96 chromosomes were observed in skipjack, and one 

 polyploid cell with 96 chromosomes was observed 

 in albacore. No polyploid cells were observed in 

 yellowfin. 



Chromosome Morphology 



The albacore and the yellowfin and skipjack tuna 

 were observed to have the same diploid chomosome 

 number; however, their karyotype differed with 

 respect to chromosome morphology. In this study, 

 the chromosome pairs were arranged according to 

 the morphology index (M), developed by Giannelli 

 and Howlett (1967), which is obtained by dividing 

 the length of the total haploid chromosome set p + 

 q by the arm ratio (q/p). Based on our evaluation of 

 256 metaphase cells (Table 1), we found that the 

 chromosome morphology of the yellowfin (Fig. 1) 

 is more similar to that of the albacore (Fig. 2) than 

 the skipjack (Fig. 3). The differences in chromosome 

 morphology were most apparent in the three largest 

 pairs of chromosomes (Table 1). The morphology 

 index (M) places the metacentric and submetacentric 

 chromosomes of the albacore and yellowfin in the 

 number 1 and 2 positions respectively. Chromosome 

 3 of the albacore is also submetacentric while chro- 

 mosome 3 of the yellowfin is referred to as sub- 

 telocentric. The subtelocentric category is used to 

 describe chromosomes in which the centromeres are 

 displaced more towards the telomere when com- 

 pared with submetacentrics. The metacentric 



chromosome of the albacore was consistently larger 

 than the metacentric of the yellowfin. The remain- 

 ing 42 chromosomes were telocentric in the albacore 

 and yellowfin. All of the chromosomes of the skip- 

 jack were telocentric. 



C-Banding Patterns 



C-banding determinations were done to differen- 

 tiate individual chromosome characteristics among 

 the three species of tunas (Table 2). The centromeric 

 regions of most of the chromosomes of all three 

 species contained C-band constitutive heterochroma- 

 tin. However, there were differences in the inten- 

 sities of staining on comparable chromosomes 

 among the three species. Intercalary C-banding was 

 observed only in the skipjack tuna and there was 

 variability in terminal banding among the three 

 species. 



In the albacore all chromosomes, except pair 10, 

 showed C-banding in the centromeric regions with 

 intense, prominent bands notably apparent in 

 chromosome pairs 2 and 3 (Fig. 2). Terminal band- 

 ing was restricted to chromosome pair 1 which had 

 obscure C-bands on one arm of each homologue. No 

 intercalary C-banding was observed in the albacore. 

 There were some minor differences in the C-band- 

 ing patterns between albacore and yellowfin tuna. 

 In the yellowfin, the centromeric regions of all 

 chromosomes were banded, the intensity of the 

 banding in the centromeric region was uniform 



Table 2.— Summary of C-banding characteristics for albacore and yellowfin and skipjack tuna. 



Location of 

 bands 



Albacore 



Yellowfin 



Skipjack 



Centromeric Present on all chromosomes Present on all chromosomes Present on all chromosomes 



region 



Terminal 

 bands 



Intercalary 



except pair 10; intensely 

 prominent on pairs 2 

 and 3 



Present on one arm of each 

 homologue on pair 1; 

 weakly developed 



None present 



with uniform prominent 

 intensity 



Weakly developed on 

 chromosome pairs 1, 3, 

 7, 8, 14, 15, 21, & 24 



None present 



except pairs 10 and 19, 

 great variability in inten- 

 sity most prominent on 

 pairs 1, 3, 4, 7, and 18 



Notably prominent in 

 pair 4 



Present on all chromosome 

 pairs except 17 and 24 



471 



