| Summary: | © 2011 Dr. Helen Mary Bradman Commercially important marine fish species often comprise of discrete stocks that have independent responses to harvesting. The documented reduction in catch rates of swordfish (Xiphias gladius) makes it clear that accurate information regarding the population structure of swordfish is required to plan effective management strategies. Investigations of population genetics can assist the development of more effective management strategies by identifying previously unknown management units. Published information demonstrates that swordfish comprise four distinct stocks: Mediterranean, North Atlantic, South Atlantic, and Indo-Pacific. The population structure within the Indo-Pacific stock is not well understood. Genetic markers are a powerful tool for investigating the population structure, however, appropriate markers need to be chosen based on the scale of subdivison under investigation. Within this project, three classes of genetic markers (mtDNA, microsatellites, and nuclear SNPs) were developed and applied to ten populations in order to elucidate Indo-Pacific structure. The mitochondrial marker of choice for swordfish has been the highly polymorphic control region. This marker was compared to the mitochondrial gene, ND2, and was found to be unsuitable for examining Indo-Pacific population structure. The level of homoplasy observed in the control region was considerably higher than that of ND2, which suggests that the use of the control region has led to an underestimation of genetic differentiation between populations. 18 tetranucleotide microsatellite markers were developed. These markers were able to detect significant structure. SNPs were targeted in fragments of three nuclear genes, glucose-6-phosphate isomerase b (gpi-b), citrate sythase (CS), and ryanodine receptor 1b (ryr-1b). Three new SNPs were successfully genotyped and these markers detected some population structure, although the development of additional SNPs is necessary in order to increase statistical power. The ...
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