دکتر محمد قلی زاده

This research was conducted to estimate the growth and mortality dynamics of the common kilka (Clupeonella cultriventris) within its primary fishing grounds in the southern Caspian Sea, specifically in the Gilan Province, over the period from October 2022 to October 2024. A total of 688 specimens, comprising 250 males and 438 females, were subjected to biometric measurements and weight analysis. The mean total lengths of males, females, and the overall population were determined to be 12.79 ± 0.21 cm, 11.47 ± 0.12 cm, and 13.34 ± 0.15 cm, respectively. Statistical analysis of length-frequency distributions between sexes indicated a significant difference (DKS = 5.43, N = 152, p < 0.05).By employing the least squares method for model fitting, the asymptotic length (L∞) and annual growth coefficient (K) were estimated for the entire population, males, and females. For the population, these values were 15.85 cm and 0.48 yr⁻¹, respectively. For females, L∞ and K were calculated as 16.47 cm and 0.45 yr⁻¹, while for males, they were 13.95 cm and 0.62 yr⁻¹. The asymptotic weights (W∞) for females, males, and the overall population were 28.38 g, 16.58 g, and 24.42 g, respectively.Total mortality rates (Z) were also evaluated, with estimates of 1.76 yr⁻¹ for males, 1.33 yr⁻¹ for females, and 1.57 yr⁻¹ for the population in Gilan’s coastal waters. The marked reduction in the stock of common kilka highlights an urgent need for the implementation of robust fisheries management strategies to ensure the sustainability of this vital species in the southern Caspian ecosystem.

Clupeonella caspia fishing in the Caspian Sea has played a significant role in the regional fisheries economy over the past decades. However, a sharp decline in the stock of this species in recent years due to overfishing, environmental changes, and the introduction of invasive species has posed major challenges to the sustainable management of these stocks. This study employs the Stock Reduction Analysis (SRA) model to assess biomass changes and predict the allowable catch of the Clupeonella caspia in the southern waters of the Caspian Sea. This research utilizes historical catch and biometric data of kilka species over the past two decades and applies the SRA model to analyze stock trends and sustainable harvesting rates. Various management scenarios, including fishing effort control, harvest limitations, and setting catch quotas, have been examined. The findings indicate a declining trend in kilka stock, with improper exploitation threatening the biological and economic sustainability of the industry. A comparison of the results with previous studies reveals an increasing share of Clupeonella caspia in the catch composition and a decrease in anchovy Clupeonella caspia harvests. Furthermore, the simulation of management scenarios suggests that implementing catch restrictions and optimizing fishing effort can play a crucial role in the recovery of this species' stock. Based on the study’s findings, it is essential to develop and implement sustainable fisheries management policies, such as setting allowable catch limits and regulating fishing efforts. Utilizing stock prediction models can assist policymakers in making informed and sustainable decisions. This study recommends continuous monitoring of Clupeonella caspia stocks and periodic assessment of their biological status to maintain ecological balance and ensure the long-term economic sustainability of the fisheries sector.

Studies on the load of heavy metals in various mammalian species in most aquatic ecosystems around the world are constantly being conducted. Investigating the concentration of heavy metals in marine organisms is important and necessary for monitoring and assessing the risks of these types of pollutants in marine ecosystems. These studies have confirmed the occurrence of these types of pollutants in top predators of the food chain such as seals. In the present study, 15 Caspian seal carcasses were examined along the Iranian coastline (Golestan, Mazandaran, and Gilan provinces) during 2021-2023. Liver, kidney, and blubber tissues were sampled for heavy metal analysis, and the samples were injected into an inductively coupled plasma mass spectrometer after preparation. The results showed that the highest arsenic concentration in liver tissue was 0.78 (mg/kg) in Gilan province. The highest levels of this element in kidney and blubber tissues were also observed in Gilan province at 1.03 and 3.99 (mg/kg) respectively, differing significantly from Golestan province (P≤0.05). The highest cadmium level was found in liver tissue in Golestan province at 0.4 (mg/kg) and in kidney tissue in Gilan province at 16.28 (mg/kg). Iron had the highest concentration among the other elements, with the maximum levels in liver, kidney and blubber tissues observed in Gilan province at 928.1, 678.9 and 81.37 (mg/kg) respectively. The highest significant level of mercury was found in liver tissue in Golestan province at 5.3 (mg/kg). Lead was also highest in liver, kidney and blubber tissues from Gilan province. Based on the results, it seems that the main sources of environmental pollution in the Caspian Sea can have significant adverse effects on the natural habitats and animal species of this unique aquatic ecosystem. Comparing the results of the present study with those of previous ones can be very effective in the continuous monitoring and surveillance of pollutants, including heavy metals, in the Caspian Sea ecosystem.

