Conservation and management of Salmo (trutta) macrostigma in Sardinian freshwathers: first results of genetic characterization

Salmonids are present in Sardinia with the autochthonous form Salmo (trutta) macrostigma and the allochthonous ones S. (trutta) trutta and Oncorhynchus mykiss. For many years repeated and uncontrolled introduction of S. (trutta) trutta of doubtful origin, have been carried out; this has enhanced hybridization and genetic pollution phenomena, progressively determining the contraction, or even the disappearance of the original S. (trutta) macrostigma populations. Currently, the majority of autochthonous fish populations, depending exclusively on natural reproduction, have disappeared from some water courses, or else have become very rare. In an attempt to satisfy the requirements of safeguarding biodiversity, the Department of Animal Biology and Ecology, University of Cagliari, together with the “SarcidanoBarbagia di Seulo” mountain district authorities, has recently set up a research program aiming at restocking the Sardinian trout populations. Sampling was carried out at four sites located in two different areas of the Flumendosa hydrographic basin in central-western Sardinia. A total of 30 trout, captured between June and November 2005, was measured, weighed, photographed and submitted to DNA mitochondrial analysis (amplifying and sequencing a portion of the D-loop control region) and of the LDH-C1* nuclear gene (amplifying and digesting the amplified part with the Bsl1 enzyme). Valid candidates for use as broodstock were considered to be those individuals found to possess an autochthonous mitochondrial haplotype (haplotype Ad, according to Bernatchez) and to be homozygous for the 100 allele for LDH-C1*, that enables the contribution of genes of Atlantic origin to be excluded. In the remaining individuals, the presence of allele 90 of northern European origin was found in homozygosity or heterozygosity, and also of the Atlantic mitochondrial haplotype (haplotype AT, according to Bernatchez). The present paper reports the first findings to have emerged from the genetic investigations, and confirms the validity of the method for distinguishing the salmonid populations.