Effects of different water hardness levels on, growth indices, survival rate, hematological parameters, and culture water quality of Caspian kutum fingerlings (Rutilus frisii)

The effect of different water hardness levels on growth indices, survival rate, hematological parameters, and water quality of Caspian Kutum (Rutilus kutum) fingerlings was investigated in a completely randomized design with six water hardness treatments (350, 600, 650, 700, 800, and 900 mg of calcium carbonate (CaCO3) each with three replications containing 13 pieces of fish (n = 300 in total) with an average weight of 2 g for 56 days. The highest final weight, body weight gain, and daily growth rate were estimated in the treatment with a hardness of 650 mg/L CaCO3 (P < 0.05); the same treatment represented the minimum feed conversion ratio and the lowest daily food intake (P < 0.05). The highest values of hardness and alkalinity of water were measured in the treatment with a hardness of 900 mg/L CaCO3 (P < 0.05). The highest levels of red blood cells were counted in well water treatment (600 mg/L CaCO3) + distilled water with a hardness of 350 mg/L CaCO3 (P < 0.05). The highest and lowest hemoglobin levels were estimated in treatments containing 700 and 900 mg/L CaCO3, respectively (P < 0.05). The highest levels of cortisol and glucose with significant differences between treatments were recorded in the treatment containing 15 g of CaCO3 with a hardness of 900 mg/L (P < 0.05). The highest amounts of sodium and calcium in fish meat were obtained in the treatment with a hardness of 650 mg CaCO3 (P < 0.05). Therefore, water hardness of 650 mg/L CaCO3 led to the highest values of final weight, body weight gain, and daily growth rate in R. kutum fingerlings in the laboratory (P < 0.05), which can be used for the culture of this valuable fish species.