Whilst the challenge was administered by i.p. injection, when fish are infected with bacteria the immune response is rapidly activated, with immune cells induced to secrete cytokines to enable the infected sites to resist pathogen invasion (Raida et al., 2011), and past studies comparing co-infection and i.p. injection of fish with Y. ruckeri have shown comparable induction of IL-22 in blood cells (Monte et al., 2016). The gene discussed is IL22; the disease is coinfection.