Water Quality of Trickling Biological Periwinkle Shells Filter for Closed Recirculating Catfish System
Studies were carried on the design, efficiency and economics of trickling biological periwinkle shells filter in recirculating aquaculture systems for catfish production. The designed biofilter and other system components were constructed, assembled and commissioned for pilot catfish production. The system with the designed biofilter served as the treatment system, while that without biofilter served as the control system. Data were collected daily (except for BOD5) on water quality parameters such as total ammonia-nitrogen (TAN), nitrite-nitrogen, unionized ammonia–nitrogen (UAN), pH, dissolved oxygen (DO), surface water temperature, secchi transparency, total alkalinity, Chloride content, total hardness free carbon dioxide and biochemical oxygen demand (BOD). The Total length and weight of fish stocked in the treatment and control systems were measured at the beginning of the study and subsequently every four weeks. Results showed that total ammonia–nitrogen for the treatment system ranged from 0.00 to 4.00 ppm, with a mean of 1.26±0.92 ppm, while that of the control varied from 0.00 to 6.50 ppm, with a mean of 2.23±1.80 ppm. The nitrite–nitrogen values of the treatment system ranged from 0.00 to 1.80 ppm, with a mean of 0.67±0.40 ppm, while that of the control system ranged from 0.00 to 2.50 ppm, with a mean of 1.18±0.79 ppm. The un-ionized ammonia–nitrogen values for the treatment system varied from 0.000 to 0.022 ppm, with a mean of 0.007±0.006 ppm, while that of the control system ranged from 0.000 to 0.036 ppm, with a mean of 0.015±0.016 ppm. Results of fish growth showed that final fish weight for the treatment system ranged from 287.50 to 1280.00 g, with a mean of 765.35±259.24 g, while that of the control ranged from 50.00 to 800.00 g, with a mean of 490.31±185.65 g. Mean value of final fish weight stocked in the treatment system was significantly (p<0.05) higher than that of the control. Apart from total hardness, nitrite–nitrogen and unionized ammonia-nitrogen the mean values of all other water quality parameters for the treatment system were not significantly (p>0.05) different from that of the control system. It is therefore concluded that the trickling biological periwinkle shells filter provided adequate biological water treatment for closed recirculating catfish system.
Keywords: Water quality, Periwinkle shells biofilter, recirculating catfish system