ALBERT

Description: Difficulties in characterisation of sprat populations in the Baltic Sea have lead to the determination of only one management unit for the ICES subdivisions 22-32. To prevent mistakes in management which could result in overfishing and exploitation, stock differentiation for the Baltic sprat is demanded from several sides. Genetic tools are considered as helpful to meet these demands and it is hoped to lead that they will provide new information about the number and distiibution of existing stocks. The use of microsatellite-loci is an approach for genetic stock identification. Microsatellites are highly informative genetic markers useful for population genetic studies, lineage mapping and parentage detection. Usually, microsatellites have to be identified anew for every species examined because the flanking regions of the repeat sequences differ between most taxa. An approach for isolation of tandem repeated sequences in the genomic DNA of the sprat, Sprattus sprattus is desciibed here. Genomic DNA was fragmented, attached linkers and prepared for ligation into a plasmid vector. Specific repeat elements were captured using biotinylated oligonucleotide probes in solution and subsequent attachment to streptavidin-coated magnetic beads. Captured fragments were amplified by PCR and cloned into the vector. The product of this expeiiment was a library enriched for defined microsatellite-sequences. Clones from this library were selected and their inserts were sequenced due to the detection of repeat motives. The results presented here show that this approach is effective to isolate dinucleotide- repeat sequences. For the enrichment two tetranucleotides, AGAT(7) and TATC(7) and one dinucleotide, GT(15) were used. GT(n) repeats were found in all of the thirty dinucleotideenriched DNA samples, sequenced. Contraiily, in none of the tetranucleotide-enriched samples repeat sequences could be identified. This study shows that in general the isolation of repeat sequences of genomic sprat DNA is possible. The development of microsatellite markers suitable for stock identification of the sprat in the Baltic Sea was discussed here.