Pre-winter feeding high-fat diet with caffeic acid phenethyl ester attenuates weight loss and improves health and muscle quality in grass carp during overwintering.

High-fat diets (HFD) are commonly used to fatten fish before overwintering; however many species of fish have limited tolerance to HFD. This study investigated the effects of supplementing HFD with caffeic acid phenethyl ester (CAPE) on overwintering performance in grass carp. A total of 300 grass carp (initial body weight 620.08 ± 1.32 g) were randomly divided into 5 groups with 3 replicate net cages in a pond, and fed a normal-fat diet (5% lipid, reference group [RFG]), or HFD (10% lipid) without or supplemented with different levels of CAPE (0, 400, 800, and 1200 mg/kg, named Control, C400, C800, and C1200, respectively). The experimental fish were fed for 40 d before overwintering, followed by a 154-d overwintering period. Growth performance did not differ among groups after the feeding period (P > 0.05). Post-overwintering, the fish in the HFD group maintained a higher body weight than those in the Control group (P < 0.001), while the CAPE-supplemented groups exhibited the least overall weight loss (P < 0.001). Compared to the RFG, the HFD showed a significantly lower rate of intraperitoneal fat loss but a significantly higher rate of hepatopancreas triglyceride utilization (P = 0.001). The HFD displayed significantly elevated levels of hepatic malondialdehyde (MDA), reactive oxygen species (ROS), pro-inflammatory cytokines (interleukin-1β and tumor necrosis factor-α), serum aspartate aminotransferase, and alanine aminotransferase (P < 0.05), indicating that HFD induced hepatic oxidative stress and inflammation. Dietary CAPE supplementation enhanced adipose tissue lipid utilization efficiency and mitigated these adverse hepatic effects. Dietary CAPE supplementation also significantly reduced muscle crude protein loss during overwintering (P < 0.001), suggesting alleviated protein degradation. Consequently, the post-overwintering textural properties (hardness, springiness, cohesiveness, gumminess, and chewiness) of both raw and cooked muscle were superior in the CAPE groups (P < 0.05). Serum levels of low-density lipoprotein cholesterol and inflammatory cytokines in the CAPE groups were normalized to levels comparable to those of the RFG (P < 0.05), indicating improved systemic health. Pre-overwintering feeding of an HFD supplemented with CAPE appears to be a promising strategy for reducing body weight loss, alleviating hepatic oxidative stress and inflammation, enhancing systemic health status, and improving the flesh quality of overwintering grass carp.