Essential cations, such as alkali and alkaline earth metals, are crucial in aquatic ecosystems, but when present in water in concentrations that have been described above as toxic to the different classes of aquatic organisms, they become toxic. This work examines the effects of acute exposure to selected alkali and Alkaline earth metals on fish fry with both the lethal and the sub-lethal effects studied. Fish fry, being at a very developmental stage, is more sensitive to environmental stressors such as chemical toxicity and is more suitable for evaluating aquatic pollution. The present investigation deals with the acute toxicity of Sodium (Na), Potassium (K), Calcium (Ca) and Magnesium (Mg) on rohu, Labeo rohita (Ham.) fry. Different concentrations of sodium chloride, potassium chloride, calcium chloride and magnesium chloride were used as test salts and their toxicity tests (LC50 values) were studied in laboratory conditions by exposing the rohu fry with different durations like 6 hrs, 12 hrs, 24 hrs, 48 hrs, 72 hrs and 96 hrs of exposure. The LC50 values of different metal ions ranged between 10001.87 ppm - 750.23ppm in the case of sodium chloride, 1096.98 ppm - 68.73 ppm in the case of potassium chloride, 9872.44 ppm to 6384.12 ppm in the case of calcium chloride and 12676.81 ppm to 11095.66 ppm in case of magnesium chloride. In the 96-hour fry toxicity test, potassium chloride is more toxic than other metals. The toxicities of the salts were observed in the order of KCl>NaCl >CaCl2 >MgCl2.
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