To investigate the relationship between the length and weight of Neogobius melanostomus, 5145 fish were captured using nets from March to February 2018. The maximum total length and weight for females were recorded at 12.2 cm and 28.08 grams, while for males, the maximum total length and weight were 11.3 cm and 33.17 grams, respectively. The length-weight relationship for both female and male populations of N. melanostomus in Gorgan Bay across the four seasons (spring, summer, autumn, and winter) showed a high coefficient of determination. The regression slope values (b) for this species in different seasons were significantly different from the isometric growth coefficient of 3 (p < 0.05). Specifically, the t-values were 3.73 for the winter population, 10.80 for the autumn population, 21.25 for the summer population, and 21.71 for the spring population, indicating positive allometric growth throughout the year. The Pauli test confirmed this growth pattern in the N. melanostomus population of Gorgan Bay. Seasonal condition coefficients showed that females had the highest values in summer and winter, while males displayed the highest values in winter.

This study examines the characteristic of microplastics (MPs) in sediments collected from the coastal areas of the southern Caspian Sea, Mazandaran province (Babolsar and Sari cities). Twelve sites for sediment sampling selected during 2022. MPs identification detected primarily under stereomicroscope and then ascertains and discovers their polymer composition by ATR-FTIR. The results showed that Babolsar areas, with 5 meters far from the shoreline, had the most abundance (660±165.15items/Kg). On the other hand, Sari station with 500 meters far from the shoreline contained the least MPs (220±81.33). Average number of detected MPs in all samples was 406.66±161.33. Fibers (80.33%) were the most abundant MPs, whereas films (3.28%) detected the least. In the case of size, the range of 1000-3000µm showed the most abundant MPs (39.34%) and MPs less than 2 µm the least ones (4.10%). Gray and black (50.82%) was the dominant color and yellow (3.28%) was rarely detected color (3.28%). Polymer constituent of examined MPs includes: (PET: 30%); (PS: 20%); (PA: 20%); and (PP: 15%). The findings of this study revealed that MPs occurrence in coastal sediments distribute from several sources; including tourism as well as wastewaters and packaging. These activities cause entering plastic litters along the coastal areas and their degradation accelerated t MPs distribution.

In this study, age and growth of Golden Grey Mullet (C. auratus) was investigated during the years 1394-1397 in the coastal waters of Golestan province. This study was the first study on the modeling and implementation of three models for estimating growth parameters of golden mullet (C. auratus) in Iranian waters (Golestan province). During the sampling period, commercial fishing with a size of 27-33 springs was used, and outside of the fishing season, a net with a size of 20 and 30 was used. Biometry of fish was done including fork length with an accuracy of 1 mm, total weight with an accuracy of 1 gram. The length range for golden mullet was 15 to 59.5 cm and the weight range was 52.5 to 1401 grams. The exponential relationship of fork length and total weight (W=0.69L0023) was obtained. Based on the multi-model approach, the best model to show the growth of this fish was the Gumpertz growth model (∆AIC = 1.71, AIC = 46.13), and the logistic model was the best model to depict the growth of this fish according to the AIC information coefficient ( ∆AIC = 1.27, AIC = 50.71). Considering the pressure of legal and illegal fishing on this valuable species, it shows that the population and the amount of fishing in the south-eastern coast of the Caspian Sea are increasing. The results of this study can be used as basic information for catching and exploiting this species in the future.

