Evaluation of some water quality parameters in a closed aquaculture recirculating-water system, submitted to diferent loads of fish

Abstract

Utilizing different loadings of biomass of the Nile Tilapia Oreochromis niloticus and rainbow trout Oncorhynchus mykiss, some water quality parameters were evaluated in a closed aquaculture recirculating system. The systems is integrated by six culture tanks, a sedimentation cistern, two submerged bio-filters, a fast sand filter, two pumps, a reconditioning-water reservoir and a unit of ultraviolet light lamps. Fishes were fed twice a day for 120 days with 2% of their total biomass. The following water quality parameters were recorded: water temperature, dissolved oxygen, pH, total ammonium nitrogen (TAN), ammonia, nitrate and chemical oxygen demand. The data were analyzed with a one-way ANOVA to determine statistical differences in the components of the system. The average values of TAN and nitrate indicated a high efficiency of the nitrification process at different fish loading of biomass. About 50% of TAN and more than 90% of ammonia was stripped into the atmosphere and this explains the low levels measured in the other components of the system. Other causes that contribute to the removal of nitrogen compounds were the assimilation by microorganism accumulated in the bottom of the sedimentation tank and the absorption and adsorption by the sludge. Results showed that the water quality parameters were satisfactory for 99% survivorship and an acceptable growth rate for both fish species.