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This research in line with fish cage culture plan in the southern coast of the Caspian Sea was carried out. Sampling was seasonally in 8 transects at the depth of 5-100 m from Astara to Torkaman areas in 2008-2009. The aim of this study was to investigate the distribution, abundance and biomass of macrobenthic invertebrate. The highest abundance and biomass were found in transects of Amirabad with average 10931.7±7301.4N/m2 and Astara with mean 86.2±160.3g/m2, respectively. This could be due to the presence of alien species into the Caspian Sea, Streblospio gynobranchiata in 2003 and is the dominant population of macrobenthic invertebrate concern up to 58.4% and increased of S. gynobranchiata (high power compatibility) and mussels of Cerastoderma glaucum (large size) is relevant, respectively. The abundance and biomass have fluctuations in different seasons and the highest abundance with average 6280.1±5693.1N/m2 and biomass with mean 66.1±126.9g/m2 was in winter and spring, respectively. A significant difference between abundance and transects (p<0.05), no significant difference between abundance and depth and seasons (p>0.05), significant difference between biomass and depth (p<0.05) and no significant difference between biomass at transect and seasons (p>0.05) were found. Also, according to multivariate analysis of benthic invertebrate on the abundance at various depths revealed that depths of 5, 10 and 20 meters from the importance of certain fisheries in terms of frequency, abundance and biomass of the macrobenthic invertebrate, slope substrate, substrate, close to the beach, the accumulation of nutrients, Nursery ground, feeding ground and Spawning ground is important for different important species in the Caspian Sea. Therefore, the establishment of fish cage culture was recommended more than 20-meter depths according to the plans of fish cage culture in the southern coast of the Caspian Sea of the Iranian Fisheries Organization.

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The establishment of aquaculture cages in the right place will be associated with the least adverse effects on the ecosystem, so the quality of sediment is very important in monitoring fish cages farming. The aim of this study was to investigate the sediments chemistry parameters around fish cage culture in the southern of Caspian Sea (Nowshahr region). Sampling was conducted in four stages of the breeding period during 2017 and 2018, underneath the cages and at 200m and 1000 m longitudinal distance in four geographical directions from the cages. Based on the results the variations in different forms of phosphorus such as Loosely-P, Fe-P, Al-P, Bioava.-P, Ca-P, TIP, Res.-P and TP were 1.2-13.8, 22-114, 12-121, 37-211, 61-2170, 150-2223, 0-937 and 203-2283 µg/g. dw, respectively. The order of different forms of phosphorous were registered as Ca-P>Res.-P >Fe-P>Al-P>Loosely-P. The variation range of pH, Eh and TOC% were 8.05-8.60, (-63)-(-83) and 1.36-7.87, respectively. The results revealed that temperature, Eh and pH had the main role in the adsorption and release of loosely-P, Fe-P and Al-P. Comparison of 25-75th percentiles of total organic carbon (1.97-2.60%) with permissible threshold showed that the sediments of Nowshahr region can be classified as moderately polluted.

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The aim of this study was to investigate the changes in the bacterial quality trend (indicator bacteria) of water and its relationship with some environmental parameters around fish cages culture in the southern Caspian Sea region (Nowshahr-Mazandaran province). For this purpose, water sampling of the southern region of the Caspian Sea in the Tuskatok region of Nowshahr city in Mazandaran province took from January 2017 to December 2016 during the rainbow trout cage culture period at different distances cage (cage shade, 200 and 1000 m).The results showed that in the whole cage culture period, the maximum average of 18750 CFU/ml water bacteria was observed in the 200 m cage station before the cage culture period and the minimum average of 3250  CFU/ml water bacteria was observed in the 200 m cage station at the end of the cage culture period. The presence of total coliform and fecal coliform in water samples was recorded as 18.75 and 2.08%, respectively, and fecal streptococcus water was not observed in any of the sampling stations and in this situation, fish cages culture did not cause contamination. Maximum and minimum water temperature, pH, turbidity, saturation percentage and biological oxygen demand are 26.50 and 7.00 °C, 8.71 and 8.29, 19.71 and 0.52 NTU, 87 and 160, respectively. Percentage of 1.32 and 8.39 mg/l were recorded. Based on the principal component analysis (PCA), the results showed that the variables of pH and water temperature had the highest variance and the total count along with water turbidity in the third component showed a significant positive correlation (p<0.05). As a result, the proper slope of the area, the proper flow of water around the small-scale cages has reduced the microbial contamination in the shade of the cage compared to the stations outside the cage.