Fish fed HF exhibited a lower expression of catalase (cat), nuclear factor erythroid 2‐related factor 2 (nrf2), zonula occludens-1 (zo-1), and occludin, and a higher expression of kelch-like ECH-associated protein 1 (keap1), compared to the control group (p < 0.05, Figure 4). The gene discussed is CAT; the disease is hydrops fetalis.