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One of the most important concerns of biological societies is the abundance and distribution of plastics, and due to their high effectiveness, aquatic environments are highly regarded. Many of the plastics such as polyethylene (HDPE) commonly used in industry, finally release in the environment and remain for several years, resulting the formation of small particles that can damage the environment. To show these process, Common carp (Cyprius carpio) juveniles were exposed to microplastic particles with dimensions of less than 50 µm in two concentrations of 1 and 5 mg/l for a period of 21 days. Results showed that, microplastic particles with a concentration of 1 mg/l injure the fish and caused liver tissue hyperplasia (HP), hypertrophy (HT), necrosis (N), blood congestion (BC), sinusoid congestion (SC) and melano-macrophage centers (MMC). Moreover, in the polyethylene microplastic treatment of 5 mg/l, necrosis and melanoma-macrophage centers were moderate, while reduction in hypertrophy, sinusoid expansion, hyperplasia, sinusoid hyperemia, and pyknosis (P) recorded. In addition, the hepatosomatic index (HSI) for the control, tween control, treatments containing 1 mg/l, microplastics, and 5 were 0.70, 0.76, 0.71, and 0.84, respectively. Treatment with microplastic concentration of 5 mg/l showed a significant difference compared to the microplastic concentration of 1 mg/l and the control group. However, the growth rates of common carp juveniles did not have significant differences between two groups containing microplastic. There is evidence that microplastic pollutants cause oxidative stress in Common carp (Cyprius carpio) juveniles due to denaturation of proteins and lipids, and damaging these macromolecules. Finally, it can be concluded that polyethylene microplastic will damage the liver tissue and these damages is higher while its concentration increase.

Habitat suitability index (HSI) modeling describes a wide range of management requirements or species habitat mapping. HSI models were used to investigate the habitat preference and habitat quality of the Brond-snout, Chondrostoma regium, in the Dinorab river, a sub-basin of the Karkheh. Sampling was done in the Dinorab river during the fall season, from the downstream to the upstream, in 5 stations in 2018, each with three replications and a total of 15 habitats. Eight environmental factors were measured, including river width, potamal width, depth, temperature, total dissolved solids, electrical conductivity, pH, and velocity. During the sampling period, 142 specimens were caught and released after restoring biological status in the Dinorab river. The results showed that the highest and lowest SI values ​​for the habitat preference of C. regium in the Dinorab river were related to potamal width (0.809) and total dissolved solids (0.499), respectively. The total habitat desirability index (0.573) showed that the Dinorab river is a medium-desirability habitat for C. regium.

The aim of this study was to investigate the effects of different levels of dietary-ascorbic acid and dark-light periods on incubation indices of rainbow trout eggs. For this purpose, 54 breeders (812 ± 50.5 g) were introduced into the fish tanks with dimensions of 1.5×1.5×1 m with the holding capacity of 910 liters of water (6 fish per tank). Fish brooders were fed with three diets containing 0, 100 and 1000 mg/kg of L-ascorbyl-2-polyphosphate as treatments in triplicates for sixteen weeks. At the end of the experimental period, the oocytes of four female brooders were striped and fertilized with sperm and incubated under absolute darkness or constant light. The results showed that ascorbic acid significantly affecting on working fecundity (P<0.05). Fertilization rates in 100 and 1000 mg/kg had significant differences compared to control (P<0.05). The highest hatching rates and eyed eggs were observed in fish fed 1000 mg ascorbic acid and incubated under darkness (P<0.05). Dietary ascorbic acid had not significant effect on mortality during stages of eyed eggs to swim-up of larvae (P>0.05), but the lowest amount (9.6 ± 0.6%) was observed in 1000 mg/kg diet. Regarding the degree-day up to the eyed stage, the results showed no interaction among treatments (P= 0.777). However, there was an interaction between ascorbic acid and light in the percentage of eyed eggs (P<0.001). Moreover, in relation to the degree-day up to the stage of alevin, the results showed no interaction among treatments (P=0.145). The results of this study showed that feeding with a diet containing 1000 mg/kg ascorbic acid compare to control and 100 mg/kg ascorbic acid leads to improved reproductive indices. The results of this study indicate the necessity to feed rainbow trout breeders with high levels of ascorbic acid and egg incubation away from light to achieve higher reproductive efficiency.

