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Furunculosis induced by motile aeromonads is a problem in farming of salmonids (brown and rainbow trout) and various other fish species in the Europe during last years. Motile aeromonads cause diverse pathological conditions that include acute, chronic and covert infections (Cipriano and Austin 2011). Severity of disease is influenced by a number of interrelated factors, including bacterial virulence, the kind and degree of stress exerted on a population of fish, the physiological condition of the host and the degree of genetic resistance inherent within specific populations (Cipriano and Austin 2011). Numerous studies support the contribution of reactive oxygen species in the pathogenesis of parasite invasion mechanisms, as well as activation of immune system (Paiva and Bozza 2014). However, the validation of oxidative stress-related biomarkers in these settings is still lacking and novel association of these biomarkers and other biomarkers such as antioxidant defenses, is just emerging. Oxidative stress has been suggested as a pathogenic factor and therapeutic target in infective mechanisms. The aim of the present study was to examine the responses of oxidative stress biomarkers in the cardiac tissue of healthy specimens of sea trout (Salmo trutta m. trutta L.) and naturally furunculosis-affected trout in Słupia, the river in basin of the Baltic Sea where trout are spawned (northern Poland, Central Pomeranian region). The activities of antioxidant enzymes (superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase, total antioxidant capacity), as well as oxidative stress biomarkers (2-thiobarbituric acid reactive substances as lipid peroxidation biomarker, aldehydic and ketonic derivatives as protein damage biomarker), and correlation between those in the cardiac tissue of healthy and furunculosis-affected trout were assayed. Furunculosis induces the production of aldehydic and ketonic derivatives of protein oxidation both in males and females. High protein oxidation occurred together with an alteration of the antioxidant defenses. Oxidative stress in cardiac tissue occurs more significantly in males of furunculosis-affected sea trout and contributes to the oxidative effect. It is probable that the cardiac cells which survive to the reactive oxygen species (ROS) have increased glutathione-dependent enzymes activity. However, this activation of the antioxidant system may not be sufficient to neutralize all the ROS, which does not allow an efficient cellular adaptation to this furunculosis-induced stress. It also explains the lower total antioxidant capacity described among males and females when compared with healthy trout. These results may be explained by the decrease of superoxide dismutase activity, which may be caused by the furunculosis-induced ROS generation. A better understanding of the bacterium-induced oxidative stress in sea trout is required to find a cures.
Key words: sea trout (Salmo trutta m. trutta L.), furunculosis, Aeromonas hydrophila, oxidative stress, antioxidant defenses, Pomeranian region