Increasing and constant pollution is causing continuous environmental damage in marine and freshwater aquatic environments. Both environments are constantly subject to pollution caused by polycyclic aromatic hydrocarbons (PAHs). To study all levels of responses provoked by contaminants, we propose that fish are excellent models. The tambaqui is an important freshwater fish endemic from the Orinoco and Amazon River Basins. In the presence of PAHs and other crude oil components, this fish accumulates PAH metabolites in the bile and presents genotoxic effects in its red blood cells. These responses are dose-dependent. Tambaqui also present changes in biotransformation and antioxidant enzymes, which are considered great bioindicators for the evaluation of PAH contamination. In the marine environment, the seahorses are usually found in estuarine and coastal environments, such as reefs, bays, seaweed banks and seagrass. Genotoxic effects are also observed in seahorse exposed to PAHs, with a significant relationship between DNA damage and increased crude oil concentration. Regarding biochemical responses, the seahorse presents decreased levels of GST in a dose-dependent manner. This fish also presents gill histopathological alterations and the damages observed were classified as defense or compensatory responses. Both tambaqui and seahorse are considered excellent bioindicators for PAH contamination since they are extremely responsive to these organic strong pollutants.