SOD1 and infection: In this study, ACP, AKP, and SOD activity were remarkably higher and the MDA concentration significantly lower in all organs of groupers which were examined after V. harveyi infection alone compared to those examined after either P. piscicida infection alone or coculture infection; this strongly indicated an immune system response to the pathological invasion in which P. piscicida, as an inhibitor of V. harveyi, effectively protected the fish from triggering an immune response caused by V. harveyi.