Rivers efficiently transfer microplastics into seas, meanwhile they can be temporarily stored in sediments, where they undergo further fragmentation due to biological and physical processes. This study was conducted with the aim of investigating the distribution and abundance of microplastics (MPs) in the surface sediments of Khormarud River, Golestan province, Iran. A total of 15 sediment samples (5 stations with 3 replicates) were taken in the spring of 2022 and the identification of MP was studied using a stereomicroscope. Their polymer compositions were characterized using weak total reflectance Fourier transform infrared spectrometer. The results showed that station 5, with high human activities, had the highest frequency of MPs with 880±160 particle/kg of dry sediments, and station 1, upstream of the river, had the lowest frequency with 200±66 particle/kg. The average of MPs observed in all studied stations was 430.17 ± 92.8 particles. The most abundant MPs were fiber (77.52%) and the least abundant were films (3.10%). The results showed that the 500-1000 µm group had the highest frequency with 44.19%, while the 3000-5000 µm group had the lowest frequency with 3.88%. Black color was the most frequent with 55.81% and blue color was the least frequent with 2.33%. The polymer composition of MPs includes polypropylene (PP, 41%), polyethylene (PE, 30%), polystyrene (PS, 16%), polyester (PS, 11%), and polyamide (PA, 2%). The results of this study showed that MPs in coastal sediments have a complex source that is mostly derived from tourism, sewage, and packaging.

The present study aimed to investigate variability in growth pattern and evaluate abundance of A. persicus based on catch data in the southern Caspian Sea water in a period of 27 years (1991-2018). The data of 72704 specimens were analyzed separately by sex (male, female and population), time (years) and region (coastal waters of Gilan, Mazandaran and Golestan provinces). The highest catch of this species was recorded in 1991 (6038 pieces of the fish) and the lowest catch was recorded in 2018 (292 pieces). During the period, the Golestan province had the highest number of catches (30851 pieces) and Gilan province had the lowest ones (11129 pieces). The maximum recorded fork length of this species was 240 cm in 2006. The results showed that the highest annual average fork length was 151 cm in 2007 and 2010 and the highest annual average total weight in 1993, 1994, 1996, 1997 and 2007, which was 26000 grams. The lowest annual average fork length was 139 cm in 2018 and the lowest annual average total weight was 600 grams in 2010 and 2012. The highest length frequency corresponded for the ranges of 136-148 and 148-160 cm in males and females, respectively. The females showed the highest catches in 1991, and the lowest in 2018, while the males had the highest in 1991, and the lowest in 2014. The females dominated the population in the period of 1991- 2013, and after that this ratio was reversed. The allometric coefficient of growth (b) varied between 1.03 and 3.49 in the study period. The growth pattern was mostly positive allometric in first decade of study (1991-2001), isometric or negative allometric in the second decade of study period (2001-2011), and negative in third decade (2011-2018). During the study period, the condition factor of the fish varied between 0.61 and 0.80, and the average of the factor for the whole period of study was 0.72. Generally, the catch of A. persicus in the southern Caspian waters decreased more than 95% from 1991 to 2018 (a period of 27 catch-years).

The Environmental variables are considered as important factors determining habitat preference and selection by fishes in the aquatic ecosystem. Therefore, it seems essential to know the habitat requirements of inhabiting species. This study in summer on Kesilian River, one of the considerable sub-basins of the Talar River in the north of country, was selected to investigate the habitat preferences of Kora Barbel (Barbus lacerta) at various ages. According to the diverse habitat characteristics, three sites were selected on the stream, and then samplings were carried out at 211 points using an electroshocker. At each point, environmental parameters including speed, depth, and type of biotic and abiotic substrate were measured and determined. The results showed that this species has different habitat preferences at different ages. General preferences of this species took place in the speed range of 15-76 cm/s and the depth of 45-75 cm. Preference for abiotic and biotic parameters of substrates included "block", "cubble" and coarse and fine particulates organic matter, wood and living parts of terrestrial plants, respectively. Regression logistic indicated that the variables including velocity and abiotic parameters of substrate are the most important factors in presence of this species in the stream. In general, the diverse environmental conditions of the stream have provided different habitat preferences for this species at different ages.

Population growth and pollution caused by the discharge of all kinds of urban, industrial, and agricultural sewage, leachate from landfills, and surface water runoff cause an increase in pollution of water sources. The entry of heavy metals into the environment, especially aquatic ecosystems, due to entering the food chain and jeopardizing human health is one of the concerns of society. This study was conducted to determine the level of heavy metals in muscles of Cynoglossus arel and Pomadasys kaakan fishes in Boushehr coastal waters, north of the Persian Gulf.

