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This study was conducted between May and Septemberin 2023 at the Gomishan shrimp farm site located in Golestan Province, aiming to investigate biological and non-biological factors of shrimp culture ponds and their relationships with each other as well as with shrimp growth. Three farms from Line 2 were selected, and from each farm, three ponds were chosen for sampling of zooplankton, phytoplankton, and benthos, as well as for collecting physical and chemical data. After conducting the experiments, the data were entered into Excel software, the relevant calculations were performed, and graphs were plotted. The Shapiro-Wilk test was used to assess the normality of the data, and Levene's test was employed to evaluate the homogeneity of variances. To compare the physical and chemical factors among stations at different times, one-way ANOVA was used, and mean comparisons were conducted using Duncan's Multiple Range Test and Dannet's test. The frequency comparison of phytoplankton, zooplankton, and zoobenthos between farms during each sampling period was carried out using non-parametric Kruskal-Wallis and Mann-Whitney U tests at a significance level of 5% (α = 0.05). Pearson's Correlation Test was utilized to examine the correlations between physical and chemical parameters and the abundance of phytoplankton, zooplankton, and zoobenthos species. Biodiversity indices were calculated using the Past 3 software. All statistical analyses were performed using IBM SPSS 22.0. The results of this study showed that five phyla of phytoplankton were identified: Bacillariophyta, Chlorophyta, Pyrrophyta, Euglenophyta, and Cyanophyta. Among these, Bacillariophyta was the most abundant phytoplankton group observed in the culture ponds, with 28 genera and 60 species. Chlorophyta ranked second with 22 genera and 34 species, followed by Cyanophyta with 18 genera and 24 species, Pyrrophyta with 9 genera and 21 species, and Euglenophyta with 4 genera and 6 species. No significant differences were observed in the number of genera and species of phytoplankton between farms during any of the sampling periods. The results of the correlation analysis between phytoplankton abundance and physical and chemical factors showed that Bacillariophyta had a positive correlation with transparency (r = 0.517), an inverse correlation with salinity (r = -0.567), and a strong inverse correlation with total dissolved solids (TDS) (r = -0.619). Pyrrophyta exhibited a strong positive correlation with temperature (r = 0.835), a positive correlation with salinity (r = 0.585), a positive correlation with TDS (r = 0.526), and a strong inverse correlation with pH (r = -0.736). Cyanophyta showed a strong positive correlation with temperature (r = 0.864), an inverse correlation with oxygen (r = -0.537), a strong positive correlation with salinity (r = 0.771), a strong positive correlation with TDS (r = 0.694), and a strong inverse correlation with pH (r = -0.888). Chlorophyta demonstrated a strong positive correlation with temperature (r = 0.765), an inverse correlation with transparency (r = -0.449), and an inverse correlation with pH (r = -0.512). Among the zooplankton, Foraminifera, copepods, copepod nauplii, free-living nematodes, polychaete larvae, juvenile worms of Streblospio gynobranchiata , amphipods, insect larvae of Ephydra sp. , and rotifers were observed. The highest abundance of zooplankton was recorded in early Mordad across all farms, with copepods being the most abundant group. The correlation analysis between total zooplankton abundance and physical and chemical factors revealed an inverse linear correlation between total zooplankton abundance and salinity (r = -0.474). Salinity also showed an inverse correlation with oxygen (r = -0.438) and pH (r = -0.302). The lowest and highest Simpson indices for zooplankton were 0.41 ± 0.2 and 0.91 ± 0.13 at the beginning and end of the period, respectively. The lowest and highest Shannon diversity indices for zooplankton were 0.14 ± 0.22 and 1.0 ± 0.38 at the beginning and end of the period, respectively. The lowest and highest Evenness indices for zooplankton were 0.63 ± 0.12 and 0.94 ± 0.08, respectively. The lowest and highest Margalef indices for zooplankton were 0.17 ± 0.14 and 0.76 ± 0.28 at the beginning and end of the period, respectively. Among the zoobenthos, the groups Nereis , Gammaridae , Chironomidae , Cerastoderma , Ecorbia , Theodonus , Dreissena caspia , Ephedra , and Streblospio gynobranchiata were observed. Cerastoderma and Ecorbia dominated among the zoobenthos. The number of zoobenthos varied throughout the study period. In Tir month, the abundance of Ephedra differed significantly among farms. The correlation analysis between benthos abundance and organic matter content of the substrate revealed an inverse linear relationship (r = -0.482). The lowest and highest Simpson indices for zoobenthos were 0.47 ± 0.03 and 0.68 ± 0.2, respectively. The lowest and highest Shannon indices for zoobenthos were 0.37 ± 0.5 and 0.91 ± 0.18, respectively. The lowest and highest evenness indices (Evenness ) for zoobenthos were 0.66 ± 0.17 and 0.94 ± 0.12, respectively. The lowest and highest Margalef indices for zoobenthos were 0.21 ± 0.0 and 0.68 ± 0.19, respectively. The highest and lowest average TOM (Total Organic Matter) levels were 8.47 ± 0.01% and 4.65 ± 0.06%, respectively. Ammonia levels ranged from 0.02 ± 0.01 to 0.11 ± 0.04 mg/L. Nitrate levels ranged from 0.07 ± 0.37 to 0.68 ± 0.03 mg/L. pH values ranged from 8.1 ± 0.07 to 8.73 ± 0.19. TDS (Total Dissolved Solids) levels ranged from 29.45 ± 0.65 to 18.63 ± 0.45 g/L. Transparency ranged from 16.0 ± 41.29 cm to 41.29 cm. Salinity ranged from 31.2 ± 0.14 to 18.8 ± 0.14 g/L. Oxygen levels ranged from 6.02 ± 0.08 to 8.66 ± 1.16 mg/L. Temperature ranged from 22.41 ± 0.2 to 29.73 ± 0.81 °C. Significant differences were observed among farms regarding total organic matter content at all sampling times. Significant differences in ammonia levels were only observed on one sampling date. The highest and lowest specific growth rates (SGR) recorded were 12.67 ± 0.23 in Farm 4 on day 25 of cultivation and 3.7 ± 0.02 in Farm 7 on day 72 of cultivation, respectively. The correlation analysis between specific growth rate and physical and chemical factors showed a direct linear correlation between specific growth rate and oxygen (r = 0.886) and an inverse linear correlation with salinity (r = -0.319). In summary, the results of this study showed that the physical and chemical characteristics of the water were within normal limits, and in the absence of exceptional environmental changes, the temperature was also very favorable. The farms, with proper water exchange, did not experience issues with oxygen or salinity levels. Additionally, considering the low stocking density, it can be said that they were not at risk regarding ammonia and nitrate levels. The abundance of phytoplankton exhibited sufficient diversity. However, the zooplankton showed very low diversity and density, maintaining uniformity only due to the stable physical and chemical conditions. This factor could negatively impact the intake of live feed and the FCR (Feed Conversion Ratio). Based on the findings, as the total organic matter increased, the density and diversity of benthic organisms decreased, and no correlation was found between the growth rate and the abundance of macrobenthos. This indicates that the existing level of macrobenthos did not significantly influence shrimp growth. This suggests that greater attention should be paid to nutrition, particularly in the later stages of the cultivation period.
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