It is not a good idea to consume any fish at all if you are mercury toxic and wish to detox. Even small intakes of mercury may hinder excretion, especially in somebody who tends to retain, rather than excrete mercury.

One doctor I listened to on audio tape (from US),says she has to continually get through to her patients about not eating any fish, no matter what levels. She said it impedes excretion.

Mercury free fish oil maybe the safer option in my opinion, but make sure it's certified.

I have tried eating low mercury fish and I feel there is a problem even then.

I think it depends also on how serious the poisoning is, and how serious a person is with getting it all out. I wouldn't take any risks with fish at all and why do so if there is any risk involved?