Assessment of Selected Metal Accumulation in African Catfish (Clarias gariepinus) Reared in Earthen, Concrete and Tarpaulin Ponds in Calabar Metropolis
Lucia Iquo-Bassey Eka
Department of Biochemistry, University of Cross River State, Calabar, Nigeria.
Godwin Eneji Egbung
Department of Biochemistry, University of Calabar, Calabar, Nigeria.
Peter O. Etinosa-Okankan
Department of Biochemistry, University of Cross River State, Calabar, Nigeria.
Akinsheye Joshua Akinsheye
Department of Biochemistry, University of Cross River State, Calabar, Nigeria.
Jeremiah Chukwuebuka Anigbo *
Department of Biochemistry, University of Cross River State, Calabar, Nigeria.
Deborah Praise Abua
Department of Biochemistry, University of Cross River State, Calabar, Nigeria.
Peter Okpagu Abua
Department of Biochemistry, University of Cross River State, Calabar, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
African catfish (Clarias gariepinus) is widely cultured in several pond systems, and production environments may be associated with differences in metal exposure and tissue accumulation. This cross-sectional study compared iron (Fe), lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) in pond water and in the muscle, gills, and liver of C. gariepinus from nine sampled farm-pond groups in Calabar Metropolis, Cross River State, Nigeria. One earthen, one concrete, and one tarpaulin pond were sampled at each of three farms; six fish were analysed per sampled pond, giving 54 fish in total. Tissue concentrations were determined by atomic absorption spectrophotometry and expressed on a dry-weight basis. Tissue data were summarised as mean ± SD and compared across the nine farm-pond groups using one-way ANOVA, while pond-water concentrations were interpreted descriptively. An operational tissue-to-water concentration ratio (L/kg) was calculated from the corresponding tissue and pond-water concentrations; because only a cross-sectional water measurement and dry-weight tissue concentrations were available, this ratio was interpreted as a comparative concentration ratio rather than a steady-state or regulatory bioaccumulation factor. Overall ANOVA indicated differences among the sampled groups for every tissue-metal combination (p < 0.001). Gills frequently contained higher concentrations than muscle, and liver concentrations were also comparatively elevated. The highest tissue Zn concentration was 8.491 ± 0.093 mg/kg dry weight in gills from the New Airport concrete pond. Pond-water concentrations were generally highest at Iyonde and lowest at New Airport; Zn reached 1.720 ± 0.070 mg/L in the Iyonde earthen pond, while Pb ranged from 0.003 ± 0.001 to 0.035 ± 0.003 mg/L. Operational ratios were highest for Zn, reaching 28.30 L/kg in New Airport concrete-pond gills. The findings demonstrate marked site- and tissue-specific variation among the sampled ponds and support continued monitoring of aquaculture water and fish tissues, while generalised pond-type effects require independent pond-level replication.
Keywords: Clarias gariepinus, aquaculture, trace metals, pond water, fish tissues, tissue-to-water concentration ratio