حسن نصرالله زاده ساروی

Seafood has been an important source of nutrients and has attracted human attention from a health perspective (Dehghani et al., 2018; Khanlar et al., 2018). Important marine sources include shrimp, which are highly perishable and are associated with microbial, chemical, and physical changes during storage (Na et al., 2018). The growth of decay-causing bacteria in shrimp leads to protein degradation, resulting in the production of ammonia, indole, methanethiol, putrescine, trimethylamine, and other odorless compounds. Hence, it is vital to maintain the quality of white shrimp using effective methods (Liu et al., 2020). In general, artificial or chemical preservatives pose potential toxicity and carcinogenicity risks; therefore, consumers tend to prefer natural additives. Many studies have focused on natural food coatings for food preservation, such as alginate/nanocomposite active films containing essential oils, which have been produced and evaluated for their antimicrobial properties. These active films exhibited antimicrobial effects on a wide range of microorganisms, and it was also found that, in the presence of nano-receptors, they maintained their antimicrobial properties for a longer duration (Albofetileh et al., 2014). Additionally, due to the microbial changes in shrimp during cold storage and the issues associated with artificial preservatives, the use of biodegradable natural materials that can simultaneously maintain the quality and safety of food products is necessary. The present study examined the comparative effects of a nanocomposite coating (alginate/nano-clay) combined with Chuchagh plant extract on the quality of western white shrimp (Litopenaeus vannamei). Chuchagh plant extract is known for its phenolic and flavonoid compounds, as well as its antioxidant and antimicrobial properties. Alginate film is recognized for its gelling properties, ability to enhance tissue strength, stabilize structures, and form films (Liu et al., 2020). The research objectives include: 1) studying the phenolic composition of chuchagh plant extract; 2) determining the physical and mechanical characteristics of alginate-based films containing various concentrations of Chuchagh essential oil; and 3) assessing the physicochemical and sensory changes in fried shrimp coated with alginate-nanoclay films containing different concentrations of Chuchagh essential oil. Overall, the use of Chuchagh extract at a concentration of 1500 ppm as a natural preservative, along with clay nanoparticles in the active edible coating structure based on alginate, delays chemical and microbial decay and increases the shelf life of western white shrimp.

Preparation and extract of the essence of Chuchagh was done and total phenolic compounds were measured (Hasanzadehaidenlu et al., 2017). The alginate-nanoclay film containing the essence of the Chuchagh plant was prepared (Ojagh et al., 2010; Eslamian, 2021). Identification of films containing a better concentration of the essence was conducted by performing physical and mechanical tests across five treatments. The thickness of the films was measured according to ASTM (1996). The humidity of the films was measured (Ojagh et al., 2010). The rate of water vapor permeability through the films and also opacity of the films were measured (ASTM, 1996; Pang and Li, 2014). The mechanical testing of the films was based on the modified method ASTM D0882-02 (1996). After examining the results of indicators related to the physical and mechanical properties of the films, better concentrations of the essence (1000 and 1500 parts per million) were identified. To evaluate the efficacy of the nanocomposite activated by the essence produced in a real environment, and to compare it with the nanocomposite without essence and the alginate coating, five treatments were selected: alginate+nanoclay+essence oil (1500 ppm), alginate+nanoclay+essence oil (1000 ppm), alginate+nanoclay, and control. Preparation and processing of shrimp were carried out (Basiri et al., 2015). Physicochemical tests conducted after frying the shrimp included measuring the moisture percentage (Avak, 2005), frying efficiency (Daraei Garmkhanei et al., 2012), measuring peroxide levels (Ronald and Ronald, 1991), and measuring the sum of volatile nitrogen bases (Avak, 2005). Chemical, microbial, and sensory tests were performed to determine the total viable count (TVC) and psychrotrophic bacteria (PTC) (Arancibia et al., 2014). The sensory test was evaluated using a five-point hedonic scale (Dehghannasiri et al., 2012).

