Stocking densities were evaluated for the rearing tambaqui in an RAS system. Experiment 1 used juveniles weighing 0.54 g at the following densities for 15 days: D_0.3—0.3; D_0.6—0.6; and D_0.9—0.9 kg m⁻³. Experiment 2 used juveniles weighing 8.22 g at the following densities for 75 days: D_0.8—0.8; D_1.2—1.2; and D_1.6—1.6 kg m⁻³. Experiment 3 used juveniles weighing 142.18 g at the following densities for 75 days: D₂—2; D₄—4 and D₆—6 kg m⁻³. In Experiment 1, density did not influence performance (p > 0.05), with the exception of biomass, which was greatest in D_0.9 (p < 0.05). In Experiment 2, final weight, weight gain and daily weight gain were highest for D_0.8 (p < 0.05), as was triglycerides (p < 0.05), whereas biomass increased with increasing density (p < 0.05). In Experiment 3, weight, weight gain and daily weight gain were greater for D₂ and D₄ (p < 0.05), while final biomass was lowest for D₂ (p < 0.05). Hemoglobin was lower for D₄ and D₆ (p < 0.05), while cholesterol and glucose levels were higher for D₂ and D₆ (p < 0.05). Colossoma macropomum demonstrated adaptive capacity for reared in RAS at high stocking densities.

The effects of different stocking densities on the growth and physiology of juvenile Piaractus brachypomus were evaluated in two experiments. Experiment I used juveniles weighing 1.5 ± 0.4 g at the following densities for 20 days: D_0.68—0.68 kg/m³; D_1.45—1.45 kg/m³; D_4.41—4.41 kg/m³; and D_7.17—7.17 kg/m³. Experiment II used juveniles weighing 6.66 ± 1.3 g at the following densities for 20 days: D_1.0—1.00 kg/m³; D_1.95—1.95 kg/m³; D_5.63—5.63 kg/m³, and D_7.90—7.90 kg/m³. Both experiments showed a reduction in dissolved oxygen levels in the water, with Experiment II showing a plateau effect from 2.34 kg/m³ (p < 0.05). Final weight, final length, weight gain, daily weight gain, and specific growth rate were inversely proportional to density (p < 0.05), while final biomass, feed intake, and feed conversion were directly related to density in both experiments (p < 0.05). At the end of Experiment II, plasma triglycerides decreased as stocking density increased (p < 0.05), and hemoglobin and mean corpuscular volume were higher at the lowest density (D_1.0) (p < 0.05). High stocking densities reduced dissolved oxygen, characterizing a hypoxic state in both experiments, affecting growth and some physiological parameters. Therefore, studies testing stocking densities for P. brachypomus in normoxic situations are still needed.

The study evaluated the impact of feeding rates (6, 8, 10, and 12% of biomass) on the growth and physiological responses of Colossoma macropomum × Piaractus brachypomus over 40 days. A total of 600 juveniles (1.61 ± 0.30 g, 4.1 ± 0.9 cm) were distributed in 12 tanks. Performance parameters were measured every 10 days, and biochemical, hematological, and somatic indices were analyzed after 40 days. Growth indicators such as final weight and feed conversion ratio improved with higher feeding rates during specific periods. Plasma glucose and red blood cells showed a quadratic response to feeding rates, while mean corpuscular volume increased proportionally. A 12% feeding rate was optimal for the initial 10 days, enhancing zootechnical indices. From 11 to 40 days, a 6% feeding rate is recommended, as growth performance did not significantly vary across rates. Feeding rates had minimal effects on biochemical, hematological, and somatic indices during the trial.

Hesperozygis ringens essential oil (HREO), rich in pulegone and limonene, has potential application in aquaculture due to its beneficial properties. This study evaluated the effects of dietary supplementation with HREO (0.0, 0.75, 1.0, and 2.0 g HREO kg feed⁻¹) for 30 days on the physiological responses of Colossoma macropomum before and after a simulated 4 h transport. Fish were sampled at four time points: before transport (Basal), immediately after transport (IAT), and at 24 h (AT24) and 48 h (AT48) post-transport. Growth performance and survival (>96%) were not affected by HREO. Hemoglobin concentration, mean corpuscular hemoglobin concentration (MCHC), and intestinal coefficient showed significant responses to dietary HREO. After transport, survival was 100% for all treatments, and hematological and biochemical parameters varied according to dose and recovery time, with 2.0 g HREO kg feed⁻¹ showing the most consistent benefits, such as stabilization of hemoglobin, MCHC, and plasma proteins during recovery at AT₂₄ and AT₄₈. Water quality parameters did not differ between treatments at transportation end. These findings suggest that dietary HREO may contribute to enhance the physiological responses to transport in C. macropomum, supporting its potential use as a sustainable nutritional strategy.

This study evaluated cherry tomato seedling production using pirapitinga RAS wastewater as the sole nutrient source in four substrate formulations: T1 (sand, gravel and coconut fiber), T2 (sand and gravel), T3 (gravel and coconut fiber), and T4 (sand and coconut fiber). No differences were observed for germination quality, germination percentage, seedling vigor index, germination vigor index, moisture content, total wet biomass, total dry biomass, or mortality. For small plants, leaf number (LN) was higher in T2 and lower in T4, while root length was greater in T3. The number of medium plants was higher in T3 and lower in T4; LN was higher in T1 and T2 and lowest in T3. For large plants, LN was higher in T1 and T2 and lower in T3; total length was higher in T1 and lower in T3 and T4. Visual differences in substrate water retention were observed: T4 exhibited rapid surface drying, T1 and T2 showed moderate moisture persistence, and T3 maintained surface water. Leaf yellowing was observed after 25 days, suggesting possible nutrient limitation or reduced nutrient availability at the measured pH. These findings indicate that substrate physical characteristics influence early seedling growth performance, whereas pirapitinga RAS wastewater can serve as a viable nutrient source.

This study evaluated the effects of feeding rates and frequencies on performance and physiological responses of pirapitinga (Piaractus brachypomus). A total of 896 juveniles (1.32 ± 0.60 g) were stocked at a density of 1 fish/L for 40 days in a recirculating aquaculture system (RAS). Four feeding rates, 6% (T6), 8% (T8), 10% (T10) and 12% (T12) of biomass, and two feeding frequencies, F2, at 08:30 and 16:00, and F4, at 08:30, 11:00, 13:30 and 16:00, were tested in a 4x2 factorial arrangement with four replicates. The results for the first 30 days showed an effect of feeding rate on growth parameters, but no effect for feeding frequency in general. Between 30 and 40 days, weight gain, specific growth rate showed an effect of feeding rate, with T6 being superior. The viscero (VSI) and hepatosomatic (HSI) indices were affected, with the lowest values for T12. When fed with F2, the lowest hemoglobin was for T6, while there was no difference among feeding rates with F4. Higher triglyceride levels were recorded when fed with F2, T6, and T8, while the lowest was for T12. Blood glucose only had an effect of feeding frequency, with higher values for F2. Hematocrit, total protein, cholesterol, and mesenteric fat index (MFI) were not affected by feeding rate nor feeding frequency. A twice-daily feeding frequency proved sufficient for juvenile P. brachypomus, with an average initial weight of 1.3 g and reared in RAS, and a 12% biomass feeding rate was most efficient.