Previous reports about the description of immune responses of turbot after infection with A. salmonicida [5,24,26,27] highlight the presence of a response characterized not only by the over-expression of tumor necrosis factor-alpha (TNFα) protein produced by mononuclear phagocytes, but also for the generation of nitric oxide (NO) by the stimulation of the inducible nitric oxide synthase pathway (iNOS) [24]. Here, NOS2 is linked to infection.