542 



Fishery Bulletin 100(3) 



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Bm32-2cut with Dra I 



Bm32-2 cut with Dde I 



Figure 3 



BM32-2 gel. Most common restriction fragment patterns of the nuclear gene region BM32-2 of istiophorid 

 biUfishes. This locus did not amplify in the swordfish. (A) Digestions with Dra I. From left to right, 1-kb DNA 

 ladder, blue marlin (pattern A), white and striped marlin (pattern B). sailfish (pattern B). black marlin (pat- 

 tern B). shortbill spearfish (pattern C), and longbill spearfish (pattern C). (B) Digestions with Dde I. From left 

 to right, 1-kb DNA ladder, blue marlin (pattern A), white and striped marlin (pattern B), sailfish (pattern D), 

 black marlin (pattern H), shortbill spearfish (pattern C), and longbill spearfish (pattern Ci. 



Dra\ 



BM32-2 



Spearfish 

 Blue Marlin 



Slriped Marlin 

 White Marhn 

 Black Marlin 

 Sailfish 



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Striped Marlin 

 White Marlin 



Black Marlin 



Sailfish 



Figure 4 



Key to distinguish species of billfishes based on the single copy nuclear 

 locus MN32-2. 



contrast, Innes et al. (1998) reported ten composite hap- 

 lotypes among 47 black marlin, six composite haplotypes 

 among 26 blue marlin, six composite haplotypes among 46 

 striped marlin, and six haplotypes among 21 swordfish, all 

 from the southwest Pacific. From the level of intraspecific 

 variation in relation to the sample sizes and the regional 

 nature of their collections, it is reasonable to assume that 

 Innes et al. ( 1998) may have missed several composite gen- 

 otypes characteristic of the different species. In fact, from 

 the level of variation exhibited by black marlin, striped 



marlin, and swordfish. Innes et al. (1998) suggested that 

 their diagnostic species markers could be of potential use 

 in population structure analyses. It occurs to us that if a 

 genetic character exhibits sufficient intraspecific variation 

 to be useful for analyses of stock structure, it is probably 

 not a good candidate for species identification. 



A high degree of genetic similarity was noted among 

 white marlin and striped marlin in our study None of 

 the molecular markers evaluated in this study was able 

 to unambiguously distinguish between the two species. 



