Morphological and genetic characterization of Sardinian trout Salmo cetti Rafinesque, 1810 and their conservation implications

The morphological and genetic structure of Western Mediterranean trout Salmo cettii inhabiting basins in Sardinia was completed to assist the design of its conservation programmes. Genetic analysis of protein-coding LDH-C1 plus sequencing mitochondrial control region gene and analyses of morphological characters described 253 specimens from seven localities in two basins in Southwest Sardinia. Nuclear and mitochondrial analyses revealed all of the fish were pure-bred native S. cettii, with no introgression from allochthonous S. trutta. The novel 18 mtDNA control region haplotypes were clustered in an 'insular' clade, strictly related to the Adriatic haplogroup, and depicted a radial network around two ancestral haplotypes. Completion of discriminant analysis using data on body pigmentation and quantitative morphologic parameters revealed three phenotypic groups within the fish. Each population and phenotype, characterised by high values of nucleotide and haplotype diversity, were not genetically differentiated and not geographically structured according to the two hydrological basins. Geometric morphometric analysis, based on 15 landmarkers, revealed pronounced and highly significant differences in body shape morphology between populations, suggesting S. cettii is locally adapting to extreme environmental conditions and so future management plans for these populations should treat the two basins as distinct morphological unit