EFEITO DA CONCENTRAÇÃO DE SÓLIDOS SEDIMENTÁVEIS SOBRE A QUALIDADE DA ÁGUA, HIGIDEZ E DESEMPENHO ZOOTÉCNICO DE JUVENIS DE TILÁPIA-DO-NILO (Oreochromis niloticus) EM TECNOLOGIA DE BIOFLOCOS (BFT)

Abstract

Aquaculture has established itself as one of the fastest-growing agro-industrial activities worldwide, playing a crucial role in ensuring global food security. This is particularly important due to the increasing demand for fish, as traditional fishing methods have failed to meet this demand and have remained stagnant for many years. Among the promising alternative systems, biofloc technology (BFT) stands out for combining environmental sustainability with production efficiency, since this technology can improve productivity with little or no water exchange. The objective of this research was to evaluate the effect of different concentrations of settleable solids on the gill health, zootechnical performance of juvenile Nile tilapia (Oreochromis niloticus), and water quality in BFT systems. Four experimental groups with different concentrations of settleable solids were used, with four replicates (7 fish per replicate), as follows: (i) a recirculating aquaculture system (RAS – CTL group); (ii) BFT20 with 20 mL L⁻¹ of settleable solids (SS); (iii) BFT60 with 60 mL L⁻¹ of SS; and (iv) BFT100 with 100 mL L⁻¹ of SS. The fish were maintained in circular polyethylene tanks with individual aeration, covered with black polyester mesh and lids, for six weeks. The following water parameters were assessed: temperature (T, °C), dissolved oxygen (DO, mg L⁻¹), pH, alkalinity (ALK, mg L⁻¹ CaCO₃), settleable solids (SS, mL L⁻¹), total ammonia nitrogen (TAN, mg L⁻¹), ammonia (NH₃, mg L⁻¹), nitrite (NO₂⁻, mg L⁻¹), and nitrate (NO₃⁻, mg L⁻¹). Gill histopathology was used to assess fish health. Productive performance was evaluated based on weight gain (g) and length (cm), apparent feed conversion ratio (FCR), and survival rate (SR). The means were subjected to analysis of variance, with a significance level of 5%. There were significant differences among groups in water quality variables. The BFT100 group, with the highest concentration of settleable solids (100 mL L⁻¹), showed the lowest dissolved oxygen levels at the end of the experiment (P < 0.0105). The control group (CTL) consistently maintained higher temperatures and pH values compared to the BFT60 and BFT100 groups (P < 0.05). There was no statistical difference in survival rate (SR) among the groups (P > 0.05). The CTL group showed higher final weight and length, as well as the lowest apparent feed conversion ratio (P < 0.05). Histological evaluations revealed gill tissue alterations, with greater incidence in the BFT60 and BFT100 treatments, likely due to fluctuations in the aquatic environment associated with higher SS concentrations. However, these changes were considered mild to moderate, with no evidence of irreversible lesions or association with mortality. Therefore, it is concluded that under the experimental conditions adopted, the tested concentrations did not cause significant morphological damage to the gill epithelium of O. niloticus.

Keywords: aquaculture, aquaculture sustainability, aquaculture systems, gill morphology.