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 objective of this work was to evaluate the predation rates of two genera of Odonata Miathyria Kirby, 1889 and Erythemis Hagen, 1861 in post-larviculture of tilapia with and without availability of Chironomidae. For that, 3 experiments were carried out, the first to analyze which size scale of these two genera would be more efficient in the predation of tilapia and the other 2 experiments with the selected size scales, to analyze the predation rates on tilapia with different Odonata densities, with and without availability of the aquatic insect Chironomidae. For statistical analysis of the data, an analysis of variance (ANOVA) was applied with the Duncan test searching for the means in all experiments. In experiments 2 and 3 a linear regression model was also applied. In experiment 1, there were significant differences between treatments, and in the phase with Miathyria the predation of tilapia post-larvae was higher among odonates that corresponded to the size scale from 7.1 to 9.9 mm and therefore the scale was also selected for the next experiments. For Erythemis, the consumption of tilapia was higher in the size scale between 12.1 to 14,2 mm. In the following experiments, there were significant differences between treatments. With the increase in Odonata densities the predation of the fish was greater. With the availability of Chironomidae, the consumption of tilapia post-larvae decreased. The consumption of Chironomidae was higher than the consumption of fish in experiment 3. Miathyria proved to be more efficient than Erythemis in predation and the use of Chironomidae can be a sustainable alternative for post-larvae predation control on fish farms.

Imaturos de libélula são encontrados em uma vasta quantidade de ambientes aquáticos de água doce, dentre eles, os tanques escavados para piscicultura. Como são predadores durante a fase aquática, acabam por causar grandes prejuízos nas fases iniciais de produção da aquicultura de água doce. No entanto, os estudos de quais são as libélulas mais comuns em tanques de piscicultura ainda são escassos no Brasil, sendo que este é primeiro passo para se pensar num controle eficaz. Por esse motivo, coletamos imaturos de libélula (Odonata) com rede “D” e macrófitas entre outubro de 218 e março de 2019. As variáveis físico-químicas foram medidas com kits de qualidade da água, sendo que se mantiveram dentro dos parâmetros para piscicultura definidos pelo CONAMA, com exceção da temperatura. Dos 692 imaturos coletados, encontramos 12 gêneros distribuídos nas duas subordens de Odonata, sendo Miathyria Kirby, 1889 e Erythemis Hagen, 1861 os mais abundantes. Após análise de correspondência e análise de componentes principais, comprovamos que os gêneros mais raros têm menor correlação com a abundância, reforçando o valor atribuído a abundância relativa dos imaturos.

The effects of acute handling stress on the physiological and antioxidant responses of tambaqui (Colossoma macropomum) and the hybrid tambatinga (C. macropomum × Piaractus brachypomus) raised in a recirculating aquaculture system were investigated. Thirty juveniles of tambaqui (27.8 ± 2.8 g) and thirty of tambatinga (26.2 ± 3.1 g) were used. Six fish/group were captured and subjected to the sample to determine basal parameters. The remaining animals were chased with hand net for 3 minutes, exposed to air for 2 minutes and subjected to biometry. Blood and oxidative parameters were determined immediately after stress (IAE) and after 1h (1hAE), 24h (24hAE) and 48h (48hAE). Stress caused an increase in the hematocrit of tambaqui at IAE, with reduction after 48hAE. For glycemia, there were differences between the fish groups and collections with higher values for tambatinga and after IAE and 1hAE. Cholesterol in tambaqui increased after 24hAE and 48hAE, decreasing in hybrid after 24hAE with return to basal after 48hAE. SOD increased in IAE while in tambaqui the response only occurred after 48hAE, resulting in an increase in lipid peroxidation. Conclude that biometric management resulted in hemodilution in tambatinga, without recovery of basal parameters. However, the antioxidant system prevented lipid peroxidation.