Here - from www.eatwell.gov.uk (food standards agency)
"You can eat most types of fish when you're pregnant. But there are a few types you should avoid and some others where you should limit the amount you eat.
Avoid eating any shark, swordfish and marlin. Limit the amount of tuna you eat to no more than two tuna steaks a week (weighing about 140g cooked or 170g raw) or four medium-size cans of tuna a week (with a drained weight of about 140g per can). This is because of the levels of mercury in these fish. At high levels, mercury can harm a baby's developing nervous system.
Have no more than two portions of oily fish a week. Oily fish includes fresh tuna (not canned tuna, which does not count as oily fish), mackerel, sardines and trout.
But remember that eating fish is good for your health and the development of your baby, so you should still aim to eat at least two portions of fish a week, including one portion of oily fish.
Raw shellfish
Avoid raw shellfish when you're pregnant. This is because raw shellfish can sometimes contain harmful bacteria and viruses that could cause food poisoning. And food poisoning can be particularly unpleasant when you're pregnant"