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Benthic diatom assemblages on the natural substrata at Balikhli River (northwest Iran) were investigated monthly. A total of 96 samples were collected from epilithic and epipelic substrata. A total of 110 taxa from 49 genera were identified. The most abundant diatom species were Cyclotella meneghiniana, Diatoma moniliformis, Nitzschia inconspicua, Planothidium lanceolatum and Gomphonema olivaceum. Non-metric multidimensional scaling (nMDS) analyses revealed explicit differences between diatom communities of stony and sediment substrates. Although common diatom taxa were not restricted to single substrates, some taxa had higher tendencies to every substrate. The nMDS analysis also showed differences between summer and autumn samples. Canonical correspondence analysis (CCA) of groups resulted from cluster analysis, showed that the nutrient concentration gradient, pH were the most important factors affecting the composition of diatom assemblages and species distribution. In our study orthophosphates had greater effect than nitrates, and Gomphonem parvulum and Navicula recenswere found in phosphate rich samples. Anthropogenic input including agricultural and domestic wastes may be responsible for high levels of these parameters. Alkali volcanic rocks and limestone sediments underlying the watershed could explain the high pH in the Balikhli River. In total 67.5% of the identified species in the river are considered as alkaliphilous. The findings of this study denote that the main determinants of variation in benthic diatom communities of Balikhli River result from a combination of land use patterns caused by human activities, river hydrology and natural phenomena including geology.

The aim of this study was to investigate the occurrence of microplastics (MPs) in the gastrointestinal (GI) tract, muscle and gonads of 193 individuals of nine commercially-important fish species from Anzali Wetland between May and July 2018. Tissues were removed, digested by 10% KOH for 24 h at 60 °C, filtered on cellulose nitrate filter and then dried. MPs were found in all tissues. There were significant differences between the numbers of isolated particles from GI tract and control groups (procedural blank containing Milli Q water without tissue), while their abundance in the muscle and gonads did not display significant differences with control groups. Higher abundances of MPs were recorded in omnivorous fish (2.26 ± 2.93 items/individual) than carnivorous species (1.10 ± 1.10 items/individual) (P 0.05). MPs were ranged from 20 to 4800 μm in size and were dominated by fiber-like in shape, polyethylene in polymer and black in color.

The present contribution gives a faunistic overview on the distribution of Caenidae in Iran. Four species have so far been reported, of which Caenis macrura Stephens, 1835 by far is the most abundant and most widely spread species. Caenis kopetdagi Kluge, 1985 was previously only known from three localities in the Kopet Dag Mountain range, which stretches along the border between Turkmenistan and Iran. We report this species from three further localities at the western border of the Zagros Mountains in southwest Iran, thus considerably expanding its distribution. The nymph of Caenis kopetdagi is re-described, its validity is confirmed, and modern diagnostic characters are added. Its CO1 sequence is provided and compared with sequences of other species of Caenis Stephens, 1835 occurring in the Middle East. The habitat of C. kopetdagi as well as the distribution of Caenidae in Iran and of Caenis in the Middle East is also discussed.

The occurrence, abundance and distribution of microplastics (MPs) were studied in sediments and surface waters of the Anzali coastal wetland, southwest of the Caspian Sea. Sediment and surface water samples were taken at 11 and 6 stations in June 2018 and January 2019 respectively. The abundances of MPs in sediment samples were 140–2820 and 113–3690 items/kg dry weight while in surface waters were 0.40–4.41 and 0.19–2.85 items/m3 in June and January respectively. Fiber was the most common shape, followed by fragment and film. Red, black and blue were the most frequent colors. Particles 1–2 mm were the dominant size. SEM/EDS and ATR-FTIR analyses were used to identify MPs. Polypropylene, polyethylene and polyester were the most frequently found polymers. Our results highlighted the widespread dispersion of MPs in Anzali Wetland which in turn might be a pathway of MPs pollution transporter to the adjacent and connected Caspian Sea.

The pre sent study analyzed the relationships of two different biological assemblages (diatom and macroinvertebrate) when they are used to characterize a set of stations (from reference stations to impacted stations) within the Shahrood River. In particular, we examined the issue of concordance among these assemblages and the physicochemical parameters detected, using both multivariate and multimetric methods. In addition, the trophic diatom index and Hilsenhoff family-level biotic index for macroinvertebrate assemblages were used to evaluate the ecological status of the Shahrood River. Diatom and macroinvertebrate assemblages in the Shahrood River differed significantly between reference and impacted stations. ANOSIM showed a significant difference in the composition and abundance of diatoms and macroinvertebrates among reference, influence and impact stations, especially between reference and impact stations. Results of CCA ordination showed that benthic diatoms and macroinvertebrate assemblages were mainly affected by DO, TSS, NO3 −, PO4 3− concentrations and heavy metals such as Zn and Cd. Biotic indices for the Shahrood River suggested a water quality category of “fair” with fairly substantial organic pollution for the impacted stations. Finally, our results suggest that an appropriate management and restoration policy needs to be implemented for the Shahrood basin.

