Effects of clove oil, essential oil of Lippia alba and 2‐phe anaesthesia on juvenile meagre, Argyrosomus regius (Asso, 1801)

The objectives of this experiment were to (i) determine the efficacy of essential oils of clove (CO) and Lippia alba (EOLA) to induce deep anaesthesia in juvenile specimens (49.0 ± 6.2 g body mass, 16.6 ± 0.8 cm; n = 8 per treatment) of meagre (Argyrosomus regius); and (ii) study the feasibility of these substances, together with 2‐phenoxyethanol (2‐PHE), as potential sedatives [low concentration: (i) EOLA: 12 mg L⁻¹; (ii) CO: 1 mg L⁻¹; and (iii) 2‐PHE: 33 mg·L ⁻¹; n = 8 per treatment] for live fish transport of this species. All test were performed at a constant temperature (18°C). Thus, the main primary stress indicator (plasma cortisol) and secondary factors (plasma metabolites) were evaluated. In addition, growth hormone (GH) mRNA expression was also evaluated in the pituitary gland. The results indicated that EOLA is considered to be effective for deep anaesthesia when the concentration is close to 160 mg L⁻¹, while CO produces the same effect when lower concentrations are added (40–50 mg L⁻¹). Regarding sedative concentrations, a significant ~3‐fold increase in plasma cortisol levels was detected in the EOLA group when compared to control specimens. In addition, glucose levels were not reduced and significantly increased (~1.6‐fold) for 2‐PHE in relation to the control fish. None of the anaesthetics promoted a significant difference for GH expression with respect to the control group, but a significant ~2‐fold increase for 2‐PHE treatment with respect to the EOLA exposition was found in this gene expression. Results show that none of the anaesthetics analysed, at least in the ranges of concentrations used in this study (EOLA 12 mg L⁻¹, CO 1 mg L⁻¹, 2‐PHE 33 mg L⁻¹), are recommended for live fish transport, as shown by the absence of inhibition on the stress parameters assessed.