In aquaculture, fish are often exposed to several stress conditions, which will cause oxidative disorder and bring about health and quality problems. Arthrospira platensis contains abundant bioactive ingredients, which are beneficial for animal health. This study was conducted to investigate the effects of A. platensis on pigmentation,
antioxidant capacity, and stress response after air exposure of fish. A total of 120 yellow catfish Pelteobagrus fulvidraco (initial weight 70.19 ± 0.13 g) were divided into three tanks per treatment and fed diets supplemented with 0 g kg−1 A. platensis (CON) and 20 g kg −1 A. platensis (AP) for 65 days. The results indicated that dietary A. platensis had no effects on the growth of yellow catfish. The AP diet significantly reduced
lactic acid (LD) and
cortisol levels stimulated by air exposure stress (p < 0.05). Dietary A. platensis significantly increased plasma
superoxide dismutase (SOD) and
glutathione peroxidase (GPX) activities and
glutathione (GSH) contents, and the relative expression levels of sod and cat, to protect against oxidative stress caused by air exposure (p < 0.05). The AP diet significantly improved the relative expression level of nrf2 (nuclear factor erythroid-2 related factor 2), while the relative expression level of keap1 (
kelch-like ECH associated protein 1) was downregulated, and the
protein levels of liver Nrf2 were significantly increased after air exposure stimuli (p < 0.05). Dietary A. platensis significantly increased skin
lutein contents, increased skin redness, yellowness and chroma (p < 0.05), and improved body color abnormalities after oxidative stress caused by air exposure stimuli. Skin yellowness was associated with
lutein contents and the expression levels of some
antioxidant genes to varying degrees. Overall, dietary A. platensis could be utilized as a feed additive to activate the
antioxidant response, as well as alleviate oxidative stress and
pigmentation disorder induced by air exposure.