It depends on the type of fish that it is. If it contains high levels of mercury then it will be dangerous to you.
Here's some information I found on WHAT NOT TO EAT.
Uncooked seafood and rare or undercooked beef or poultry should be avoided because of the risk of contamination with coliform bacteria, toxoplasmosis, and salmonella.
Fish with Mercury:
Fish that contain high levels of mercury should be avoided. Mercury consumed during pregnancy has been linked to developmental delays and brain damage. A sample of these types of fish include: shark, swordfish, king mackerel, and tilefish. Canned, chunk light tuna generally has a lower amount of mercury than other tuna, but still should only be eaten in moderation. Certain types of fish used in sushi should also be avoided due to high levels of mercury. Please see Mercury in Fish for specific types of fish and further information on how to calculate mercury levels.
Smoked Seafood -
Refrigerated, smoked seafood often labeled as lox, nova style, kippered, or jerky should be avoided because it could be contaminated with Listeria. (These are safe to eat when they are in an ingredient in a meal that has been cooked, like a casserole.) This type of fish is often found in the deli section of your grocery store. Canned or shelf-safe smoked seafood is usually OK to eat.
Fish Exposed to Industrial Pollutants:
Avoid fish from contaminated lakes and rivers that may be exposed to high levels of polychlorinated biphenyls. This is primarily for those who fish in local lakes and streams. These fish include: bluefish, striped bass, salmon, pike, trout, and walleye. Contact the local health department or Environmental Protection Agency to determine which fish are safe to eat in your area. Remember, this is regarding fish caught in local waters and not fish from your local grocery store.
The majority of seafood-borne illness is caused by undercooked shellfish, which include oysters, clams, and mussels. Cooking helps prevent some types of infection, but it does not prevent the algae-related infections that are associated with red tides. Raw shellfish pose a concern for everybody, and they should be avoided altogether during pregnancy.
another site you might find useful: