According to the Health Unit Canada, cusk is a fish that should be eaten only once a week during pregnancy. Owing to the mercury content in this fish, experts recommend pregnant women to have only 1/2 servings (equals 37.5 grams) of cusk every week. Over consumption of this fish can lead to mercury poisoning in expecting mothers. It can also cause irrepairable brain damage to the unborn child. Hence, it is advisable to have cusk with caution.