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

Background This study was carried out to monitor the levels of faecal pollution markers in catfish (Clarias gariepinus) and their growing waters in selected earthen and concrete ponds. Water and catfish samples were collected weekly in the months of February, March, April, May, June and July, 2019. The concentrations of enteric bacteria in the water and catfish samples were determined using membrane filtration and pour plate methods, respectively. The rate of bioaccumulation of faecal indicator bacteria was obtained by dividing the log concentration of each organism in catfish by the corresponding log concentration in the growing waters. Result The concentration of faecal coliforms in catfish samples from concrete and earthen ponds ranged from 1.41 to 2.28 log10 CFU/100 ml and 1.3 to 2.47 log10 CFU/100 ml respectively and in growing waters from the concrete and earthen ponds; 1.43 to 2.41 log10 CFU/100 ml and 1.50 to 2.80 log10 CFU/100 ml respectively. Faecal coliforms exhibited positive relationships with alkalinity in 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, respectively, whereas Salmonella and enterococci had the highest and least bioaccumulation in catfish raised in concrete pond, respectively. Faecal coliforms and E. coli had the highest and least counts in water samples from the earthen pond during the dry and wet months, Salmonella and E. coli had the highest and least counts in water samples from the concrete pond during the dry and wet months. Conclusion There were high levels of bacterial faecal pollution markers in water and C. gariepinus from the earthen and concrete ponds. Physicochemical characteristics of the water and seasonality played major roles in the rate of bioaccumulation of the faecal pollution markers in C. gariepinus raised in the earthen and concrete ponds.

Ecological Impacts of the African Catfish Clarias Gariepinus at Environmental Protection Area in Southeastern Brazil

The African catfish (Clarias gariepinus) is considered one of the most important species of catfish for aquaculture. It has a great capacity to withstand several stress factors, such as harsh abiotic conditions, in addition to wide feeding flexibility. However, the species was detected in the Guapimirim Environmental Protection Area in southeastern Brazil, threatening native fish diversity and ecosystem functioning of this ecosystem. In 2018, during the dry and wet seasons, samples of the fish community were collected at thirty-two sites of the Guapi-Macacu River, in addition to abiotic variables (salinity, pH, temperature, turbidity, dissolved oxygen, and transparency) to diagnose which factors influence the distribution of the alien species along the river. Multivariate analyses indicated that African catfish dominate the region in the buffer zone to the Environmental protection area, benefiting from higher levels of dissolved oxygen and temperature. However, C. gariepinus does not dominate yet the most protected area of Guapimirim, where the highest percentage of native fish species inhabit. Climate change associated with changes in abiotic factors might significantly contribute to the dominance of the invasive alien species in this protected area, which might colonize the entire river.