During the previous couple of decades, the world aquaculture industry has considerably developed and remained one of the fastest-growing food-producing sectors. The global increase in aquaculture production has resulted in increased worldwide demand for fish oil to meet ever developing aquafeed industry. It has been shown that terrestrial lipid sources including vegetable oils are promising alternatives for dietary fish oil due to their increased production, price stability, and availability. Incorporating vegetable oil instead of fish oil in aquafeed formulation could improve the sustainability of aquaculture development and also increase the profitability of aquaculture industry (Xie et al., 2018; FAO, 2020). The present research was conducted to elucidate the effects of different dietary MUFA contents and LA:ALA ratios, by dietary incorporation of different propositions of vegetable oils including sunflower, linseed, coconut and olive oils instead of fish oil on growth indices and muscle fatty acids profile of Oncorhynchus mykiss fed on a plant-based diet without any marine ingredients.

This study was conducted to evaluate the effect of different dietary levels of MUFA and different ratios of linoleic acid (LA) to linolenic acid (ALA) on growth performance and muscle fatty acid profile of rainbow trout fingerlings. 650 juveniles of triploid rainbow trout with an average initial body weight of 14.5 ± 0.17 g were randomly allocated into seven triplicated experimental groups in 300-liter polyethylene tanks. Therefore, seven iso-nitrogenous and iso-lipid experimental diets including diet 1 (55.33, 1.00; dietary MUFA content and LA:ALA ratio), diet 2 (25.30, 1.00), diet 3 (55.13, 2.05), 4 (24.92, 2.03), diet 5 (54.94, 8.06) and diet 6 (24.91, 8.06) and a control diet containing fish oil, diet 7 (33.60, 5.97) were formulated. The basal diet did not contain any fish meal. The experimental fish were fed the diets for 4 months during the first stage of the trial. Afterwards, during the second stage of the trial, all experimental groups were fed diet 7, the basal diet which contained fish oil as the only dietary lipid source for one month. At the end of each stage, the fish were weighed to the nearest 0.1 g to calculate growth indices. Muscle samples were also taken after humanly sacrificing fish for fatty acid profile studies.

At the end of the first four-month feeding period, there was no significant difference among various experimental groups regarding weight gain (WG), relative WG, daily weight gain (DWG), specific growth rate (SGR), and survival rate (p>0.05). Similarly, feeding various experimental groups with diet containing only fish oil as the only dietary lipid source for one month also did not result in any significant differences among the groups (p>0.05). At the end of the first stage, there were no significant differences regarding muscle SFA contents of various experimental groups (p>0.05). Muscle MUFA contents reflected dietary MUFA content so that the highest MUFA proposition was observed in treatment 1 (p<0.05). However, n-6 PUFA and n-6 HUFA contents of fish in treatments 5 and 6 fed diets contained the highest dietary LA:ALA ratio (i.e., 8.0) was the highest (p<0.05). Muscle n-3 HUFA contents of the fish fed diets with lower dietary LA:ALA diet (≤2.0) were considerably higher than treatments 5 and 6 (p<0.05). However, those fish fed with diet 7 showed the highest muscle n-6 HUFA content (p<0.05). At the end of the first experimental period, muscular contents of EPA, DHA and PUFA of all experimental groups were significantly decreased (p<0.05) comparing to those fish fed diet containing fish oil (treatment 7). At the end of the both periods, muscle n-6 PUFA/n-3PUFA was significantly increased in treatment 5 (fish fed diet containing 55% MUFA and LA:ALA ratio of 8) compared to the control group (treatment 7, p<0.05). At the end of the second feeding period, there were no significant differences regarding muscle SFA and PUFA contents among various experimental groups (p>0.05). Similar to the previous stage, muscle MUFA contents of those fish that had previously been fed diets with higher MUFA contents was higher but the difference was milder compared to the first feeding period. Muscle n-3 PUFA and n-3 HUFA contents of fish did not show any differences among various experimental groups (p>0.05). However, muscle C20:4n-6, n-6 PUFA and n-6 HUFA contents still showed significant differences among groups to the extent that treatments 5 and 6 showed the highest propositions (p<0.05). Feeding all experimental groups with the finisher diet containing fish oil could to some extent restore the muscular contents of the aforementioned fatty acids, although muscle DHA content of treatment 5 was significantly lower compared to treatment 7 (p<0.05).

