In addition, key genes involved in resistance to its infection in certain fish species have been identified, such as galectin−9, which was involved in the immune response against infection in koi carp (Cyprinus carpio) [19]; the CD4-1 gene, which activated NF−κB signaling in response to infection [20]; and the mRNA expression levels of CaCD3γ/δ, which significantly changed in the spleen, head kidney, intestine and gill after infection in Qihe crucian carp (Carassius auratus) [21]. The gene discussed is NFKB1; the disease is infection.