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Many populations of Caspian Sea trout (Salmo caspius)—a nationally endangered species in Iran—have been extirpated or depleted due to anthropogenic impacts. The Lar National Park hosts large populations of Caspian Sea trout, which have not been subject to fisheries management programs before, but the population/s also face different human-related threats that may endanger their sustainability. A total of 357 Caspian Sea trout collected from different streams in Lar National Park were genotyped at 7978 filtered SNP using Genotyping-By-Sequencing to document population genetic structure and the contribution of each population/habitat to lake-run trout fisheries. Our results revealed a fine-scale population genetic structure, which is probably a product of factors including natural and artificial barriers to gene flow, geographic distance, and behavioral differences between resident and lake-run trout. Mixed-Stock Analyses revealed a high contribution from four panmictic populations of the national park to lake-run fish and almost no contribution from streams located in upper reaches or from streams with hydro-chemical or physical barriers. Our results highlighted the necessity for a more serious conservation plan for both the populations contributing greatly to lake fisheries and the highly diverged upstream populations due to their uniqueness.

In Lar National Park (Caspian Sea basin, Iran), the Caspian trout (Salmo caspius) population faces different threats, including introduced fish species. Due to the harsh environmental conditions and limited accessibility, monitoring of fish species via conventional approaches proves difficult. Hence, environmental DNA metabarcoding may prove an appropriate tool for monitoring fishes within the park. Environmental DNA samples from eight stream sites in the National Park were sequenced via metabarcoding of the 12S rRNA gene, and the species identified via eDNA metabarcoding were compared to the results of electrofishing performed at the same localities on the same day. No significant difference in the number of Caspian Sea trout DNA sequence reads was detected among the collection sites (p > 0.05). The highest number of reads was detected in Dalichay Stream, but the highest population density determined via electrofishing was in Siahpalas Stream. The discrepancy between the eDNA read count and trout population density, as well as the limited sampling scheme within this study, limit our ability to provide a robust conclusion about the application of environmental DNA metabarcoding for assessment of fish density in Lar National Park. Environmental DNA metabarcoding detected more species than electrofishing, but no significant differences in the composition of the local fish community were observed. Introduced fish species were all observed or detected in Siahpalas Stream, which is characterized by high water temperature, muddy substrate, and lower flow rate. A significant effect of flow rate and total dissolved solids on the presence of introduced fish species (p = 0.02) and of flow rate alone on relative abundance of introduced fish species (p = 0.03) was detected. To standardize the application of eDNA metabarcoding as a biodiversity assessment tool in Lar National Park, future studies should characterize the parameters that affect eDNA persistence and detectability in the system. In Lar National Park (Caspian Sea basin, Iran) Caspian Sea trout populations and non‐native fish diversity and distribution was assessed and compared using eDNA metabarcoding and electrofishing. The results revealed that non‐native fish species were distributed in limited habitats in accordance with distribution of suitable environmental factors, but the Caspian Sea trout existed all over the studied region. Overall, eDNA metabarcoding appeared to better represent fish diversity compared to electrofishing.

The eastern-most members of the Salmo trutta species complex in the Aralo-Caspian Sea region were studied to infer their population genetic structure and biogeographic origin. A total of 68 individuals collected from Iranian endorheic inland basins (Namak and Urmia lakes), tributaries of the Caspian (Haraz, Kura, Samur, Volga, and Ural river drainages) and Aral (Amu River) seas, and the Baltic Sea basin were genotyped using 26,202 SNPs via Genotyping-by-Sequencing. The data were analyzed using admixture, discriminant analysis of principal components (DAPC), analysis of molecular variance (AMOVA), species tree, genetic differentiation (FST), allele frequency difference (AFD), and neighbor network approaches. Trout in the southern Caspian Sea basin differ from those of the western and northern Caspian Sea. Based on our results, the Lake Namak trout is divergent from the southern and western Caspian trout populations. Aral Sea and Lake Namak trouts likely originated from the northern and southern Caspian Sea populations, respectively. Although only few populations were considered in this study, six conservation/management units of trouts are proposed.

