High levels of mercury

Mercury may affect the nervous system, and some fish contain more mercury than others.

Source

Alligator

Make sure it is well cooked.

Source
Careful
Source
Unsafe

Bass

Moderate levels of mercury have been detected in this fish. Avoid where possible but it should be fine in very limited quantities.
Source
Careful

Bluefish

There are moderate levels of mercury in this fish, and you should avoid if possible. It should be fine in very limited quantities.
Source
Careful

Bombay Duck

Unsafe levels of mercury have reportedly been found in Bombay Duck found off the shore of India. Be sure to double check the source.
Source
Careful

Crocodile

Make sure it is well cooked.

Source
Careful

Kingfish (King Mackarel)

This is not recommended for pregnant women due to the levels of mercury found in the fish's system.
Source
Unsafe

Lamprey

High levels of mercury have been detected in lampreys.
Source
Unsafe
Source
Unsafe

Mahi Mahi (Dorado)

Moderate levels of mercury mean you shouldn't consume more than six six-ounce portions per month.
Source
Careful
Source
Unsafe

Patagonian Toothfish (Chilean Seabass)

There are moderate levels of mercury in this fish, and you should avoid if possible. It should be fine in very limited quantities.
Source
Careful
Source
Unsafe

Portuguese Dogfish (Siki)

Don't eat more than 150g a week.
Source
Careful
Source
Careful

Sablefish (Black Cod)

There are moderate levels of mercury in this fish, and you should avoid if possible. It shouldn't be an issue in strictly limited amounts.
Source
Careful
Source
Unsafe
Unsafe
Source
Unsafe
Source
Unsafe