Effects of astaxanthin addition in feeds on the response to alkalinity stress of Gymnocypris przewalskii

Objective This study aimed to investigate the mechanism of astaxanthin addition in feeds on the response to alkalinity stress of naked carp （Gymnocypris przewalskii）， and to provide a theoretical basis for application of astaxanthin in feed of the naked carp.Method Nine hundred one-day-old juveniles were randomly divided into five groups： the control group （AS0） was fed a basal diet； while the experimental groups received feeds added with astaxanthin at 25 mg/kg （AS25）， 50 mg/kg （AS50）， 100 mg/kg （AS100）， and 200 mg/kg （AS200）， respectively. Following the experiment， the effects of astaxanthin addition in feeds on growth performance， antioxidant capacity， and immune functions were investigated. The alkalinity stress test was conducted on a group of naked carp fed diets with the optimal astaxanthin addition to analyze the effects of astaxanthin addition in feeds on the response of naked carp to alkalinity stress.Result Adding 50 mg/kg astaxanthin in feeds significantly increased the specific growth rate， weight gain rate， and liver-to-body ratio of naked carp （P<0.05， the same below）. The serum total protein content in the AS50 group was significantly higher than those in the AS0， AS25， and AS200 groups； the albumin content in the AS50 group was significantly higher than that in the AS0 group； the glutathione peroxidase and glutathione reductase activities in the AS50 group were higher than those in the AS0， AS25， AS100， and AS200 groups； the highest total superoxide dismutase and catalase activities were observed in the AS100 group. In livers of the naked carp， the highest total protein content， malondialdehyde content， total superoxide dismutase activity， glutathione peroxidase activity， and catalase activity were observed in the AS50 group， while the highest glutathione reductase activity was observed in the AS100 group. Compared with the AS0 group， the AS50 group showed significantly decreases in interleukin-1β， interleukin-6， interleukin-8， and tumor necrosis factor-α， whereas significantly increases in of interleukin-10 and transforming growth factor-β. In the group of AS0L96 vs AS0C， key genes in the ferroptosis signaling pathway （acsl4b， acsl1b， tfr1b， and gpx4a） were significantly down-regulated in the AS0L96 group. In the group of AS50L96 vs AS0L96， the key gene hsd17b7 in the steroid biosynthesis signaling pathway was significantly up-regulated in the AS50L96 group.Conclusion The optimal astaxanthin addition in feeds of naked carp was 50-100 mg/kg， and addition at 50 mg/kg is the most effective for resisting alkalinity stress. Astaxanthin can regulate signaling pathways such as liver metabolism and immune response in naked carp to respond to alkalinity stress， and among them， acsl4b， acsl1b， tfr1b， gpx4a and hsd17b7 genes may play important roles in the response of naked carp to alkalinity stress.