Numerous riverine ecosystems in Iran are currently suffering due to various human activities, which are directly affecting the physico-chemical conditions of running waters and influencing the aquatic biota. In this study, we chose the cold-water streams of the Southern Caspian Sea Basin in Iran to analyse human pressures and develop a multi-metric fish index for the cold-water streams dominated by brown trout, Salmo trutta in this Basin. To do this, the fish and environmental data were sampled in 67 medium sized streams in the Caspian Mountains. In total, nine fish metrics were calculated. Moreover, 27 criteria describing major anthropogenic pressures for the entire sampling area were used to generate a regional pressure index that accounted for potential effects of multiple human pressures. For the index development, we first defined reference sites and then quantified differences of fish metrics between the reference and impacted sites. The multiple linear regressions were used for describing metric responses to natural environmental differences in the absence of any human pressures. Finally, by testing the ability of each metric for discrimination of impacted and reference sites as well as their sensitivity to a gradient of regional pressure index, the metrics density of brown trout and biomass of sub-adult brown trout explained human pressures best. Our multi-metric fish index performed well in discriminating between reference and impacted sites, giving a significant negative linear response to a gradient of regional pressure index. In general, the development of such an index offers an opportunity to enhance national bio-monitoring programmes in Iran.

The purpose of this study was to investigate the physical and chemical factors of seawater to determine the water quality index around two marine farms of rainbow trout in the south of the Caspian Sea. Each farm had four floating polyethylene cages with a final fish harvest of 60 tons. The water sampling was performed in January and March 2014 as well as May and August 2015 from around the cages (close: cage shade, 50 m and 100 m; distant: 1000 m) in three geographical directions: east, west, and south. The water quality parameters including pH, temperature, transparency, salinity, electrical conductivity (EC), total dissolved solids, dissolved oxygen, and nutrients (nitrogen and phosphorus compounds) were determined. The results of the analysis of variance of data at both farms showed that changes in physical and chemical parameters of water had only significant differences at the time of sampling (p < 0.05). The highest value of variance in the principal component analysis (PCA; 30.23% from 84.75%) was related to EC, temperature, salinity, total nitrogen, pH, and organic phosphorus. Iran Surface Water Quality Index (IRWQISC) at near and far distances from farms was determined to be moderate (40-55). The main reasons for this result can be attributed to the small-scale and short fish farming period along with the hydrological conditions of the region.

Fungi and yeast species as good sources of arachidonic acid and polyunsaturated fatty acids have been attracting a lot of attention from scientists in recent years. In this study, we used the oleaginous yeast Wickerhamomyces siamensis SAKSG isolated from the gills of trout caught from the Caspian Sea. Low-cost polysaccharides hydrolyzed by enzymatic digestion of immobilized whole cells of Bacillus amyloliquefaciens ATCC 23350 served as substrates to evaluate the effects of each on the biomass and the fatty acid profiles of Mortierella alpina CBS 754.68 and Wickerhamomyces siamensis SAKSG. By using sprouted wheat, millet and wheat as starch sources adjusted to 150 g/L we obtained reducing sugar content of 102.57, 57.50 and 51.62 g/L, respectively. The highest and lowest dry weight (biomass) of M. alpina was obtained in sprouted wheat (3.7% of media) and rice-formulated media (1.72% of media), respectively. Each formulated media significantly affected the profiles of M. alpina fatty acids. The highest content of linoleic acid (41.873%), oleic acid (30.061%) and arachidonic acid (27.054%) was obtained with corn, rice and potatoes used as the carbon sources. The yeast lipid content was high, consisting of C6 up to C12 fatty acids, accounting for about 55.7% of the total fatty acids. Some amount of docosahexaenoic acid (DHA) and (ecosapentanoic acid) EPA was also observed in W. siamensis.

The Caspian Sea, the largest inland closed water body in the world, has numerous endemic species. The Caspian brown trout (Salmo trutta caspius) is considered as endangered according to IUCN criteria. Information on phylogeography and genetic structure is crucial for appropriate management of genetic resources. In spite of the huge number of studies carried out in the Salmo trutta species complex across its distribution range, very few data are available on these issues for S. trutta within the Caspian Sea. Mitochondrial (mtDNA control region) and nuclear (major ribosomal DNA internal transcribed spacer 1, ITS-1, and ten microsatellite loci) molecular markers were used to study the phylogeography, genetic structure, and current captive breeding strategies for reinforcement of Caspian trout in North Iranian rivers. Our results confirmed the presence of Salmo trutta caspius in this region. Phylogenetic analysis demonstrated its membership to the brown trout Danubian (DA) lineage. Genetic diversity of Caspian brown trout in Iranian Rivers is comparable to the levels usually observed in sustainable anadromous European brown trout populations. Microsatellite data suggested two main clusters connected by gene flow among river basins likely by anadromous fish. No genetic differences were detected between the hatchery sample and the remaining wild populations. While the current hatchery program has not produced detectable genetic changes in the wild populations, conservation strategies prioritizing habitat improvement and recovering natural spawning areas for enhancing wild populations are emphasized.