This study investigates the effects of alginate and nanocomposite coatings containing Chuchagh essential oil on the microbial load, chemical properties, sensory characteristics, and oxidation properties of white shrimp during their shelf life at refrigeration and frying temperatures. First, the phenolic compounds in the Chuchagh essential oil were determined. The results indicated that the Chuchagh oil contained high levels of phenolic compounds. Five edible films were then prepared: alginate; alginate combined with nano-clay; alginate combined with nano-clay+Chuchagh essential oil at 500 parts per million (ppm); alginate combined with nano-clay+Chuchagh essential oil at 1000 ppm; and alginate combined with nano-clay+ Chuchagh essential oil at 1500 ppm. The physical and mechanical characteristics of the films were examined according to ASTM standards. Based on the results of the physical and mechanical tests, the optimal concentrations of Chuchagh essential oil (1000 and 1500 ppm) were identified. The mechanical tests demonstrated that increasing the concentration of Chuchagh essential oil decreased the tensile strength of the alginate film until the point of tearing, while the physical tests indicated that the addition of Chuchagh essential oil improved the film's physical properties. Overall, the best characteristics of the film were observed in the formulations containing nano-clay+Chuchagh essential oil at 1000 ppm and at 1500 ppm (Ojagh et al., 2017). To further explore the effects of the alginate-nanocomposite coating and Chuchagh essential oil on extending the shelf life of shrimp during storage, five treatments were produced: a control group, alginate, alginate+nano-clay, alginate+nano-clay+ Chuchagh essential oil at 1000 ppm, and alginate+ nano-clay+Chuchagh essential oil at 1500 ppm. These treatments were periodically evaluated for microbial and chemical properties (Arancibia et al., 2014). The results of the present study indicated that the alginate-nanocomposite coating possesses antioxidant and antimicrobial properties, and the addition of Chuchagh essential oil enhanced these characteristics. Specifically, shrimp treated with alginate+nano-clay+Chuchagh essential oil at 1500 ppm exhibited a significant delay in the processes of microbial growth and oxidation, thereby increasing their shelf life (Dehghannasiri et al., 2012). In conclusion, the addition of Chuchagh essential oil helps maintain the quality of shrimp in terms of chemical and microbial indicators and extends their shelf life in refrigeration compared to the other samples.

The present study showed that the alginate- nanoclay coating possesses antioxidant and antimicrobial properties. Compared to previous research on the addition of essential oils, this study demonstrated that shrimp containing the alginate-nanoclay-essence not only exhibited antioxidant properties (similar to those of (Thymus vulgaris and Froriepia subpinnata plant) but also significantly delayed the microbial spoilage and oxidation processes, thereby increasing the shelf life of the shrimp. According to the results, incorporating essence into shrimp preserves its quality in terms of chemical and microbial indicators and extends the shelf life in refrigeration compared to other samples. Recommendations for the use of natural preservatives include: 1) investigating the feasibility of replacing artificial preservatives with alginate film combined with nano-clay and clay essence at a concentration of 1500 ppm in meat products such as sausages and hamburgers, 2) using native nano-capsule essences with alginate film and nano-clay to produce active packaging to extend the shelf life of meat products and reduce microbial contamination, and 3) studying the simultaneous application of essential oil in both free-form and micro-encapsulated forms, as well as packaging under vacuum conditions, to enhance the shelf life of various meat products.

