عبدالعظیم فاضل

This study aimed to investigate inter-population variation in the population dynamics of the Caspian kutum (Rutilus frisii) based on catch data from the coastal waters of Golestan Province (southeast Caspian Sea) over 26 years (1991-2016). The biometric data of 20,438 kutum samples were analyzed, with sizes ranging from 18 to 70 cm. The average values of L∞ and k were 59.83 cm and 0.44 per year, respectively. The weight infinity (W∞) ranged from 1,738.97 to 6,380.03 grams, with an average of 2,867.96 grams. Cohort analysis revealed five distinct cohorts in the exploited population. The natural mortality rates varied between 0.60 and 0.84, with an average total mortality (Z) of 1.35. The exploitation rate (E) ranged from 0.13 to 0.73, exceeding 0.5 in 8 years. The results indicate significant temporal variability in the kutum population over the study period.

The excessive growth of the aquaculture industry, in addition to using more natural resources, causes a disturbance to the biological and non-biological balance through effluent releases, and water quality indicators provide the possibility of better management of pollution and direction for targeted biological monitoring. The purpose of this research was to evaluate the nitrogen load of the basin and rainbow trout breeding farm on the water quality of Zarin Gol River in Golestan province, Iran, based on a standard index (WQI) by measuring water quality parameters including: pH, total phosphate, temperature, nitrate, dissolved oxygen, turbidity, and total coliform. Sampling was done seasonally at five stations (before and after the first and second fish farm and 1000 meters downstream from the second fish farm) in 2018. The results showed that the concentration of nitrogen and phosphorus in the River during the six months of fish breeding on the second farm was estimated to be 16.5 tons of nitrogen and 2.9 tons of phosphorus. According to the WQI, the results showed that the water quality values in all the studied stations are 79.7 to 87.8, which indicates excellent water quality according to the descriptive table. It seems that under the current conditions, the Zarin Gol River has the ability to self-purification the effluent of two fish farms with the expected capacity.

The lake’s trophic state can well represent human disturbances on these ecosystems. The present study was conducted seasonally to investigate the trophy status of Bostan Dam Lake (Golestan Province) from spring 2019 to summer 2020 in five study stations. A number of physicochemical parameters were determined such as pH, electrical conductivity, temperature, dissolved oxygen concentration, Secchi disk depth, salinity, dissolved solids, total hardness and turbidity. While nitrate, phosphate, total nitrogen, total phosphorus, ammonia, total alkalinity and chlorophyll evaluated using standard method. Carlson's index, the amount of nutrition in different parts of the lake estimated based on total phosphuros, chlorophyll and transparency. The result of Carlson's index showed different values between 52.44 to 60.46 and eutrophic condition in lake. The present research can provide a decision support system in the future to achieve optimal monitoring and exploitation and water quality management of the reservoir behind the Bostan Dam.

The aim of this study was to evaluate the environmental effects of growing rainbow trout Oncorhynchus mykiss (Walbaum, 1792) culture in cages. Data analysis was performed using information related to the storage of rainbow trout in floating cages located in the southern part of the Caspian Sea. The results showed that according to estimating the amount of nitrogen and phosphorus output of the studied cages and their concentration at a depth of 25 meters sea level, the maximum fish farming capacity in the cage is about 100 tons of biomass produced. In the study of the average effects by the Iranian Leopold method, breeding 100 tons of rainbow trout in sea cages has negligible and weak destructive effects. The results of this study confirm the maximum production capacity of about 100 tons in each breeding complex in the southern part of the Caspian Sea by maintaining a distance of at least 500 meters from other complexes.

