[CaringParent]

That is a problem, which each and every mother faces with their child. When my son was of that age, i thought there is some problem, i showed him to so many doctors, but every one said he is fine. But mom's heart doesn't understand anything. So, I went for Ayurveda too. But nothing helps. Actually children eat whenever they want to eat. My son has started taking food at the age of 2.5 years. My sister's son also started taking full time food about that age. So, Let him eat whatever he wants too. I must say children like fish very much. I have seen it with so many kids.
Don't force food on him. Whatever he wants to eat, let him eat that.
I must say your son is a "cutie".
Take care.