The purpose of this research was to determine the concentration of poly aromatic hydrocarbons (PAHs) in the surface sediments during four seasons at different transects of the southern basin of the Caspian Sea and to investigate the causes of their temporal and spatial changes, to compare with the standard limits, and to find the origin of these compounds. The samples from the surface sediments were collected using a grab (van Veen grab) from depths of 10 and 30 m in the coasts of Guilan, Mazandaran, and Golestan provinces at eight transects (Astara, Anzali, Sefidroud, Ramsar, Nowshahr, Babolsar, Amirabad, and Torkaman) during the autumn and winter seasons of 2018, spring and summer of 2019. The sediment samples were prepared in order to investigate PAHs using a standard method (extraction with organic compounds by the Soxhlet apparatus). The results showed that the mean (±SE) annual concentration of PAHs in the four seasons of autumn, winter, spring, and summer was 29.6±11.5, 2125±611, 4.2±3.0, and 5.3±3.1 µg/kg dry weight, respectively, and the maximum concentration of PAHs was recorded in the Nowshahr transect in the winter season. The results of the current research showed that 2 and 6 rings compounds had a low percentage of abundance in the sediments and the mean concentrations of PAHs and BaP in most of the samples were lower than the international threshold standards. The origin of PAHs compound in the sediment was recorded in more pyrogenic sources based on the diagnostic ratio (LMW/HMW=0.3).

Considering the increasing speed of destruction of natural aquatic habitats in the rivers leading to the southern basin of the Caspian Sea and the importance of investigating the habitat conditions of the release sites of juvenile fish with economic value, in this research for the first time (at the national level) in order to investigate the suitability of Tajan River from the point of view of releasing Caspian kutum fingerlings, habitat suitability index (HSI) was used. Considering that currently the only available option of the Iran Fisheries Organization for the release of the fingerlings in the Tajan River is in the estuary of this river, therefore, in the current research, this area was selected to sample the fingerlings and investigate various biotic parameters (phytoplankton and zooplankton) and abiotic (water temperature, pH, salinity, dissolved oxygen, turbidity, total suspended solids, total dissolved solids, electrical conductivity, total hardness, ammonium nitrogen, NH3, biochemical oxygen demand, chemical oxygen demand, nitrite nitrogen, nitrate nitrogen, total nitrogen and total phosphorus). The above-mentioned biotic and abiotic parameters were determined during the months of July, August and September 2022 and August and September 2023. The highest selectivity index values for R. frisii were related to NH3. HSI values of Tajan River estuary for R. frisii fingerlings in the studied time period was calculated as 0.592. Therefore, on this basis, the study area can be classified as "suitable habitat" for the fingerlings. Nevertheless, the comparison of the range of changes of the habitat variables measured in this research with the respective permitted ranges showed that the conditions of the release area of the fingerlings were not suitable from the point of view of the range of changes of some parameters (including total suspended matter, total nitrogen, total phosphorus, ammonium nitrogen, electrical conductivity and turbidity) during the study period.

In order to evaluate the quality of effluent pollutants from the rainbow trout breeding farms in the selected farms of Kohgiluyeh and Boyer Ahmad Province, water samples were taken from five individual farms during the years 2021-2022. The physical and chemical indicators of water including acidity, biological oxygen demand, dissolved oxygen, electrical conductivity, nitrite, nitrate, phosphate, total suspended solids, total dissolved solids, total hardness, alkalinity, iron, oxygen saturation were measured once in each season from the inlet and outlet water (each treatment with 3 replicates). Based on the results, the range of pH changes (5.93-7.29), biological oxygen demand (6.41-7.56 mg/l), ammonium (0-0.319 mg/l), nitrite (0-0.181 mg/l), nitrate (2.19-19.2 mg/l), phosphate (0. 1-0.18 mg/l), total alkalinity (132-238), dissolved oxygen (3.35-8.11 mg/l), electrical conductivity (311-899 microsiemens/cm), TDS (203.7-607.9), and total hardness (312-157.77 mg/l) were obtained. The results showed that the concentrations of ammonium, nitrite, nitrate, phosphate, EC, and total dissolved solids parameters in the effluent compared to the input from the different farms has increased due to the increase of metabolism, fish density, concentration of nutrients, drugs and disinfectants, intensity and speed of water and the oxygen concentration in the effluent of the farms has decreased due to more metabolic activities than the input from the rearing ponds. Also, the amount of biochemical oxygen demand (BOD) and environmental chemical oxygen demand (COD) were increased and the dissolved oxygen was consumed and its amount decreased due to the increase of organic substances, nitrate, and the provision of oxidation conditions.

