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Oxynemacheilus bergianus is found in several inland water basins of Iran. Due to its wide distribution, this study was conducted to investigate its morphological variation in basins of Caspian Sea and Namak Lake of Iran using geometric morphometric technique. For this purpose, a total of 115 specimens from five river (Sefid and Ghezel Ozan (Caspian Sea basin), Jajrood, Kordan, Qom (Namak Lake basin)) were caught and compared using geometric morphometric method. The results indicated a completely different body shape patterns in the studied populations. The results also showed a significant difference between the body shape of the studied and groups the most differences were related to tail length and depth, body depth, head length and position of the dorsal, anal and pectoral fins. The observed shape patterns can indicate habitat-dependent morphological separation and geographical distances that the geometric morphometric method was highly capable of separating morphological features due to their high capability.

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For osteological studying of Paraschistura delvarii, thirty-three specimens of this species were collected from Gharah-aghaj river in Gulf basin (Fars Provance) by electro shocker. Fish were preserve 10% formaldehyde. Osteological studies were performed on all specimens following transportation to the laboratory samples were cleared and stained. The most important skeletal characteristics to distinguishthis species from other members included: T shaped Basihyal bone, 3 basibranchial in apparatus bones and small sesamoeid bone in snout.

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During 2018-2019, to study the morphological diversity of Oxynoemacheilus elsae, a total of 51 specimens were collected from the Godarchai, Barandozchai, Zarrinehrood and Mahabadchai rivers, Urmia Lake basin using electrofishing. From the collected samples, 22 morphometric characteristics were measured using a digital caliper with an accuracy of 0.1 mm. Also, in geometric morphometric (GM) method, the side of the samples were photographed, and 14 landmarks were digitized using tpsDig2 software. The extracted data were analyzed to understand morphological variation between the studied populations using multivariate analysis i.e. PCA, MANOCA /CVA and cluster analysis. The results showed a significant difference between the studied populations in terms of the morphological characters (P<0.05). In traditional method, there were significant differences in 10 traits between the studied populations (P<0.05). The main differences in GM method were related to the body and head depth, mouth position and caudal peduncle height. The observed morphological variations show the high adaptability of this species, especially in the pectoral fin length and body height traits with habitat adaptation.

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In the issue of aquatic management and assessment of freshwater fish species, it is important to examine habitat preference and habitat suitability indices, because the presence of many species in an aquatic ecosystem indicates the suitable conditions of their habitat. Therefore, this study was carried out to investigate and preference habitat of Oxynoemacheilus zarzianus in the Sirvan River. Sampling was done from different parts of the river (regarding depth, width and etc.)  in 7 stations each with 3 repetitions and a total of 21 stations. Sampling was performed along 30 m at each station against the direction of the river velocity, from the downstream of the river to the upstream. Ten environmental factors including pH, temperature, total dissolved solids, electrical conductivity, Altitude, depth, river width, velocity, and bed slope were measured. The results showed that the highest and lowest total SI values ​​for studied species were obtained for the altitude (0.237) and river width (0.1), respectively. The results showed that the highest abundance and presence of O. zarzianus were in places with gravel beds, which probably preferred these places to avoid predators. The value of the total suitability index also showed that this river is not a suitable habitat for Zarzian loach. Therefore, it is necessary to consider special management measures for this species, whose presence has been reported in this river recently.