The size and number of chloride cells and serum ion concentrations in kutum, Rutillus frisii kutum Nordman, from brackish (Caspian Sea) and fresh water (Khoshkrood River) environments were studied to gain a better understanding of osmoregulation in this species. Twenty mature kutum specimens were collected from the Caspian Sea (Anzali coasts, 8.49 ppt salinity and 12.4°C temperature) and 20 specimens from Khoshkrood River (0.18 ppt salinity and 18°C temperature). Gill samples were analyzed histologically and concentrations of Na+, Cl- , K+, and Mg2+ ions were determined in the blood serum. Concentrations of Na+, Cl- , K+, and Mg2+ ions and osmotic pressure in mature kutum from brackish water were significantly higher than in specimens from fresh water. The average size and number of chloride cells in the fish from seawater were considerably larger than those from fresh water. The mean size of chloride cells was 6.89 ± 1.16 μm in brackish water samples and 5.1 ± 0.81 μm in river samples. The average number of chloride cells in brackish and river water samples were 16.92 and 6.57, respectively. The density and size of chloride cells increased with increases in salinity

The demographic variables of pike (Esox lucius ) were studied at the southern edge of the species' distribution in the Anzali Wetland, south-western Caspian Sea. The main aim was to provide data for the assessment of the stock and to explore possible fisheries management measures such as setting minimum landing size based on length-at-maturity. Pike collected from commercial landings ranged from 15.4 to 75.4 cm in fork length (FL), from 52.9 to 3462.5 g in weight and were between 0 and 8 years old. Von Bertalanffy growth function parameters were L∞ = 90.6 cm FL, k = 0.12 yr−1 and t 0 = −1.74 yr−1 . Male pike matured at 1–2 years with L 50 of 28.6 cm FL, whereas females matured at 2–3 years with a L 50 of 33.9 cm FL. Instantaneous total mortality (Z ) was estimated as 0.93 yr−1 , while fishing mortality (F ) was estimated to be 0.66 yr−1 . Yield-per-recruit analysis indicated that pike in the Anzali Wetland seems to be growth-overfished under the current fishing regime with no management measures, and substantial increases in yield could be achieved by increasing the length at first harvest. The results indicated that management actions such as enforced legislation are required to obtain a better stock status and higher yield. Management could be more effective if the number of fishers and their catch could be controlled, e.g., through the allocation of fishing licenses.

Aim This contribution reports the first regional occurrence of Pleurosira laevis in the Masuleh River, Iran and additionally describes the pattern of occurrence along the Masuleh River and among four substrate types. The aim of this study was to assess the effects of substrate type and physical and chemical variables on distribution of centric diatom P. laevis. Methods At each station, triplicate samples were collected from 4 substrata. Epilithic (assemblages on rock), epidendric (assemblages on wood), epipsammic (assemblages on sand), and epipelic (assemblages on mud) diatom and water quality sampling was done four times at 5 stations. Physical and chemical variables including total nitrate, total phosphate, silicate, Fe2+, EC, and pH were also determined. Samples preserved in 2% for formalin solution and transferred to the laboratory, boiled with acid (HNO3: H2SO4; 2:1), centrifuged, identified, and counted. Cluster analysis was performed to indicate the main differences and similarities in diatom abundance amongst substrates sampled and amongst sampling stations. Results The highest (12.54 ± 1.54) and lowest (0.74 ± 0.10) abundance was obtained from wooden and muddy substrates at stations S5 and S4, respectively. The highest abundance was observed in the wooden substrate among all of sampling stations where showed significant differences (P < 0.05) with the other substrates. The hierarchical clustering based on relative abundance of P. laevis distinguished two clusters amongst the four substrate types. Rougher and more stable substrates (wood, sand, and stone) clearly separated from smooth and unstable substrates (mud). Based on relative abundance of P. laevis on rougher substrates, epidendric and epipsammic species had the highest similarity. Results of Pearson correlation showed that relative abundance of P. laevis had a significant correlation with EC, TN, TP, and Fe2+ concentrations (P < 0.05) whilst no significant correlation was observed with pH, temperature, and SiO2 concentration (P > 0.05). Conclusion We conclude that wood substrata can be substituted for one another during field surveys. Results from this study demonstrate that the type and roughness of the substrate both influence the attachment of P. laevis and its subsequent growth conditions. Resumo: Objetivo Este trabalho relata a primeira ocorrência regional de Pleurosira laevis no rio Masuleh (Irã) e adicionalmente descreve o seu padrão de ocorrência ao longo do rio e em quatro tipos de substrato. O objetivo deste trabalho foi avaliar os efeitos do tipo de substrato e as variáveis físicas e químicas na distribuição da diatomácea cêntrica P. laveis. Métodos Em cada estação, amostras em triplicara foram coletadas em quatro substratos. Diatomáceas epifíticas (assembléias sobre rochas), epidendricas (assembléias em troncos), episâmicas (assembléias em areia) e epipélicas (assembléias em lodo) e amostras da qualidade de água foram obtidas quatro vezes em cinco estações. Variáveis físicas e químicas incluindo nitrato total, fosfato total, silicatos, Fe2+, CE, e pH também foram determinadas. As amostras foram preservadas em solução de formalina 2% e transferidas para o laboratório, fervidas em ácido (HNO3: H2SO4; 2:1), centrifugadas, identificadas e contadas. Uma análise de Cluster foi aplicada para indicar as principais diferenças e similaridades na abundância de diatomáceas entre substratos e entre estações de amostragem. Resultados A maior (12,54 ± 1,54) e a menor (0,74 ± 0,10) abundância foi obtida a partir de substratos de troncos e lodo nas estações S5 e S4, respectivamente. Entre todas as estações de amostragem a maior abundância foi observada no substrato de troncos, com diferenças significativas (P 0,05) . Conclusão Nós concluímos que o substrato de tronco pode ser substituído por um outro durante o levantamento de campo. Os resultados deste estudo demonstram que o tipo e a rugosidade do substrato influencia a fixação de P. laevis e as suas condições de crescimento subsequentes.