It's good thing for human nutrition that some fish live in cold waters. Some of the fats in coldwater fish consist of long, kinked carbon chains, which fill up space to add insulation. These are high-quality omega-3 acids, the EPA and DHA that are essential to human life. Atlantic salmon, bluefin tuna, Atlantic mackerel and anchovies are especially good sources.
This bounty comes with strings attached. First is the question of sustainability. The bluefin tuna population, for example, is being depleted by overfishing. This fish may be caught in ways that endanger sea turtles, birds and other wildlife. Fish farms, on the other hand, can release contaminants into local waters. And if they escape, the farm fish can threaten native wild species.
Food safety is another issue. Some very good wild-caught sources of omega-3 are at the top of the food chain. Any toxins in the fish they eat can accumulate in their flesh. Mercury poisoning is one well-documented example.
Eating fish, whether for omega-3 or any reason, proves the wisdom in knowing where your food comes from. Educating yourself on your food supply and its impact on the environment is an investment of time and effort. The payoff is a healthier life for you and for the planet.