The present study was conducted to provide a detailed descriptive osteology of Barbus cyri from SOUTHERN CASPIAN SEA for the first time and comparing it with those of B. lacerta from the Tigris and Urmia lake BASINs. For this purpose, twelve specimens of B. cyri were collected from Safidrud River using electrofishing device and fixed in 10% buffered formalin. Then, the specimens were cleared and stained with alcian blue and alizarin red for osteological examination. A detailed description of the osteological features of B. cyri was provided. Based on the results, several differences were observed between the two species. Barbus cyri can be distinguished from B. lacerta by having three pharyngobranchial, a consumptive neural spine of second centrum and having 3rd and 4th vertebra with posterior position of neural spines.

In this reSEArch 47 genus of different phylum of phytoplanktons such as Cyanophyta, Chlorophyta, Pyrophyta, Chrysophyta and Euglenaphyta were surveyed that their numbers (ind. /m^3) and biomasses (mgr/m^3) were estimated. Frequncy of phytoplantons (ind. /m^3) was 131. 2, 1. 6, 65. 3, 18. 9 and 23. 8 million respectively. Furthermore, their biomasses was 08. 4, 1. 9, 1358. 9, 295. 1 and 124. 7 mgr/m^3, respectively. The maximum and minimum numbers were observed in Leptolingbaya belonged to Cyanophyta and diatoms of Chrysophyta 84. 3 and 0. 025 million ind. /m^3 respectively. The maximum and minimum biomass was observed in Gyrosigma (Chrysophyta) and Tetradron (Chlorophyta), 12317. 3 and 0. 014 mg/m^3 respectively.

Biodiversity conservation is one of the global concerns, so the comprehensive study of diversity and its possible risks are recognized as a tool for natural resource management. This study was carried out to investigate the diversity and abundance of fishes in the Masule River, the SOUTHERN CASPIAN SEA BASIN. Samplings were carried out SEAsonally during 2021-2022 using an electrofishing device in 5 sampling sites from 7 km below Masule City to Chamesghal. A total of 20 fish species belonging to 11 families were identified, and the Leuciscidae and Cyprinidae families were the most diverse with 6 and 4 species, respectively. Of these, 15 native species and 5 exotic species were found, and in terms of habitats, 16 freshwater, 2 migratory, and 2 species with two forms living in the SEA and River were found in the studied area. The fish species abundance from upstream to downstream increased from 5 to 16 species. Also, their abundance fluctuated according to the sampling sites in different SEAsons and these fluctuations existed to a lesser extent between the sites in the whole period. Generally, Capoeta razii, Alburnoides samiii, and Ponticola iranicus accounted for the highest numbers, 31.3, 26.2, and 25.4%, respectively. In conclusion, this river has a small variety of migratory fish species, and it is suggested to make a fishway, especially on the Lulman Dam, so that the migratory fishes can regenerate their generation naturally.

Introduction Environmental flow requirement (EFR) is defined as the flow that is necessary to ensure the existence of habitats in water resources systems. Hydrological methods are almost the most straight-forward approach in rivers. These types of methods are also known as desktop methods that rely on annual, monthly or daily flow discharge data of the river. There are two main limitations for desktop approach. First, in this type of approach, regional ecological values are not considered directly. Secondly, this type of approach has little defense capability in interactions of water allocation, but because of having some advantages such as simplicity, it is used in many countries. But it is obvious which development of localized desktop approach is so necessary and also is so useful. It can be used as a flow index for environmental flow assessment in different projects. Main contribution of present reSEArch is development of new desktop method for environmental flow assessment in SOUTHERN CASPIAN SEA BASIN with focusing on regional ecological values. Material & Methods The Lar National Park is located 55 km at east of Tehran. Its mean elevation from open SEAs is 2531 m and its area is 27000 Ha approximately. In this park, Brown Trout (one of Iranˈ s most unique species) inhabits. This park is one of the original habitats of Brown Trout which has unique properties. In this park, predation of Brown Trout is forbidden and is protected by the Iranian Department of Environment (DOE). Water quality in all of the streams in the park in a good condition and there are minimum water quality issues for brown trout habitats, also brown trout is dominant aquatic so there is no effective competition in streams. Hence this park is an ideal place for development of hydrological flow index based on real life of aquatic in their habitats and physical habitat effects. Since the development of physical habitat simulation, physical habitat models became an important tool for river management. Aquatic habitat simulation models have been used for fish in water resource management, particularly in North America. The Physical Habitat Simulation is considered to be the first of these fish habitat models and is now being applied worldwide. In the present reSEArch 1-D hydraulic simulation in combination of physical habitat simulation is used to simulate physical habitat for Brown Trout. Quantified ecological modeling describes flow changes in physical components of the system and translates them into an estimate of the quality and quantity of microhabitat for aquatic organisms. The most commonly used output from these types of models is Area Weighted Suitability (AWS). This factor is computed within the reach at a specific discharge from: (1) Where Ai is the surface area of cell i and Ci is the combined suitability of cell i (i. e., composite of depth, velocity and channel index individual suitability). Common method in estimation of C is consideration of minimum value of depth, velocity and substrate suitability for development of combined habitat suitability in each habitat cell. Description of river condition is carried out in three main conditions which are maximum protection or outstanding, mid protection or good and minimum protection or poor. Two main habitats are selected for implementation of ecological modeling which are Elarm which is as a main habitat for fry and juvenile Brown trout and Absefid which is as a main habitat for adult Brown trout. Slope of Elarm is smaller than 2% and slope of Absefid is larger than 2%. Hence development of flow index for environmental flow is carried out based on these two types of rivers. Because popularity of mean annual flow(MAF) as an acceptable index in determination of environmental flow requirement, development of hydrological flow index was based on MAF in each river. Results & Discussion Habitat time series is shown in figure 1. In this figure you can see the alteration of AWS in different months Figure 1. Habitat time series in simulated habitats( figure above is Absefid and figure below is Elarm) According to habitat time series, environmental flow regime is assessed in two habitats in three stages. First stage was maximum protection or outstanding condition which maximum area weighted suitability is available for aquatics in river. Based on ecological negotiations, minimum acceptable AWS was 50% of maximum AWS, hence In stage 2 and 3, 75% and 50% maximum area weighted suitability is available. Estimated environmental flow regime is displayed in figure 3. Lar method recommendations for assessment of environmental flow requirement are displayed in Table 1. It should be noted that SEAsonal scale is considered. Figure 2. Environmental flow regime ( figure above is Absefid and figure below is Elarm) Table 1: Lar method recommendations in EFR assessment River condition Spring Summer Fall Winter 2%> 2%< 2%> 2%< 2%> 2%< 2%> 2%< Outstanding 70 130 135 425 120 300 70 135 Good 60 35 105 100 100 60 60 35 Poor 45 20 85 30 80 25 45 20 Conclusion In the present reSEArch, a desktop method is developed based on regional ecological modeling in SOUTHERN CASPIAN SEA BASIN. Because of special features of Brown trout habitats in Lar national park, This place is chosen for ecological modeling and development of hydrological flow index based on mean annual flow. According to results, minimum flow need for rivers which slope is larger than 2% are 20%, 30%, 25% and 20% percentage of MAF in spring. Summer, fall and winter respectively but these values in river which slope is smaller than 2% are 45%, 85%, 80% and 45% percentage of MAF.

