Spatial and temporal distribution of physicochemical parameters of water in Gorgan Bay (the southeast of the Caspian Sea - Iran): Fundamentals for the monitoring of the Caspian Sea coastal areas.

Gorgan Bay as a main part of the Miankaleh (a natural biosphere reserve registered by UNESCO) is one of the richest ecological area in the West Asia and very important internationally recognized refuge for the wildlife. To date, multi physicochemical parameters have not been examined on a large scale. To fill this knowledge gap, the present study aimed to explore the seasonal and spatial variability of water quality parameters of the bay. The results showed that except for depth and transparency, there are significant variations in most parameters across the four seasons. The patterns of these changes in the bay vary, as evidenced by a comparison of the distribution maps of the various factors throughout the year. Notably, alkalinity declined from east to west, reaching its highest levels at important entry points such as the Qarasu River, Bandar-Gaz, and the pier. TDS, on the other hand, increased westward, reaching its highest concentration in the shallow western regions. Maximum depth (310 cm) and transparency (250 cm) were observed in the central bay. While the pH was higher in deeper areas, the distribution of PO4 was more uniform. With lower levels in the east (salinity = 0.40 ‰) and higher levels in the west (salinity = 28.9 ‰), the salinity showed a coherent gradient. Agricultural land use in the basin of the bay and fluxes of nutrients and sediments of the rivers entering the bay has significant contribution to the bay pollution situation. These results will serve as a guide for improving our understanding of the Gorgan Bay ecosystem. They also have implications for informed conservation and management plans adapted to the specifics of this special region within the Caspian Sea.

The fate of nitrogen in the Zarin-Gol River receiving trout farm effluent.

This study investigated the Zarrin-Gol River ecosystem in Iran to trace organic matter in the food web and evaluate the impact of aquaculture farm effluent using stable isotopes of nitrogen (δ15N) and carbon (δ13C). Using a previously-developed model (Islam 2005), we estimated that a trout farm in the vicinity released 1.4 tons of nitrogen into the river. This was comparable to an estimated total nutrient load of 2.1 tons of nitrogen for the six-month fish-rearing period based on a web-based constituent load estimator (LOADEST). A model estimate of river nitrogen concentration at the time of minimum river discharge (100 L/s) was 2.74 mg/L. Despite relatively high nitrogen loading from the farm, isotope data showed typical food web structure. Several biological groups had elevated δ13C or δ15N values, but there was limited evidence for the entry of organic matter from the trout farm into the food web, with sites above and below trout farms having inconsistent patterns in 15N enrichment. By coupling nitrogen load modeling with stable isotope analysis we showed that stable isotopes might not be effective tracers of organic matter into food webs, depending on surrounding land use and other point sources of nutrients. The Zarrin-Gol River ecosystem, like other basins with high human population density, remains vulnerable to eutrophication in part due to trout farm effluent.

Assessing nitrogen dynamics model and the role of artificial lagoon in effluent loading of shrimp farms in Gomishan wetland, southern Caspian Sea.

Shrimp farming increases the nutrients, especially nitrogen in the water resources reducing water quality. This study was conducted to evaluate the nitrogen dynamics in white shrimp (Litopenaeus vannamei) farms and the role of artificial lagoon (24 ha) in reducing nitrogen levels in Gomishan coastal wetland, the eastern Caspian Sea. The results indicated that at the end of the 4-month breeding period, the amounts of nitrogen and phosphorus introduced into Gomishan wetland were calculated as to 220.157 and 39 tons, respectively in a breeding area covering 830 hectares. Nitrogen values (based on nitrate) calculated based on the relationship between the basin and the discharge of the outlet channel of the site at the time of complete emptying of the farms, were calculated to be approximately 121.8 tons per breeding time that it had an important role in eliminating about 45% of nutrient pollution and reducing the concentration of dissolved nitrogen. Moreover, nitrogen isotopic trace was observed in shrimp samples, in similar levels in the samples of both shrimp pond and lagoon, which emphasizes the role of feeding from natural food, especially benthic fauna. Overall, due to the decline of Caspian Sea water level, Gomishan coastal wetland is drying, and the output of shrimp farms is currenly the only source supplying water for the wetland. Hence, appropriate management strategies could minimize the amounts of nutrients into the natural water whilst aiding wetland's survaival.

