White flesh fish are great introductory fish for babies. You can introduce Flounder, Haddock, Cod, and Sole because they are the most easily digestible and lowest on the allergen list and as such, are best to use when first introducing baby to fish.
“White flesh” fish types (like flounder and cod) are considered some of the safest to introduce. Popular suggestions from my friends are threadfin, cod, kurau, and ikan bilis. Be careful with the bones. :)