Our results showed that different vegetable oils blends could replace fish oil in plate-sized rainbow trout feed. Complete replacement of dietary fish oil by such terrestrial oils blends with different MUFA contents and LA:ALA ratios could affect muscle fatty acid profiles of fish which were characterized by high MUFA, ArA, and LA and lower EPA and DHA contents when compared to those fish fed diet containing fish oil. Although, rainbow trout was considerably able to de novo synthesis of EPA and DHA, increasing dietary LA:ALA ratio, i.e., >2.0, resulted in decreased muscle EPA and DHA content revealing that increased dietary LA:ALA ratio might affect liver desaturation and elongation enzymes activity which finally affect muscle fatty acid deposition requiring further studies regarding the enzymes activity and expression. Such decreased EPA and DHA contents warrant further consideration in terms of the nutritional quality of fish fillet for human consumption when replacing dietary fish oils with vegetable oils. In addition, feeding the fish with a finisher diet contained fish oil for a short period could restore the muscular fatty acids profile to improve the nutritional quality of fish. The efficacy of such a feeding strategy was considerably higher in those fish previously been fed diet 2 contained 25% MUFA with LA:ALA ratio of 1.0. However, the complete conclusion warrants more detailed studies in in terms of nutrient digestion and absorption, immune competence and finally reproductive performance of fish.

Among all marine organisms, seaweeds are considered as one of the sources of bioactive compounds. The most important compounds found in brown seaweed include phenolic compounds, polysaccharides, polyunsaturated fatty acids, proteins, peptides, pigments, vitamins, terpenoids and sterols (Sadeghi et al., 2023). Phlorotannins are compounds containing a benzene ring with one or more hydroxyl group substitutions, which are found only in brown seaweeds. So far, more than 150 algal polyphenol structures have been reported (Asaduzzaman et al., 2020). Reports indicate that these compounds have several medicinal properties such as antimicrobial and antioxidant (Milledge et al., 2015). Phycocolloids or hydrocolloids are another group of bioactive compounds found in brown seaweeds. The most important hydrocolloids found in seaweeds include alginate, agar, and carrageenan (Cmikova et al., 2022). Sargassum cristaefolium and Nizimudinia zanardinii are brown seaweeds species with good distribution on the southern coasts of Iran that can be considered as potential options for investigating the presence of compounds with antioxidant and functional properties. Therefore, the objectives of the present study included 1) extraction of bioactive compounds (including phenolic compounds and alginate) using different solvents and 2) investigation of the extraction efficiency and antioxidant properties of the extracted compounds.

Brown seaweeds S. cristaefolium and N. zanardinii were collected from the Chabahar coast, washed and dried in the shade. Extraction was performed using methanol (100%, 70%, 30%), ethyl acetate (100%, 70%, 30%) and water (100%) and the extraction yield, phlorotannins content, DPPH free radical scavenging activity and copper chelating ability of different extracts were measured. To purify phenolic compounds in N. zanardinii, the methanol extract was fractionated using chloroform, dichloromethane and ethyl acetate solvents. Alginate was extracted using distilled water and the residue obtained from the extraction in the previous section was used for extraction. Total phenol content was measured based on the standard phloroglucinol (PHG) and using the Folin-Ciocalteu indicator. DPPH free radical scavenging activity was measured according to the method of Shimada et al. (1992). Cupric chelating ability of different extracts was measured according to the method mentioned by Wong et al. (2006).

In S. cristaefolium, among the different treatments, the highest extraction yield was obtained in 70% methanol solvent (5.50 g/100 g), while in N. zanardinii the highest yield was in 100% methanol solvent and equal to 43.6 g/100 g seaweed. The extract yield in N. zanardinii was higher than S. cristaefolium in most treatments. In both seaweeds, the highest phlorotannins content was observed in 100% ethyl acetate treatment and the lowest in 100% water treatment. The highest DPPH scavenging activity was obtained in 100% ethyl acetate treatment of N. zanardinii at 84.38%. The lowest DPPH scavenging activity was observed in 100% water extract. Among the different fractions, the highest extraction yield by weight was associated with the ethyl acetate fraction (2.54 g). The highest amount of phlorotannins, i.e. 19.14 mg phloroglucinol/g extract, was found in the ethyl acetate fraction, while the lowest amount (1.35 mg PHG/g) was found in the chloroform fraction. The highest radical scavenging activity, 98.95%, was found in the ethyl acetate fraction. When comparing the fractions with the first extract, only the cupric chelation rate in the ethyl acetate fraction (73.44%) was higher than in the first extract (43.45%), and lower chelating ability was observed in the other fractions.

In the present study, organic solvents in pure form were more effective than those mixed with water in both S. cristaefolium and N. zanardinii. These results are in agreement with the study of El-Sheekh et al. (2023) who reported that the extraction yield and antioxidant properties varied depending on the type of solvent and ...

