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

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.

Toxic Effects of Aflatoxin B1 in Chinese Sea Bass (Lateolabrax maculatus)

This study was performed to assess the effects of dietary aflatoxin B1 (AFB1) on the growth, antioxidant and immune response, digestive enzyme activities, and intestinal morphology of Lateolabrax maculatus during a 56-day feeding trial. Four diets were formulated including 0, 0.1, 0.5, and 1.0 mg/kg of AFB1. Each diet was randomly assigned to 3 fish tanks with 40 fish per tank. Results indicated that the fish’s final body weight, weight gain rate, specific growth rate, feed intake, condition factor, viscerosomatic index, hepatosomatic index, and intestinesomatic index decreased (p < 0.01) as dietary AFB1 increased. AFB1 levels in diets increased (p < 0.05) serum total antioxidant capacity (TAOC), superoxide (SOD), catalase, malondialdehyde (MDA), alkaline phosphatase (AKP), and lysozyme (LZM), and increased (p < 0.05) the TAOC, SOD, MDA, AKP, LZM, and immunoglobulin M in the livers of the fish. Dietary AFB1 decreased (p < 0.05) intestinal trypsin activity and induced intestinal injury. In summary, dietary AFB1 up to 1.0 mg/kg was toxic to L. maculatus as judged by reduced growth, enhanced antioxidant and immune response, decreased intestinal trypsin activity, and impaired intestinal morphology.

HSP90 and HSP70 Families in Lateolabrax maculatus: Genome-Wide Identification, Molecular Characterization, and Expression Profiles in Response to Various Environmental Stressors

Heat shock proteins (HSPs) are a large class of highly conserved chaperons, which play important roles in response to elevated temperature and other environmental stressors. In the present study, 5 HSP90 genes and 17 HSP70 genes were systematically characterized in spotted seabass (Lateolabrax maculatus). The evolutionary footprint of HSP genes was revealed via the analysis of phylogeny, chromosome location, and gene copy numbers. In addition, the gene structure features and the putative distribution of heat shock elements (HSEs) and hypoxia response elements (HREs) in the promoter regions were analyzed. The protein-protein interaction (PPI) network analyses results indicated the potential transcriptional regulation between the heat shock factor 1 (HSF1) and HSPs and a wide range of interactions among HSPs. Furthermore, quantitative (q)PCR was performed to detect the expression profiles of HSP90 and HSP70 genes in gill, liver, and muscle tissues after heat stress, meanwhile, the expression patterns in gills under alkalinity and hypoxia stresses were determined by analyzing RNA-Seq datasets. Results showed that after heat stress, most of the examined HSP genes were significantly upregulated in a tissue-specific and time-dependent manners, and hsp90aa1.1, hsp90aa1.2, hsp70.1, and hsp70.2 were the most intense responsive genes in all three tissues. In response to alkalinity stress, 11 out of 13 significantly regulated HSP genes exhibited suppressed expression patterns. Alternatively, among the 12 hypoxia-responsive-expressed HSP genes, 7 genes showed induced expressions, while hsp90aa1.2, hsp70.1, and hsp70.2 had more significant upregulated changes after hypoxic challenge. Our findings provide the essential basis for further functional studies of HSP genes in response to abiotic stresses in spotted seabass.