Biomagnification of Copper Along the Aquatic Food Chain (Artemia franciscana, Danio rerio, and Astronotus ocellatus).

Nowadays, pollution of aquatic ecosystems with heavy metals is one of the most important environmental challenges due to toxicity, stability, and bioaccumulation in the environment. Heavy metals accumulate in aquatics and plant tissues and can eventually threaten human health by transmission into the food chain. For this reason, in the present study, the effect of copper sulfate (CuSO4) and its transmission in the food chain of Artemia franciscana, Danio rerio (Zebra), and Astronotus ocellatus (Oscar) were investigated. Initially, lethal concentration of Cu on Artemia was obtained in 24 h. In the first step, Zebra fishes fed with Artemia (under copper sulfate exposure (LC50)) and water (clean and 10% of CuSO4) treatments. In the second step, Oscar fishes fed with Zebra (under copper sulfate exposure (LC50)) and water (clean and 10% of CuSO4) treatments. In the last step, the concentration of Cu was measured in liver tissues of Zebra and Oscar fishes. Also, the variation of glucose and enzymes including Alanine aminotransferase (ALT), Aspartate aminotransferase (AST), and Autologous Conditioned Plasma (ACP) was measured. The results of this study showed that Cu causes histopathological changes liver tissues including hyperemia, necrosis, hepatic portal vein, hepatocyte destruction, nucleolysis, bile stasis, and biliary edema. Also, a strong positive and significant correlation was observed between Cu and increasing glucose and ALT, AST, and ACP.

Spatial and temporal variations in stable isotope values (δ13C and δ15N) of the primary and secondary consumers along the southern coastline of the Caspian Sea.

Spatial and temporal variations in stable isotope values of the coastal communities in the Caspian Sea remain poorly understood. We followed carbon stable isotope ratios (δ13C) and nitrogen stable isotope ratios (δ15N) of primary (gammarids) and secondary (common carp) consumers at four sites with different organic matter loadings along the southern coastline of the Caspian Sea from May to November 2019. Consumers from the site receiving higher sewage effluent and aquaculture wastes were more enriched in δ15N whereas those from the site receiving lower terrestrial-derived organic matter had enriched δ13C values. Trophic position of consumers varied among sites as a function of organic matter inputs but was independent of month. The observed temporal and spatial variations in the stable isotope values and C:N ratios of the primary and secondary consumers with regards to organic matter loadings, suggesting a possible effect of anthropogenic disturbance on the Caspian Sea ecosystem function.

The effects of dietary vitamin C on mucosal immune responses and growth performance in Caspian roach (Rutilus rutilus caspicus) fry.

This study was conducted to investigate the effects of different levels of dietary vitamin C on some skin mucus immune parameters, mucus antimicrobial activity and growth performance of Caspian roach (Rutilus rutilus caspicus) fry. Six hundred sixty Caspian roach (1.4 ± 0.02 g) fry were allocated to 12 tanks (55 fish per tank), and triplicate groups were fed diets containing 0, 1,000, 1,500 and 2,000 mg kg(-1) vitamin C for 60 days. At the end of the trial, the epidermal mucus protein level, alkaline phosphatase and antimicrobial activity against two gram-positive bacteria (Streptococcus faecium and Micrococcus luteus) and gram-negative bacteria (Escherichia coli and Serratia marcescens) as well as growth performance were measured. The results demonstrated that feeding on vitamin C significantly elevated skin mucus alkaline phosphatase and protein levels compared to the control group (P < 0.05). However, lysozyme activity was undetectable in both the vitamin C-fed roach fry and the control group. Skin mucus antimicrobial activity was increased following vitamin C administration, and the bacterial growth inhibition zones were significantly elevated in vitamin C-fed roach (P < 0.05). Similar results were obtained in case of the minimum inhibitory concentration of skin mucus. Also fish fed the control diet had a significantly lower weight gain, specific growth rate and condition factor compared to the other treatments (P < 0.05). These results revealed that dietary vitamin C beneficially affects the skin mucus immune parameters and growth performance of Caspian roach fry.