E. Olatunji Ayotunde, B. Obeten Offem, and F. Bekeh Ada, “Heavy metal profile of water, sediment and freshwater cat fish, Chrysichthys nigrodigitatus (Siluriformes: Bagridae), of Cross River, Nigeria”, Rev. Biol. Trop., vol. 60, no. 3, pp. 1289–1301, Sep. 2012.