Aquaculture is increasingly vital for meeting the protein needs of a growing global population. Successful production relies on efficient feed, which accounts for 60% of costs, and the development of high-quality products. Disease management in aquaculture is challenging due to factors like poor nutrition and environmental conditions, making prevention more critical than treatment (Ndashe et al., 2023). Current strategies focus on using immune stimulants and additives, such as organic acids, probiotics, and prebiotics, to enhance fish health and resilience against diseases (Dawood et al., 2018). The use of natural growth stimulants like chitin, chitosan, and lactoferrin has surged due to their economic benefits and minimal environmental impact. These substances not only improve immune responses but also enhance the antibacterial activity of phagocytic cells, contributing to sustainable aquaculture practices. Overall, the shift towards these natural alternatives reflects a growing recognition of their value in promoting fish health and reducing reliance on chemical treatments. Chitosan is a biodegradable and biocompatible polysaccharide derived from glucosamine through the deacetylation of chitin, predominantly found in the exoskeletons of crustaceans, particularly shrimp shells. It offers numerous benefits in aquaculture, notably enhancing fish health and growth. Chitosan stimulates the immune system by increasing levels of immunoglobulin M (IgM) and lysozyme activity, which improves disease resistance. It also boosts antioxidant capacity by enhancing the activity of enzymes like superoxide dismutase (SOD) and catalase (CAT), thereby reducing oxidative stress. Additionally, chitosan promotes gut health by increasing intestinal villi length and digestive enzyme activity, facilitating better nutrient absorption (Mukarram et al., 2023; Zhang et al., 2024). Moreover, chitosan can chelate heavy metals such as cadmium, mitigating their toxic effects on fish, and its antibacterial properties help maintain gut microbiota balance by preventing pathogenic bacteria while promoting beneficial ones. Overall, dietary chitosan supplementation has been shown to enhance growth, health, and stress resistance in various fish species, making it a valuable additive in aquaculture. In the context of sturgeon (Huso huso) farming in Iran, reducing juvenile fish mortality and increasing growth rates are critical for economic efficiency, highlighting the importance of suitable diets and micronutrient balance to enhance immune function and production efficiency.

The extraction of chitosan from shrimp shells was carried out through four stages: demineralization, deproteinization, decolorization, and deacetylation. 1260 fish (2.87 ± 0.07 g) after passing the acclimatization period, were fed in 18 tanks with six experimental diets, including control diet (without chitosan, T1), 0.15% (T2), 0.3% (T3), 0.45% (T4), 0.6% (T5) and 0.75% (T6) of chitosan (n=3) for 12 weeks. Then all growth indices such as final weight, growth rate, Protein Efficiency Ratio, and FCR, immunological parameters like lysozyme, ACH50, total immunoglobulin, and IgM were measured. The body composition also was measured after 12 weeks.

The final body weight and body weight gain in treatments containing 0.45%, 0.6%, and 0.75% chitosan were significantly higher compared to the control, 0.15% and 0.3% chitosan treatments. The specific growth rate significantly increased with the higher levels of chitosan, and no significant difference was observed in the group fed with 0.15% chitosan compared to the control group. The hepatosomatic index significantly improved in all chitosan-fed treatments compared to the control group (P≤0.05). The feed conversion ratio significantly improved with increasing levels of chitosan compared to the control group. The protein efficiency ratio also increased in the treatments fed with 0.45%, 0.6%, and 0.75% chitosan compared to the control group, but no significant differences were found in the treatments fed with concentrations of 0.15% and 0.3% chitosan (P≥0.05). The lowest carcass protein level was observed in the control treatment, which showed a statistically significant difference compared to the carcass protein levels of other treatments, except for the 0.15% chitosan treatment (P ≤ 0.05). The carcass protein levels in the 0.45%, 0.6%, and 0.75% chitosan treatments were the highest, but no significant differences were observed among them. The carcass fat level in the 0.45%, 0.6%, and 0.75% chitosan treatments was significantly lower compared to the control group (P≤0.05). With the increase in chitosan concentration in the diets, the serum lysozyme levels significantly increased except for the group consuming 0.15% chitosan (P≤0.05). The results obtained from the complement activity (ACH50) measurements showed that with the increase in chitosan levels in the diet, this indicator significantly increased in the serum (P≤0.05). The total serum immunoglobulin and IgM levels, also increased significantly compared to the control group (P≤0.05).

