If tuna is hatched and raised in non-mercury containing water, does that make it mercury-free?

Question

Will heavy metals travel from parent to offspring? If not, why aren’t fish that contain heavy metals hatched in places where water can be monitored?

In: Biology

Answer 1

Tuna cannot presently be farm raised. They are huge fish that live in the open ocean, where they roam very long distances. The closest thing to captive raised tuna are open ocean “farms” that are large netted areas that keep the tuna in one area. The nets are open enough for other fish to swim through, which feed the tuna.

Tuna are very high on the food chain. They are apex predators that rely on a pretty large food web to survive. Because they are such active swimmers, they don’t thrive in enclosed spaces.

So, that’s why we can’t raise mercury-free tuna.

The mercury comes from their food. Mercury is hard for living tissue to get rid of. Once it gets into your fatty tissues, it tends to stay there. The organisms lowest in the food web that are filter feeders accumulate some low levels of mercury from the environment. The predators that eat them take in all that mercury and can’t get rid of it. Since they eat a lot of those small organisms, they accumulate much more mercury than their food does individually.

Larger predators eat those predators and accumulate even *more* mercury, and so on. Each step up in the food web means more mercury accumulates. Since tuna are pretty much at the top of the food web, they end up consuming a lot of mercury, which ends up in their own tissues. They also have a lot of oil and fat, which is where the mercury ends up, so they can hold a lot of it.

If it were possible to raise tuna without any of these natural food sources, yes, we could raise tuna to be much lower in mercury. However, since they are so high in the food web we would first have to raise their food source without much mercury, which itself would have its own food that would have to be raised without mercury. Since we’re already overfishing the oceans just to feed ourselves, it wouldn’t be feasible to grow that much food just to feed the food that feeds our food.