In this article, the total concentration of toxic heavy metals such as lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As), which are mandatory elements of the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO), were determined to measure the health of the edible tissue of the Caspian Sea Rutilus kutum. 90 samples of Rutilus kutum were collected in three northern provinces (Gilan, Mazandaran, and Golestan) during 2021-2022. The concentration of Pb, Cd, Hg, and As of Caspian Sea Rutilus kutum samples were prepared by standard method and acid digestion. All samples were analyzed using flame, graphite furnace, and cold steam of the atomic absorption spectroscopy instrument. The results showed that 90% of all data samples (90th percentile) concentration of toxic metals in Rutilus kutum tissue decreased in the order of Cd >As>Hg>Pb. The amounts of Cd, As, Pb, and Hg in Rutilus kutum tissue were observed at not detected-0.31, 0.001-0.15, 0.001-0.060, and 0.001-0.020 mg/kg wet body weight, respectively. Also, the statistical analysis showed that two types of correlations were found between the concentration of metals and the total length and weight of Rutilus kutum: for Cd with total length (r=-0.46) and with fish weight (r=-0.51), for As with total length (r=0.30) and with fish weight (r=0.27), It showed negative and positive, respectively, but mercury and lead metals did not show correlation with biometric parameters. Comparing the current results with international standards showed that the four toxic metals Cd and As, Pb, and Hg were lower than the FAO and WHO standards concentration. The findings showed that the health risk assessment parameters (EDI, HQ, and THQ) for all metals were much lower than the recommended values. This showed that the consumption of Caspian Rutilus kutum in the study area did not have any adverse effects on human health due to the contamination of toxic metals.

The Zhaveh dam is located on the Sirvan River containing two main branches of Gaveh Rood and Qeshlaq. The dam was designed for industrial and agricultural use. Surface sediment samples were collected at 5 selected stations in the two branches of the Sirvan River, Qeshlaq and Gaveh, as well as in the dam reservoir. In this study, nine sediment parameters (different forms of nitrogen and phosphorus, TOC, pH, Eh) were investigated to determine the quality and the prediction of the eutrophication trend of the Zhaveh Dam. The quality of sediments in different stations showed that they contain high organic and mineral pollution. Based on the TOC% of the sediment, the region was considered as slightly to highly polluted, especially in stations 2 and 3, but station 4 (Gaveh Rood branch) was classified as moderate quality. The changes in the OPI and ONI indices and comparison with the organic index standard also indicated the high pollution of the sediments in this region. These conditions are due to the high mean concentration of total phosphorus (2075±178 mg/kg.dw) and bioavailable phosphorus (666±142 mg/kg.dw) in the rivers feeding the dam, which deal with a high risk of eutrophication. In addition, after the water intake of the Zhaveh Dam and the high concentration of organic and mineral pollutants during the retention time of the water, it will be difficult to control the eutrophication

The aims of the present study were to investigate the macrobenthos communities in the Caspian Sea and to investigate the pollution of this ecosystem based on the pollution indices ABC (Abundance Biomass Comparison), BC (Biotic Coefficient) and ABC curve in 2018 (autumn and winter) and 2019 (spring and summer). According to the results, polychaetes, crustaceans, and bivalvia formed the major groups of macrobenthos communities with 4, 11 and 1 species, respectively. The polychaetes (mainly Streblospio gynobranchiata) included about 70% of the total abundance and the group of bivalvia (Cerastoderma glucaum) included about 76-93% of the macrobenthos in all seasons except in spring. The mean values of the Shannon index and evenness indices were calculated as (1.56) and (0.55), respectively. The annual pollution (ABC) and BC indices were obtained as -3.1 and 2.7, respectively. These values along with characteristics of ABC curve indicate severe stress caused by pollution in the Caspian Sea ecosystem. In this study, the percentage abundance of the invasive species S. gynobranchiata in macrobenthos communities was 52%, which is about 10% decrease compared to 2009 and 2010. This decreasing trend can be considered as positive evidence in the improvement process of the ecosystem in this part of the food chain. However the continuity of recovery trend needs more time, no force by new stressors, proper management, and reduced pollutions into the ecosystem.