This descriptive study was conducted on twenty pieces of Cynoglossus arel and twenty pieces of Pomadasys kaakan fishes take place from three coastal stations of Boushehr, north of the Persian Gulf, Iran during spring of 2022. The samples were randomly selected from the fish market. After preparation, bioassay, and digestion of fish muscle by concentrated nitric acid, the concentration of heavy metals including nickel, zinc, copper, lead, and cadmium (µg/g) in the muscle tissue was measured by ICP-OES device. The concentration of heavy metals in the fish muscle tissue for human consumption was compared with international standards (FAO, WHO, FDA, NHMRC, and UKMAFF). According to the method of the US Environmental Protection Agency for fish consumption, daily absorption estimates and heavy metal risk indicators were calculated.

The risk potential index for both species was less than one. The daily and weekly absorption of Cynoglossus arel (zinc > copper > nickel > lead > cadmium) and Pomadasys kaakan (copper > zinc > nickel > lead > cadmium) were determined. The mean concentration of heavy metals nickel, zinc, copper, lead, and cadmium in the muscle tissue of the studied species was determined to be 1.88±0.07, 27.16±8.11, 11.55±4.12, 1.14±0.06, and 0.19±0.03 µg/g, respectively. The highest amounts of studied metals in aquatic animals were zinc > copper > nickel > lead > cadmium. The concentration of metals in the analyzed samples was lower than the international standards.

Regarding toxicity, the concentration of metals in Cynoglossus arel and Pomadasys kaakan was evaluated as acceptable for human consumption. In addition, the amount of risk potential and risk index for non-cancerous diseases in adults and children in fish muscle tissue was less than 1, and the consumption of this fish does not cause any problems for human health.

Nowadays, plastic pollution is regarded as one of the most threatening environmental pollution. In this regard, microplastics may enter the food web and produce some negative impacts in aquatics. The goal of the present study was to study effects of polystyrene microplastic on antioxidant and immune genes expressions in gold fish (Carasius aurata). For this, polystyrene microplastic was synthetized via suspension and emulsion polymerization method in two sizes of 0/25 and 8 µm. The fish were exposed to the microplastic with sizes of 0.25 and 8 µm and concentrations of 0.05, 0.5 and 5 mg/L during 28 days under 6 treatments. Based on the results, polystyrene microplastic induced gene expression of SOD, CAT and HSP70 that were dependent on the microplastic concentration and size. Smaller size of microplastic showed higher induction effect on the studied genes expressions so that in most cases, the highest level in the same concentrations was observed in the treatments exposed to 0.25 µm microplastic. With increase in microplastic concentration from 0.05 to 5 mg/L, a similar decreasing-increasing trend was observed in the investigated genes expressions but the CAT gene reaction was slightly different. Overall, more studies seem necessary to understand polystyrene microplastic effects on aquatics and its potential mechanisms. With respect to the results from the present study indicating the changes in antioxidant and immune genes expressions under microplastic exposure, establishing some strategies seem to be obligatory to manage the effluents entered to the aquatic ecosystems and prevent more microplastics increase in the environment. Totally, based on the results, it could be said that polystyrene microplastic as a pollutant can induce the antioxidant and immune system of gold fish.

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.

Benthic macroinvertebrate communities are a biological indicator in aquatic ecosystems. The aim of this study was to investigate the abundance and biodiversity of macroinvertebrate communities in Khormarud River, Golestan Province. Macroinvertebrate samples were collected seasonally from 5 stations with three replications in 2020 using a Vanveen grab with a cover area (225 cm2). A total of 819 specimens of macroinvertebrate belonging to 6 orders and 10 families were identified, with the highest diversity belonging to the order of insects with 7 families and the highest abundance belonging to Chironomidae (31.5%) and then Tubificidae (22.47%). Spring with 45% had the highest and winter with 22% had the lowest abundance. The highest distribution of macroinvertebrate was obtained in station 1 in upstream (40.66%) and the lowest in station 5 in downstream (5.86%). The results showed that the highest Shannon and Simpson diversity indices were obtained in station 1 in upstream of autumn season (1.96 ± 0.32) and (0.85 ± 0.11), respectively. Also, the highest values ​​of Margalf species richness index in station 3 in midstream of winter (2.06 ± 0.4) and Pielou's evenness index in station 3 (0.94 ± 0.19) were spring. According to the Multidimensional Scale Analysis (MDS), the distribution of macroinvertebrate among the stations showed three distinct groups. PCA results showed that organic matter and clay are the most important environmental factors in the changes of macroinvertebrate communities in Khormarud river, Golestan province. The results showed that this river due to increased organic matter from agricultural areas, adjacent urban and rural wastewater caused increased contamination of the benthos resistant to the pollution, including Tubificidae and Chironomidae, these indicators could be used as useful tools for evaluating water supplies quality.

