Bioaccumulation of sodium, potassium, calcium and magnesium in Rohu, Labeo rohita (Ham.) fry ANUSAYA MALLICK*, B.C. MOHAPATRA and N. SARANGI

The bioaccumulation of alkali and alkaline earth metals such as Na, K, Ca and Mg were studied in the fry of rohu, Labeo rohita (Ham.), a species of freshwater aquaculture importance in India. The experiments were conducted in laboratory conditions exposing the rohu eggs up to fry stage in one experiment; and fry to advanced fry stage in other experiment, to different concentrations of the salts. Sodium chloride (0.15, 1.5, 15, and 150 mg/l), potassium chloride (0.015, 0.15, and 1.5 mg/l), magnesium chloride (0.15, 1.5, 15, and 150 mg/l), and calcium chloride (0.15, 1.5, 15, and 150 mg/l) were used as test salts. The tests were conducted in 20-litre capacity glass aquaria stocked with 800 eggs up to fry stage; and in the second experiment with 60 numbers of fry up to advanced fry stage. Control animals were reared in the laboratory without addition of salts. The experiments were conducted in triplicate and each one continued for one-month duration. Normal rearing practices were followed and 50 per cent test solutions from each aquarium were replaced with fresh ones in every week. The bioaccumulations in wet weight basis in whole tissue of fry reared from eggs and in advanced fry exposed to respective salts at the end of the experiment were 100-572 and 91-147 ppm for sodium; 71104 and 13-22 ppm for potassium; 16-32 and 24-48 ppm for calcium; and 210-660 and 150-300 ppm for magnesium respectively. In control the bioaccumulations for fry reared from eggs, and in advanced fry were 150-212 and 371-412 ppm for sodium; 85-99 and 80-85 ppm for potassium; 18-22 and 5.5-7.8 ppm for calcium; and 250-260 and 15 ppm for magnesium respectively. No definite relationship could be established between the alkali and alkaline earth metals concentration in aquatic environment and bioaccumulation in fish tissue, except sodium and calcium in fry stage.