The taxonomic status of the `sea trout' from the north Adriatic Sea, as revealed by mitochondrial and nuclear DNA analysis

Abstract

Aim Unclassified salmonids, generally named ‘sea trout’, have been spotted on occasion in the north Adriatic Sea, although autochthonous salmonids have not been reported in the Mediterranean Sea. On the basis of their phenotype, these fish were regarded as the rainbow trout or salmon-like fish. The aim of the study was to determine the taxonomic status of the ‘sea trout’ and its origin. Location The specimens originate from the coastal waters of the Gulf of Trieste, northern Adriatic Sea, and from hatchery-reared stock of brown trout (Salmo trutta), derived from Trentino fish-farm. Methods Meristic measurements, nucleotide identity-test of mitochondrial DNA (mtDNA) (control region) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of nuclear DNA (lactate dehydrogenase C1* gene) were performed. Results Morphological characters of the ‘sea trout’ specimens analysed, correspond best with those used for S. trutta and S. marmoratus. Genetic tests denoted explicit similarity between the ‘sea trout’ and hatchery-reared brown trout. Mitochondrial DNA analysis of the ‘sea trout’ revealed 100% nucleotide identity with brown trout of the Atlantic phylogeographical lineage. Results inferred from nuclear DNA analysis, confirmed the Atlantic descent of the ‘sea trout’ and demonstrated also a certain level of introgression with the brown trout of Danubian lineage.