The aim of the study was to determine the quality of the inlet and outlet water of five selected rainbow trout breeding farms in Mazandaran Province (Haraz, Chalous, Tonekabon, and Sari) based on environmental parameters during four seasons in 2021-2022. Forty samples were collected and measured based on standard methods. According to the results, the range of water temperature (3.0-24.0°C), air temperature (2.0-25.0°C), DO (6.16-12.24 mg/l), BOD5 (0.24-2.76 mg/l), COD (2.40-93.70 mg/l), EC (284-783 µs/cm), turbidity (1.12-220-0 NTU), TSS (2-288 mg/l), pH (7.44-8.62), total phosphorus (0.2-2.12 mg/l), phosphate (0.01-0.206 mg/l), ammonium (0.012-0.538 mg/l), ammonia (0.001-0.018 mg/l), nitrite (0.001-0.426 mg/l), nitrate (0.52-6.10 mg/l), fecal coliform count (6-1000 CFU/100ml) and water quality index (WQIIR) (62.0-91.0) were registered. The water quality of this river was placed in class III (low pollution) based on the average parameters of organic pollution (BOD5 and COD) and human activities were not one of the main factors in the increase of organic matter in the river. The concentration of ammonium and nitrite was within the threshold limit, but the concentration of phosphate in all the inlet and outlet stations and in different seasons was more than the maximum limit of unpolluted rivers. The results showed that the WQIIR was in the range of 62-91. 7.5% of the total data and the mean of this index indicated the relatively good quality of the inlet and outlet water of the rainbow trout breeding farms. The highest quality of water, i.e. very good quality, is recorded in 12.5% of all data, which is observed at the inlet water of rainbow trout breeding farms. The outlet quality index of the farms was lower than its inlet, but it was categorized as good quality. The overall WQIIR (77.4±6.6) in all inlet and outlet stations indicates that the water of this farm is suitable for fish and wildlife and also suitable for rainbow trout breeding.

The Caspian Sea is a unique brackish system in terms of water salinity, so evaluation of pollution criteria based on the water quality of the same sea is past and present. In this study, information was collected from 2008 to 2010 and analyzed during the project during these years, sampling of eight transects shorelines was performed seasonally at stations 10, 20, 50 and 100 m of depth in two summer and winter seasons for water and sediment. The results showed that the concentration of organochlorine toxins in the aquatic environment depends on its entry through the rivers leading to it and its concentration in water varies in different seasons and regions. The results showed that the concentration of organochlorine pesticides in the aquatic environment increased in winter of 2008 with the highest percentage of pesticides in spring, summer, autumn and winter in middle, middle, east and west and maximum percentages, respectively. Toxins were found in the water samples of the eastern part of the region by 75% in spring. Also the maximum concentration of organochlorine toxin belonged to α-Endosulfan toxin with a concentration of 3.86μg/l which was recorded in Nowshahr at 50 m depth of surface water. Conclusion In the current situation, the concentration of chlorine toxin compounds in the appropriate range and distance from the shore of water quality conditions is more suitable for fish farming in cages. Therefore, it is suggested to consider the establishment of fish cage culture at 50 m of depth.

