Electromyography and oculomotricity as markers of benzocaine anesthesia in juvenile tambaqui (Colossoma macropomum)

Aquaculture is increasingly focused on management practices that take into account animal welfare and stress reduction; hence, the demand for effective and low-cost anesthetic substances is growing, in line with the increase in aquaculture yields. The assessment of the anesthetic potential of substances is carried out through various physiological parameters, including electromyography (EMG). This technique, when applied to fish, allows a comprehensive evaluation of general anesthesia, providing evidence of efficacy and potency. When combined with other markers, such as oculomotricity, EMG can provide a full and reliable picture of general anesthesia. Thus, the objective of this study was to evaluate the association of EMG with oculomotricity as markers of anesthetic response. For this purpose, juvenile tambaqui (Colossoma macropomum) were subjected to immersion baths in three concentrations (60 mg L-1, 80 mg L-1, and 100 mg L-1) of benzocaine (BZE). All concentrations induced loss of postural reflex in a dose-dependent manner, with the 60 mg L-1 concentrations showing shorter latency. EMG revealed that the three tested concentrations of BZE resulted in a gradual decrease in muscle tone until the complete absence of dorsal muscle contraction. In the oculomotricity parameter, we observed the cessation of saccadic eye movement at all tested concentrations. This demonstrates that oculomotricity is an effective marker for determining the complete loss of postural reflex. In conclusion, the combination of EMG and oculomotricity offers a robust and effective approach to assessing the anesthetic response in fish. These findings have significant implications for the management of animal welfare in aquaculture, providing valuable and alternative tools to ensure that anesthetic procedures are carried out effectively and safely.