The Iranian native salmonids (Salmo caspius and S. trutta), distinct species or two forms of the same species; a geometric-morphometric based hypothesis

This study aimed to investigate the taxonomic status of Salmo trutta inhabiting the Mardoogh, Liqvanchai (Urmia Lake basin), Haraz (the Caspian Sea basin) and Jajrud and Karaj (Namak Lake basin) rivers, and Salmo caspius (from the Caspian Sea) using the geometric morphometric method. Samplings were done using an electrofishing device in the rivers and beach seine/gillnet in the sea. To prepare geometric data, the photographs were taken from the left side of the specimens, then 16 landmark points were defined and digitized on the two-dimensional (2D) images. The data were analyzed using Discriminant Function Analysis (DFA), Principal Component Analysis (PCA), Canonical Variate Analysis (MANOVA/CVA), and cluster analysis. The intra-species morphological variations between the two studied species from the Caspian Sea basin showed significant differences in the morphometric traits, including snout position, body depth, and caudal peduncle length and depth. Based on the DFA and PCA, they were separated from each other. The results related to the interspecies examination categorized the S. trutta populations of the three studied basins in three clusters, separated from the S. caspius cluster. The resulting differences showed the morphological flexibility of these populations to their environmental conditions. The geometric morphometric method identified the studied groups at the intra and inter-species levels in terms of morphology, which helps to evaluate the stock assessment of these species and consider them as separate species in the future.