FISHERY BULLETIN: VOL. 81, NO. 1 



polymorphic by the normal criteria (common 

 allele at a frequency of 0.99 or less) with five loci 

 (Ada, Mpi, Pgdh, Pgm, and Umb) having the 

 most common allele at a frequency of between 

 0.95 and 0.99 and four loci (Aat-1, Adh, G-3-Pdh- 

 2, and Iddh) having the most common allele at a 

 frequency of <0.95 (Table 2). All 11 variable loci 

 exhibited two or three alleles except for Aat-1 

 which had five different alleles, three of which 

 were reasonably common. 



Heterozygosity values for the individual loci 

 ranged from zero for all of the apparently mono- 

 morphic loci to 0.494 for G-3-Pdh-2. The average 

 heterozygosity (H) across all 35 loci was 0.0605. 



Where possible, the observed genotype distri- 

 butions were tested for goodness-of-fit to Hardy- 

 Weinberg equilibrium expectations (Gpi-A, Idh- 

 1, Mpi, and Pgm were not tested because of the 

 very small number of observed variants in the 

 sample). Where necessary, rare alleles were pool- 

 ed prior to the tests. All tests were nonsignificant 

 except that for Adh ( x 2 = 6.97, df = 1; P<0.01) 

 where there was a significant deficiency of het- 

 erozygotes. 



Further analysis of the Adh data was under- 

 taken to attempt to identify the major contribu- 

 tors) to this significant chi-square value. Since 

 sex linkage of a locus can result in a deficiency of 

 heterozygotes, the sample of blue marlin was 

 subdivided into males and females. A chi-square 

 test of the Adh genotypes of the 81 male fish also 

 revealed a significant deficiency of heterozygotes 

 (x 2 = 9.36, df = 1; P<0.005). Another possible 

 source of the deficiency of heterozygotes could be 

 the pooling of different year classes which actu- 

 ally had different frequencies of the Adh alleles. 

 Indeed, year class fluctuations of allele frequency 

 have been reported in other fishes (Williams et 

 al. 1973; Mitton and Koehn 1975; Smith et al. 

 1978; Smith 1979). In the absence of growth data 

 for this species, the only subdivision we could 

 make was on the basis of size. The 95 blue marlin 

 were subdivided into two groups: 1) 100-200 lb 

 total weight and 2) 201-450 lb. There were 74 fish 

 in the 100-200 lb group and the statistical analy- 

 sis of this group once again revealed a deficiency 

 of heterozygotes ( x 2 = 9.95, df = 1; P<0.005). The 

 similarity of the results for small fish and for 

 males is not unexpected since all of the female 

 fish (N = 13) were in the large size class (>200 

 lb). Therefore, the deficiency of heterozygotes 

 seems to characterize the overall sample and 

 cannot be attributed to sexual or gross age (= 

 size) differences. 



Table 2.— Allele frequencies and 

 heterozygosities for 11 variable loci 

 in Makaira nigricans from Hawaii. 



'Sample size = 95 fish for each locus ex- 

 cept for Mpi where N = 94, Aat-1 and Adh 

 where N = 93, and Iddh where N = 84. 



DISCUSSION 



In spite of the low levels of genetic variation re- 

 ported in the literature for skipjack tuna(Fujino 

 1970; Fujino et al. 1981; Lewis 1981; Richardson 

 in press) and suggested by Selander (1976:34) 

 that "...levels of variability are unusually low in 

 large marine vertebrates such as tuna fish and 

 porpoises," the above data clearly indicate that 

 the Pacific blue marlin does not have abnormally 

 low levels of genetic variation. The level of poly- 

 morphism (P.99) observed for marlin in the pres- 

 ent study (P = 0.26; i.e., 9 out of 35 loci), although 

 slightly lower than the average for fish (P = 0.31) 

 reported by Selander (1976), is higher than the 

 averages for reptiles, birds, and mammals (0.23, 

 0.15, and 0.23, respectively). Furthermore, the 

 average heterozygosity (H) of 0.0605 for the 35 

 loci screened in the Pacific blue marlin is greater 

 than the average of 0.0494 calculated by Nevo 

 (1978) for 135 species of vertebrates and the aver- 

 age of 0.0478 calculated by Winans (1980) for 82 

 species of fishes. Although perhaps somewhat un- 



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