Aquatic organisms are exposed and adjust to a wide variety of environmental challenges including natural and
anthropogenic factors. Natural sources are understood the effects of temperature, and saline fluctuations, oxygen
availability, the relative abundance of chemical elements and pathogenic invasion. On the contrary, anthropogenic factors
are considered the availability of heavy metals, the presence of hydrocarbons, industrial and urban wastes, and pesticides.
Moreover, these organisms suffer, in order to maintain homeostasis, growth and reproduction, the effect of temporal and
spatial variations. All the environmental changes (natural and non-natural) may cause a different degree of stress in
aquatic organisms, via induction of disbalance between the generation and elimination of reactive oxygen species and
reactive nitrosative species. A brief summary on the actual knowledge on the establishment, by environmental effects, of
oxidative/nitrosative stress and the effect on the antioxidant system in marine organisms, is presented in this review to
contribute to the deeper understanding of the complexity of the metabolic and physiological changes that aquatic
organisms are constantly suffering.