"Mackerel are thiaminase free, right?"

The Atlantic are safe but its the Chub/Pacific mackerel (Scromber japonicus)that contains Thiaminase.

"The risk of heavy metals tends to be with fish that are longer lived and therefore have longer to accumulate in the tissue. Mackerel are smaller with short lifespan aren't they?"

That's good to know. I guess I should give them a go and see if they're to her liking