Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


John E. Graves


The results of life history studies involving the sailfish, Istiophorus platypterus, from the Atlantic, Pacific, and Indian oceans were reviewed. Results of studies agree on several aspects of sailfish biology; sailfish exhibit opportunistic feeding behavior, follow the 28??C isotherm, spawn in summer mature at approximately age 3, and are the least migratory of the billfishes. However, results are in conflict concerning sex ratio and whether sailfish are single or multiple spawners. Although many researchers have reported that sailfish are sexually dimorphic, their fragile otoliths make them difficult to age, aging studies have not been validated, and sexual dimorphism has not been adequately separated from differences in age at first maturity. Life history studies are further compromised because identification of early life history stages is difficult and effect of genetically distinct stocks on these studies is unknown. Molecular markers representing a range of genetic resolution were used to investigate the genetic stock structure of the sailfish within and between oceans and to discriminate sailfish from other istiophorid billfishes. to investigate the genetic basis of stock structure, a 1700 by region of mitochondria) DNA which included the control region, was surveyed with five restriction endonucleases and representative individuals were sequenced. In addition, five nuclear microsatellite loci were assayed. Approximately 647 sailfish were collected from throughout the species' range over a six-year period from the Atlantic, Pacific, and Indian Oceans. Both mitochondrial and nuclear markers found that Atlantic, eastern Pacific, and Indo-west Pacific sailfish represent distinct genetic stocks. In addition, mitochondrial data revealed the presence of diverse clades, which were probably formed during Pleistocene glaciation. Independent molecular markers based on mitochondrial and nuclear DNA were developed to provide positive identification of istiophorid and xiphiid billfishes. Both classes of markers are based on amplification of short segments (<1.7 kb) of DNA and subsequent digestion with informative restriction endonucleases. ND4 and MN32-2, the selected markers, allow unambiguous specific identification, although it was not possible to differentiate white marlin and striped marlin. The resulting keys provide two independent means for the forensic identification of fillets and for specific identification of early life history stages.



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