Spurge (Euphorbia rigida) exhibits anaesthetic effect in rainbow trout (Oncorhynchus mykiss) without altering plasma cortisol levels

Abstract

This study was conducted to investigate a potential new organic anaesthetic for aquaculture practices. Aqueous macerate of spurge stem (Euphorbia rigida) was obtained by adding 200 g of plant powder to 1.5 L of distilled water and applied to rainbow trout (Oncorhynchus mykiss) at 5 different concentrations (30000, 40000, 50000, 60000 and 70000 µL L−1) to determine induction (loss of equilibrium and deep anaesthesia) and recovery (recovery of equilibrium and full recovery) durations. In addition, plasma cortisol levels of fish within 0 hours were determined to evaluate stress response. It was determined that there were 4 concentrations that can be used as suitable anaesthetics for rainbow trout: 40000, 50000, 60000 and 70000 µL L−1. These concentrations provided deep anaesthesia in 196.67±1.45, 173.00±11.24, 138.33±8.29 and 136.33±5.23 seconds, respectively. Plasma cortisol levels of the mentioned groups were measured as 4.49±1.04, 8.64±0.73, 8.18±0.64 and 9.64±0.78 ng mL−1, respectively. On the other hand, the plasma cortisol level of the control group (anaesthetized with 2-phenoxyethanol) was 10.95±0.89 ng mL−1. These findings suggest that 40000–70000 µl L−1 of E. rigida can be used as an alternative anaesthetic in rainbow trout. However, further studies need to be conducted to evaluate the long term effects of the plant, especially in consecutive use.