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The sand goby Neogobius pallasi (Berg, 1916) belongs to the family Gobiidae which has a wide distribution in the south of the Caspian Sea basin and its tributaries. The purpose of this study was to determine some of the morphological parameters of sand goby and the appropriate characteristics for the separation of populations in Kaboodval, Zaringol and Shirabad Streams. Both males and females consisted of five age groups (0⁺-4⁺). Seven meristic and 31 distance-based morphometric characters from 104, 30 and 62 specimens were investigated in three streams during the summer in 2008. The comparison of the morphological characteristics among the samples of sand goby showed the significant differences in three Streams (p<0.05), but principal components analysis (PCA) showed that the low characteristics play a role in the population separation. Only the mouth width, lower jaw and upper jaw coefficients were greater than 0.75. It seems that there is more overlap between the samples of Kaboodwal and Zaringol compared to those of Shirabad. This finding is also consistent with their geographic distances

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In this study, morphological characteristics of two populations of Pike (Esox lucius) were compared in Anzali and Amirkelayeh wetlands at Southern Caspian Sea basin using morphometric and meristic characters. A total number of 57 speciemens of Esox lucius including 28 and 29 specimens from Anzali and Amirkelayeh wetlands, respectively, were caught by fyke nets. In this study 32 morphometric and 11 meristic characteristics were investigated and standardized first with Beacham formula, and then the data were subjected to a Principal Components Analysis (PCA), Discriminant Function Analysis (DFA) and UPGMA dendrogram. Based on PCA results, the two populations of Esox lucius were differentiated by 9 principal factors in morphometric characters. DFA revealed that the two populations were distinct in morphometric characters (87%). Also, the UPGMA dendrogram separated E. lucius populations of the Anzali and Amirkelayeh wetlands. It is possible that the different habitat conditions were the cause of distinct fish population of the two wetlands.

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A comparative study of species in different habitats at the population level is very important because such studies provide significant information about the diversity of species. In this study the growth characteristics of bitterling was investigated in two different aquatic waters in Anzali lagoon and Siyahrood River. The sampling was monthly done by plankton-collector from February to June 2013 and a total of 538 specimens were collected. To determine age opercula and scales were utilized .There were 7 age groups of 2+ till 8+ in Anzali lagoon and 8 age groups of 1+ till 8+ in Siahrood River. The result showed that the largest length and weight were 75.44 mm and 6.674 g for males in Siyahrood River. A significant weight-length relationship was observed for the populations in different areas (P<0.05). Growth pattern was measured as positive allometric for males and females. The condition factor was larger in males than females in Siyahrood and Anzali lagoon.

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This study aimed to investigate some of serum electrolytes and white blood cells of wild stellate sturgeon (A. stellatus) which have been caught off the coast of Mazandaran by trawl methods during 5 maritime patrol from 2009 to 2010.  Initially, 2 ml blood samples of 30 wild juvenile stellate sturgeon were extracted for spread of differential blood count, and serum electrolyte to test factors such as calcium, magnesium, cholesterol, albumin and total protein were separated. To conduct statistical evaluation and comparison, fishes were divided into two weight groups of 10 – 30 gr and 31 – 50 gr. Result of differential count  showed that the most and the least abundance of leukocytes were belonged to lymphocyte and monocyte in both two groups, respectively. Serum electrolytes results showed that mean levels of cholesterol, calcium, magnesium, albumin and total protein in A. stellatus at group 1 were 28.1 ± 10.6 mg/dl; 24.7 ± 1.6 mg/dl; 26.7 ± 1.8 mEq/l; 1.4 ± 0.3 g/dl and 2.2 ± 0.3 g/dl, respectively. At group 2, these parameters levels were 71.14 ± 2.4 mg/dL, 20.6 ± 0.8 mg/dL, 17.4 ± 3.4 mEq/L, 1.6 ± 0.2 g/dl and 2.3 ± 0.2 g/dl, respectively. No significant difference was observed between the white cells counts of the two groups. There was a significant difference between cholesterol, calcium, and magnesium levels in each two groups, but results showed no significant difference in total protein and albumin between the two groups. Overall, based on the results of this study it can be concluded that in natural environments, due to the weight of fish, there is little difference between the measured blood indexes.

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To determine inter- and intra- population morphological variation of Caspian vimba (V. persa), a total of 135 specimens were caught by cast net and beach seine in southern Caspian from Gorganrud and Valiabad rivers and Larim and Mahmoudabad coastal waters. In the present study, 27 morphometric and 10 meristic characteristics were examined. Based on principal component analysis, linear combination of 27 morphometric and 10 meristic characteristics resulted in factors that showed certain specifications of relationships among characteristics. In morphometric characteristics, 6 factors with 79.26% and in meristic characteristics, 5 factors with 71.86% of phenotypic variation among individuals were chosen and Eigen values were greater than one. Discriminant functional analysis showed high similarity percentages among individuals in different regions. Cluster analysis revealed that Larim and Valiabad populations were separated from the rest of populations regarding morphometric and meristic characteristics, respectively. Significant difference was observed regarding most of morphometric characteristics among the populations, while this significant difference was observed only in a few meristic characteristics among the populations. Principal component analysis, discriminant functional analysis and cluster analysis showed that populations in four regions were not entirely separable. However, it is possible that they are from different populations due to different ecological conditions among study areas.