FISHERY BULLETIN: VOL. 81. NO. 1 



tory, subjected to an oceanwide multinational 

 fishery, and which, because of relatively low 

 catches, are not well suited to tag-recapture 

 studies. In fact, the pressing need to understand 

 blue marlin stock structure has been recognized 

 for some time (Shomura 1980; Yoshida 1981). 



The electrophoretic analysis of protein poly- 

 morphisms in natural populations can be a pow- 

 erful approach for analyzing genetic aspects of 

 population structure in sexually reproducing or- 

 ganisms. For this reason, the technique has been 

 applied to the study of racial or subpopulation 

 differentiation in numerous invertebrates and 

 vertebrates (Ayala 1976). Because of the basic 

 importance of information on subpopulation or 

 stock structure to fisheries management (Berst 

 and Simon 1981), population genetic studies have 

 been conducted for many species of fishes [re- 

 viewed by de Ligny (1969) and Allendorf and Ut- 

 ter (1979)]. Most of the fishes investigated to date 

 have been freshwater species or marine forms 

 which are either inshore shallow-water species 

 or demersal species. 



Stock heterogeneity for oceanic species has not 

 generally been reported (but see Fujino 1976; 

 Fujinoet al. 1981). Although open water, pelagic 

 species may be characterized by large panmictic 

 cosmopolitan populations, this pattern has not 

 yet been clearly established. One problem in test- 

 ing this hypothesis has been the unusually low 

 levels of genetic variability observed to date in 

 several large marine vertebrates such as skip- 

 jack tuna (Fujino 1970) and seals (McDermid et 

 al. 1972; Bonnell and Selander 1974). Indeed, 

 Selander and Kaufman (1973) have even sug- 

 gested that large, mobile vertebrates may gener- 

 ally have low levels of heterozygosity— a charac- 

 teristic which, if true, would preclude definitive 

 stock analysis using electrophoretic techniques 

 (but see Ryman et al. 1980). The general lack of 

 progress in defining stock structure in oceanic 

 fishes, such as scombroids, using electrophoretic 

 methods, is attributable to several factors. Many 

 of the reports in the literature have been prelimi- 

 nary in nature dealing with small samples of fish 

 and few variable loci. Although such small sam- 

 ple sizes are not unexpected given the remote, 

 far-seas nature of many of the commercial fish- 

 eries, they severely limit the subsequent statisti- 

 cal treatment of the data. Similarly, the analysis 

 of only one or two polymorphisms reduces the 

 likelihood of demonstrating any population sub- 

 division which may exist. Finally, the schooling 

 and/or highly migratory nature of many of these 



fishes makes it difficult to plan and execute ade- 

 quate sampling programs. 



The study described in the present report was 

 designed to determine the suitability of utilizing 

 electrophoretic techniques to study stock struc- 

 ture in the Pacific blue marlin. Three specific 

 questions were addressed: 



1 ) How much and what kind of electrophoreti- 

 cally detectable genetic variation is there in 

 the Pacific blue marlin? Specifically, is there 

 enough genetic variation to allow an electro- 

 phoretic analysis of stock structure in this 

 species? 



2) What combinations of enzymes, tissues, and 

 buffer systems can be utilized in a study of 

 genetic variation in this species? 



3) What allele frequency distributions charac- 

 terize the population of Pacific blue marlin 

 in Hawaii? 



MATERIALS AND METHODS 



Muscle, liver, heart, eye, and brain samples 

 were dissected from Pacific blue marlin landed 

 at the Hawaiian International Billfish Tourna- 

 ment held at Kailua-Kona, Hawaii, in August 

 1980. All tissue samples were taken immediately 

 after each fish had been weighed, and all fish had 

 been dead for at least 1 h but <8 h. The dissected 

 tissues were initially placed on ice and subse- 

 quently transferred to a freezer within 12 h. The 

 time delay between fish capture and the freezing 

 of dissected tissues did not seem to adversely 

 affect any of the polymorphic enzymes screened 

 with the possible exception of L-iditol dehydro- 

 genase which could only be scored in 84 of the 95 

 fish analyzed. Tissues were stored frozen at 

 -20°C until extracted. 



Tissue extracts were prepared by homogeniza- 

 tion using a loose-fitting, motorized stainless 

 steel pestle in polycarbonate centrifuge tubes. 

 The extraction buffer consisted of 0.1M Tris-HCl 

 pH 7.0 containing 1 X 10" 3 M EDTA and 5 X 

 10~ 5 M NADP\ After homogenization, the ex- 

 tracts were centrifuged at 25,000 X gfor at least 

 30 min. Supernatants were transferred to indi- 

 vidually labeled glass vials, capped, and stored 

 at — 75°C until the electrophoretic analysis was 

 completed. 



The supernatants were subjected to horizontal 

 starch gel electrophoresis (modified from Selan- 

 der et al. 1971), using some 15 different buffers. 

 The gels were made using Lot 60F-0558 starch 



86 



