Assessment of faecal contamination in selected concrete and earthen ponds stocked with African catfish, Clarias gariepinus

Abstract

Background: Microorganisms constitute significant fraction of the aquatic ecosystem and have been reported to be the cause of emerging novel infectious diseases in aquacultural practices. The prevalence of infectious diseases has been observed to depend on the interaction between fish pathogens and the aquatic environment. This study was conducted to assess the levels of faecal pollution markers in catfish (Clarias gariepinus) and their growing waters in selected earthen and concrete ponds in the teaching and research fish farm of the Federal University of Technology, Akure (FUTA), Nigeria in the dry (February-April) and wet seasons (May-July) of the year.

Methodology: Two earthen and 2 concrete ponds were randomly selected as sampling sites due to their frequent usage. A total of 120 grabs of catfishes from the earthen (n=60) and concrete (n=60) ponds, and 84 pond water samples from earthen (n=42) and concrete (n=42) ponds, were randomly collected over a 6-month period of study. Enteric bacteria count in the water and catfish samples were determined using membrane filtration and pour plate methods respectively. The physiochemical characteristics of the water samples were determined using standard methods. The rate of bioaccumulation of faecal indicator bacteria was obtained by dividing the log count of each organism in the catfish by the corresponding log count in the growing waters.

Results: Faecal coliforms count (log₁₀ CFU/100ml) in the catfish from concrete and earthen ponds ranged from 1.41 to 2.28 and 1.3 to 2.47, and in the growing waters; 1.43 to 2.41 and 1.50 to 2.80 respectively. There was positive correlation of faecal coliforms with alkalinity of water samples from the earthen (r=0.61) and concrete ponds (r=0.62). Salmonella and faecal coliforms had the highest and least bioaccumulation in catfish raised in earthen pond while Salmonella and enterococci had the highest and least bioaccumulation in catfish raised in concrete pond respectively. Faecal coliforms and Escherichia coli had the highest and least counts in water samples from the earthen pond during the dry and wet months while Salmonella and E. coli had the highest and least counts in water samples from the concrete pond during the dry and wet months.

Conclusion: High levels of bacterial faecal pollution markers in water samples and catfishes from the earthen and concrete ponds are reported in this study. Physicochemical characteristics and seasonality played major roles in the rate of bioaccumulation of the faecal pollution markers in catfishes raised in both earthen and concrete ponds.