Carotenoid-based skin coloration signals antioxidant defenses in the brown trout (Salmo trutta)

Carotenoid-based signals may function as indicators of individual quality because, being exclusively obtained from the diet, they indicate the ability of individuals to intake high-quality food. Moreover, carotenoids are involved in several important physiological functions, including antioxidant defense, so that carotenoid-based colorations have been suggested to reflect the antioxidant status of their bearers. The present correlative, cross-sectional study aimed at investigating if the skin carotenoid-based coloration is a signal of antioxidant defenses in the brown trout (Salmo trutta Linnaeus, 1758). We investigated the relationships between carotenoid-based coloration traits (including the number, density and redness of red spots, as well as the ventral yellowness), and both non-enzymatic (plasma and liver total antioxidant capacity) and enzymatic antioxidant defenses (activity of hepatic superoxide dismutase —SOD, catalase —CAT and glutathione peroxidase —GPx). We found significant positive covariations between antioxidant defenses and carotenoid-based skin coloration, in terms of ventral yellowness. Brown trout individuals displaying intense carotenoid-based coloration (i.e., ventral yellowness) had a high non-enzymatic antioxidant capacity both in plasma and in liver and, interestingly, an elevated activity of hepatic SOD and CAT. Our data suggest that carotenoid-based skin colorations may be considered a signal of individual quality in terms of antioxidant defenses in the brown trout.