Fish provides important nutrients, including the omega-3 fatty acids (£s-3 PUFAs) but it also contains toxic contaminants, such as mercury (Hg) that may decrease the advantage of fish consumption. Therefore, balancing the nutritional requirements for £s-3 PUFAs and risks associated with mercury is an important issue for fish consumption. The aim of this study is to analyze the fatty acid compositions and mercury concentrations of several common wild and farmed fishes in Taiwan in order to evaluate the potential health benefits and risks of fish consumption. Wild and farmed fish sample were collected between 2010 and 2012 from trawlings, local fish markets, and aquaculture farms in western Taiwan. A total of 32 species of fish were collected. Dorsal muscle was dissected, dried, and homogenized. The proximate composition including crude lipid, crude protein, moisture, ash, and fatty acid composition, as well as mercury concentration in the muscle were analyzed. The fishes that were investigated were lean to medium in fat content. Content of £s-3 PUFAs were higher in the carnivorous fishes (0.96¡Ó0.62 g/100 g flesh weight) than in the herbivorous or omnivorous species (0.86¡Ó0.35 g/100 g flesh weight). The crude lipid contents in the wild fishes (6.7¡Ó3.7%) were lower in crude lipid contents than their farmed counterparts (12.1¡Ó7.5%). Fish £s-3 PUFAs concentrations were significantly increased with crude lipid content (p< 0.05). Mean mercury concentrations of all samples (0.048¡Ó0.038 mg/kg flesh weight) were lower than the common food safety standard (0.5 mg/kg flesh weight). Similar to the £s-3 PUFAs, the mean mercury concentrations were higher in the carnivorous fishes (0.06¡Ó0.04 mg/kg flesh weight) than in the herbivorous and omnivorous fishes (0.02¡Ó0.01 mg/kg flesh weight) and higher in the wild fishes (0.052 mg/kg flesh weight) than farmed fishes (0.031 mg/kg flesh weight). From the results of the present study, we can conclude that: to obtain the health benefits of the omega-3 fatty acids with a safe amount of mercury intake, the consumption of high EPA+DHA species (EPA+DHA concentrations are higher than 2 g/100 g flesh weight), such as croaker twice a week (3 oz/serving), or medium EPA+DHA species (EPA+DHA concentrations are between 1.02 to 1.34 g/100 g flesh weight),like fourfinger threadfin, Belanger¡¦s croaker, blue mackerel, and flathead grey mullet 3-4 times a week are desirable. In the case of consume tilapia or milkfish (EPA+DHA concentrations are between 0.60 to 0.72 g/100 g flesh weight) for cardiovascular disease preventative purposes, daily consumption of the fishes are beneficial. Furthermore, those people who have potential cardiovascular disease should double the amount of fish consumption suggested above. Accordingly, for those in the tropical Asian region, consumption of the amount of fish intake stated in this thesis would not exceed the safe Hg intake limit.