Scale morphology and its structural details were studied with morphometry, geometric morphometrics, and scanning electron microscopy in five IranianAphaniusspecies and examined comparatively with molecular phylogeny. Scales were cycloid and circular inA. farsicusTeimori, Esmaeili & Reichenbacher andA. vladykoviCoad, cycloid and polygonal inA. isfahanensisHrbek, Keivany & Coad andA. sophiae(Heckel), and were spined and polygonal inA. disparRüppell. Univariate analysis indicated that the relative length of anterior margin of radii played a significant role in the separation of some species studied (P < 0.05). Canonical Variates Analysis (CVA) based on seven landmarks showed clear separation between the Iranian inland and inland-relatedAphaniusspecies (IIRAS) group (four species) and the brackish water species (A. dispar). The lepidonts were conical in the IIRAS group with the exception ofA. isfahanensis(rounded) and were rounded inA. dispar. Based on the basal position of the brackish waterAphaniusspecies in the phylogenetic trees of the genusAphanius,it can be assumed that the presence of rounded lepidonts was a primary state in their scales or is the result of convergent evolution. Also, the polygonal state in the scales ofAphaniusspecies was a primitive shared character state.

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Otoliths are aragonitic mineralizations located in the inner ear of bony fishes and play a principal function in the senses of hearing and balance (Popper, Ramcharitar, & Campana, 2005). Since otoliths functionally considered as a fundamental and specialized object of the acoustic-lateralis system (Nolf, 1985; Popper, Rogers, Saidel, & Sox, 1988), therefore, they play an important role in the communication between fish individuals. Sagitta is the largest otolith in most teleosts and the main one that has been studied. It has been suggested that the general morphology of otolith is species-specific, and its variation in size and contour is used to study fish taxonomy (Reichenbacher, Kamrani,

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Aphanius hormuzensis is an endemic tooth-carp found in the Hormuzgan drainage in S-Iran. This study aimed to investigate the size-dependent alternations of scale surface ornamentation in this species by conducting scanning electron microscopy and morphological analysis. A total of 50 wild fish individuals were captured from Shur River, and were classified into five size classes based on the standard length; SC-I (SL = 10-20 mm), SC-II (SL = 21-30 mm), SC-III (SL = 41-50 mm), SC-IV (SL = 51-60 mm), and SC-V (SL = 61-70 mm), and their scales were removed from below the dorsal fin (key scale) and caudal peduncle regions. The results revealed a clear trend of scale structural development in A. hormuzensis. The scale of small-sized (TL < 30 mm) and large-sized fishes (TL > 30 mm) differed, respectively, in the following characters; the overall shape (often circular vs. polygonal), relative focus size (large, FL/SL = 440-610 μm vs. intermediate and small, FL/SL = 100-330 μm), types of radii (only primary vs. three types), relative radii length (short, RL/SL = 100-180 μm vs. long, RL/SL = 320-450 μm), lepidont (absent or undeveloped vs. present and developed), and the relative lepidont length (short, LL/SL = 0.83-0.90 μm vs. intermediate and long, LL/SL = 1.2-2.2 μm). These character alternations could explain certain developmental stages in this species. The size-dependent changes in the surface micro-ornamentations as shown in this study suggest that these characters should be used cautiously for taxonomic studies of the aphaniid fishes.

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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. The urohyal bone is considered to be a synapomorphic structure in teleostean fish. The urohyal bone of six brackish water Aphanius species (i.e., Aphanius hormuzensis, A. stoliczkanus, A. furcatus, A. ginaonis, A. mento, A. sirhani) was compared using morphological description and linear measurements to explore the effectiveness of urohyal bone morphology in the separation of the Aphanius species. Description of the urohyal bones and their morphological variation allowed identification of the A. furcatus, A. mento and A. sirhani from their relatives. Moreover, the UH.UL separates significantly A. dispar and A. ginaonis, and the MH.UL discriminates significantly A. mento from others studied relatives. Discriminant function analysis (DFA) separated the studied species with high classification success (overall mean 94.7%). These results suggest the power of urohyal bone morphology in separating of the Aphanius species analyzed, and highlighting the taxonomic value of the urohyal bone. By considering the phylogenetic relationships among the studied species, it can be concluded that the observed variation in their urohyal morphology is largely consistent with their phylogeny. This indicated that at least some morphological characters in the shape of urohyal bone in Aphanius are encoded probably by genetic factors, which can be used for species discrimination.