Qualidade da água e biofiltragem em Sistema de Recirculação Aquícola (RAS) de tilápia: relato de caso

Abstract

This study describes a case report involving chemical instability and biofiltration failures in a recirculating aquaculture system (RAS) used for the super-intensive culture of tilapia in the Southwest of Parana. The research was motivated by the need to understand the factors that compromised water quality, caused significant mortality, and affected productive performance throughout the cycle. The objective of the study was to analyze the causes of system instability by relating the structural conditions and their impacts on the fish. For this purpose, monitoring data of total ammonia, nitrite, pH, alkalinity, dissolved oxygen, and temperature were evaluated, as well as information related to management routines and zootechnical performance. The results demonstrated that the absence of a functional biofilter, the accumulation of solids, and the low initial alkalinity prevented nitrification and favored peaks of toxic nitrogenous compounds. These events were associated with the mortality observed during the first months of culture and with the reduction in weight gain and feed conversion. The corrective interventions adopted, such as liming, increased water renewal, flow adjustments, and intensified waste removal, contributed to partially reducing the effects of instability but did not eliminate the structural cause of the problem. It is concluded that RAS systems depend directly on the efficiency of biofiltration, solid control, and the maintenance of alkalinity to ensure chemical stability and satisfactory performance, as these elements are essential for safe and efficient operation in super-intensive cultures.