Effects of Melissa officinalis L. Essential Oil in Comparison with Anaesthetics on Gill Tissue Damage, Liver Metabolism and Immune Parameters in Sea Bass (Lateolabrax maculatus) during Simulated Live Transport

SIMPLE SUMMARY: The traditional method of transporting live fish in water often involves long driving durations and a high transport density. These conditions can induce stress in the fish, severely effecting their immune system and organs, such as the gills, liver and gut. In this study, Melissa officinalis L. essential oil (MOEO) and two kinds of common anaesthetics were applied to live fish during transport to reduce mortality and stress responses in sea bass (Lateolabrax maculatus). Sea bass were transported for 72 h with a transport density of 250 kg/m(3) in different concentrations of MOEO and anaesthetics. The effect of MOEO on tissue damage, energy metabolism and on some oxidative stress and immune parameters of the animals were determined and compared with the effect of the anaesthetics. The results of this study indicated that the energy metabolism, gill and liver tissue damage and immune responses of anesthetized and sedated fish were lower than the control fish. MOEO can reduce the effects of stress and tissue damage in live fish when used as a novel sedative and anaesthetic. ABSTRACT: In the current study, Melissa officinalis L. essential oil (MOEO), a novel sedative and anaesthetic, was employed in transport water to obtain a lower stress effect and higher survival rate for live marine fish. The effect of MOEO and various types of anaesthetics, administered at a low temperature on gill morphology, liver function and immunological parameters of living sea bass (Lateolabrax maculatus) subjected to transport stress, was evaluated to optimize the anaesthetic and sedative concentrations during live sea bass transport. Light microscopy and scanning electron microscopy of sea bass, subjected to simulated live transport for 72 h, demonstrated that the changes in the morphological characteristics of gill tissue treated with 40 mg/L MOEO (A3 group) were minimal in comparison to those observed in untreated sea bass. The results of pyruvate kinase (PK), phosphofructokinase (PFK), hexokinase (HK), hepatic glycogen (Gly), superoxide dismutase (SOD), lipid peroxides (MDA) and Caspase-3 assays indicated that the glycolysis rate, energy consumption, lipid peroxidation and hepatocyte apoptosis were the lowest in the A3 group. The values of the two immune parameters, lysozyme (LZM) and fish immunoglobulin M (IgM), indicated the strongest immunity ability in the A3 group. After 12 h recovery, sea bass treated with 30 mg/L MS-222 (B group) displayed a 100% survival rate, sea bass treated with 20 mg/L (A2 group) and 40 mg/L (A3 group) MOEO displayed a 96% survival rate, sea bass treated with 20 mg/L eugenol (C group) had a 94% survival rate, and untreated sea bass (CK group) had a 50% survival rate. Therefore, the addition MOEO to the transport water had anaesthetic and sedative effects similar to MS-222 and eugenol. The results confirmed that the addition of MOEO to the transport water could reduce tissue damage, energy metabolism, and the oxidative stress response in sea bass during transport.