Fish antioxidant defenses--a comparative approach.

There are few comparative studies of vertebrate antioxidant defenses (AD) in the literature. Enzymatic (superoxide dismutase, SOD, and catalase, CAT) and non-enzymatic (alpha-tocopherol, beta-carotene, ubiquinol 10 and blood glutathione) antioxidant defenses were investigated in the liver and blood of 37 fish species, 15 marine species of the southeastern Brazilian coast and 22 freshwater species from the Central Amazon basin. More active marine species displayed in general higher concentrations of SOD and CAT in the liver and blood, compared to those of sedentary or bottom-dwelling species. AD status in marine fish m ay be related to the oxygen consumption of the tissues and of the whole organism, while in freshwater AD may be related to physical and chemical characteristics of the environment rather than to activity level. As thermoconformer organisms, most fish must routinely cope with environmental temperature changes and, consequently, with changes in their metabolic rates. The relatively high antioxidant defense levels that typify fishes, even when compared to endotherms such as birds and mammals, may protect aquatic organisms against the consequences of temperature oscillations.