MUNICH, Germany - The heart health benefits from fish like salmon and mackerel seem to be weakened when the fish are fed vegetable oil instead of fish oil, new research indicates.

So the answer might be to feed them more fish oil.

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But that raises a different concern. Other studies have indicated fish oil increases the levels of pollutants in farm-raised salmon. That has encouraged some fish farmers to move to vegetable oil - which apparently decreases the heart benefits.

It's yet another fish conundrum for consumers, like the debate about whether the mercury in some fish offsets their health benefits.

Still, many experts argue that for most adults, the benefits are probably greater than the concerns about pollutants linked to cancer. They note that many more people are at greater risk of cardiovascular disease than cancer.

Wild fatty fish such as salmon, tuna, mackerel, sardines and herring are rich in omega-3 fatty acids, the healthy fat that scientists believe raises the good HDL cholesterol, lowers unhealthy tryglicerides and slows the growth of plaque, protecting the heart from disease.