GENETIC STRUCTURE OF THE SWORDFISH (XIPHIAS GLADIUS) STOCKS IN THE ATLANTIC USING MICROSATELLITE DNA ANALYSIS

The genetic structure of the swordfish (Xiphias gladius) in the Atlantic Ocean was examined by genotyping 1179 individuals for 4 microsatellite loci. These individuals were collected during the years 1999-2002 from the following regions: south Atlantic (up to 5oN), mid-Atlantic (9oN to 20oN), northeast Atlantic (North of 30oN and East of 31oW), northwest Atlantic (North of 30oN and West of 31oW). Gene diversity was very high (>0.96) for all four loci. Heterogeneity tests and pairwise Fsts showed that the South Atlantic group was significantly different from all the other groups (p<0.000).These results are in agreement with previous mitochondrial DNA data and do not support a need for changing the 5oN latitude as a boundary for fisheries. Some individuals were also genotyped for the Calmodulin intron 4 gene (CaM) to compare with an earlier dataset for this marker. Allele frequencies found for CaM were in agreement with previous observation and showed a different population structure pattern compared to that revealed by microsatellites. However, the pattern reflected in CaM should be treated with caution, since CaM is only a single diallelic locus, possibly under strong selection. The genotyping of the samples for more microsatellite loci, which is in progress, is expected to further elucidate the genetic structure of the swordfish in the Atlantic, by further increasin