Chitosan, has gained attention in aquaculture for its potential as a growth promoter and immunostimulant. Research indicates that dietary chitosan enhances growth performance, feed efficiency, and immune responses in various fish species, including Nile tilapia, common carp, and golden pompano. Optimal chitosan levels, typically ranging from 0.5% to 2%, have been shown to improve weight gain, feed conversion ratios, and overall health status by promoting gut health and enhancing digestive enzyme activities. Studies also highlight chitosan's role in modulating serum biochemical parameters, reducing fat accumulation in the liver, and improving intestinal morphology. The balance of chitosan dosage is crucial, as it can enhance beneficial bacteria while inhibiting harmful ones, thereby supporting the fish's immune system. Overall, chitosan represents a promising, eco-friendly alternative to antibiotics in aquaculture, contributing to sustainable fish farming practices while improving the health and productivity of cultured species. Chitosan also enhances nonspecific immunity and reduces mortality in fish, as evidenced by studies on common carp (Maqsood et al., 2010). However, its effects on feed consumption and conversion ratios can vary, with some studies showing no significant impact on these parameters despite improvements in liver health (Stanek et al., 2023). Overall, chitosan's role in aquaculture highlights its potential as a dietary supplement to improve fish health, growth, and resistance to environmental stressors. Serum parameter measurements are crucial for assessing the metabolic and physiological health of fish, particularly in aquaculture where they are susceptible to opportunistic bacterial infections. Lysozyme activity, an indicator of immune health, was found to increase with dietary chitosan levels. Research indicates that chitosan enhances lysozyme activity across various fish species, including loach, cobia, silver carp, vannamei shrimp, and rainbow trout. Additionally, chitosan supplementation in diets for beluga sturgeon and hybrid sturgeon also boosted lysozyme levels. Chitosan's immune-boosting effects are attributed to its ability to scavenge free radicals, enhancing innate immunity. Complement activity, vital for non-specific immune responses, also increased in fish like Nile tilapia and mrigal when fed chitosan. However, responses to chitosan vary by species and concentration, with some studies indicating potential negative effects at higher doses. Furthermore, IgM levels, a key immunoglobulin in fish, significantly increased with chitosan supplementation, reinforcing its role in adaptive immunity. Overall, optimal chitosan levels in fish diets can significantly enhance immune responses and health. The increase in IgM levels with dietary chitosan is not fully understood, necessitating further research to clarify the mechanisms involved (Salam et al., 2024). Studies indicate that chitosan enhances IgM and total protein levels in fish, such as rainbow trout and golden pompano, although excessive chitosan (10 g/kg) can reduce these benefits (Yu et al., 2023). In tilapia, IgM levels increased significantly up to 1.5% chitosan but decreased at 2% (Zhang et al., 2024). Additionally, recombinant chitosan nanoparticles show promise as alternatives to antibiotics in aquaculture, potentially enhancing disease resistance. This research supports using chitosan in beluga fry diets to improve growth and immune performance while reducing antibiotic reliance, particularly at levels of 0.45% to 0.6%, which positively affected growth, body composition, and immune parameters.

Microplastics (MPs) have garnered significant attention due to their widespread presence in the environment and the potential threats they pose to aquatic organisms (Wang et al., 2021). These particles, smaller than 5 millimeters, are classified into primary and secondary types. Primary microplastics are manufactured in micrometer sizes for use in various industries, including aerospace, medicine, and cosmetics (Alomar et al., 2016). In contrast, secondary microplastics are formed from the breakdown of larger plastic debris into smaller particles (Duis and Coors, 2016). Microplastics readily accumulate in aquatic environments and, due to their resistance to degradation, are dispersed globally (Wang et al., 2021). These particles can adversely affect aquatic organisms due to their physical and chemical properties, leading to disturbances in feeding, reproduction, and immune functions (Oliviero et al., 2019). Additionally, microplastics can adsorb pollutants such as heavy metals, exacerbating their harmful effects on aquatic ecosystems. This combination presents a significant threat to marine life health (Prunier et al., 2019). Furthermore, microplastics provide a substrate for microorganisms, facilitating the formation of biofilms. These biofilms can alter the physical and chemical properties of microplastics, influencing their ability to adsorb contaminants (Tu et al., 2020). The objective of this study is to examine the correlation between microplastic pollution and potentially toxic elements in the sediments of the southwestern Caspian Sea coast and assess their impacts on the region marine ecosystem.

