An investigation of the effects of an artificial wetland on water quality and the consequent growth of Mozambique Tilapia (Oreochromis mossambicus) in an extensive fish production unit

Abstract: In South Africa freshwater aquaculture is currently dominated by the use of earthen dams to rear fish for production purposes. Rural fish farmers use river water for their aquaculture activities. In many areas in the Limpopo Province there are sewage treatment works that discharge directly into the rivers. A concern exists that this may pose a threat to the growth of fish. In view of this, a study on water quality management was done which looked at the effects of an artificial wetland on water quality and the consequent growth of Oreochromis mossambicus. To determine the effect of artificial wetlands on water quality, the water quality of the “untreated” water received at the fish dams was measured and compared with that of “treated” water that has flowed through an artificial wetland. The study took place between April and July 2014. The parameters measured were pH, temperature, dissolved oxygen, total ammonium, nitrite, nitrate and total phosphorous. Chemical variables ranged between; total phosphorous (0.08-0.33 mg.L-1), nitrate (1.0-3.0 mg.L-1), nitrite (0.04- 0.07 mg.L-1) and ammonium (0.1-0.77 mg.L-1). Results showed that ammonium concentrations were significantly different (P<0.05) in Dam A as compared to Dam B. However there was no significant difference (P>0.05) on phosphate, nitrate and nitrite concentration in both dams. The physical parameters ranged between: temperature (12.21-27.2 ºC), dissolved oxygen (2.45-9.17 mg.L-1) and pH (5.56- 7.06), but there was no significant difference (P>0.05) in physical parameters between the two dams. Growth measurements were recorded on commencement of the study and every two weeks until the end of the experiment. Results showed that fish growth in weight was slightly higher in a dam that receives “treated” water as compared to a dam that receives “untreated” water. This study revealed that the constructed wetland had an impact on water quality, and the improved water quality had an impact on the growth of fish in Dam A as compared to Dam B.M.Sc. (Aquatic Health