Zootechnical and hematobiochemical parameters, lipid profile, oxidative status, and intestinal morphology of Piaractus brachypomus in the early grow-out phase (70 g) at different stocking densities in RAS and BFT systems

Abstract This study evaluated the effects of two rearing systems – recirculating aquaculture system (RAS) and biofloc technology (BFT) – as well as two stocking densities (3.75 and 7.5 kg m⁻ 3 ) on the performance, physiology, lipid profile, oxidative status and intestinal health of Piaractus brachypomus (70.75 ± 0.72 g, 15.87 ± 0.30 cm) over 60 days. BFT exhibited higher concentrations of dissolved oxygen, nitrite, nitrate, and alkalinity compared to RAS. The lower density (3.75 kg m⁻ 3 ) resulted in greater final weight and length, weight gain, daily gain, specific growth rate, and improved feed conversion, whereas the higher density (7.5 kg m⁻ 3 ) led to greater final biomass, feed intake and survival. Fish reared in RAS presented higher levels of plasma glucose, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, albumin, total proteins, and hepatic enzyme activities (alanine aminotransferase and aspartate aminotransferase), whereas fish reared in BFT showed higher erythrocyte counts, mean corpuscular hemoglobin concentration, triglycerides, very low-density cholesterol, and urea. Histologically, fish maintained in BFT displayed taller intestinal mucosal folds, whereas those in RAS showed better mucosal integrity and a higher density of goblet cells. No changes in fish oxidative status were detected among the evaluated systems or stocking densities. Furthermore, the stocking density of 3.75 kg m⁻ 3 favored greater hepatic lipid deposition. Taken together, the results indicate that P. brachypomus demonstrates high physiological and morphological plasticity, maintaining satisfactory productive performance in both intensive systems. Stocking density was the main modulating factor, with better growth and anabolic metabolism indices at the lowest density.