Effects of pomegranate (Punica granatum) peel extract on hypoxia tolerance and biochemical markers in organs of Jian carp (Cyprinus carpio var. Jian)

The purpose of this study was to evaluate the effects of dietary pomegranate peel extracts (PPE) on hypoxia tolerance in carp ( Cyprinus carpio var. Jian). In the first trial, 300 carp (12.01 ± 0.53 g) were fed diets containing 0.5 % of PPE for 15 days. The findings indicated that the inclusion of dietary PPE led to an augmentation in hypoxia survival time (DT) and a reduction in oxygen consumption rate (OCR) of carp under hypoxic conditions ( P < 0.05). Moreover, the effects of four PPE (petroleum ether extract, ethyl acetate extract, ethanol extract (EE), and aqueous extract) on the DT and OCR were found to be closely associated with their polyphenol content. EE, which had the highest polyphenol content, showed the strongest effect. In a follow-up trial, 420 carp were fed diets containing increasing levels of EE (0–1.8 %) for 15 days. The results showed dose-dependent decreases in OCR and plasma ammonia levels, along with improved hematological parameters including hematocrit, hemoglobin concentration, and MCHC ( P < 0.05). Activities of transaminases (GOT, GPT) and lactic dehydrogenase in hepatopancreas, muscles, and gills were significantly increased ( P < 0.05). Optimal EE levels for carp were estimated to be 1.337 % and 1.279 % based on broken-line regression analysis of DT and OCR, respectively. Furthermore, dietary EE decreased ROS generation and lipid oxidation by enhancing both enzymatic antioxidant activities and non-enzymatic antioxidant levels in red blood cells, gills, or muscles of carp ( P < 0.05). In conclusion, dietary EE enhances hypoxia tolerance in carp by improving protein and carbohydrate metabolism and boosting antioxidant capacity of respiratory organs, suggesting that EE from pomegranate peel could serve as a natural solution to alleviate hypoxic stress in fish. • Dietary PPE enhanced the hypoxia tolerate, especially EE having the strongest effect. • The effects of PPE on hypoxia are closely related to their polyphenol content. • Optimal EE addition levels for carp were found to be 1.337 % and 1.279 %, respectively. • EE can act as a natural inhibitor of hypoxia-induced stress in fish.