Novel insights into eugenol anaesthesia in poeciliid larvae: Preliminary study of gill histology

Abstract

The increasing use of fish in research emphasizes the need for effective and safeanaesthetic protocols, particularly for early life stages. Eugenol has been proposed asa promising anaesthetic, yet information regarding its effects on Cnesterodon decem-maculatus larvae remains scarce. This study assessed anaesthesia and recovery times,as well as gill tissue integrity, in larvae exposed to different eugenol concentrations.A randomized controlled trial was conducted using four treatment groups (6, 12.5,25 and 50 mgL1) and a control group (10 mgL1 ethanol). Significant differences were observed in both anaesthesia and recovery times across treatments (p < 0.05).Morphometric analyses showed that branchial filament area was significantly smallerin all eugenol-treated groups compared to the control (p ≤ 0.02), and filament perimeter was also significantly reduced in all treatments (p < 0.001). Regarding necrosis, larvae exposed to 6 and 50 mgL1 exhibited significantly more necrotic foci than controls (p < 0.001). Necrosis was highest at 6 mgL1, decreased at 12.5 and 25 mgL1 (p < 0.01) and increased again at 50 mgL1 (p < 0.001). No significant dif-f vacuolization (p ≥ 0.08). However, oedema was higher at 6 mgL1 than at12.5 mgL1 (p = 0.02), and congestion was lower at 12.5 mgL1 than 25 mgL1(p = 0.04). Overall, the results indicate that 12.5 mgL1 eugenol provides effectiveanaesthesia with minimal histological alterations, representing the optimal concentra-tion for use in C. decemmaculatus larvae.