Dietary L-carnitine supplementation for heat stressed juvenile pearl gentian grouper(Epinephelusllanolatus (Epinephelus♂×Epinephelusfuscoguttatus♀): Effects on the antioxidant enzyme, survival, and gene expression

Abstract

The effects of increasing dietary inclusion levels of L-carnitine at 0 (control group) 200, 400, 600, 1200, 1400, and 1600 mg/kg were evaluated in juvenile hybrid groupers exposed to heat shock stress. The feeding trial was conducted for eight weeks. After the feeding trial, hybrid groupers were subjected to a heat stress test for an hour at a temperature of 36 °C to determine the influence of the treatments on survival, biochemical parameters, and gene expression. The results of the current study showed that the survival rate of hybrid grouper was low in fish fed the control diet. A large number of survivors were observed in the treatment group with 400 mg/kg L-carnitine supplementation (LC 400), obtaining the highest survival rate. Heat stress decreased (P < 0.05) the activities of alkaline phosphatase and acid phosphatase in the control group but was increased in fish fed the LC 400 diet. Additionally, in the LC 400 treatment, malondialdehyde content decreased considerably (P < 0.05) compared to LC0. Hybrid grouper exposed to a high temperature of 36 °C for 1 h without L-carnitine (LC0, control group) supplementation showed the most increased Aspartate Aminotransferase activity (2.04 U L−1). Additionally, the LC 400 group reached the maximal value for the expressions of genes in the PPARs (peroxisome proliferator-activated receptors) signaling pathway, which showed a tendency of downregulation and, subsequently, up-regulation. The gene expression of FAS (fatty acid synthase) was discovered upstream and downstream (P < 0.05). The lowest mRNA level was found in the lowest L-carnitine supplementation treatment (200 mg/kg). A CPT-1 (carnitine palmitoyltransferase) that controls fatty acid oxidation showed upstream and downstream activity in response to increasing doses of L-carnitine supplementation. Our findings showed that dietary supplementation with L-carnitine 400 mg/kg reduced heat stress-related mortality and oxidative damage by enhancing the survival and oxidative enzymes of grouper, which provides a nutritional method of minimizing the consequences of heat exposure.