The current research was conducted in 2021 in 5 stations in order to investigate the quality of water before the operation of Javeh Dam in Kurdistan Province. Sampling of fish and Macrobenthos was done using an electrofishing device and Surber sampler, respectively. A total of 13 fish species were identified, which belonged to 3 families: Cyprinidae, Mastacembelidae and Nemachielidae. Out of the total of 2003 fish caught in all the stations, more than 96.6% belonged to the Cyprinidae family. The highest relative frequency of 32.4% belonged to Capoeta damascina species. In addition, 2 exotic species, Carrasius auratus and Carrasius gibelio had an abundance percentage of 1.4. The diversity of fish species decreased from station 1 (upstream) to stations 2 and 3, which was probably influenced by human activities such as various types of pollution, but in station 5 of It had the maximum amount, which is due to the change in habitat conditions, such as the increase in flow rate and water depth. The results showed that the species diversity of fish had changes in different seasons, so that its minimum was estimated at 0.91 in winter and its maximum at 1.29 in summer. Macrobenthos included 10 families Chironomidae, Lumbriculidae, Simulidae, Baetidae, Hydropsychidae, Erpobdelidae, Glosiphonidae, Gamphidae, :union:idae and Potamidae. The classification of water quality based on the Karr ecological integrity showed that stations 1 and 4 were placed in the good quality class with a numerical value of 40 and 42, respectively, and stations 3 and 5 were placed in the very low and medium water quality classes with a numerical value of 9 and 34, respectively. In this way, it is necessary to manage and organize all sources of point and non-point pollutants in Gheshlagh and Gavehroud tributaries.

Haraz River has an important role in the development of aquaculture and the production of rainbow trout in Mazandaran province. Since 2015, the production of rainbow trout has been decreased in the farms along the river and almost halved. This study have been investigated the microbial indices and heavy metals in water as well as the identification of common bacterial pathogens and their resistance to antibiotics and used them as effective factors in the fish health and production. This study was conducted during four seasons (summer, autumn and winter 2017 and spring 2018) in 6 rainbow trout farms along the Haraz River. The results showed that the amount of the water mercury in all seasons was from minimum 2 to maximum 12 times the allowable limit but the arsenic level was standard in all sampling times. The most important clinical symptoms were observed in the fish including fin rot, erratic swimming, inflammation and hyperemia of the liver and kidneys. From 420 fish with clinical signs, 12.15% and 87.85% of fish were positive and negative bacterial culture respectively. The all of bacterial isolates were gram-negative and no gram-positive bacteria were isolated. The bacterial agents identified were including, Yersinia (37.25%), Aeromonas (33.35%), Eduardzilla (11.76%), Vibrio (7.84%), Pasteurella (5.88%) and Citrobacter (3.92%). The highest and lowest antibiotic resistances were found against amoxicillin and trimethoprim sulfamethoxazole respectively. In evaluation of the microbial water indices including total bacterial count, coliform count, fecal coliform count and E. coli, the results showed that the all of microbial indices were not allowable level in the most of the sampling time.

The aim of the present study was to evaluate the feasibility of using biosilage produced from chicken waste and to replace this product in the diet of rainbow trout instead of fish meal. Because biosilage has higher properties and lower prices than fish meal. For this purpose, after producing biosilage based on fermentation of autogenous bacteria, is added to the diet formulation in the form of two treatments of 50% biosilage -50% fish meal and 100% biosilage and the growth performances and feed efficiency (WG, CF, SGR, FCR, PER) indices of these two treatments along with the control treatment (100% fish meal) on days 30 and 50 were evaluated and compared. The results showed that the indicators of WG, CF and SGR, in the treatment with 50% biosilage -50% fish meal are significantly higher than the other two treatments. It was also found that this treatment is more favorable than the other two treatments in terms of FCR and PER. According to the results, biosilage produced from chicken waste is a good alternative to fish meal. In addition, 50% biosilage-50 fish meal treatment is more desirable in terms of growth and feed index than 100% fish meal and 100% biosilage treatment.

