Genetic characterization of sturgeons (Genus Acipenser ): A molecular survey in the mtDNA control region gene and its potential applications to fish breeding for Conservation Aquaculture

All extant sturgeon and paddlefish species within the order Acipenseriformes are currently in need of protection because of human threats such as increasing fishing pressure, illegal international trade, poaching and destruction of their native habitats. At least two sturgeon species, Acipenser brevirostrum and A. sturio face extinction (Appendix I, CITES 2006a). The other 23 sturgeon species can become extinct if effective fisheries management actions at the national level and more stringent international trade regulations are not developed and enforced. Concerted international efforts are needed to save these valuable genetic resources.;The implementation of artificial reproduction programs for sturgeons in captivity has been suggested as a temporary measure to help the recovery of endangered wild populations. For many decades, sturgeon hatcheries from various European countries have been releasing sturgeon fingerlings into rivers inhabited by native sturgeon populations. However, knowledge of genetic characteristics of prospective broodstock and hatchery produced sturgeons is needed to assess their potential genetic contribution or possible adverse impacts to the genetic diversity of remnant native populations.;This thesis presents findings on a study of the genetic diversity of nine groups of European sturgeons held at five aquaculture commercial and research facilities in the states of Hawaii and Florida. A section of the mtDNA "control region" between 210 and 660 base pairs long from 182 sturgeon DNA samples using PCR, electrophoresis and DNA sequencing. Gene genealogies were constructed and statistical analyses conducted using PAUP 4.0b10, MODELTEST 3.7, TCS 1.21, and ARLEQUIN 3.1 software packages.;Sixty four A. gueldenstaedtii (Russian sturgeon) haplotypes (distinctive DNA sequences) and 55 A. baerii (Siberian sturgeon) haplotypes were identified. Based on comparisons with homologous mtDNA sequences available through NCBI GeneBank data base I found that mtDNA sequences of the control region from fish group 2 showed a closer genetic affinity with Acipenser baerii than with A. gueldenstaedtii. Heteroplasmy (the presence of more than one mitochondrial genome in one organism) was identified in 6 out of 9 groups investigated, with all A. baerii groups showing 100 % heteroplasmic specimens.;The nucleotide diversity for the A. gueldenstaedtii groups was pi=0.0331, a value 40% lower than that reported for wild Russian sturgeons (pi=0.05), and 15.3% lower than the nucleotide diversity value calculated for the control group (Ag_Control, pi=0.0427). The mean nucleotide diversity for all A. baerii groups was pi=0.0307, a value higher than that calculated for the control group (pi=0.00282) and higher than values reported for wild Siberian sturgeons (pi=0.0040).;A. gueldenstaedtii and A. baerii haplotype groups were tested for phylogenetic relationships with 1000 replicates' bootstrap analyses. The resulting majority rule (50%) consensus tree yielded low percentage supports for the observed group partitions.;FST (theta) values calculated between fish groups were used as short term genetic distances to conduct pairwise group comparisons. For A. gueldenstaedtii groups, this test revealed statistical significant differences (P<0.05) between most, but not all, groups. For A. baerii groups, the pairwise group comparisons yielded statistically significant differences (P<0.05) among all group comparisons. Exact test of sample differentiation yielded similar results with most A. gueldenstaedtii and all A. baerii comparisons found to be statistically significant.;The results of this investigation show the wealth of genetic information that can be found in the mtDNA control region and proves the usefulness of the mtDNA control region to conduct inter and intra-species group comparisons to evaluate genetic diversity. Based on this, these groups of fishes still possess genetic value and their progenies, if they are ever produced in captivity, would still have the potential to contribute to the improvement of the genetic diversity of wild populations.