This is a tough question. I think that some toxins are specific to the fish feed (ie, preservatives in dry fish feed), but generally my understanding is that fa

This is a tough question. I think that some toxins are specific to the fish feed (ie, preservatives in dry fish feed), but generally my understanding is that factory farming or large scale farming that results in a race-to-the-bottom on price can often yield food practices that are long term harmful but not obvious. Ideally, you would actually know how the food you're eating is raised. There are a lot of resources and bodies out there doing research on contaminants etc, and there are certain actually reputable certification programs. However, it takes a very discerning consumer to understand this. For example, eggs can be marketed as "cage free" and "100% vegetarian fed" -- but this can just mean that the chickens are housed in giant indoor structures and might never be allowed to forage outside, and that they are fed grain or corn or soybeans.