addition to those of the centromeric regions. 

 An interesting condition was the polymorphic ter- 

 minal heterochromatic block that occurred in chro- 

 mosome pair number 4 of the skipjack, but not in 

 the albacore or yellowfin. While the four specimens 

 of skipjack analyzed had this polymorphism, it is not 

 possible to comment on the frequency with which 

 it might occur in the population. This type of dif- 

 ferential banding also occurs in other fishes as 

 demonstrated by Zenzes and Voiculescu (1975) who 

 observed a difference in the size of C-bands in Salmo 

 trutta. The C-band polymorphism we observed in 

 skipjack could be related to the sex determining 

 mechanism of the fish. However, we do not have any 

 information on the sex of the skipjack used in this 

 study and most fish do not have heteromorphic sex 

 chromosomes (Zenzes and Voiculescu 1975; Thor- 

 gaard 1976; Kligerman and Bloom 1977). An excep- 

 tion occurs in the eels which have highly hetero- 

 morphic sex chromosomes (Park and Grimm 1981). 



Analysis of C-banding patterns associated with the 

 morphological differences in chromosomes has per- 

 mitted us to identify all of the chromosome pairs of 

 the albacore, yellowfin tuna, and skipjack tuna. We 

 have demonstrated that karyotype analysis may pro- 

 vide a chromosomal basis for placing albacore and 

 yellowfin in Thunnus and skipjack in Katsuwonus. 

 Although C-banding techniques did not allow a 

 detailed evaluation of the Thunnus chromosomes, 

 we believe that the use of multiple banding pro- 

 cedures could provide important information on the 



speciation and cytotaxonomy of the species of this 

 commercially important genus. In addition, use of 

 G-banding procedures will be an important next step 

 in determining if genetic heterogeneity exists in the 

 North Pacific albacore population. 



Acknowledgments 



We wish to thank A. Dean Stock (City of Hope 

 Hospital, Duarte, CA) and James Mascarello 

 (Children's Hospital, San Diego, CA) for many 

 helpful suggestions, Raymond Kelly (University of 

 California Medical School, San Diego, CA) for help 

 in procurement of materials, and the personnel of 

 the San Diego Sportsfishing Association, Captains 

 Ed McEwen and Buzz Brizendine for space aboard 

 their boats to make this work possible. 



Literature Cited 



Alexander, N., R. M. Laurs, A. McIntosh, and S. N. 

 Russell. 



1980. Haematological characteristics of albacore, Thunnus 

 alalunga (Bonnaterre), and skipjack Katsuwonus pelamis 

 (Linnaeus). J. Fish. Biol. 16:383-395. 



Arrighi, F. E., and T. C. Hsu. 



1971. Localization of heterochromatin in human chromo- 

 somes. Cytogenetics 10:81-86. 

 Brock, V. E. 



1943. Contribution to the biology of the albacore (Germo 

 alalunga) of the Oregon coast and other parts of the North 

 Pacific. Stanford Ichthyol. Bull. 2:199-248. 

 Blaxhall, P. C. 



1981. A comparison of methods used for the separation of 

 fish lymphocytes. J. Fish. Biol. 18:177-181. 



Boyum, A. 



1968. Separation of leukocytes from blood and bone marrow. 

 Scand. J. Clin. Lab. Invest., 21, Suppl. 97:77. 

 Clemens, H. B. 



1961. The migration, age, and growth of Pacific albacore 

 (Thunnus germo), 1951-1958. Calif. Dep. Fish Game, Fish 

 Bull. 115, 128 p. 

 Collette, B. B. 



1978. Adaptations and systematics of the mackerels and 

 tunas. In G. D. Sharp and A. E. Dizon (editors), The 

 physiological ecology of tunas, p. 7-88. Acad. Press, N.Y. 

 GlANNELLI, F., AND R. M. HOWLETT. 



1967. The identification of the chromosomes of the E group 

 (16-18 Denver): an autoradiographic and measurement 

 study. Cytogenetics (Basel) 6:420-435. 

 Gibbs, R. H., Jr., and B. B. Collette. 



1967. Comparative anatomy and systematics of the tunas 

 Genus Thunnus. U.S. Fish Wildl. Serv., Fish. Bull. 66: 

 65-130. 

 Graham, J. B., and K. A. Dickson. 



1981. Physiological thermoregulation in the albacore tuna 

 Thunnus alalunga. Physiol. Zool. 54:470-486. 

 Kligerman, A. D., and S. E. Bloom. 



1977. Distribution of F-bodies, heterochromatin, and nucleo- 

 lar organizers in the genome of the central mudminnow, Um- 

 bra limi. Cytogenet. Cell Genet. 18:182-196. 



475 



