Heavy metal accumulation in Oreochromis niloticus and Clarias gariepinus from an integrated chicken-fish system

Abstract

Accumulation of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn) and zinc (Zn) in fish from integrated laying chicken-fish ponds was investigated in order to determine the possible health risks to humans from heavy metal contamination. The 20 m2 fish ponds were stocked with Oreochromis niloticus and Clarias gariepinus in a 3:1 ratio and a stocking density of 8 fingerlings/m2. Treatment 1 (T1) consisted of chicken integrated at the rate of 2000 birds/ha; Treatment 2 (T2), 3000 birds/ha; Treatment 3 (T3), 4000 birds/ha, while Treatment 4 (T4) was the control without integration. Fish in T4 were fed compounded feed at 5% of body weight, while those in T1, T2 and T3 were fed on chicken manure and spilled feed that fell directly into the ponds. The ponds were sampled monthly and fish growth and water quality parameters were measured accordingly. Results of the experiment showed that tissue metal concentrations for both species were lowest in the muscles and highest in the kidney and liver. Final metal concentrations in the muscles of both fish species in T1 and T4 were below FAO (1983) and EU (2001) the limits and the consumption of fish muscle from such systems is considered safe. However, there is risk of Pb concentrations accumulating above the recommended levels in C. gariepinus at 3000 chickens/ha and above.   Key words: Oreochromis niloticus, Clarias gariepinus, integrated, laying chicken.