The aim of this study was to evaluate the level of neuronal depression in juvenile tambaqui, Colossoma macropomum, exposed to geraniol (GRL) and citronellol (CTL) in immersion baths. A total of 36 juveniles weighing 35.2 ± 9.4 g were used, organised into six experimental groups: I—control (clean water); II—ethanol (water containing the highest volume of ethanol used in the anaesthetic pre-dilution); III—GRL induction (70 µL·L⁻¹); IV—CTL induction (90 µL·L⁻¹); V—GRL recovery; VI—CTL recovery. Electroencephalographic (EEG) recordings were performed for 300 s in each group. EEG tracings of the control and ethanol groups showed regular and similar activity. Upon exposure to the anaesthetics, irregularities were observed in the tracings showing neuronal excitability and increased amplitudes, mainly in the case of CTL. Overall, GRL-exposed fish showed depression of the central nervous system with low and regular tracings throughout induction, presenting a gradual recovery and stable tracings, which were consistent with an adequate general anaesthetic effect. On the other hand, fish exposed to CTL showed altered EEG activity during induction, that could be considered incompatible with an appropriate anaesthetic effect and smooth recovery, presenting high and irregular EEG tracing amplitudes.

Morphine is widely used as an analgesic in vertebrates, yet its cardiorespiratory safety and effective therapeutic range remain poorly explored in fish. This study investigated the dose-dependent effects of morphine on cardiac and respiratory parameters of juvenile tambaqui (Colossoma macropomum). Juveniles (25.95 ± 4.08 g) were randomly assigned to control, sham (0.9% saline) or morphine groups (24, 28, 32, 36 and 40 mg kg⁻¹, i.p.). Electrocardiogram (ECG) recordings were used to assess heart rate (HR), PQ, RR and QT intervals, and QRS amplitude, while opercular beat rate (OBR) and opercular beat intensity (OBI) were measured to evaluate respiratory responses. Morphine induced a significant dose-dependent bradycardia and QT prolongation, without affecting QRS amplitude or conduction integrity. Respiratory frequency and intensity also decreased with increasing doses, with responses plateauing above 32 mg kg⁻¹. The EC₅₀ for HR reduction was 27.18 mg kg⁻¹, aligning with a safe therapeutic range of 24–32 mg kg⁻¹. By establishing this dose–response dynamic, the study provides the first characterization of a physiologically safe therapeutic window of morphine in tambaqui and highlights its safety profile for cardiorespiratory parameters. Moreover, the present results demonstrate that the opioid system of juvenile tambaqui is functionally developed, providing a physiological basis for future studies on nociception and analgesic efficacy, with relevance to welfare-oriented practices in aquaculture.

As macrófitas aquáticas desempenham um papel fundamental nos ecossistemas aquáticos, influenciando a qualidade da água, a estabilidade dos habitats e a biodiversidade local. Este estudo teve como objetivo analisar a riqueza florística, a estrutura ecológica e a função ambiental das macrófitas aquáticas no reservatório da Universidade Federal Rural da Amazônia (UFRA), em Castanhal-PA. Para isso, utilizou-se a metodologia dos quadrados de Howard-Williams (1975), permitindo a amostragem sistemática da vegetação aquática. Foram identificadas 45 espécies pertencentes a 24 famílias botânicas, com predominância de Poaceae, Cyperaceae e Asteraceae. Espécies como Cabomba aquatica e Utricularia gibba destacaram-se pela sua relevância ecológica, atuando como substrato e bioindicadores ambientais, contribuindo para a retenção de nutrientes no ecossistema. Além disso, a análise dos parâmetros físico-químicos indicou que a água do reservatório se classifica como Classe II, adequada para aquicultura e recreação, conforme a Resolução CONAMA nº 357/2005. Os resultados reforçam a importância das macrófitas na estabilidade ecológica dos ecossistemas aquáticos, evidenciando sua função na retenção de nutrientes e no suporte à biodiversidade. Esses achados destacam a necessidade de estudos contínuos para avaliar a dinâmica dessas comunidades vegetais e sua relação com fatores ambientais.