Effects of triterpene-rich olive extract alone or in combination with green tea extract and Eucommia ulmoides extract on growth performance and health status of mandarin fish (Siniperca chuatsi)

This research was conducted to investigate the effects of triterpene-rich olive extract (OE) alone, or in combination with green tea and Eucommia ulmoides extracts (OEC), on growth performance, oxidative defense ability, and inflammation response of mandarin fish to develop a natural antioxidant for improving the artificial feed of mandarin fish (Siniperca chuatsi), based on a 57 days' feeding trial. Five isonitrogenous and isolipidic diets were prepared: a control (CTR), two with 0.15 % and 0.30 % OE (OE-L and OE-H), and two with 0.15 % and 0.30 % OEC (OEC-L and OECH). The results of feeding trial revealed that no significant differences were observed in final body weight, specific growth rate, and feed conversion ratio (P > 0.05). Both OE and OEC supplementation increased crude protein levels in muscle and visceral tissues, while reducing muscle crude fat content. Specifically, the reductions in muscle crude fat were 11.03 %, 26.47 %, 27.94 %, and 32.35 % in the OEC-L, OECH, OE-L, and OE-H groups, respectively (P < 0.05). Furthermore, OE and OEC supplementation decreased hepatic malondialdehyde and elevated catalase activity (P < 0.05). Hepatic antioxidant genes (gpx, sod2, cat, nrf2 and gst) were significantly upregulated in high-dose groups (P < 0.05). Both additives enhanced serum lysozyme activity and hsp70 expression, while suppressing pro-inflammatory genes (mapk14 and cox-2) (P < 0.05) in the head kidney. Notably, the OEC-H group exhibited a significant reduction in head kidney relA expression (P < 0.05). In conclusion, dietary supplementation with OE and OEC can enhance antioxidant capacity and immunity in mandarin fish, and the OEC-H group presents the best effects based on gene expression results.