Fish is rich in protein content. Omega 3 in fish contains EPA and DHA and these substances are not found in any other protein resource. 
Most of the babies eat less fish then they are supposed to. Generally mothers don't perceive fish as a baby/child food and they are not knowledgeable about fish types. The children who don't see their parents eating fish will not be eager to eat fish in the future. So, to set an example for their future nutritional habits, we must consider making fish, one of the main dishes of our households. 
As fish is not very popular among chef mothers, fish oil is. Eating fish is always a better option than taking fish oil. If the diet of your child does not include enough fish, fish oil can be a good Omega 3 source. But don't forget that it is also a nutritional support and you should not give fish oil to your child before consulting your doctor.  
Keep in mind 
Different time is given in each source for introducing fish to your baby. Recommendations vary from 8 months to 12 months. It is important that you talk to the doctor before introducing fish to your baby.  Because fish is an allergenic food and if your baby has allergy history, you should take this into consideration. 
When introducing fish, start with the ones with white meat that has more neutral taste. Fish bone may pose a threat. So make sure you pick all the bones before giving the meat to your baby. Just like it is true for vegetables, cooking fish in extreme temperatures will lower its nutritional value. So try to cook it with steam. Click here for our delicious fish recipes.
Buying fish... 
If you are not very knowledgeable about fish Types, make sure that you buy fish of the season and saltwater fish. Most fish sold by fisherman are farm fish. Try to learn the names of fish.  Farm fish are given artificial feed and their nutritious value is low compared with saltwater fish and they are exposed to pollution. Click here to learn which fish to give in each season. 
Omega 3 levels of each fish is different. Coldwater fish have high fat concentration and is a good Omega 3 source. Salmon is one of the fish with highest Omega 3 level. Salmon comes from northern countries so unfortunately all salmon are grown in fish farms. Some are transferred from northern countries in frozen form and you can also find some fresh salmon sold in some gross markets. 
Gurme Bebek recommends giving your baby local, fresh saltwater fish. How can you be sure that the fish you are buying is fresh enough; 
- The flesh should be tight and the skin should appear bright - Gills should appear bright red - When you press the flesh, it should spring back to its natural shape - It should have a neutral odor and should not smell too much like fish. 
Avoid giving your baby bottom fish like turbot. Prefer surface fish like horse mackerel.  Bottom fish may contain heavy metals. Hazardous substances and specifically heavy metals that deposit at the seabed may pass to human body through these fishes. 
Big fish contain more heavy metals than small fish. Heavy metals concentrate more in the skin of the fish. Fish with longer lifespan are more polluted than younger fish. Considering the heavy metal risk, consult your doctor about how many times you can give fish to your baby. 
Don't give your child shellfish like mussel, shrimp, lobster before age of 1 and talking to your doctor. These may cause fatal allergic reactions.