Comparative morphology of urohyal bone in brackish water species of the genus Aphanius Nardo, 1827 in the Persian Gulf and Southeastern Mediterranean Sea basins (Teleostei: Aphaniidae)

Abstract

Among the skeletal elements in fishes, the urohyal bone which lies in the lower part of the head - the central part of the mandibular skeleton- has proved to be of special significance in fish systematics. In the present study, the urohyal bones of six brackish water Aphanius species (i.e., Aphanius hormuzensis, A. stoliczkanus, A. furcatus, A. ginaonis, A. mento, A. sirhani) were compared using morphological description and linear measurements to explore the effectiveness of this structure in the separation of the studied Aphanius species. The description of the urohyal bones and their morphological variations allowed identification of A. furcatus, A. mento and A. sirhani from their relatives. Moreover, the urohyal height/urohyal length (UH.UL) significantly separated A. hormuzensis from A. ginaonis, and the maximum height/urohyal length (MH.UL) significantly discriminated A. mento from its relatives. Discriminant function analysis (DFA) separated the studied species with high classification success (overall mean 94.7%). These results showed the power of urohyal bone morphology in separating the Aphanius species analyzed, and highlighted the taxonomic value of the urohyal bone. The observed variation in the urohyal bone of Aphanius species is largely consistent with their phylogeny. This designated that at least some morphological features of the urohyal bone in Aphanius are probably encoded by genetic factors, which can be further used for species discrimination.