number of endemic species described in Italy. Among these, Mediterranean trout (Salmo cettii, syn. Salmo macrostigma) has considerable economic significance for fisheries management, aquaculture and conservation biology. Unfortunately, especially in Italian rivers, due to anthropogenic disturbance as pollution, water depletion for irrigation, dam constructions for power production, habitat alteration and over-fishing, the native Mediterranean trout populations are decreased during the past decades. For this reason, alien trout as the domesticated strains of Salmo trutta have been introduced in freshwater basins for the implementation of fishing activities without considering the presence of wild autochthonous populations of the interfertile Salmo cettii, leading to the introgression by alien genomes. The restocking with non-native domesticated strains produces the ‘founder effect’ due to low genetic variability of spawners. The described scenario is also common to Molise watersheds in which no data of genetic variability has ever been reported. Here we present preliminary results of gene variation study to assess trout population structures in Biferno and Volturno rivers. A total of 300 samples in 30 different areas (15 for each river) were collected. Adipose fin tissue fragments were cut, immediately transferred into a tube containing 100% ethanol and, once in the lab, stored at −20 °C until DNA isolation (by Qiagen blood and tissue kit). PCR-RFLP analysis on nuclear gene LDH- C1* using the Ldhxon3F/Ldhxon4R primer pair and BslI restriction enzyme was carried out. Preliminary results, carried out on a representative subset of samples, showed a different introgression level considering the two rivers. In the Volturno river drainage, the degree of homozygous specimens for the native allele (S. cettii) was 86.9% vs. 13.1% of heterozygous fishes. The Biferno river basin, instead showed 50.0% of specimens with homozygous native alleles vs. 41.2% of heterozygous fishes and 8.8% of specimens with homozygous alien alleles (S. trutta). Further investigations are required using all the samples and analysing also mitochondrial 16S rDNA.
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