As for Barbus capito, two subspecies have been reported by L. S. Berg (1949) and other authors. To distinguish these two forms, 35 specimens were examined according to the main reported differences. All of these specimens have been collected in SOUTHERN parts of CASPIAN SEA and are part of CMN (Canadian Museum of Nature) fish collection mainly collected by B. W. Coad. To analyze patterns of morphological variation in these specimens, PCA and DFA were used. The main differences were in head length, dorsal body length, caudal length and barbells length. There were no distinguishable characters for separating these two forms into two species. Considering other differences, the head length was not stable and could not be regarded as a distinctive character. However, in south of CASPIAN SEA, in addition to typical B. capito there were variations within this species with bigger head, longer caudal fork and longer pectoral.

The CASPIAN bighead goby (Ponticola gorlap), a member of the family Gobiidae, is found on the SOUTHERN CASPIAN SEA BASIN. Since little information is available about the skeletal structure of this species, therefore, this study was conducted to describe its detailed skeletal structure in the SOUTHERN CASPIAN SEA. For this purpose, a total of 17 specimens were collected from Sefid River by electrofishing device. After anesthesia, they were fixed into 10% buffered formalin, and for osteological examination, they were cleared and stained and, their bony characteristics were described in detail. The results showed that Iranian populations of this species can be identified by having traits, including sharp point of the lateral ethomoid, lack of the nasal, separation of the horizontal part from the vertical part of the premaxilary, presence of an ascending process in the dentary and separation of the symplectis and metapterygoid.

The length-weight relationships,(LWRs) were calculated for 14 fish species belonging to five families (Cyprinidae,Cobitidae,Nemacheilidae,Salmonidae,and Gobiidae) collected from the Tajan River,north of Iran.Significant length-weight relationships with high correlation coefficients were found for all species.

Traditional morphometric measurements and meristic counts were used to investigate the hypothesis of population fragmentation of Mash mahi, Aspius aspius taeniatus (Eichwald, 1831) among two fishing areas in SOUTHERN CASPIAN SEA BASIN (Tonekabon: 32 specimens and Sari: 34 specimens). Univariate analysis of variance showed significant differences between the means of the two groups for 12 out of 26 standardized morphometric measurement and three out of nine meristic counts. In discriminant function analysis (DFA), the proportion of individuals correctly classified into their original groups was 82.1% and 61.2% for morphometric and meristic characteristics, respectively. Clustering based on Euclidean distances among groups of centroids using an UPGMA and also principal component analysis’ results (PCA) for morphometric and meristic data indicated that two samples of Mash mahi were distinct from each other in these regions, while there were a relatively high degree of overlap between two locations.

In this study 16 groups of zooplankton belong protozoa, arthropoda, rotifer and cyliophora were investigated. The number of these zooplanktons were accounted in m3 and also their biomass (mg/m3) was measured. The average biomass of zooplankton was measured 531. 74, 30. 77, 225. 07 and 96. 26 mg/m3 respectively and the total was attained 883. 83 mg/m3. The maximum and minimum biomass of all zooplanktons was estimated in November and July, 3446. 23 and 6 mg/m3 respectively. Furthermore, the maximum and minimum numbers of zooplanktons were found in September and July which were 48. 4 and 0. 002 millions respectively and the average number was 8. 4 ind/m3.