The Caspian Sea, the largest enclosed lake in the world, is significantly impacted by human activities such as oil and gas extraction, agriculture, and industrial development. Rivers such as the Volga, Kura, and Ural transport pollutants, including heavy metals, to the sea, posing a threat to the ecosystem, particularly along the southwestern coast (Efendieva, 1994; Simonett, 2006). Sediment sampling was conducted at three polluted stations in Kiashahr, Anzali, and Astara (Kostianoy et al., 2005). Sediment sampling was performed in the spring of 2022 using Van Veen grabs (20×20 cm) with three replicates at each statio (Claessens et al., 2011; Löder and Gerdts, 2015). After being transferred to glass bottles and sent to the laboratory. Microplastic extraction from sediments involves two essential stages. In the first stage, the organic materials in the sediments were digested using hydrogen peroxide (H2O2, 30%). The digestion time varies between 1 and 10 days, depending on the type and amount of organic material (Erkes-Medrano et al., 2015; Zhang et al., 2016). After digestion, the samples were dried at 60°C for 48 hours (Vianello et al., 2013). In the second stage, density separation was used to extract the microplastics. In this step, 100 g of dried sediment was placed in a glass beaker, and 800 mL of saturated NaCl solution (293 g/L) was added (Thompson et al., 2004). After shaking for five minutes, the beaker was left to stand for 45 minutes to allow the high-density particles to settle. The resulting supernatant, containing the floating particles, was filtered through a nitrocellulose filter (Hidalgo-Ruz et al., 2012; Wagner et al., 2014; Duis and Coors, 2016). This process was repeated three times, and the filters were dried at 60°C (Law et al., 2010). Finally, the microplastic particles were examined and counted using a 40x magnification loop, and the number of microplastic particles per gram of dry sediment was reported (Reddy et al., 2006; Morét-Ferguson et al., 2010). The polymer types of the extracted microplastics were identified using FT-IR spectroscopy with ATR, analyzing spectra in the 400-4000 cm⁻¹ range and comparing characteristic peaks with standard polymer databases (Veerasingam et al., 2021). Data analysis was performed using SPSS version 27. The Kolmogorov-Smirnov test was used to check for normality, and to compare pollution levels across stations, ANOVA and Kruskal-Wallis tests were applied. To examine the correlation between microplastic pollution and potentially toxic elements, Pearson and Spearman correlation coefficients were used. All analyses were conducted at a %95 confidence level. Graphs were plotted using Excel 2022.

The average concentration of elements at the three stations revealed that the highest and lowest average concentrations of elements in the sediment were for manganese (Mn) with 760661.80±53.41 µg/kg dry weight at the Anzali station and cadmium (Cd) with 41.44±1.93 µg/kg dry weight at the Astara station. The results of the Kolmogorov-Smirnov test for the distribution of potentially toxic elements in the sediment samples from the stations indicated that some elements did not follow a normal distribution (p˂0.05). To compare the average concentrations of elements across the stations and examine the correlation between elements, parametric tests (one-way analysis of variance and Pearson correlation coefficient) were used for normally distributed data, while non-parametric tests (Kruskal-Wallis and Spearman correlation coefficient) were employed for non-normally distributed data. One-way analysis of variance (ANOVA) results for comparing the average concentration of elements across the stations showed that manganese and zinc had significant differences at all stations (p˂0.05). The cadmium element showed no significant difference between the Kiashahr and Astara stations, but significant differences were observed between Kiashahr and Anzali, as well as Anzali and Astara stations (p˂0.05). The Kruskal-Wallis test results also indicated significant differences for arsenic, cobalt, chromium, copper, iron, mercury, nickel, and lead among the stations (p˂0.05). The Anzali station, with 67±4 pieces per 300 grams of dry sediment, exhibited the highest contamination, while the Kiashahr station, with 45.33±2.30 pieces per 300 grams of dry sediment, showed the lowest contamination. One-way analysis of variance (ANOVA) revealed that the Anzali station had a significant difference when compared to both Kiashahr and Astara stations (p˂0.05). However, no significant difference was observed between the Kiashahr and Astara stations. The microplastics extracted from the sediment samples were categorized into two color groups: blue and red. At the Kiashahr station, red microplastics accounted for 53%, representing the highest abundance, while blue microplastics constituted 47%, representing the lowest abundance. At the Anzali station, blue microplastics were the most abundant, comprising 75%, while red microplastics represented the lowest abundance, constituting 25%. At the Astara station, red microplastics accounted for 53%, representing the highest abundance, while blue microplastics constituted 47%, representing the lowest abundance. A total of 496 microplastic pieces were extracted from the sediment samples at the three stations. All the extracted microplastics were fiber type. The microplastics found in the sediment samples were classified into seven categories: less than 0.5 mm, 0.5-1 mm, 1-2 mm, 2-3 mm, 3-4 mm, 4-5 mm and greater than 5 mm. At the Kiashahr station, the highest abundance of microplastics was found in the 4-5 mm range, followed by the 3-4 mm range. The lowest abundance was observed in the 1-2 mm particles. At the Anzali station, the highest abundance was found in particles larger than 5 mm, followed by the 4-5 mm range, while the lowest abundance was observed in particles smaller than 0.5 mm. At the Astara station, the highest abundance was found in particles larger than 5 mm, followed by the 4-5 mm range, while the lowest abundance was observed in the 1-2 mm particles. The extracted microplastics from the sediments of the southwestern Caspian Sea coast were identified using FTIR-ATR spectroscopy. Five different polymers were identified, including polyethylen (PE), polypropylene (PP), polyester, polystyrene (PS) and nylon. Overall, polyethylene was the dominant polymer in the extracted microplastics from the sediments. The correlation analysis results between the abundance of microplastics and the concentration of potentially toxic elements in the sediments from the Kiashahr, Anzali, and Astara stations indicated no significant correlation between these two variables at the stations under study. Manganese, zinc, and cadmium had a normal distribution in all stations, thus Pearson's correlation coefficient was used to assess the correlation between microplastic pollution and potentially toxic elements. For other elements, whose data did not follow a normal distribution and successful normalization techniques were not applied, the Spearman correlation coefficient was employed. 