The purpose of this study was to investigate the population of benthic invertebrates and their relationship with environmental factors of Gorgan Bay Inlet. The abundance of benthic invertebrates during 2017 in three seasons from 9 stations in three sites, bay mouth, Ashuradeh coast and sturgeon culture area was studied using three replicates (225 cm2). In this study, in total, fauna was identified: 3 phyla, 6 classes, 12 families and 12 Genus. Streblospio gynobranchiata (2347±177, 47%) and Hediste diversicolor (873±101, 17%) had the highest abundance. The highest species abundance was observed in spring and the lowest species abundance in autumn. The lowest Shannon (1.12) and Pielu index (0.62) were obtained in the sturgeon culture area. Also, the dbRDA graph based on DistLM model showed that temperature, salinity and clay temperature variables and sand, silt and dissolved oxygen variables were responsible for causing abundance of fauna among different stations in the sampling seasons. According to these results, it can be concluded that macrobenthos in different seasons and areas have many changes in abundance and diversity index. Therefore, when using these communities to assess the impact of environmental factors, their natural changes should be considered.

River restoration and protection of the natural and ecological life of the river in besides to using it for various purposes is one of the most prominent areas of applied water resources science. Environmental flow provision is recognized as a prominent tool to reduce the negative effects of regulation river flow and conservation, restoration, and improvement of natural river habitat quality in watershed management and integrated water resources management. In this study, in order to evaluate and estimate the environmental flow regime of Kordan River, the Flow Duration Curve method based on hydrological statistics of the hydrometric station during the 35-year statistical period (1985-2020) and MesoHABSIM hydromorphocological model based on field studies and observations were used and accordingly, the available habitat suitability of the target fish species in different scenarios of the flow regime was examined. The results showed that the distribution of the minimum amount of ecological flow during the year is relatively uniform and within the river basin flow range (maximum of 1.8 m3/s in April and minimum of 0.3 m3/s in October). However, the optimal ecological flow distribution to provide optimal hydromorphological habitats throughout the year is unequal. Also, the maximum required amount of optimal ecological flow in May is equal to 3.6 m3/s, and the minimum amount of optimal ecological flow in October is equal to 0.7 m3/s. On the other hand, according to the analysis, at most times of the year, flow less than the average annual flow in the studied river which is equal to 3.95 m3/s, while these flows are insufficient to meet the ecological needs of aquatic. The results of the present study show that changes in the hydromorphology of Kordan River due to long-term regulation of river flow, lead to changes in the distribution of optimal morphological habitats. It is noteworthy that the MesoHABSIM model simulates the desirability and availability of fish species habitats for different scenarios of flow regime and river morphology and can also be used in river ecological restoration projects and environmental flow determination.

The aim of this study was to evaluate the health of Kabudal and Shirabad Streams and Zarrin Gol River in Golestan Province using biological indices (benthic invertebrate community). Aquatic invertebrates are one of the most important and beneficial organisms in biological monitoring. In this study, based on the existing barriers and the possibility of access to the river, 5 stations in Kaboudwal Stream, 3 stations in Shirabad Stream and 10 stations in Zarrin Gol River were determined. In order to sample large benthic invertebrates using a surber sampler with dimensions of 30.5 30 30.5 cm and with 3 replications in each station seasonally in a period of one year (2018-2019) were collected and identified based on reliable identification keys. Then alpha, beta and multivariate biodiversity indices of water quality health assessment were studied. The results of this study showed that the effluent of fish farms had a significant effect on river water quality so that the percentage of pollution-sensitive families in the stations after fish farms decreased and increased the frequency of resistant families. The streams of Golestan province generally experience moderate ecological conditions and move towards poor conditions, which with the increasing trend of destruction of ecosystems along riparian zone and the impact of agricultural and aquaculture activities, it seems that we will have these conditions in the future.

