It’s well known that in coastal countries parents include fish in their child’s diet from an early age, basically as one of the first solid foods introduced at around their sixth of seventh month.
Until recently, people were very careful in including fish into a child’s diet, even freshwater fish, which has been a popular ingredient in many cookbooks for hundreds of years.
Fish, just like cow milk and nuts, is one of the most common allergens. This is the reason why many parents were reluctant in including fish in the diet of the smallest children. Studies have shown however, that eliminating these allergens from ones diet is necessary only if one truly has an allergic reaction to them. It’s ineffective and unnecessary to exclude fish from a child’s diet, even if he has a family history of allergies, only to prevent one from developing allergies. We cannot influence whether or not a child will be allergic. For more please read about the anaphylaxis on fish in children here.
Fish (especially freshwater fish) can be fed to a nursing baby. If a baby has a family history of allergies, it’s advised to be careful, but we don’t have to wait until our child is two (as was previously advised) to give him this very nutritious food.

Opinions on a balanced, nutrition diet change so quickly that many recommendations loose their validity. Nevertheless it’s true that regarding nutrition, it pays to learn form our ancestors.
Nursing unquestionably remains the best diet for a baby in his first months. Between his fourth and sixth month, it’s appropriate to start introducing additional liquids and solid foods, while still breastfeeding. It’s unnecessary to hurry or to give a child his first spoon of vegetables right at the end of his fourth month. If you start after his seventh month, nothing happens, but the child can refuse some solid foods and his tolerance to new foods (i.e. fish) can be lower then the month before. The same is also true for gluten.