The twaite shad Alosa fallax (Lacepede, 1803), belonging to the family Clupeidae, is a polytypic species characterized by both landlocked and anadromous populations. These two forms have been known by historical times in Italian waters and often considered as distinct taxonomic units. However, taxonomy of Italian shads has been questioned, since it is based on morphological characteristics, not always reliable. To clarify the phylogenetic relationships among Italian twaite shad populations, both landlocked and anadromous ones were investigated by molecular markers, namely mitochondrial Cytochrome b (Cytb) gene sequencing. In particular, new samples from Lake Omodeo (Sardina Island), Taro and Po Rivers were compared with previously analyzed populations from Northern and Central Italy. Genetic analyses showed that the landlocked twaite shad population from Lake Omodeo was characterized by a single Cytb haplotype (A. fallax hap1), whilst the new samples from Taro River and Po River by two haplotypes (A. fallax hap3 and A. fallax hap5). These three haplotypes are the most represented both in landlocked and anadromous Italian populations. These additional data confirmed the occurrence of different Management Units (MUs) belonging to a single phylogenetic lineage within Italian waters, without evidence of a separation at specific level of the A. fallax group. The Cytb phylogenetic analysis do not support the existence of a separated species for Italian landlocked populations, as previously hypothesized.
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