Acute toxicity of alkali and alkaline earth metals on Rohu, Labeo rohita (Hamilton) egg and hatchlings

The acute toxicity of salts of alkali and alkaline earth metals, such as sodium (Na), potassium (K), calcium (Ca) and magnesium (Mg) were studied on the egg and larval stages of Indian major carp Labeo rohita (Hamilton). The acute toxicity experiments were conducted followed by the range finding bioassay tests. The experiments were conducted in triplicates. The cumulative percentage of dead or damaged eggs at the end of 6, 12, 18, 24, 36, 48, 60, 72 and 96 hours was recorded for the calculation of LC₅₀. The increase in salt concentrations in water increased their toxicity and reduced the duration to damage 50% of the eggs. The eggs became smaller than their normal size and whitish before being damaged in the test solutions. Most of the exposed eggs and hatchlings tended to lay on the floor of the tank. The toxicity of the metals was in the order of K>Na>Mg>Ca. The 96 hours LC₅₀ values were 3.25, 2.73, 28.9 and 20.52 ppm for sodium, potassium, calcium and magnesium, respectively.