Discussion and conclusion: 

In this study, the Anzali station exhibited the highest contamination, with an average of 67 ± 4 microplastic pieces per 300 grams of dry sediment. This finding is consistent with the study by Rasta et al. (2020) which reported a high concentration of microplastic contamination in the sediments of Anzali Wetland. All the microplastics extracted from the sediments in this research were of the fiber type, with blue being the most dominant color, accounting for 58%. Similar results were found in the study by Zhang et al., (2020) in the Shengsi region of China, where fiber-type microplastics were the most abundant, with blue identified as the predominant color. Microplastics at the Kiashahr station were most abundant in the 4-5 mm size range, while the Anzali and Astara stations exhibited the highest abundance in microplastics larger than 5 mm. Similar findings were reported by Kühn et al., (2018) on the coasts of the Netherlands, where microplastics in the size range of 500-2000 micrometers were predominant. In this study, no significant correlation was observed between microplastics and the concentration of elements in the sediments. This lack of correlation may be attributed to differences in the sources of microplastics and elements, the physical and chemical properties of these pollutants, and the varying environmental conditions (Napper and Thompson, 2016). Finally, it can be concluded that the Anzali station has the highest microplastic pollution, primarily composed of fiber type and secondary microplastics, with blue being the predominant color. Anthropogenic sources, such as laundry runoff, fishing gear, and the release of plastic packaging by tourists, contribute to the spread of this pollution in the marine environment. Correlation analysis revealed no significant relationship between microplastics and elements, likely due to differences in sources and the physical and chemical characteristics of these pollutants. A comparison of element concentrations with global standards indicates that the pollution levels are within safe limits; however, continued monitoring and management are crucial to mitigate pollution levels.

The agricultural export sector plays a significant role in Iran's non-oil exports, particularly in food and agricultural products. These products are crucial for securing foreign currency and supporting the national economy. In 2022, Iran's agricultural product exports reached over 5.2 billion dollars, representing 9.77% of total non-oil exports. However, the sector remains highly reliant on imports, which amounted to around 17.8 billion dollars, highlighting the importance of domestic production growth and export development to achieve a positive trade balance. One of the key products in Iran's agricultural export portfolio is shrimp. According to Iran's Fisheries Statistical Report, shrimp exports in 2022 totaled over 37,000 tons, accounting for nearly 21% of the country's fishery exports. This generated over 600 million dollars in foreign currency, with shrimp contributing more than 180 million dollars. With total shrimp production in 2022 reaching 68,267 tons, more than 55% was exported, underscoring shrimp's importance as a major export product. China is one of the largest shrimp markets globally and has been a consistent top destination for Iran's shrimp exports. In 2021, China imported over 4 billion dollars worth of shrimp, and the demand for imports continued to rise in the first half of 2022, showing a growth of 25.8%. From 2017 to 2021, China consistently ranked as the primary destination for Iran’s shrimp, except for 2020 when the UAE took the lead. Recently, Russia has also emerged as a growing export market for Iran's shrimp, with exports to Russia surpassing 17 million tons in 2022. This research aims to rank the obstacles to expanding Iran's shrimp exports to China and provide recommendations for overcoming these challenges. Understanding the factors influencing this market is vital to enhancing Iran's shrimp export capacity and maintaining its competitive position in the global shrimp trade.

Through the review of scientific sources, reports from relevant organizations, library studies, and interviews with experts from both government and private sectors, and exporters, 36 factors influencing the export of Iranian shrimp to China were identified, and a questionnaire was developed. The research variables were measured using the Likert scale, with respondents answering the questionnaire questions on a scale from 1 to 5, where 1 = very low, 2 = low, 3 = moderate, 4 = high, and 5 = very high. The overall framework of the questionnaire questions and each of the potential factors included in the questions were validated through interviews with experts and confirmed for content validity. The target population consisted of individuals who had significant experience in shrimp exports or had worked in the fisheries sector, in either executive, research, or production roles. The data collected from the questionnaires were analyzed using SPSS analytical software. The results were then evaluated, and based on the analysis; answers to the research questions were derived.

