Development of functional fish feed with natural ingredients to control heavy metals

The effects of two natural ingredients, Chinese parsley (CP) and chitosan (CT), on growth, accumulation, and excretion of cadmium in fish body and preservation of essential trace metals in the body were investigated by using rainbow trout that had been fed cadmium-added diet, low and high concentration, for 3 weeks. This pretest confirmed that cadmium was accumulated in the liver, kidney, and intestine of the test fish. The cadmium level of the fish, fed diet with CP or CT, was decreased by 18% and 24%, respectively, compared to that of the fish given the control diet. But CP and CT did not have an influence on normal growth of test fish and the levels of essential trace metals in the body. In addition, the level of cadmium was higher in liver than kidney in the high-cadmium dietary group, indicating the Cd level in kidney follows that of liver as kidney lies in the final stage of metabolism. The cadmium accumulation in the fish body was supposed to be reduced, by giving CP to increase the solubility of Cd to body fluid by conjugation into metallothioneins (MTs), while CT was supposed to be responsible for the physical adsorption of cadmium ions by glucosamine groups.