Abstract
Perkinsus mediterraneus is a protozoan parasite that can cause marine mollusc diseases known as perkinsosis being a serious threat for clam cultures worldwide. The aim of the present study was first to determine the Perkinsus species infecting the variegated scallop Mimachlamys varia and then to evaluate the existence of oxidative stress in gills of M. varia according to different degrees of infection. DNA sequencing confirmed that P. mediterraneus was the species infecting M. varia . ROS production was progressively increasing with the degree of infection although the differences were only significant in the high‐infected group. Low degree of infection significantly increased superoxide dismutase (SOD) and glutathione S ‐transferase (GST) activities and nitrite levels with respect to the control group. In the high‐infected group, a significant increase was evidenced in all analysed enzymes, catalase, SOD, glutathione reductase and GST. Non‐significant differences in MDA levels were observed between the control and low‐infected groups; however, a significant increase in MDA levels was observed in the high‐infected group. In conclusion, the infection by Perkinsus mediterraneus in M. varia induces oxidative stress and an antioxidant response directly related to the infection degree that can contribute to the pathogenicity of the infection.