Effects of <italic>Haematococcus pluvialis</italic> powder on hepatopancreatic immune performance and expression of related genes in formaldehyde stress in <italic>Penaeus monodon</italic>

[Objective] This study aims to investigate the effects of different dosages of Haematoccus pluvialis(HP)powder on the immune system, enzyme activity, and stress response gene expression in the hepatopancreas of Penaeus monodon.[Methods] P.monodon with an initial body mass of(2.38±0.25)g were divided into 9 groups and fed with gradients of 0 to 0.8%(by mass, groups A0 to A8)HP powder in the basal diet for 42 d.The activities of acid phosphatase(ACP), alkaline phosphatase(AKP), glutathione peroxidase(GPx), and total antioxidant capability(T-AOC), as well as the relative expression levels of immune response genes Toll and myeloid differentiation factor 88(MyD88)in the hepatopancreas, were measured.After the feeding trial, an acute stress experiment was conducted in water with a formaldehyde mass concentration of 300 mg/L for 36 h, with the group fed 0 HP powder+0 formaldehyde exposure serving as the blank control to measure the relative expression levels of stress response genes, such as heat shock protein 70(HSP70), nuclear factor erythroid 2-related factor 2(Nrf2), manganese superoxide dismutase(MnSOD), and p53 in the hepatopancreas.[Results] 1)Feeding an appropriate amount of HP powder for 42 d increased the activities of ACP, AKP, GPx, and T-AOC in the hepatopancreas of P.monodon(P&lt;0.05).It also increased the relative expression levels of immune response genes Toll and MyD88(P&lt;0.05)while decreasing the relative expression levels of stress response genes HSP70, Nrf2, MnSOD, and p53(P&lt;0.05).2)Adding 0.3% to 0.8% HP powder improved the survival rate of P.monodon under formaldehyde stress(P&lt;0.05).3)After formaldehyde stress, the expression levels of HSP70, Nrf2, MnSOD, and p53 genes in the A0 group were significantly lower than those in the Blank group(P&lt;0.05), and adding an appropriate amount of HP powder significantly restored the expression levels of these stress response genes(P&lt;0.05).[Conclusion] Adding HP powder to the diet can enhance the immune and antioxidant properties of the hepatopancreas of P.monodon.Furthermore, it can enhance the ability of P.monodon to resist formaldehyde stress by regulating the expression levels of stress response genes.