Flank spot number and its significance for systematics, taxonomy and conservation of the near-threatened Mediterranean trout Salmo cettii: evidence from a genetically pure population.

The number of spots on the flank of the Mediterranean trout Salmo cettii population from Tellesimo Stream in Sicily, Italy, varied between seven and 37, with a median and mode of 21, numbers much lower than those reported in the literature and different from those of other Italian trout populations. This finding could be ascribed to the phenotypic plasticity of the species or, alternatively, could provide evidence to support the different origin of Sicilian autochthonous trout. Given the ease of use of this character for the identification of native fish, it could be particularly important for conservation and management purposes.