251 specimens of kutum fish caught by bony fish persine on the southern shores of the Caspian Sea (Mazandaran) during the years 2017-2019 were studied to study the growth trend of this species. In this study, maximum estimated length (L∞) and annual growth coefficient (K) of kutum fish were estimated 71.79 cm and 0.13, respectively. The results of natural reproduction of this species in Kheirud river with a length of 2 km showed that in 2017-2018, more than 30,000 breeders (female) of anadromous fish migrated to Kheirud river for reproduction and more than 97% of it were kutum fish. As a result of this study, more than 525,000 kutum fish fry were produced and prepared to migrate to sea. (2017-2018). The results showed that the partnerships of fishermen and local rural communities can have a positive effect on the natural reproduction Influence coefficient of kutum fish (P <0.05). The results showed that the penetration coefficient (effectiveness) of fishermen (35%) and rural women (30%) ) were more than the students' effectiveness (16.7) (P <0.05). Thus, by protecting the natural reproduction of kutum fish, other species of anadromous fish have reproductive successes in the Kheirud river, which will establish the desired ecological balance and exploit the ecological carring capacity of the ecosystem.

This research was carried out based on ecological monitoring of the Caspian Sea in depth of 30 meters project during 2018-2019. Sampling from the bed sediments of the southern Caspian Sea in 8 transects including Astara, Anzali, Sefidrood, Tonekabon, Nowshahr, Babolsar, Amirabad and Turkmen was done by a cat sampler. Sampling was done seasonally. The aim of this study was to investigate the species diversity, density and biomass and local distribution of different macrobenthos species. A total of 16 species were identified, belonging to 7 families which of Polychaeta, Crustacea and Bivalvia were found. In addition, Oligochaeta have been identified. The polychaeta comprised 59% of the total macrobenthos density. In contrast, Cerastoderma glaucum, although the frequency was 6.3% of the total density of macrobenthos, but comprised 59.9% of the total biomass. The results showed that the diversity indices had the highest value in spring and the lowest in summer. Polychaeta had the highest local distribution (100%) and Malacostraca Pterocuma sowinskyi and Cardiophila baeri had the lowest (8.2%). The lowest and highest mean (±SE) densities were recorded in winter and spring with 408±81.1 ind.m-2 and 1225±246.2 ind.m-2, respectively. In conclusion, the increase in biomass of bivalve molluscs versus the decrease in density can be due to the large size and having oyster shell and the increase in diversity indices in spring can be due to the presence of different species for reproduction after wintering period which is consistent with the density of macrobenthos in the spring.

The purpose of this study was to investigate the seasonal variation of distribution, abundance and biomass Streblospio gynobranchiata of substrate sediments on the Southern coasts of the Caspian Sea (Bandar Torkman and Babolsar) in 2018-2019. Sampling was done seasonally and 6 stations at depths of 5, 10 and 30 meters of the 2 transects. The results showed that the mean (±SE) of abundance and biomass were in the Babolsar transect (respectively) 207.06±51.40 ind.m-2 and 0.042±0.006 g.m-2 and seasonal study, the highest abundance and biomass in Babolsar transect with mean (respectively) 1297.47±284.95 ind.m-2 and 0.222±0.040 g.m-2. So there was a significant difference between the abundance and biomass in different seasons (p<0.05). Also showed that the mean (±SE) of abundance and biomass were in the Bandar Torkman transect (respectively) 206.51±53.07 ind.m-2 and 0.043±0.005 g.m-2. According to seasonal study, the highest abundance in Bandar Torkman transect with mean 942.27±180.07 ind.m-2 in summer and highest biomass 0.153 ± 0.03 g.m-2 recorded in spring, so there was a significant difference between the abundance and biomass in different seasons (p<0.05), which is due to their reproductive cycle. The total organic matter in different seasons was fluctuating, which could be due to the depth, substrate and ecological origin.