A total of 53 participants completed the survey, with an average age of 62 years. The sample was predominantly male, as 92% of respondents were men, while only 8% were women. In terms of age distribution, 38% of participants were over 60 years old, which constituted the largest group, followed by 26% in the 51-60 age range. Regarding educational qualifications, 40% of respondents held a doctoral degree or higher, while 53% had at least a master's degree. This indicates a highly educated respondent pool with substantial expertise in the field of shrimp export. The majority of respondents (72%) had more than 20 years of experience in the shrimp and fisheries sector, indicating an experienced sample. Only 13% had less than 10 years of experience. Of the participants, 43% were involved in shrimp export, and 42% were engaged in shrimp processing. The sample also included experts from various subfields of the fisheries sector: 38% were fisheries experts, 19% were researchers, 34% were shrimp farmers, and 9% were involved in fishing. Many respondents were active in multiple areas of the shrimp industry.
Data Analysis: The data collected using a 5-point Likert scale (ranging from 1 = very low to 5 = very high) were ordinal in nature, which necessitated the use of non-parametric tests. To ensure the validity of the statistical methods, the Kolmogorov-Smirnov test was applied to assess the normality of the data distribution. The results indicated that the data did not follow a normal distribution (p-value<0.05), supporting non-parametric methods for further analysis.
Chi-Square Analysis: The Chi-square test was employed to explore the relationships between the identified barriers and export outcomes. The null hypothesis posited that no significant relationships existed between the variables while rejecting this hypothesis would indicate meaningful relationships. The Chi-square results revealed that 9 factors, including limited production capacity, poor product quality, lack of product diversity, and weak adherence to health standards in the destination country, did not show a significant relationship with export outcomes (p > 0.05). This suggests that these factors did not substantially affect the success of shrimp exports. However, 27 factors exhibited significant relationships with export outcomes (p-value < 0.05). These factors included limited access to international banking services, restrictions on money transfers for purchasing inputs, weak branding, low competitiveness of Iranian exporters in the Chinese market, fluctuations in exchange rates, misalignment between production and export strategies, limited financial and operational capacity of exporters, lack of marketing knowledge, lack of coordination between export-related agencies, absence of export consortiums in the Chinese market, and insufficient banking support for production and export financing. These variables were identified as the most pressing barriers to the growth of shrimp exports from Iran to China.
Friedman Test: To evaluate the importance of each identified barrier, a Friedman test was conducted, ranking the barriers based on the respondents’ ratings. The null hypothesis assumed no differences in the rankings of the barriers, but the results indicated significant differences (p-value < 0.05), meaning the barriers were ranked differently by the participants. The rankings highlighted that the top challenges to shrimp exports were “Limited access to international banking services,” ranked first, followed by “Restrictions on money transfers for inputs and funds repatriation” in second place, and “Weak branding” in third. These were considered the most critical factors that needed to be addressed to improve export performance. Other important barriers included “Low competitiveness of Iranian exporters in China,” “Exchange rate fluctuations,” “Misalignment between production and export strategies,” and “Limited capacity and ability (financial and operational) of exporters.” 

Discussion and conclusions:

The study identified 27 significant factors influencing the development of shrimp exports to China, with marketing being the most impactful area, followed by banking, laws and regulations, transportation, production, and veterinary regulations. The top ten barriers included issues like limited access to international banking services, weak branding, low competitiveness of Iranian exporters, exchange rate fluctuations, misalignment between production and export strategies, and insufficient banking support. Previous studies, such as Heidarian (2011), also highlighted that increased production facilities and government support boost exports. However, access to financial resources did not significantly affect shrimp exports. Similarly, Ali Akbarzadeh Bidgoli (2018) found that domestic shrimp production, global shrimp prices, and farm area ratios significantly affected exports, while exchange rates did not. Norouzi (2019) emphasized the importance of factors like improved packaging, reducing exchange rate fluctuations, and expanding preferential tariffs to enhance export performances. The findings suggest that the Iranian government can play a key role by offering clear support to the aquaculture sector, attracting foreign investment, improving international relations, and reforming customs regulations. Additionally, addressing production costs, enhancing marketing knowledge, and establishing an export consortium can further improve export performance. Furthermore, implementing an efficient traceability system would help meet sanitary standards in China and improve overall export processes. The study advocates for a coordinated approach to addressing financial and operational challenges to boost shrimp exports.