Physical and chemical quality of water in closed recirculation system during the cultivation of Nile tilapia juveniles

The study aimed to evaluate the effect of the filter and time of cultivation of Nile tilapia juveniles in water quality in closed recirculating system. There were used 1,350 fingerlings of Nile tilapia (Oreochromis niloticus) in a randomized block experimental design and split-plot time with twelve treatments and three replicates. The treatments were a combination of two local of water harvesting (before the mechanical filter and after the biological filter) and six periods of cultivation (14, 28, 42, 56, 70 and 84 days), in a split plot arrangement. The water temperature, dissolved oxygen, oxygen saturation, electrical conductivity and pH did not affect the development of the fish in closed recirculating water. It was observed that the water collected after the biological filter had better physical and chemical quality than that collected before the mechanical filter. The dissolved oxygen levels in the water after the biological filter were higher (P<0.05) to those observed before the mechanical filter and there was a gradual linear reduction of dissolved oxygen concentrations in terms of days of cultivation. Concerning the values of total solids, total suspended solids, total ammonia and nitrate was observed that the reduction in water quality of the system was more evident (P<0.05) within 56 to 84 days.