The spatial salinity patterns which give a picture of the area affected by eutrophication and trophic status changes at the ecosystem. The aim of this study was to determine the area affected by freshwater eutrophication using trophic level (TRIXcs), the risk of eutrophication (UNTRIX) and the nutrient-salinity scatter diagram. Also, the data of the present study are compared with previous year of studies. This research was conducted during 2018 to 2019 in eight transects and at 5, 10 and 30 meter depths of Iranian coasts of southern Caspian Sea. The results showed that mean seasonal changes of TRIXcs and UNTRIXcs were 4.94-5.59 and 3.57-4.17, respectively, which the highest trophic level and risk of eutrophication was observed in summer season. In addition to, trophic level (TRIXcs) risk of eutrophication (NUTRIX=4.30) of near the coast (5m depth) were high. Mean of TRIXcs and UNTRIX between different regions (western, middle and eastern) were not significant. In the present study, the maximum amounts of ammonium and soluble silica near the west coast were recorded in Anzali transect and also under the influence of the largest river Sefidrud in the southern shores of the Caspian Sea, but the points with maximum NOx and phosphate values were observed in the east (Amirabad and Bandar-e-Turkmen transects). The nonlinear relationship between NOx, NH4, DIP and DSi with salinity indicates that river flow and water mixing were affected nutrient concentration and changes of trophic levels in the study area.

The aim of this study was to investigate the changes in the bacterial quality trend (indicator bacteria) of water and its relationship with some environmental parameters around fish cages culture in the southern Caspian Sea region (Nowshahr-Mazandaran province). For this purpose, water sampling of the southern region of the Caspian Sea in the Tuskatok region of Nowshahr city in Mazandaran province took from January 2017 to December 2016 during the rainbow trout cage culture period at different distances cage (cage shade, 200 and 1000 m).The results showed that in the whole cage culture period, the maximum average of 18750 CFU/ml water bacteria was observed in the 200 m cage station before the cage culture period and the minimum average of 3250  CFU/ml water bacteria was observed in the 200 m cage station at the end of the cage culture period. The presence of total coliform and fecal coliform in water samples was recorded as 18.75 and 2.08%, respectively, and fecal streptococcus water was not observed in any of the sampling stations and in this situation, fish cages culture did not cause contamination. Maximum and minimum water temperature, pH, turbidity, saturation percentage and biological oxygen demand are 26.50 and 7.00 °C, 8.71 and 8.29, 19.71 and 0.52 NTU, 87 and 160, respectively. Percentage of 1.32 and 8.39 mg/l were recorded. Based on the principal component analysis (PCA), the results showed that the variables of pH and water temperature had the highest variance and the total count along with water turbidity in the third component showed a significant positive correlation (p<0.05). As a result, the proper slope of the area, the proper flow of water around the small-scale cages has reduced the microbial contamination in the shade of the cage compared to the stations outside the cage.

Sediments are considered as the most important storage and absorption of metals and other pollutants in aquatic ecosystems and can reflect the quality of aquatic systems. The aim of this study was to estimate the severity of sediment contamination with cadmium, lead, zinc and copper based on ecological hazard potential (RI) and land accumulation (Igeo) indices in surface sediments of rivers in the southeast coast of the Caspian Sea. 

In order to measure and determine the indicators of metal element pollution, sampling of estuarine surface sediments and a distance of 1000 meters from the estuary of some rivers in the southeastern shores of the Caspian Sea, including Gorganrood, Gharasoo, Nekaroud, Tajan, Talar and Babolrood was performed. Samples in the laboratory based on the method of sequential extraction were prepared and then analyzed by atomic absorption apparatus and the results were determined in micrograms per gram of dry matter. 

The results showed that the values ​​of Igeo indexof metallic elements in the sediments of the rivers of the southern shores of the Caspian Sea ranged from -3.41 to 1.08 and the values ​​of RI index ranged from 62.66 to 101.93.  

Although the pollution of these areas with metallic elements is not dangerous at the border, but the continuation of the pollution process will certainly lead to many environmental risks in the long run. Therefore, applying proper management guidelines such as the proper disposal of urban, rural and industrial wastewater and the use of appropriate pesticides can be effective in improving the current situation in the region, and periodic research is necessary, especially for the entry of other pollutants into the environment.