IDENTIFICATION OF THUNNUS TUNA SPECIES BY THE POLYMERASE CHAIN-REACTION AND DIRECT SEQUENCE-ANALYSIS OF THEIR MITOCHONDRIAL CYTOCHROME-B GENES

Four commercially important tuna species in the genus Thunnus are caught off the east coast of Canada. The harvest of bluefin tuna (T. thynnus) is regulated, but that of bigeye (T. obesus), yellowfin (T. albacares), or albacore (T. alalunga) is not. Enforcement of the regulations governing the bluefin fishery has been difficult because of the close genetic relationships among these species and the ease with which morphological characters may be removed once a fish has been landed. Isoelectric-focusing of water-soluble muscle proteins does not resolve these four tuna species beyond two groups: one consisting of bluefin and yellowfin and the other comprising bigeye and albacore. The polymerase chain reaction was used to amplify a 307 base pair segment of the mitochondrial cytochrome b gene from members of these species. There is intraspecific variation at this locus in each of the species. More importantly, there are differences between the four species and these genetic markers can be used to determine the species identity of an individual tuna with a high degree of confidence. This methodology should prove very useful for enforcing the regulations governing Canada's bluefin tuna fishing industry.