Effects of compost manure on the body burden of cadmium and growth of common carp, Cyprinus carpio (L.)

One-hundred-and-eighty-day bioassays were made in outdoor cement tanks (volume 300 L) with common carp, Cyprinus carpio (L.), exposed to eight different treatments, each with three replicates. Four treatments contained 2.5 mg L-1 cadmium (Cd): Cd alone; Cd with 6.7 g L-1 of compost manure made from the freshwater macrophyte Pistia stratiotes (L.); Cd with 1.0 g L-1 of the same manure; and Cd with a cumulative treatment of the manure (1.0 g L-1 month(-1)). Four treatments contained no Cd: the control (without manure); and treatments with only manure (6.7 g L-1, 1.0 g L-1 and 1.0 g L-1 month(-1)). The concentration of dissolved (filterable) Cd in water ranged from 0.74 to 0.89 mg L-1 after 24 h (one day) of treatment. The addition of compost manure significantly reduced the Cd concentration of the water and induced a quicker removal of Cd from the water. The quickest removal of Cd from water (60 days) was found when a high dose of compost manure (6.7 g L-1) was added. The cumulative (monthly) treatment and the one-time treatment of the manure at a low dose (1.0 g L-1) required 75 and 90 days, respectively, for removal of Cd, while the metal persisted for up to 120 days in water when no manure was added. All doses of compost manure significantly reduced the bioaccumulation of Cd in plankton, but maximum reduction was found under cumulative treatment at a low dose of the manure, A single treatment at a high dose or cumulative treatment at a low dose of the manure helped in reducing the total body burden of Cd. A dose of 2.5 mg L-1 Cd did not show any adverse effect on the growth of fish, but compost manure, irrespective of its dose and combination with Cd, markedly increased the growth of fish and primary productivity of water. On the other hand, a high dose of manure resulted in much higher levels of NH3-N, NO2-N and PO4-P in the water in comparison with other treatments.