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Background. Many natural aquatic bodies have been contaminated with heavy metals released from domestic, industrial and other anthropogenic activities. Fish are an important bioindicator species and play an important role in the monitoring of water pollution.Objectives. This study shows the effect of heavy metals on the distribution of glutathione S-transferases (GST), catalase, rhodanese and 3-mercaptopyruvate sulphur transferase (3-MST) isolated from the liver, gills, fins and muscle of Clarias gariepinus.Methods . Glutathione S-transferase, catalase, rhodanese and 3-mercaptopyruvate S-transferase enzymes were isolated from the liver and gills of fish by homogenization of each tissue (with specific buffers for each enzyme) and centrifugation. Serial dilutions of the crude enzymes were then assayed for residual enzymatic activities using standard enzyme assay protocol.Results. The results showed heavy metals in the liver and muscle of the investigated fish. This study indicated significant accumulation of heavy metals in the tissues/organ of the fish from Ilesha, Osogbo and Yakoyo fish ponds. These are three main towns in Osun State where the major occupation is fish farming. The relationship between enzymatic activities and heavy metal content in C gariepinus tissue showed positive and significant (pConclusions. The study concluded that the pattern of response of GST, catalase, rhodanese and 3-MST activities in the various organs/tissues of C gariepinus to the heavy metals suggests that the excitation or inhibitions of their activities are organ specific. Further biochemical studies of fish tissues/organs are needed to characterize the enzymatic changes associated with heavy metal pollution.Competing Interests: The authors declare no competing financial interests

Cyanide pollution of aquatic environment has become a great concern in Nigeria because of the increase in cassava cultivation. In Nigeria, cassava processing milling plants are usually situated around streams or rivers such that the waste from each stages of processing easily find their way into these water bodies as effluents and waste waters. Extracellular rhodanese of Klebsiella edwardsii isolated from Atutulala stream, Modakeke, where cassava is being processed, was assessed for its bioremediation potential. Cyanide concentration of the stream was analysed for six months. Four bacterial isolates were screened for their ability to degrade free cyanide and the best strain was further screened for rhodanese producing ability. The enzyme was purified by 85% ammonium sulphate precipitation and diethyl aminoethyl-cellulose ion-exchange chromatography. The pure enzyme had a specific activity of 0.0473 Rhodanese Unit mg-1 with a purification fold of 4.56 and a percentage yield of 30.30%. The enzyme demonstrated a broad pH range but the optimum pH was at 6.0 while the optimum temperature was 60°C. The bioremediation potential of the enzyme was assessed under various conditions such as the field pH and temperature as well as optimum pH and temperature using the cyanide contaminated water as substrate source in a typical assay protocol. The enzyme was able to convert 1.6481 μmol of cyanide to thiocyanate in the water sample at optimum pH and temperature of the enzyme. It could be concluded from the study that at optimum pH and temperature, rhodanese exhibited remediation activity in cyanide contaminated aquatic ecosystems and thus, can be used for its restoration.