The hemodynamic activity of Melipona flavolineata workers was evaluated during restraint stress for a period of 30 min. The observed parameters were power variation in the elapsed time, and subsequently, six periods of one second were divided and called A, B, C, D, E and F; in each period, the electrocardiographic parameters were evaluated: spike frequency, amplitude, spike intervals and spike duration. The experiment was carried out with eight worker bees of M. flavolineata, for which electrodes of a nickel–chromium alloy were made. The bees were previously anesthetized with isoflurane and properly contained and fixed in a base for stereotaxis in which the electrode was implanted. All these procedures were performed inside a Faraday cage. The results showed power oscillations during the recording, with the highest energy level being between 300 and 600 s. Spike frequency, spike amplitude, interval between spikes and spike duration parameters underwent changes during the restraint stress period. Thus, the cardiac activity of M. flavolineata can be used as a biomarker and can be used to clarify physiological issues or alterations caused by toxic agents and indicate risk factors for these animals.

Manganese (Mn²⁺) is an abundant chemical element in the earth’s crust and is present in soil, water, and industrial environments, including mining, welding, and battery manufacturing. Manganese (Mn) is an essential metal needed as a cofactor for many enzymes to maintain proper biological functions. Excessive exposure to Mn in high doses can result in a condition known as manganism, which results in disorders of the neurological, cardiac, and pulmonary systems. The aim of this study was to assess cardiac susceptibility to manganese intoxication in Colossoma macropomum subjected to a fixed concentration of 4 mg/mL for a period of up to 96 h. This study used 45 Tambaquis (30.38 ± 3.5 g) divided into five groups of 9 animals/treatment. The treated groups were exposed to the manganese concentration for a period of 24, 48, 72, and 96 h, after which the animals’ ECGs were recorded, showing heart rate, R-R interval, P-Q interval, QRS complex duration and S-T interval. The results showed that cardiac activity decreased as the contact time increased, with an increase in the P-Q and S-T intervals. This indicates that the breakdown of circulatory homeostasis in these animals was caused by contact time with manganese.

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.

The present study aimed to characterize the behavior and evaluate the electromyographic (EMG), electrocardiographic (ECG), and respiratory responses of Nile tilapia (Oreochromis niloticus) when exposed to different concentrations of Camphor (CPR) as a potential anaesthetic in immersion and recovery baths. The goal was to determine the impact of CPR on muscle, cardiac, and respiratory functions, and assess its suitability as an anesthetic for tilapia. Therefore, juvenile fish (38.2 ± 5.5 g) were acclimatized in aquaria for 20 days under controlled environmental and water quality conditions. Four concentrations of CPR (150, 200, 250 and 300 mg L⁻¹) were used in immersion baths to evaluate behavioral, EMG, ECG changes and recordings of opercular beats during the short-term treatment (5 min of exposure). The latency time for loss of the postural reflex was dependent on the CPR concentration. The EMG recordings demonstrated muscle activity during treatment and recovery. The ECG and opercular beat recordings demonstrated a decrease in heart and respiratory rates, with changes in the recorded tracings being more evident at higher concentrations. However, the use of a concentration of 300 mg L⁻¹ makes the cardiac and respiratory effects more evident, with changes in the tracing, which can harm the animal’s hemodynamics. However, lower concentrations (150 mg L⁻¹) showed tachycardia and opercular hypermotility, demonstrating changes not compatible with anesthesia. This article demonstrated that CPR in high concentrations can be harmful to the hemodynamics of tilapia, causing electrocardiographic and respiratory changes for a long period, even after recovery of muscular activity and postural reflex.

A mortality of bees (Apis mellifera) caused by fipronil intoxication, due to its indiscriminate use in crops, has long been attracting the scientific community’s attention, either due to its acute or residual effects. In this study, we assessed the cardiac activity as a biomarker of fipronil intoxication through electrophysiological recordings of bees. Eighteen foragers, from the apiary of EMBRAPA—Eastern Amazon (Belém-Pará), bees were previously anesthetized at low temperature (− 10 °C) for 5 min and properly restrained and fixed on a stereotaxic base, where electrodes were implanted. All these procedures were carried out within a Faraday cage. Eighteen bees were used in the study. Worker bees engaged in foraging activities were selected. The bees were divided into a control group and a group treated with fipronil at 0.025 mg/bee (n = 9). The recordings lasted for 4 min and were evaluated at 1-s intervals represented by the following letters: A = (2–3 s), B = (59–60 s), C = (119–120 s), D = (179–180 s), and E = (239–240 s). The results showed that fipronil reduced the frequency and intensity of cardiac activity, exhibiting rapidly evolving effects, and promoting a disruption of homeostasis in bee hemodynamics. Through the obtained data, it was observed variation in spike amplitude, with a loss of cardiac strength and magnitude of the electrical impulse in the bee’s heart during exposure to fipronil.