Aquaponic is considered a sustainable semi-closed system for food production that combines aquaculture and hydroponics. The aims of this study were to evaluate the influence of aquaponic on the growth and feed performance, digestive enzyme activity and blood parameters of Common carp juveniles for 60 days. This experiment consisted of three groups (three replications per group) which included; cultivation of common carp without plants (T0), use of aquaponic system for culturing common carp with lettuce (TL) and cucumber (TC). A total of 225 carp (initial body weight: 11.59 ± 0.41g) were randomly distributed in nine 60-L tanks. Results showed that aquaponic system in TL and TC groups could increase the weight gain (WG) and specific growth rate (SGR) and reduce the feed conversion ratio (FCR) of common carp. Total protease, amylase, and lipase activities were also significantly higher in TL and TC groups than control group, respectively. After 60 days, serum lysozyme activity and total immunoglobulin were significantly higher and serum cortisol and glucose levels were lower in aquaponic groups than the control group. The highest serum catalase and superoxide dismutase were observed in TL and TC group. The best effect on growth, digestive enzymes, and immune response were shown in TL and TC groups (Aquaponic system) compared to control.

The aim of this research conducted in the lower zone (or estuary) of Gharesou River was to study biodiversity of the macrobenthos and changes in sedimentary organic matter in river litter. No sample collected in summer 2018 due to drying river. Sampling was undertaken over five surveys, (May, June, November, and December 2018 and March 2019), in four sites (with two replications). The results of split plot analysis showed that sedimentary organic matter in river litter reduced significantly in autumn 2018 and winter 2019 (P<0.05). Whilst, biodiversity indices like species abundance, species richness, and evenness showed significant differences among surveys, Shannon, Simpson, and Berger-Parker indices had no significant differences (P>0.05). Species abundance reduced to -0.87 in autumn, and also species richness reduced to 3 species in autumn, including Tubificidae, Chironomidae, and Spionidae (Streblospio sp.). In addition, Species abundance was the only biodiversity index which had significant difference among sampling sites (P<0.05), as species abundance reached to the highest level (i.e., -0.7) in the fourth site. Thus, river drying in summer reduced species abundance and richness in autumn. But, when water reflowed in river in autumn, two species belonging to Tuificidae and Shironomidae were emerged first in river, which might be associated to the higher resistance of these two families to the rigid environmental conditions, like river drying.

Concerns about the negative effects of microplastics on human health have led to increasing attention to the occurrence of microplastics in the aquatic environments. Recent studies have focus from the marine environment to inland waters, particularly the spatio-temporal distribution of microplastics in rivers. Qarasu basin, leading to Gorgan Bay, is the site of many permanent rivers and the levels of microplastic pollution in those rivers are unknown. This study was conducted along 8 different rivers in 2020. Some 9 fish species were identified and the presence of microplastics was confirmed in 87% of fish. The prevalence of microplastic particles among species were Chelon spp.> Carassius gibelio> Gambusia holbrooki> Rutilus rutilus> Neogobius melanostomus> Cyprinus carpio = Vimba persa> Rutilus caspicus> Barbus cyri. The highest type, color and size of fish microplastics were fiber, black, 0.5-0.1mm, respectively. In conclusion the rivers of Qarasu basin have been polluted by microplastics not only in developed areas with intense human activity but also in upstream areas, which can be considered as a source of pollution in Gorgan bay.

Oxynoemacheilus kurdistanicus related to the Tigris and Euphrates basins and has been distributed in a wide range of Iran, Iraq and Turkey, There is limited information on the biology of this fish in Iranian waters. This study was carried out to evaluated growth pattern of this species with 209 fish samples that obtained from May up to October 2015 with Electroshocker devices. Sex ratio of male to female was 1: 0.62 that showed significant difference between sex ration of male to female in population (X2 = 11.49, p < 0.05). The weight - length relation of female was W = 0.0157 TL2.77 (r2 = 0.90) and the weight- length relation of male was W = 0.0127 TL2.86 (r2 = 0.93) and the total relation was W = 0.0141 TL2.81 (r2 = 0.98). The results showed positive allometric growth (t-test, tmale= 2.07, tfemale = 2.15, tpopulation= 3.33, p < 0.05).