In this study, the trophic status of the Bustan dam reservoir was investigated using Palmer and Carlson indices. Biological parameters including phytoplankton and environmental factors such as phosphate, nitrate and chlorophyll were sampled at the depth of 0.5 meter in five stations in three replicates seasonally in 2019, repetitions and Then the Palmer and Carlson indices were determined. The Palmer index in Bustan dam was estimated as 24, 31, 27.6, and 28.8in spring, summer, autumn, and winter, respectively.  According to the Palmer index classification, in all four seasons, Bustan dam water is in the category of water with high organic matter. The highest value of Palmer's index was obtained in summer (31) and its lowest value was obtained in spring (24). The highest nutritional status of Carlson's index was related to summer (60.46 eutrophication) and the lowest level was found inwinter (52.44 eutrophication), which indicates that the reservoir has moved to semi-nourishing condition in winter season. Also, the highest nutritionism status was observed in station 3 (54/23). According to Palmer's and Carlson's indices and the ratio of phosphate to total nitrogen, the main factor of nutritionism in the reservoir of Bustan dam was phosphorus compounds that enteres the reservoir from external sources of the dam and ultimately causes the decrease of water quality.

The lakes behind the dam considered as semi-natural resources and have a special role in aquaculture. In order to achieve management goals, it is necessary to know the pattern of changes in biotic and abiotic parameters in the lake behind the dam. For this purpose, in order to determine water quality using water quality indicators (WQI) 12 physicochemical properties (water temperature, dissolved oxygen, salinity, acidity, electrical conductivity, suspended solids, total hardness, total alkalinity, nitrate, ammonia, phosphate and phosphorus Total) was evaluated in 2018 on a monthly basis for one year at 7 stations of Golestan dam in Gonbad city. Although temporal and spatial changes observed in some measured factors; According to the WQI index in Golestan Dam, it was relatively average to good in different months. Therefore, it evaluated as favorable for the breeding of tropical and subtropical fish.

*, This study carried out to determining the normative of artificial and semi-artificial reproduction of wild common carp (Cyprinus carpio. L. 1758) in 2019. In this study, 70 samples were caught from Gomishan region. Mean weight and length of 29 wild males were 1146±151.62 g and 44.79±2cm, and for 41 wild females were 1152.25±235.14 g and 44.87±2.4cm, respectively. Mean age of males were 7.16±0.75 and females were 9.5±0.67 years old, respectively. Artificial and semi-artificial propagation methods were performed. Artificial propagation was done by Ovulin injection in two steps for females at 1 ml / kg fish weight and half the dose was injected at the same time in the second stage of female infusion after 12 hours for males.14 males and 13 females broodstocks for artificial, and 7 and 10 for semi-artificial propagation were selected. The number of eggs per gram was 783±53. The fertilization rate was 91±4 and hatch rate was 58±7.23.Maximum and minimum relative fecundity were 209707 and 61200 per kilogram of body weight and Maximum and minimum working fecundity were 325728 and 53244 respectively. Mean relative and working fecundity was 104795.6±49663.32 and 128981.5±84102. Hatch rate was 58±7.23. A total of 729800 larvae were transferred to the Sijaval Center pond . 200000 juveniles with 0.8g weight and 36500 juveniles with 2.6g weight producing of semi artificial propagation rearing in Gharasu River in order to restocking. For reproduction of wild common carp, choosing the broodstocks in right time (in winter), region of catching, transfer it from the sea to breeding centers are the most important effective point. Therefore, the manipulation, relocation and transfer of these newly catch wildlife from the shores of the sea or river requires equipment, handy net, disinfect materials, anesthesia, Oxygen tank and time table.

Four streams with different sizes were selected for studying the effects of environmental factors on fish assemblages using indirect (Detrended Correspondence Analysis, DCA) and direct (Redundancy Analysis, RDA) gradient analysis in Golestan province. DCA of presence-absence and relative abundance data showed well gradient and linear model of species variability. In the within-site RDA, environmental factors explained 74.8 % variability for presence–absence data and 77.5% for the relative abundance data. Evaluation of two first axis of RDA showed that first axis has a high correlation with habitat characteristics and second axis correlated with channel morphology attributes. Based on RDA diagrams, Paracobitis malapterura and Capoeta capoeta gracilis presented in Zaringol and Tilabad Streams and had a high correlation with percent of in-stream vegetation and percent of cobble in first axis and low flow mean depth and low flow width in second axis. While Alburnoides bipunctatus and Neogobius fluviatilis had high correlation with percent of snag, pool and sand within streams. It should be stated that factors such as the size of the catchment, hydrographical and geomorphological characteristics, and land use change the morphology and stream habitats, and ultimately lead to the removal of some species in adjacent streams.