Biotic indices for water quality monitoring are useful tools for assessing the health of rivers and lakes. The aim of this study was to compare biotic indices using benthic macroinvertebrate to evaluate the water quality of Mubarakabad River, Minudasht, Golestan Province. Macroinvertebrate samples were collected seasonally from 4 stations in three replications using a Surber sampler with a coverage area (900 cm2) in 2020. A total of 2828 specimens of macroinvertebrate identified and classified into 8 orders and 12 families, of which Diptera with 4 families was the most diverse group of macroinvertebrate and the highest frequency belonged to Chironomidae (46.99%) and then Baetidae (22.52%). Spring with 39% had the highest and winter with 12% had the lowest frequency. The highest distribution of macroinvertebrate was obtained in station 4 (33%) and the lowest in station 1 (19%). The studied indicators were: 1) EPT (percent of Ephemeroptera, Plecoptera and Trichoptera); 2) BMWP (Biological Monitoring Work Party System); 3) ASPT (Average Score per Taxon); 4) HFBI (Hilsenhoff Family Biotic Index); and 5) the Shannon-Wiener and Simpson index. According to the cluster analysis of macroinvertebrate distribution among the stations, it showed two separate groups. The results of biotic indices showed that the Hilsenhof, BMWP and ASPT are suitable for assessing the water quality of the Mubarakabad River. Finally, water quality was assessed as good condition for the upstream station and poor condition for the downstream station. The results of a combination of biotic indices showed that stations located in rural and agricultural areas are more polluted than upstream stations and control and management of pollutant sources is necessary to protect the study area.   .

Fish are among the organisms that have the ability to bioaccumulate these metals. The aim of this study was to investigate the concentrations of aluminum, vanadium, tin and chromium in the muscle tissue of tapeworm and assess its potential risk. For this purpose, 30 pieces of fish were caught in July 2017 from Bushehr port, Persian Gulf. Samples were prepared according to standard laboratory methods and the concentration of heavy metals was measured using ICP-OES. The concentration of elements in the muscle tissue of fish for human consumption was compared with international standards, as well as the estimated daily, weekly absorption in children and adults, their permissible consumption and risk indicators of consumption of this fish against carcinogenic diseases. The results showed that the mean concentrations of aluminum (23.9 ±10.3), vanadium (0.15 ±0.07), tin (5.41 ±2.2) and chromium (0.34 ±0.12), based on micrograms per gram, fresh weight was observed in muscle tissue.  The absorption of the studied metals in the muscle tissue of fish was Al> Sn> Cr> V. The results showed that the permissible consumption of heavy metals with the exception of aluminum was lower than the standard of the World Health Organization. The calculation of the risk index showed that aluminum in both groups of adults and children and chromium in children have values ​​of more than one, in this regard, with continuous monitoring of heavy metal surfaces in fish offered in the market

Aquatic ecosystems have changed dramatically over the last decades. For example, by reducing the water flow in the rivers, organic material would increase in the lower zone of rivers resulted in fluctuating biodiversity of macro-benthic communities. The aim of this study was to determine the changes in macrobenthic diversity in the lower zone (or estuary) of Gharesou river - southeastern Caspian Sea, in where hatchery-reared juvenile fish like Rutilus rutilus (Linnaeus, 1758) and Sturgeon fish (Acipenser sp.) are released for stock enhancement. Sampling was undertaken over five surveys in four sites in the lower zone (or estuary) of river to study the abundance, species richness, and biodiversity indices of macrobenthos. The results of split plot analysis showed that sedimentary organic matter in river litter reduced significantly in the second survey, due to relatively heavy rain fall occurred before second sampling. Whilst, biodiversity indices had no significant differences among surveys (p>0.05), these indices showed significant differences among sampling sites. Species abundance in the third survey increased significantly (p<0.05), related in sharp increment of Tubifex abundance in the fifth site. Rising abundance of Tubifex in the fifth site resulted in significant reduction of diversity indices like Shannon index and inverse-Simpson, and also significant increment of Berger-Parker index, which was probably associated with higher resistance of this species to the hard environmental condition like reduction of water flow in the river. Whilst, diversity indices in the release site for hatchery-reared juvenile was not significantly more (diverse) than the other sites(p>0.05), and also dissolved oxygen and NO3, and NH4 in the release timing had the higher and lower rates, respectively; higher fluctuations of salinity and total dissolved solids in the release site could impact survival of released hatchery reared juvenile. Thus, it is recommended that hatchery reared juveniles being released more far from the estuary towards the upstream.